Rationally designed conductive hierarchical nanostructures are highly desirable for supporting pseudocapacitive materials to achieve high-performance electrodes for supercapacitors. Herein, manganese molybdate nanosheets were hydrothermally grown with graphene oxide (GO) on three-dimensional nickel foam-supported carbon nanotube structures. Under the optimal graphene oxide concentration, the obtained carbon nanotubes/reduced graphene oxide/MnMoO4 composites (CNT/rGO/MnMoO4) as binder-free supercapacitor cathodes perform with a high specific capacitance of 2374.9 F g–1 at the scan rate of 2 mV s–1 and good long-term stability (97.1% of the initial specific capacitance can be maintained after 3000 charge/discharge cycles). The asymmetric device with CNT/rGO/MnMoO4 as the cathode electrode and the carbon nanotubes/activated carbon on nickel foam (CNT-AC) as the anode electrode can deliver an energy density of 59.4 Wh kg–1 at the power density of 1367.9 W kg–1. These superior performances can be attributed to the synergistic effects from each component of the composite electrodes: highly pseudocapacitive MnMoO4 nanosheets and three-dimensional conductive Ni foam/CNTs/rGO networks. These results suggest that the fabricated asymmetric supercapacitor can be a promising candidate for energy storage devices.Keywords: carbon nanotubes; graphene oxide; manganese molybdate; nickel foam; supercapacitors;

It is demonstrated that the performances of supercapacitors are often affected by the electrochemical interface in their electrodes. In this work, the electrochemical interface in carbon nanofiber (CNF)/carbon nanotube (CNT) hierarchical composites was well optimized by tuning the diameters of electrospun CNF skeletons and the densities/lengths of CNT hierarchies. The optimized CNF/CNT composites decorated with MnO2 exhibited high specific capacitance (∼631.0 F g−1 at current density of 0.9 A g−1) and excellent cycling stability (over 95% after 1500 cycles). Moreover, the assembled symmetric supercapacitors show a high flexibility and an excellent dynamic cycling stability, outputting the maximum energy density of 19.11 W h kg−1 and the maximum power density reaching 25,000 W kg−1. This research confirmed that the performances of the electrodes based on CNF/CNT hierarchical composites and their counterpart devices can be well tuned by tailoring their three-dimensional electrochemical interface.

•Two types of hierarchical nanostructures were constructed using NiCo2O4 scaffolds.•Areal capacitance of 7.29 F cm−2 is obtained for NiCo2O4-UNSA@NiMoO4 electrodes.•The UNSA scaffold can provide more efficient electron transport channels.•The NiCo2O4-UNSA@NiMoO4 electrodes show high rate capability (84.1% at 60 mA cm−2).It’s demonstrated that transport channels of electrons are very crucial to the performances of supercapacitor electrodes and different morphologies of nanomaterials usually imply different properties on electron transport in them. Hence, we constructed two types of NiCo2O4@NiMoO4 hierarchical core-shell nanostructures, in which NiCo2O4 scaffolds are in form of uninterrupted nanosheet arrays (UNSAs) or nanoneedle arrays (NNAs) and NiMoO4 hierarchies in form of nanosheets, and investigated electron transport properties of their resultant electrodes. Results showed that NiCo2O4-UNSA@NiMoO4 and NiCo2O4-NNA@NiMoO4 electrodes respectively exhibit high areal capacitances of 7.29 F cm−2 and 5.96 F cm−2 (current density of 2 mA cm−2), both of which are much improved compared with the previous work. And more interestingly, the capacitances from NiCo2O4-UNSA@NiMoO4 electrodes are enhanced by 22–39% compared to those from NiCo2O4-NNA@NiMoO4 ones at various current densities. And theoretical simulations and electrochemical impedance spectroscopy results confirmed that compared to the NNA ones, the UNSA scaffolds can provide more accessible and efficient electron transport channels (especially at high-rate charge-discharge processes), which leads to a much lower charge-transfer resistance and superior rate capability. Furthermore, the assembled asymmetric supercapacitors of NiCo2O4-UNSA@NiMoO4//active carbon show a high energy density (52.6 Wh kg−1 at 332.4 W kg−1) and a high power density (2632.8 W kg−1 at 36.9 Wh kg−1).

•Facile and economical approach was reported to fabricate wire electrode.•MoO3 sheath works as the active material and the Mo core as the facilitated channel for electrons.•The resultant wire electrodes and devices show high capacitance and excellent cycle stability.Due to their high pseudocapacitance and laminated structure, α-MoO3 nanosheets have been considered as one of the promising electrode materials of energy storage devices. In this work, hierarchical α-MoO3 nanosheet arrays have been in-situ grown on Mo wires (MoO3-Mo wires) via one-step calcination in air. The obtained MoO3-Mo wires possess well aligned laminated structure, which will benefit intercalation of Li-ion into the electrodes. Thus, a type of Li-ion electrolyte was applied in the assembled wire-based supercapacitors (WSCs). Electrochemical tests showed that the MoO3-Mo single wire electrodes can exhibit high capacitance (7.68 mF cm−1 at 2 mV s−1) and excellent cycling stability (nearly 100% after 4000 cycles). Moreover, series of optimization tries indicated that the laminated structure of MoO3 nanosheet arrays can be well tuned by calcination temperature and time, accordingly resulting in the optimized electrochemical performance. Furthermore, the assembled all-solid state symmetrical WSCs based on MoO3-Mo wires showed high energy density (∼1.04 mW h cm−3), high cycling stability, and good flexibility.Download high-res image (73KB)Download full-size image

•Sandwiched core–shell carbon nanotubes/hematite@carbon arrays were fabricated.•The conformal coating of hematite and carbon were achieved by magnetron sputtering.•The composite electrode exhibits high specific capacitance and high stability.Rationally designed carbon-based conductive nanostructures are highly demanded to improve the electrochemical performance of hematite-based supercapacitors. In this research, we have successfully designed and synthesized three-layer sandwiched core–shell carbon nanotubes/Fe2O3@carbon arrays on carbon cloth substrate via commercially available magnetron sputtering and chemical vapor deposition methods. The carbon nanotube core (prepared by chemical vapor deposition) and the carbon shell (prepared by magnetron sputtering) both can improve the specific surface area and electrical conductivity of Fe2O3 (prepared by magnetron sputtering), restrain the active materials and thus enhance its electrochemical performance and long-term stability. X-ray diffraction and Raman results demonstrate the obtained hematite is α phase. Scanning electron microscopy and high-resolution transmission electron microscopy images indicate the Fe2O3 and carbon shell are conformally coated on the carbon nanotube core. Consequently, under the optimal mass of Fe2O3 and carbon shell, the carbon nanotube/Fe2O3@carbon composite electrode exhibits a high specific capacitance of 787.5 F g−1 at the scan rate of 5 mV s−1 and a high stability (92% of the initial capacitance remains after 7000 cycles). The remarkable performance of these binder-free carbon cloth/carbon nanotube/Fe2O3@carbon electrodes suggest their huge potential use as negative electrode material for high performance supercapacitors.Download high-res image (301KB)Download full-size image

Germanium is a promising anode for lithium ion batteries (LIB) because of its potential rate capability and high theoretical specific capacity. Here we demonstrate a seamlessly connected graphene and carbon nanotube (GCNT) hybrid that serves as an integral current collector for a Ge anode. A vertically aligned CNT (VA-CNT) forest grown on graphene provides a high surface area for Ge deposition. The seamless connection between graphene and VA-CNT facilitates electron transport from the Ge to the Cu current collector. Graphene serves to alleviate mechanical strain between the electrode and current collector. The mechanical resilience of the GCNT lessens Ge pulverization on charge/discharge of the LIB. As a result, the Ge/GCNT anode has a high specific capacity of 1315 mAh/g after 200 cycles at 0.5 A/g and a high rate performance of 803 mAh/g at 40 A/g.Download high-res image (347KB)Download full-size image

It was demonstrated that suitable interfaces between two materials can enhance the separation of photogenerated carriers. In this study, ZrO2/ZnO interfaces with type I structure were designed and prepared by the electrospinning technique. The obtained ZrO2/ZnO:Eu3+ (ZZOE) composites are highly porous in the form of nanobelts with width of 600–700 nm, comprising ZnO and ZrO2 nanocrystals, and the Eu doping can hinder the t–m phase transition of ZrO2. By tuning the annealing temperature, the inner stress and defects can be well controlled to improve the photoluminescence (PL) of the ZZOE porous nanobelts. Macro- and micro-PL spectra indicated that the body oxygen vacancies benefit the PL from Eu3+ ions, whereas the surficial ones do not. The optimal parameters for the preparation of ZZOE porous nanobelts were also investigated. Finally, a charge transfer mechanism was proposed to illuminate the PLs from the ZZOE porous nanobelts.

It is reported that Li ions can contribute a lot to the capacitance of aqueous Li-ion capacitors (LICs), which might be due to the intercalation/de-intercalation processes of Li+ ions that also occur at the anodes. However the energy storage mechanism in the aqueous LIC system still requires further proof. In this work, a type of aqueous fiber-shaped LIC has been designed and developed using hydrogenated Li4Ti5O12 (H-LTO) anodes, active carbon (AC) cathodes, and LiCl/PVA gel electrolytes with a double-helical structure. The obtained single LTO wire electrode exhibits a high specific capacitance in volume (34.1 F cm−3) and superior cycling stabilities (∼100% over 100 000 cycles), both of which are due to the formed amorphous layers at the surface of the electrodes. Moreover, it is found via sweep voltammetry analysis that most of the energy stored in an aqueous fiber-shaped capacitor electrode is attributed to the Li ions’ intercalation, whose content exceeds 85% at a low scan rate and gradually decreases with increasing scan rate; while the energy stored by the double electric layers remains almost unchanged with different scan rates. Furthermore, the well-matched wearable fiber-shaped LICs show high capacitive behaviors (18.44 μW h cm−2) and superior static/dynamic cycling stabilities. This research would provide some insight into the charge storage mechanism in electrodes in the aqueous system, and give more suggestions to develop high-energy-density fiber-shaped energy storage devices.

Nanostructured photocatalysts are often attractive due to their enhanced photocatalytic performance by the quantization effect. In this study, BiVO4 quantum dots were decorated on the surface of screw-like SnO2 nanostructures by successive ionic layer absorption and reaction method. The distinctions from bulk materials and the role of BiVO4 quantum dots were investigated in their function as a water splitting photoanode. It was demonstrated that the band-gap of BiVO4 could increase to 2.6 eV when the particle size decreased to about 5 nm, but the band gap of the bulk was only 2.4 eV. Moreover, the decrease in particle size and the coupling with screw-like SnO2 nanostructures enhanced the photocurrent density up to two times under visible light irradiation. The incident photon to current conversion efficiency also increased up to 13.47% at 400 nm. Furthermore, by depositing Pt as cocatalyst, splitting water into hydrogen was realized on the BiVO4 quantum dot/screw-like SnO2 nanostructures under visible light irradiation, and the generation rate is up to 1.16 μmol h−1 cm−2. The improved photoelectrochemical properties and the enhanced photocatalytic activity for hydrogen evolution are attributed to the effective electron-transfer between BiVO4 quantum dots and screw-like SnO2 nanostructures, and the accordingly prolonged photogenerated charge carrier lifetime, as well as the elevated conduction band bottom level of BiVO4 and SnO2 due to the band-gap widening and energy level realignment.

It is challenging to design a photocatalyst with high-efficiency light absorption, charge separation and even high-efficiency charge transfer. Here, we report a demonstration by utilizing a three-dimensional multilayered core–shell nanowire array (rGO-ITO@BiVO4) as the composite photocatalyst. The core–shell structure can shorten the length of charge transfer and enhance light absorption through multireflection. RGO with defects can work as the charge transfer medium to improve the hole injection from semiconductor to electrolyte. Associated with the above effects, the Co-pi electrocatalyst modified rGO-ITO@BiVO4 photocatalyst yields a photocurrent of about 6.0 mA cm−2 at 0.6 V vs. Ag/AgCl. Transient-state surface photovoltage measurement shows that the rGO layer can prolong the lifetime of the photogenerated holes through π–π interactions, so that more holes can participate in the water oxidation reaction.

Rational design and synthesis of core/shell nanostructures as binder-free electrodes has been believed to be an effective strategy to improve the electrochemical performance of supercapacitors. In this work, hierarchical ZnCo2O4@NixCo2x(OH)6x core/shell nanowire arrays (NWAs) have been successfully constructed by electrodepositing NixCo2x(OH)6x nanosheets onto hydrothermally grown ZnCo2O4 nanowires and investigated as a battery-type electrode for hybrid supercapacitors. Taking advantage of the hierarchical core/shell structures and the synergetic effect between ZnCo2O4 nanowires and NixCo2x(OH)6x nanosheets, the optimised core/shell electrode exhibits remarkable electrochemical performance with a high areal capacity (419.1 μA h cm−2), good rate capability and cycling stability. Moreover, the assembled ZnCo2O4@NixCo2x(OH)6x//activated carbon (AC) hybrid device can be reversibly cycled in a large potential range of 0–1.7 V and deliver a maximum energy density of 26.2 W h kg−1 at 511.8 W kg−1. Our findings indicate that the hierarchical ZnCo2O4@NixCo2x(OH)6x core/shell NWAs have great potential for applications in energy storage devices.

In recent years, as a new member of ultraviolet photodetectors (UV-PDs), photoelectrochemical UV-PDs (PEC UV-PDs) have received great attention. Compared to conventional photoconductors, PEC UV-PDs exhibit a number of merits, including low cost, environmentally friendly nature, being self-powered, and fast response. This tutorial review provides a comprehensive introduction to this research field, covering from the basics of performance evaluation of PEC UV-PDs, the state-of-the-art advances in structural design, electrolyte matching, and electrode fabrication of PEC UV-PDs, to the integration of multiple functions into a PEC UV-PD. In the end, we present our perspectives on the future development of PEC UV-PDs and highlight the key technical challenges in aiming to stimulate further developments in this research field.

•Ca-doped α-Fe2O3 nanotubes were synthesized by a simple electrospinning method.•Grain size of the samples is significantly affected by Ca contents.•Ca-doped sensors exhibit enhanced responses toward both ethanol and acetone.•A sensing mechanism is proposed based on the grain refining effect of Ca dopants.Here we report a type of electrospun α-Fe2O3 nanotubes doped with different mole percentage of calcium (Ca) elements and the grain refining effect of Ca on the properties of the obtained samples. Results show that the microstructures and morphologies of the as-prepared α-Fe2O3 nanotubes are significantly affected by doping contents (1–15 mol%). With increasing Ca doping content, the grain size of α-Fe2O3 nanotubes decreases monotonously (named “grain refining effect”). This is due to the low calcination temperature and a large mismatch between the radii of Ca2+ and Fe3+ ions. Moreover, gas-sensing tests show that the Ca-doped α-Fe2O3 nanotube based sensors exhibit enhanced gas-sensing properties toward both ethanol and acetone. At an optimal operating temperature of 200 °C, 7 mol% Ca-doped sensors present the highest response value to ethanol (26.8/100 ppm) and acetone (24.9/100 ppm) with a fast response/recovery rate. Furthermore, a possible gas-sensing mechanism is proposed, which suggests the grain refining effect of Ca dopants plays a dominant role in improving the sensing performances of α-Fe2O3 nanotubes.

•Screw-like SnO2 nanostructure was used as photoanode for PEC water-splitting.•The novel structure combined the advantages of 1D nanowire and 2D nanosheet.•The water-splitting efficiency has been significantly improved.We report the fabrication of screw-like SnO2 nanostructure and its application as photoanode for photoelectrochemical water splitting. The structure was formed by growing thread-like SnO2 nanosheets onto rod-like single-crystalline SnO2 nanowires. Such a structure offers an efficient light absorption, high speed electron transport and a large surface-to-volume ratio. The light absorption efficiency of the screw-like SnO2 nanostructures can be increased by up to 33% than that of the pristine SnO2 nanowires. After decorated with CdS quantum dots, the photocurrent density can reach 9.9 mA cm−2 at 0 V (versus saturated calomel electrode) which corresponding to a hydrogen generation of 159.6 μmol (h cm2)−1 and the faradic efficiency is around 86%. The result demonstrated that the water-splitting efficiency of photoelectrochemical cell has been significantly improved by using such a screw-like structure. Our work provides an efficient solution to improve the water-splitting performance and it can also be a model structure for similar electrode materials.Screw-like SnO2 nanostructure that serves as a model architecture for efficient photoelectrochemical water splitting devices.

Hierarchical hybrid electrodes were successfully fabricated by electrodeposition of ultrathin cobalt sulfide (CoSx) nanosheets on NiCo2S4 nanotube arrays grown on Ni foam for high-performance supercapacitors. The hierarchical NiCo2S4@CoSx core/shell nanotube arrays exhibit a high areal capacitance (4.74 F cm−2 at a current density of 5 mA cm−2), a good rate capability (2.26 F cm−2 at 50 mA cm−2) and cycle stability (76.1% capacitance retention after 1500 cycles at a high current density of 50 mA cm−2), which are much better than those of NiCo2S4 nanotubes. Such superior electrochemical performance could be attributed to the smart configuration of the two electroactive materials, which can provide more pathways for electron transport and improve the utilization rate of the electrode materials. This effective strategy shows the feasibility of designing and fabricating metal sulfides with core/shell hybrid structures as electrode materials for high-performance supercapacitors.

This study reports the preparation of 3D hierarchical carbon nanotube (CNT) @MnO2 core–shell nanostructures under the assistance of polypyrrole (PPy). The as-prepared CNT@PPy@MnO2 core–shell structures show a perfect coating of MnO2 on each CNT and, more importantly, a robust bush-like pseudocapacitive shell to effectively increase the specific surface area and enhance the ion accessibility. As expected, a high specific capacity of 490–530 F g−1 has been achieved from CNT@PPy@MnO2 single electrodes. And about 98.5% of the capacity is retained after 1000 charge/discharge cycles at a current density of 5 A g−1. Furthermore, the assembled asymmetric CNT@PPy@MnO2//AC capacitors show the maximum energy density of 38.42 W h kg−1 (2.24 mW h cm−3) at a power density of 100 W kg−1 (5.83 mW cm−3), and they maintain 59.52% of the initial value at 10000 W kg−1 (0.583 W cm−3). In addition, the assembled devices show high cycling stabilities (89.7% after 2000 cycles for asymmetric and 87.2% for symmetric), and a high bending stability (64.74% after 200 bending tests). This ability to obtain high energy densities at high power rates while maintaining high cycling stability demonstrates that this well-designed structure could be a promising electrode material for high-performance supercapacitors.

We report the fabrication of cadmium sulfide (CdS) quantum dot-decorated barium stannate (BaSnO3) nanowires and their application as photoanodes for photoelectrochemical water splitting. First, polycrystalline BaSnO3 nanowires, which have a perovskite structure, were prepared by electrospinning their polyvinylpyrrolidone polymer precursors and calcining the resultant polymer fibres. Then, CdS quantum dots were decorated onto the BaSnO3 nanowires by a wet-chemical method. Our results show that the hybrid photoanode made of the CdS quantum dot-decorated BaSnO3 nanowires exhibits a high photocurrent density up to 4.8 mA cm−2 at 0 V (vs. saturated calomel electrode), which corresponds to a hydrogen generation rate of 71.8 μmol (h cm2)−1 with a faradaic efficiency of around 80%. Its favourable performance was attributed to the effective charge separation at the type II staggered gap heterojunction formed at the BaSnO3/CdS interface, and the low charge recombination in BaSnO3 nanowires during transport. Our findings indicate that the water splitting performance of photoelectrochemical cells can be highly improved by rationally building a type II band alignment heterojunction with sensitizing quantum dots and wide band gap semiconductor nanowires which have a low charge recombination rate during transport.

Highly flexible porous carbon nanofibers (P-CNFs) were fabricated by electrospining technique combining with metal ion-assistant acid corrosion process. The resultant fibers display high conductivity and outstanding mechanical flexibility, whereas little change in their resistance can be observed under repeatedly bending, even to 180°. Further results indicate that the improved flexibility of P-CNFs can be due to the high graphitization degree caused by Co ions. In view of electrode materials for high-performance supercapacitors, this type of porous nanostructure and high graphitization degree could synergistically facilitate the electrolyte ion diffusion and electron transportation. In the three electrodes testing system, the resultant P-CNFs electrodes can exhibit a specific capacitance of 104.5 F g–1 (0.2 A g–1), high rate capability (remain 56.5% at 10 A g–1), and capacitance retention of ∼94% after 2000 cycles. Furthermore, the assembled symmetric supercapacitors showed a high flexibility and can deliver an energy density of 3.22 Wh kg–1 at power density of 600 W kg–1. This work might open a way to improve the mechanical properties of carbon fibers and suggests that this type of freestanding P-CNFs be used as effective electrode materials for flexible all-carbon supercapacitors.Keywords: electrospinning; flexible; graphitization; porous carbon nanofibers; supercapacitors

•SnO2 nanowires network with high crystallinity is directly grown on FTO glass.•A 3D SnO2/TiO2/CdS multi-heterojunction is developed for PEC hydrogen production.•A high photocurrent of 8.75 mA cm−2 at 0 V vs. SCE is observed.Here, we present a kind of SnO2 nanowires/TiO2 nanoneedles/CdS quantum dots multi-heterojunction structure. In this rational heterojunction structure, three dimensional SnO2 nanowires were directly grown on conductive fluorine doped tin oxide (FTO) glass by chemical vapor deposition method and served as the faster electron transport network for highly efficient photoelectrochemical system. Moreover, after artful design of branched TiO2 nanoneedles on this network and then sensitized by CdS quantum dots, a multi-heterojunction structure of SnO2/TiO2/CdS was formed. This novel three dimensional multi-heterojunction structure exhibited remarkable performances on photoelectrochemical hydrogen production. The photocurrent density is as high as 8.75 mA cm−2 at a potential of 0 V vs. saturated calomel electrode (SCE) by using the optimized conditions. More impressively, the photocurrent density is more than 4 times larger than that of single SnO2–TiO2 heterojunction (1.72 mA cm−2) at 0 V vs. SCE.

•ZnCo2O4 microspheres were grown on Ni foam by a hydrothermal method.•The ZnCo2O4 microspheres are consisted of ultrathin porous nanosheets.•The microspheres were directly used as a binder-free electrode for supercapacitor.•The ZnCo2O4 microspheres exhibit remarkable electrochemical performance.Flowerlike ZnCo2O4 microspheres were synthesized using Ni foam substrates by a facile hydrothermal method combining post-annealing treatments. The obtained microspheres are about 5 μm in diameter and composed of porous ultrathin nanosheets. And the supercapacitors based on these microspheres show a high specific capacitance (689.4 F/g at the current density of 1 A/g), good rate performance (336.6 F/g at 15 A/g), and excellent cyclic stability (97.1% capacitance retention after 1500 cycles at a high current density of 10 A/g). These remarkable electrochemical performances imply that the flowerlike ZnCo2O4 microspheres would have great potential applications in SCs.

Assembly techniques of graphene have attracted intense attention since their performance strongly depends on the manners in which graphene nanosheets are arranged. In this work, we demonstrate a viable process to synthesize winged graphene nanofibers (G-NFs) which could generate optimized pore size distribution by the fiber-like feature of graphene. The G-NF frameworks were achieved by processing the precursor graphene oxide nanosheets with the following procedures: microwave (MW) irradiation, salt addition, freeze-drying, and chemical reduction. The resultant framework composed of winged G-NFs with a diameter of 200–500 nm and a length of 5–20 μm. Moreover, the crimp degree of G-NFs can be rationally controlled by MW irradiation time. A formation mechanism of such winged G-NFs based on the synergistic effects from MW irradiation and solution ionic strength change has been proposed. With a practice in flexible electrode, after decorated with amorphous MnO2, the G-NF frameworks shows an enhanced specific capacitance compared to graphene nanosheets (G-NSs). This research has developed a controllable method to synthesis G-NFs, which can offer hierarchical pore structures, this kind of graphene nanostructure might enhance their performance in supercapacitor and related fields.Keywords: capacitive performance; graphene nanofiber; ionic strength; microwave irradiation; three-dimensional framework

A type of freestanding three-dimensional (3D) micro/nanointerconnected structure, with a conjunction of microsized 3D graphene networks, nanosized 3D carbon nanofiber (CNF) forests, and consequently loaded MnO2 nanosheets, has been designed as the electrodes of an ultralight flexible supercapacitor. The resulting 3D graphene/CNFs/MnO2 composite networks exhibit remarkable flexibility and highly mechanical properties due to good and intimate contacts among them, without current collectors and binders. Simultaneously, this designed 3D micro/nanointerconnected structure can provide an uninterrupted double charges freeway network for both electron and electrolyte ion to minimize electron accumulation and ion-diffusing resistance, leading to an excellent electrochemical performance. The ultrahigh specific capacitance of 946 F/g from cyclic voltammetry (CV) (or 920 F/g from galvanostatic charging/discharging (GCD)) were obtained, which is superior to that of the present electrode materials based on 3D graphene/MnO2 hybrid structure (482 F/g). Furthermore, we have also investigated the superior electrochemical performances of an asymmetric supercapacitor device (weight of less than 12 mg/cm2 and thickness of ∼0.8 mm), showing a total capacitance of 0.33 F/cm2 at a window voltage of 1.8 V and a maximum energy density of 53.4 W h/kg for driving a digital clock for 42 min. These inspiring performances would make our designed supercapacitors become one of the most promising candidates for the future flexible and lightweight energy storage systems.Keywords: 3D micro/nanointerconnected structure; flexible; supercapacitors; ultralight; uninterrupted charges transfer pathways;

•SnO2–TiO2 branched nanostructure serves as model architecture for DSSCs.•The novel structure combines fast electron transport, slow recombination and high specific surface area.•A maximum efficiency of 7.06% was achieved.We report a branched hierarchical nanostructure of TiO2 nanoneedles on SnO2 nanofiber network (B-SnO2 NF) that serves as model architecture for highly efficient dye-sensitized solar cells (DSSCs). The nanostructure simultaneously offers a low degree of charge recombination, a fast electron transport and a large specific surface area. The power conversion efficiency for B-SnO2 NF52 (with SnO2 NF diameter ∼52 nm) is up to 7.06%, increased by 26% and 40% compared to B-SnO2 NF113 (5.57%, with SnO2 NF diameter ∼113 nm) and TiO2 nanoparticle (5.04%, P25), respectively, and more than five times as large as SnO2 NF52 (1.34%). The distinct photovoltaic behavior of the B-SnO2 NF52 is its large short-circuit current density (Jsc, 20.5 mA cm−2) as compared with the commonly used P25 photoanode (11.7 mA cm−2). Our results indicate that Jsc enhancement derived by the slower electron recombination associated with the SnO2–TiO2 core–shell heterojunction and faster electron transport in SnO2 NF network could synergistically contribute to high efficiency.

Porous Co3O4 nanonetworks (NNWs), converted from precursor CoOOH nanosheets, have been synthesized via a controllable chemical reaction route followed by calcination at 400 °C in air. The morphologies and microstructures of the precursor nanosheets and the final products were characterized by high-resolution transmission electron microscopy and X-ray diffraction, respectively. The growth mechanism of CoOOH nanosheets and the structural transformation processes of NNWs were investigated in detail. Significantly, the porous Co3O4 NNW based sensor showed an enhanced response to toluene gas at low concentration, which was mainly due to its porous neck-connected networks.

The enhanced luminescent properties of Tb3+ and Gd3+ doped ZrO2 nanoparticles (NPs) modified by coating with a shell were investigated. The pure cores, synthesized by a hydrothermal process, are in a high quality tetragonal phase and a monoclinic phase with an average size constant of ~7 ± 2 nm. The thickness and composition of the SiO2 shell can make a difference to the luminescent properties of the NPs. The intensity of the green light emission was enhanced remarkably after coating the active shell (containing Gd3+) around the ZrO2:Gd3+, Tb3+ NPs. The increased photoluminescence (PL) intensity is attributed to a reduced non-radiative recombination based on a longer luminescence decay time and an energy transfer from the Gd3+ in the shell to the adjacent Tb3+ ions. These results are important for the future optoelectronic applications of the Tb-doped ZrO2 nanoparticles.

Ni(OH)2 nanosheet/3D graphene (3DG) framework hybrid materials have been prepared by combining chemical vapor deposition (CVD) technology and a facile hydrothermal method. The free-standing Ni(OH)2 nanosheet/3DG composite was investigated as the cathode material for supercapacitors without the need for addition of either binder or metal-based current collector. Consequently, the obtained Ni(OH)2 nanosheet/3DG composite electrode exhibits superior specific capacitance and rate capability to the Ni(OH)2 nanosheet/Ni foam and Ni(OH)2 nanosheet/carbon fiber cloth composite electrodes. This novel structure brings the composite an electrochemical capacitance as high as 2860 F g−1 at a current density of 2 A g−1, and maintains 1791 F g−1 at 30 A g−1. Moreover, the composite electrode also exhibits a high specific capacitance of 2461 F g−1 at a scan rate of 5 mV s−1.

•The diamond particles after repair have smooth surface and neat edges.•This method to prepare micron sized crushed diamond particles is efficient.•The mechanism of using HFCVD to repair diamond particles is very simple.Defects on diamond surface have a profound effect on certain properties of the diamond, enabling these properties to be tailored to the specific needs of important applications. A simple and practical method is described to repair the diamond particles with surface defects. The low grade diamond particles were repaired by hot-filament chemical vapor deposition with low carbon concentration in feed gases, and the defects on the surfaces disappeared because of the simple film formation and homoepitaxial growth mechanism during the CVD process. This efficient and simple method provides a way to extend its useful life during the actual application.

•An ultrathin, transparent SnO2–TiO2 core–shell structure was developed.•This structure was used in self-powered UVPDs.•UVPDs deliver large responsivity (0.6 A/W) and high on/off ratio (440,563%).We have fabricated SnO2 nanosheet film directly on conductive glass and further designed branched TiO2 nanoneedles on SnO2 nanosheets, forming a heterojunction core–shell structure. The resultant ultrathin and high transparency film can serve as the fast electron transport network for a new developed photoelectrochemical cell based UV photodetector. The UV photodetector shows great responsivity (0.6 A/W); high on/off ratio of the Jsc signal (440,563%); very fast response (0.02 s for rise time and 0.004 s for decay time) under 40 mW cm−2 UV irradiation. Compared with the previous reported devices, our detector emerges comparable and even better self-powered UV light detecting properties just using less material.

•Tungsten carbide porous films have been prepared by HFCVD.•The contact angle measurements show that the films exhibit excellent hydrophilicity.•The film after the treatment of hydrogen has a contact angle of 8.6°.Tungsten carbide porous films have been prepared by hot filament chemical vapor deposition with carbonized tungsten filaments as precursors. The structural properties and morphologies of the nanofilms were characterized by XRD, SEM and Raman. There are many nanocones and channels in the surface. A possible formation mechanism of the structure was proposed. And the contact angle measurements show that the films exhibit excellent hydrophilicity, especially the film after the treatment by hydrogen has a contact angle of 8.6°. The high roughness and chemical composition on the surface are responsible for its hydrophilicity. Therefore, this film maybe has potential as electrocatalyst and electrocatalyst support.The films exhibit excellent hydrophilicity, especially the film after the treatment of hydrogen has a contact angle of 8.6°.

ZnO-silver (Ag) heterostructure nanoparticle films were prepared by spin-coating, followed by annealing at 700°C for 2 h. The films were then used as UV photodetector which show high photoresponse. The heterostructure-film device displayed an ultrafast decay time of 18 ms and a rise time of 50 ms upon ultraviolet irradiation. Additionally, the time-dependent photocurrent upon UV switching reveals a rectangularly shaped profile, rarely reported in previous literature. The highly improved photoresponse properties of ZnO-Ag heterostructure-film device could be attributed to the Schottky barrier height (SBH) and depletion width reduction from the embedded Ag nanoclusters. Compared to a pure ZnO film, both the responsivity (Rλ) and external quantum efficiency (EQE) of the ZnO-Ag heterostructure-film photodetectors were improved more than 13-fold. This research provides a promising strategy for fabricating UV-photodetectors with ultrafast response.

Wire-in-tube structures have previously been prepared using an electrospinning method by means of tuning hydrolysis/alcoholysis of a precursor solution. Nickel–zinc ferrite (Ni0.5Zn0.5Fe2O4) nanowire-in-nanotubes have been prepared as a demonstration. The detailed nanoscale characterization, formation process and magnetic properties of Ni0.5Zn0.5Fe2O4 nanowire-in-nanotubes has been studied comprehensively. The average diameters of the outer tubes and inner wires of Ni0.5Zn0.5Fe2O4 nanowire-in-nanotubes are around 120 nm and 42 nm, respectively. Each fully calcined individual nanowire-in-nanotube, either the outer-tube or the inner-wire, is composed of Ni0.5Zn0.5Fe2O4 monocrystallites stacked along the longitudinal direction with random orientation. The process of calcining electrospun polymer composite nanofibres can be viewed as a morphologically template nucleation and precursor diffusion process. This allows the nitrates precursor to diffuse toward the surface of the nanofibres while the oxides (decomposed from hydroxides and nitrates) products diffuse to the core region of the nanofibres; the amorphous nanofibres transforming thereby into crystalline nanowire-in-nanotubes. In addition, the magnetic properties of the Ni0.5Zn0.5Fe2O4 nanowire-in-nanotubes were also examined. It is believed that this nanowire-in-nanotube (sometimes called core–shell) structure, with its uniform size and well-controlled orientation of the long nanowire-in-nanotubes, is particularly attractive for use in the field of nano-fluidic devices and nano-energy harvesting devices.

Flexible and high performance supercapacitors are very critical in modern society. In order to develop the flexible supercapacitors with high power density, free-standing and flexible three-dimensional graphene/carbon nanotubes/MnO2 (3DG/CNTs/MnO2) composite electrodes with interconnected ternary 3D structures were fabricated, and the fast electron and ion transport channels were effectively constructed in the rationally designed electrodes. Consequently, the obtained 3DG/CNTs/MnO2 composite electrodes exhibit superior specific capacitance and rate capability compared to 3DG/MnO2 electrodes. Furthermore, the 3DG/CNTs/MnO2 based asymmetric supercapacitor demonstrates the maximum energy and power densities of 33.71 W h kg−1 and up to 22727.3 W kg−1, respectively. Moreover, the asymmetric supercapacitor exhibits excellent cycling stability with 95.3% of the specific capacitance maintained after 1000 cycle tests. Our proposed synthesis strategy to construct the novel ternary 3D structured electrodes can be efficiently applied to other high performance energy storage/conversion systems.

Under the background of the quick development of lightweight, flexible, and wearable electronic devices in our society, a flexible and highly efficient energy management strategy is needed for their counterpart energy-storage systems. Among them, flexible electrochemical capacitors (ECs) have been considered as one of the most promising candidates because of their significant advantages in power and energy densities, and unique properties of being flexible, lightweight, low-cost, and environmentally friendly compared with current energy storage devices. In a common EC, carbon materials play an irreplaceable and principal role in its energy-storage performance. Up till now, most progress towards flexible ECs technologies has mostly benefited from the continuous development of carbon materials. As a result, in view of the dual remarkable highlights of ECs and carbon materials, a summary of recent research progress on carbon-based flexible EC electrode materials is presented in this review, including carbon fiber (CF, consisting of carbon microfiber-CMF and carbon nanofiber-CNF) networks, carbon nanotube (CNT) and graphene coatings, CNT and/or graphene papers (or films), and freestanding three-dimensional (3D) flexible carbon-based macroscopic architectures. Furthermore, some promising carbon materials for great potential applications in flexible ECs are introduced. Finally, the trends and challenges in the development of carbon-based electrode materials for flexible ECs and their smart applications are analyzed.

Pt-functionalized NiO composite nanotubes were synthesized by a simple electrospinning method, and their morphology, chemistry, and crystal structure have been characterized at the nanoscale. It was found that the Pt nanoparticles were dispersed uniformly in the NiO nanotubes, and the Pt-functionalized NiO composite nanotubes showed some dendritic structure in the body of nanotubes just like thorns growing in the nanotubes. Compared with the pristine NiO nanotube based gas sensor and other NiO-based gas sensors reported previously, the Pt-functionalized NiO composite nanotube based gas sensor showed substantially enhanced electrical responses to target gas (methane, hydrogen, acetone, and ethanol), especially ethanol. The NiO–Pt 0.7% composite nanotube based gas sensor displayed a response value of 20.85 at 100 ppm at ethanol and 200 °C, whereas the pristine NiO nanotube based gas sensor only showed a response of 2.06 under the same conditions. Moreover, the Pt-functionalized NiO composite nanotube based gas sensor demonstrated outstanding gas selectivity for ethanol against methane, hydrogen, and acetone. The reason for which the Pt-functionalized NiO composite nanotube based gas sensor obviously enhanced the gas sensing performance is attributed to the role of Pt on the chemical sensitization (catalytic oxidation) of target gases and the electronic sensitization (Fermi-level shifting) of NiO.Keywords: chemical sensitization; electronic interaction; electronic sensitization; Fermi-level shifting; pristine NiO; Pt-functionalized NiO;

•Preparation of ZnO nanostrawberry aggregates with excellent light scattering.•ZnO nanostrawberry aggregates film induces large Jsc and PCE in DSSCs.•Self-powered, ultrafast and visible blind UV detection based on photoelectrochemical cell.We report ZnO nanostrawberry aggregates (ZnO NS) structure that serves as photoanode for efficient DSSCs as it offers a large specific surface area, excellent light scattering characteristics, and low degree of charge recombination simultaneously. The short-circuit current density (Jsc) of the ZnO NS DSSC is more than two times higher than that of commercially-obtained ZnO nanocrystallines (ZnO NC) due to the excellent light scattering of the ZnO NS film, resulting in a 46% improvement in the power conversion efficiency (PCE). The introduction of TiO2 coating layer on to the ZnO NS (ZnO NS–TiO2) results in more than 82% enhancement in the PCE from 1.40% to 2.56%. Moreover, the photoelectrochemical cell (PECC) with unsensitized ZnO NS–TiO2 film as photoanode is applied to detect the UV light without a power source. This self-powered UV-photodetector exhibits a high on/off ratio of 37,900, a fast rise time of 0.022 s and a decay time of 0.009 s for Jsc signal, together with the excellent self-powered, “visible blind” characteristics and photosensitivity linearity in a wide light intensity range.

In2O3/α-Fe2O3 (IFO) heterostructure nanotubes, with cubic-In2O3 nanocrystals randomly distributed on the surface of α-Fe2O3 nanotube-based backbones, were successfully prepared through a facile single-capillary electrospinning method. The morphologies of the resulting electrospun products were characterized by scanning electron microscopy and transmission electron microscopy. The crystal structures and components were determined by X-ray diffraction and energy-dispersive X-ray spectra, respectively. The results show that the morphology and structure of the products could be tailored by changing the content of indium nitrate in the precursor solutions and the calcination temperatures. Moreover, the IFO-0.1 (In/Fe = 1:9, molar ratio) nanotubes based sensor shows a high sensitivity to ethanol with a fast response/recovery time, and the performance is stable at a low operating temperature, which gives a potential application in ethanol gas sensors. A possible gas sensing mechanism based on the role of In2O3 in such a heterostructure is also discussed in detail.

Porous ultrathin NiO nanosheets have been synthesized by a simplified chemical bath deposition method with subsequent thermal decomposition of a layered precursor of nickel hydroxide (Ni(OH)2). The crystalline and morphological structures of products, which were characterized by X-ray diffraction, field-emission scanning electron microscopy and high resolution transmission electron microscopy, show that the nanopores form with a phase transition at the calcination process. The pure cubic NiO phase, with an average grain size of 4.67 nm and a thickness less than 5 nm, forms at 450 °C for 2 h in air. Moreover, the NiO nanosheets synthesized here show an enhanced response to ethanol at a low temperature of 200 °C. The unique architecture with neck-connected networks and a high specific area was applied to explain the enhancement of the ethanol sensing performance. Furthermore, the sensor exhibits an excellent selectivity to ethanol against methanol, acetone, toluene, hydrogen, and methane by a cross-response test.

•We demonstrated that the solvent plays a critical role in the nanotubes formation process which can be controlled by the ambient temperature.•For a selected solvent, the saturated vapor pressure was the intrinsic factor for the morphologies determining during the electrospinning process.•The formation process of nanotubes was observed by TEM and a possible formation mechanism was proposed.•The magnetic properties of magnesium ferrite calcined at different temperature stages were systematically studied.In this work, we have demonstrated that the solvent plays a critical role in the nanotubes formation process which can be controlled by the ambient temperature. It is believed that the ambient temperature and the rate of evaporation of the solvent during the electrospinning process are the major factors controlling the formation of different electrospun nanofibre morphologies. By their very nature, electrospun different nanofibre morphologies depend on the competition between the phase separation dynamics and the evaporation rate of solvent controlled by the phase diagram of the polymer solution. In our experiments, MgFe2O4 nanotubes are prepared by using different solvent mixtures at a specific ambient temperature (ethanol at room temperature and deionized water homogeneous temperature field of 45 °C) by single capillary electrospinning process, and compared with MgFe2O4 nanofibers obtained using deionized water at room temperature. A possible formation mechanism, morphology template effect combined with phase separation theory, is proposed to interpret the formation process of the MgFe2O4 nanotubes. Detailed morphology, structural characterizations show that individual MgFe2O4 nanotubes are made of MgFe2O4 nanocrystals stacking along the nanotubes with no preferred growth directions and individual nanocrystals are single crystal with a cubic spinel structure. In addition, the magnetic properties of MgFe2O4 nanotubes calcined at different temperature will be reported and discussed.

A new microwave plasma process is developed to refine and purify metallurgical grade silicon (MG-Si) effectively. Inductively coupled plasma-atomic emission spectrometry analysis (ICP-AES) indicates that the concentrations of impurities in silicon decrease significantly in the process, particularly for phosphorus, whose average removal rate is close to 100% after microwave plasma treatment of only 5 min. The underlying mechanisms of the ultra-high removal rate of impurity atoms are discussed in detail in this paper. The photoresponse switching behavior of n+-Si wafers that are made of as-purified silicon provides further evidence for the unique advantage arising from the use of microwave plasma in the purification of MG-Si.Highlights► A new microwave plasma purification technique was proposed. ► The purification effect was significant after treatment for 15 min. ► The removal rate of the element P is 100% only for 5 min treatment. ► The experimental temperature was 1000 °C, lower than other plasma techniques.

A lightweight, flexible, and highly efficient energy management strategy is needed for flexible energy-storage devices to meet a rapidly growing demand. Graphene-based flexible supercapacitors are one of the most promising candidates because of their intriguing features. In this report, we describe the use of freestanding, lightweight (0.75 mg/cm2), ultrathin (<200 μm), highly conductive (55 S/cm), and flexible three-dimensional (3D) graphene networks, loaded with MnO2 by electrodeposition, as the electrodes of a flexible supercapacitor. It was found that the 3D graphene networks showed an ideal supporter for active materials and permitted a large MnO2 mass loading of 9.8 mg/cm2 (∼92.9% of the mass of the entire electrode), leading to a high area capacitance of 1.42 F/cm2 at a scan rate of 2 mV/s. With a view to practical applications, we have further optimized the MnO2 content with respect to the entire electrode and achieved a maximum specific capacitance of 130 F/g. In addition, we have also explored the excellent electrochemical performance of a symmetrical supercapacitor (of weight less than 10 mg and thickness ∼0.8 mm) consisting of a sandwich structure of two pieces of 3D graphene/MnO2 composite network separated by a membrane and encapsulated in polyethylene terephthalate (PET) membranes. This research might provide a method for flexible, lightweight, high-performance, low-cost, and environmentally friendly materials used in energy conversion and storage systems for the effective use of renewable energy.Keywords: 3D conductive network; flexible; graphene; MnO2; supercapacitor; ultralight

CoFe2O4 nanotubes have been directly fabricated by single-capillary spinneret electrospinning. The external diameter of the CoFe2O4 nanotubes ranges from 60 nm to 160 nm. The morphology and structure characterizations show that individual CoFe2O4 nanotubes are made of CoFe2O4 nanocrystals stacking along the nanotubes with no preferred growth directions and these individual nanocrystals are single crystal with a cubic spinel structure. Each nanocrystal was shown to be a single magnetic domain. The magnetic measurements show that the coercivity (Hc) of the CoFe2O4 nanotubes decreases from 10400 Oe at 5 K to 300 Oe at 360 K. The CoFe2O4 nanotubes have a spin reorientation (SR) at 5 K, which is different from CoFe2O4 nanorods and nanoparticles. Based on the observed morphology and crystal structure, a micromagnetic model, “chain-of-rings”, is developed to interpret the magnetic behavior of the CoFe2O4 nanotubes. The theoretical coercivity (534 Oe) is in good agreement with the experimental results (509 Oe). It is believed that our work should open a new route to prepare various magnetic ferrite nanotubes and is significant for expanding the application of CoFe2O4 into the new fields.

A high-efficiency photoelectrode for dye-sensitized solar cells (DSSCs) should combine the advantageous features of fast electron transport, slow interfacial electron recombination and large specific surface area. However, these three requirements usually cannot be achieved simultaneously in the present state-of-the-art research. Here we report a simple procedure to combine the three conflicting requirements by using porous SnO2 nanotube–TiO2 (SnO2 NT–TiO2) core–shell structured photoanodes for DSSCs. The SnO2 nanotubes are prepared by electrospinning of polyvinyl pyrrolidone (PVP)/tin dichloride dihydrate (SnCl2·2H2O) solution followed by direct sintering of the as-spun nanofibers. A possible evolution mechanism is proposed. The power conversion efficiency (PCE) value of the SnO2 NT–TiO2 core–shell structured DSSCs (∼5.11%) is above five times higher than that of SnO2 nanotube (SnO2 NT) DSSCs (∼0.99%). This PCE value is also higher than that of TiO2 nanoparticles (P25) DSSCs (∼4.82%), even though the amount of dye molecules adsorbed to the SnO2 NT–TiO2 photoanode is less than half of that in the P25 film. This simple procedure provides a new approach to achieve the three conflicting requirements simultaneously, which has been demonstrated as a promising strategy to obtain high-efficiency DSSCs.

We use electrospinning to prepare chitosan–PVA nanofibers containing graphene. The nanofibers can be directly used in wound healing: graphene, as an antibacterial material, can be beneficial for this. A possible antibacterial mechanism for graphene is presented.

NiFe2O4 multi-particle-chain nanofibres have been successfully fabricated using electrospinning followed by calcination, and their morphology, chemistry and crystal structure were characterized at the nanoscale. Individual NiFe2O4 nanofibres were found to consist of many nanocrystallites stacked along the nanofibre axis. Chemical analysis shows that the atomic ratio of Ni:Fe is 1:2, indicating that the composition was NiFe2O4. The crystal structure of individual NiFe2O4 multi-particle-chain nanofibres proved to be polycrystalline with a face centered cubic (fcc) structure. The nanocrystallites in the nanofibres were revealed to have a single-crystal structure with random crystallographic orientations. The magnetic measurements reveal that the NiFe2O4 multi-particle-chain nanofibres have a coercivity force of 166 Oe. A “chain of sheets” micromagentism model was proposed to interpret the observed magnetic behaviour of the NiFe2O4 multi-particle-chain nanofibres. Simulation studies of the coercivity are in good agreement with the experimental results at room temperature. It is believed that this work will significantly expand the use and application of these compounds in the field of biomagnetic nano-devices and improve understanding of the magnetic origin of spinel ferrites.

A novel method is reported of producing nanofibers/nanotubes (measuring from tens of nanometres to several hundreds of nanometres) containing living cells, mechanically and with ultrahigh speed and at low cost. High-pressure gas was used to extrude viscous precursors through a spray with micron-sized holes into air. The sprayed micro-sized droplets had high velocity and were continuously elongated into uniform nanofibers/nanotubes in a temperature field during their flight. We demonstrated that the throughput of this spinning method to fabricate nanofibers/nanotubes from an individual setup could be as high as 10 g s−1. A possible mechanism for this extrusion method was proposed based on flow mechanics and the experimental results. Additionally, it was shown that the new method could be used to directly prepare nanofibers containing living cells. It was demonstrated that the living cells with high survival rate can be used in bioengineering.

A simple procedure for preparing highly porous TiO2 nanotubes is reported. The nanotubes were prepared in the form of a nonwoven mat by emulsion electrospinning a solution containing poly(vinyl pyrrolidone), titanium tetraisopropoxide and oil, followed by calcination in air at 500 °C. The mixed crystalline material comprised anatase and rutile TiO2 particles, whose diameters were about 11 nm and 21 nm, respectively. The highly porous TiO2 nanotube membranes, which had large specific surface areas and excellent ratios of anatase phase to rutile phase, were shown to have excellent catalytic activities. Also the mixture of crystal forms improved the efficiency of photocatalysis because at the mixed interface electrons and holes are separated effectively. The new method for producing highly porous TiO2 nanotubes is versatile and could be extended to the fabrication of various types of highly porous nanotubes.

Highly transparent nanocrystalline TiO2 films have been fabricated by electrospinning (ES) technique based on a transmutation process from as-spun nanofibers with an appropriate amount of tri-ethanolamine (TEOA) added to the precursor. A possible evolution mechanism of the transparent nanocrystalline TiO2 films is proposed. It is found that the films prepared via transmutation from electrospun nanofibers possess rich bulk oxygen vacancies (BOVs, PL band at 621–640 nm) by using photoluminescence (PL) spectroscopy. Contrastively, the dominant peak in PL spectrum of the spin-coated film is the emission from surface oxygen vacancies (SOVs, PL band at 537–555 nm). The electrospun TiO2 films with rich BOVs induce large open-circuit voltage (Voc) and fill factor (FF) improvements in dye-sensitized solar cells (DSCs), and thus a large improvement of energy conversion efficiency (η). In addition, these performance advantages are maintained for a double-layer cell with a doctor-bladed ∼7 μm top layer (P25 nanometer TiO2, Degussa) and an electrospun ∼3 μm bottom layer. The double-layer cell yields a high η of 6.01%, which has increased by 14% as compared with that obtained from a 10 μm thick P25 film.Highlights► Transparent TiO2 films were prepared by electrospinning. ► TiO2 films with rich bulk oxygen vacancies induce large Voc and FF in DSCs. ► We first used an unsensitized cell to investigate the trap-to-trap electron transport. ► The results from PL measurement show useful information.

Single-phase tungsten carbide nanopillar arrays have been prepared by hot filament chemical vapor deposition with carbonized tungsten filaments as precursors. The structural properties and morphologies of the nanopillar arrays were characterized by XRD, SEM and HRTEM, respectively. A possible formation mechanism for the morphology was proposed. Moreover, the field emission properties of the nanopillar arrays have been studied. The Fowler–Nordheim plot of the nanopillar arrays shows an interesting linear dependence demonstrating their suitability as emitters. The nanopillar arrays show remarkable stability for several hours at a current intensity of about 5.6 × 10−7 A at 2000 V with a distance between the anode and sample of 150 μm.

ZnO nanoparticles-embedded diamond-like amorphous (DLC) carbon films have been prepared by electrochemical deposition. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) results confirm that the embedded ZnO nanoparticles are in the wurtzite structure with diameters of around 4 nm. Based on Raman measurements and atomic force microscope (AFM) results, it has been found that ZnO nanoparticles embedding could enhance both graphitization and surface roughness of DLC matrix. Also, the field electron emission (FEE) properties of the ZnO nanoparticles-embedded DLC film were improved by both lowering the turn-on field and increasing the current density. The enhancement of the FEE properties of the ZnO-embedded DLC film has been analyzed in the context of microstructure and chemical composition.Graphical abstractHighlights► ZnO nanoparticles were embedded within DLC matrix by electrochemical deposition. ► The ZnO nanoparticles were in wurtzite structure. ► ZnO embedding enhanced both surface roughness and graphitization of the films. ► The FEE properties of the films have been enhanced by ZnO embedding.

Detection of ultraviolet (UV) light is usually based on the photoconductivity effect of semiconductors. Here, we demonstrate the application of a photoelectrochemical cell (PECC) as a self-powered UV-photodetector for detecting the UV light. It is based on the photovoltaic effect of PECCs. By connecting a PECC to an ammeter, the intensity of UV light have been quantified using the output short-circuit photocurrent (Isc) of the PECC without a power source. This self-powered UV-photodetector exhibits a high photoresponse sensitivity of 269,850%, a rise time of 0.08 s and a decay time of 0.03 s for Jsc signal. The fast time response, high photosensitivity, and good photosensitivity linearity combined with low-cost, environment-friendly, as well as the facile manufacturing process, make this new type of UV-photodetector suitable for practical applications.Graphical abstractHighlights► Photoelectrochemical cell as a self-powered UV-photodetector. ► Detection of UV light with fast response time and high photosensitivity. ► Preparation technology is compatible to that of DSSCs.

Carbon nanotubes and carbon nanobelts were obtained via single-needle electrospinning on a basis of water-in-oil (W/O) emulsion technique, respectively. The morphology of electrospun products can be controlled by controlling the temperature of the collector during the electrospinning process. The mechanism of fabricating PAN nanotubes and nanobelts by emulsion electrospinning is discussed in detail. Transmission electron microscopy and scanning electron microscope results show that the carbon nanotubes (the inner diameter of 25–50 nm and the outer diameter of 50–100 nm) have a wall thickness of 10–50 nm, and the width and thickness of the nanobelts range from 100 to 300 nm, and 1 to 5 nm, respectively. A slight difference of bonding configuration of the carbon nanofibers, carbon nanotubes and carbon nanobelts is attributed partly to their different topological structures. The novel method is versatile and could be extended to the fabrication of various types of nanotubes and nanobelts.

A novel structure of carbon nanonodules containing fewer than 10 layers graphene has grown on amorphous carbon nanofibers by carbonization-induced self-assembly. It is found that a successive processes containing pre-oxidation in air at 220 °C and carbonization in a high vacuum (1 × 10−4 Pa) at 750 °C are necessary for the fabrication of the carbon nanonodules. Possible mechanism for the evolution of amorphous nanofibers to carbon nanonodules is presented. It is also found that the temperature of the collector during electrospinning of the fiber and the pressure of carbonization are critical factors for growth of the nanonodules. With these mechanisms, carbon nanonodules can be selectively grown on the prepared amorphous carbon nanofibers using pre-oxidation and carbonization of an electrospun glycerol–polyacrylonitrile fiber.

Terbium-doped SiCN (SiCN:Tb) thin films were deposited by rf magnetron reactive sputtering at 800 °C. The as-prepared samples were characterized by XRD, FTIR, and XPS. The results showed that SiCN:Tb films mainly contained both SiC and Si3N4 nano-compositions with complicated chemical bond networks. Photoluminescence measurements indicated that the undoped SiCN films exhibited a blue-green light emission, while SiCN:Tb films emitted a strong green one. The SiC nanocrystallites formed in the undoped SiCN films might be responsible for the blue-green light emission, while the formed quaternary Si–C–Tb–O compositions in the doped samples could account for the strong green PL behaviors.Research Highlights► Strong green light emissions were detected from sputtered Tb-doped SiCN thin films at 800 °C. ► SiC nanocrystallites formed in the undoped SiCN films account for the blue-green light emission. ► Si–C–Tb–O compositions account for the strong green PL.

M2Si5N8:Eu2+-based (M = Ca, Sr) red-emitting phosphors were fabricated at relatively low temperature (1200 °C) and atmospheric pressure using a simple solid-state reaction process. Several processing parameters were systematically investigated to optimize the phosphors structural characterization and photoluminescence performance, including the amount of europium and the properties of the precursor and activated materials. The as-prepared M2Si5N8:Eu2+-based (M = Ca, Sr) phosphors were orange in color and emitted intensively in the red region of 580–670 nm under 465 nm excitation. This simple fabrication technique can be readily used for the optimization of phosphor microstructures and high-performance red-emitting phosphors since it eliminates many air-sensitive precursors.Highlights► Phosphors were fabricated at 1200 °C and atmospheric pressure. ► Precursor and activated materials are crucial factors for phosphors. ► Emission intensity increases nonlinear with increasing the Eu content.

Titanium (Ti)-capped ZnO samples with different roughness were prepared to investigate the effect of ZnO morphology on surface plasma energy of ZnO/Ti interface. ZnO nanoparticle samples with diverse particle shapes, sizes and filling factors were obtained by annealing at different temperatures. Ti-capped ZnO films annealed at 700 °C exhibit excellent photoluminescence property, which can attribute to the high degree of crystallinity (DC) and appropriate surface roughness. Tuning the microcrystalline structure and the ratio of inter-particle distance to the nanoparticle diameter of ZnO can facilitate the surface plasma resonance energy at ZnO/Ti interface close to the near-band-gap emission energy of ZnO, leading to an enhancement of the near-band-gap emission.Highlights► UV emission of ZnO is enhanced by surface plasmon resonance (SPR) with Ti capping. ► SPR energy of ZnO/Ti interface is mainly tailored by changing morphology of ZnO. ► Different morphologies of ZnO are obtained by annealing at different temperatures. ► ZnO film annealing at 700 °C forms optimal surface structure for SPR coupling. ► UV emission intensity of 700 °C annealed film reaches 15 times larger than 500 °C.

Hafnium oxide (HfO2) films were prepared using a pulsed sputtering method and different O2/(O2 + Ar) ratios, deposition pressures, and sputtering powers. Spectroscopic ellipsometry (SE) and positron annihilation spectroscopy (PAS) were used to investigate the influence of the deposition parameters on the number of open volume defects (OVDs) in the HfO2 films. The results reveal that a low O2/(O2 + Ar) ratio is critical for obtaining films with a dense structure and low OVDs. The film density increased and OVDs decreased when the deposition pressure was increased. The film deposited at high sputtering power showed a denser structure and lower OVDs. Our results suggest that SE and PAS are effective techniques for studying the optical properties of and defects in HfO2 and provide an insight into the fabrication of high-quality HfO2 thin films for optical applications.

Silica nanotubes were fabricated via single-nozzle electrospinning based on phase separation effect. TEM and SEM results showed that the diameter of silica nanotubes ranged from 150 nm to 350 nm. The diameter and wall thickness of silica nanotubes could be tuned by different molar ratios of H2O to tetraethyl orthosilicate (TEOS). Based on phase separation effect, a mechanism was proposed to explain the formation of the tubes. The photoluminescence (PL) properties of these silica nanotubes were also discussed.

Terbium-doped SiCN (SiCN:Tb) films were prepared by radio frequency (rf) reactive sputtering at room temperature (RT) and then annealed in a carbothermal ambience at 800 and 1250 °C, respectively. The RT prepared and 1250 °C annealed samples have shown blue–green and blue–violet light emissions, respectively; whereas strong green light emissions were observed only from the 800 °C annealed samples. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) results revealed that the change of PL properties can be attributed to the evolution of microstructure and chemical compositions of the SiCN films. In addition, photoluminescence excitation (PLE) spectrum indicated that the best PL performance of the 800 °C annealed samples might be mainly attributed to the direct band gap (about 3.81 eV) of crystalline SiCN.

We have illustrated a new approach to fabricate two forms of AlN/ZnO heterostructures―AlN/ZnO coaxial nanotubular heterostructures (CNHs) and AlN-nanotube/ZnO-nanoparticles heterostructures (AlN/ZnO NPs). X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that ZnO nanotubes and nanoparticels have grown on the inner surface of amorphous and polycrystalline AlN shell layer, respectively. A possible growth mechanism on the formation of different AlN/ZnO heterostructures is given. Compared with bare ZnO nanofibers, AlN/ZnO CNHs exhibited remarkable enhanced ultraviolet (UV) emission, while AlN/ZnO NPs showed significant visible emission. With the aid of classical optical diffraction effect theory, it can be calculated that nanoscale luminescent materials have a higher external luminescent efficiency with increasing surface/volume ratio. The influence of carrier confinement effect and surface defects for the PL properties is also investigated in the AlN/ZnO heterostructures. In addition, the photoluminescent (PL) properties of AlN/ZnO CNHs with various AlN shell layers thickness are further discussed.

ZnO/HfO2:Eu nanocables were prepared by radio frequency sputtering with electrospun ZnO nanofibers as cores. The well-crystallized ZnO/HfO2:Eu nanocables showed a uniform intact core–shell structure, which consisted of a hexagonal ZnO core and a monoclinic HfO2 shell. The photoluminescence properties of the samples were characterized. A white-light band emission consisted of blue, green, and red emissions was observed in the nanocables. The blue and green emissions can be attributed to the zinc vacancy and oxygen vacancy defects in ZnO/HfO2:Eu nanocables, and the yellow–red emissions are derived from the inner 4f-shell transitions of corresponding Eu3+ ions in HfO2:Eu shells. Enhanced white-light emission was observed in the nanocables. The enhancement of the emission is ascribed to the structural changes after coaxial synthesis.

Nanoparticle TiO2 electrodes are fabricated using an improved electrostatic spray coating (ESC) method which is more simple, low cost and well reproducible comparing with the conventional method of preparing electrode for dye-sensitized solar cells (DSSC) by introducing monoethanolamine (MEA) into precursor solution. It is surprised to find that high transparency of films and good adhesion between film and substrate achieve and that particles size can be easily controlled by adjusting the proportion of MEA. The relationship between particles size and proportion of MEA added is presented in our work. After samples with various particle sizes are applied in DSSC, an increase of open-circuit voltage (Voc) from 620 mV to 765 mV is observed with the increase of particle size from 8 nm to 48 nm. Associated with photoluminescence results, we ascribe the change of Voc to the different dominative states of films: surface defects and oxygen vacancies in 8 nm films, oxygen vacancy defects in 25 nm films and higher crystal quality with little of both defects in 48 nm films. In addition, different thickness films with optimized proportion of MEA is applied in DSSC, an overall light to electricity conversion efficiency (η) of 2.91% is obtained with a thickness of 2.0 μm.

The Mg- and In-doped zinc oxide (MgxZn1−xO, InyZn1−yO) nanoparticles were successfully prepared by flame spray synthesis method. According to the results obtained from X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis absorption spectra, it was concluded that the Mg or In doping induced the lattice constants to change to some extent; the band gap of MgxZn1−xO also increased with respect to the decreasing band gap of InyZn1−yO. Moreover, the strong UV emission and weak visible emission were investigated by photoluminescence spectra, while the mechanisms of Mg or In doping on PL spectra have been discussed in detail.

(Ba,Sr)TiO3 film was epitaxially grown on a cleaved single crystal 〈1 0 0〉1 0 0 MgO substrate by pulsed laser deposition (PLD). Less exponential values m (m < 2) were observed in current–voltage (I–V) characteristics measured at different temperatures in the space-charge-limited (SCL) region. m is defined by current–voltage relationship: I ∝ Vm. This behavior was explained with a developed space-charge-limited current (SCLC) model based on field-dependent dielectric constant. Considering field-dependent constant, there must be a shallow energy level near the conduction band according to I–V characteristics. The distribution of this level is exponential with a characteristic temperature Tt = 1141 K. The total density of states is Nt = 4 × 1016 cm−3 determined by charge-based deep-level transient spectra (Q-DLTS). We suppose this level is introduced by oxygen vacancies. The temperature-dependent I–V characteristics account for the capturing and detrapping electrons from this level with activation energy Ea = 0.309 eV.

The MgxZn1−xO films were prepared in different Ar–O2 mixture ambience by magnetron sputtering. According to the X-ray diffraction (XRD) patterns and the energy dispersive X-ray spectroscopy (EDS) results, it was found that the Mg contents in the films varied with the different ratios of O2/O2+Ar, and the crystal quality of the films improved with the increasing of Mg contents. Meanwhile, the ultraviolet and visible (UV–vis) absorption spectroscopy indicated that the band gap of the films also increased. Moreover, it could be seen that the photoluminescence (PL) spectrum was different from that of undoped Zinc oxide (ZnO) films or the results in other reports on the MgxZn1−xO films: there was no blueshift effect happening for the near-band-edge (NBE) emission in MgxZn1−xO films with different Mg contents.

Nanocrystalline GaN films were prepared by thermal treatment of amorphous GaN films under flowing NH3 at a temperature of 600°C to 950°C for 1 h to 2 h. X-ray diffraction and field-emission scanning electron microscopy confirmed the formation of high-crystal-quality hexagonal GaN films with preferential (002) orientation. The photoluminescence spectrum showed a sharp peak near the band gap emission located at 368 nm and a broad blue peak centered at 430 nm. Five first-order Raman modes near ∼143 cm−1, 535 cm−1, 555 cm−1, 568 cm−1, and 731 cm−1 with two new additional Raman peaks at 257 cm−1 and 423 cm−1 were observed. The origin of these new Raman peaks is discussed briefly.

Er3+-doped TiO2 nanofibres were fabricated with electrospinning method followed by annealing in air at 420, 600, 800 and 1000 °C, respectively. The obtained nanofibres are relatively straight and have an average diameter of ∼ 75 nm. X-ray diffraction measurements showed that the crystal structure transforms from anatase to rutile phase with the increase of annealing temperature. Visible photoluminescence peaking at 528.1, 566.6 and 669.3 nm is detected which is ascribed to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions and the PL intensities increase with the increase of annealing temperature. Meanwhile at high annealing temperatures, near-infrared photoluminescence peaking at 815 nm due to the defect states associated with Ti3+ ions is also found. The strong green photoluminescence of Er3+ ions may have potential applications in one-dimensional luminescent nanodevices.

It has been reported that sustained arc discharge induced by electrostatic discharge (ESD) could cause permanent damage to high-power and high-voltage solar array of spacecrafts. The paper focuses on ESD simulating experiments on Si and GaAs samples, and induces sustained arc discharge. The physical mechanism of sustained arc discharge is discussed by comparing the charging/discharging phenomena between Si and GaAs samples. The experiments show that sustained arc discharge can produce a permanent short-circuit channel between solar cell strings through which the solar array’s photovoltaic power may flow out sustainedly. The analyses show that sustained arc discharge strongly depends on solar array structure, solar array operating voltage, ESD characteristics and cell materials.

Indium-doped zinc oxide (ZnO:In) films were prepared in an Ar:O2 plasma by reactive magnetron sputtering. The x-ray diffraction (XRD) patterns presented the crystal structures of ZnO:In films, while transmission spectra and photoluminescence (PL) spectra showed the changed band gap and the visible emission from defects, as compared to the PL spectra of undoped ZnO films. It was concluded that the increase of substrate temperature enhanced the crystal quality of ZnO:In films; the incorporation of In made the c-axis constant of the samples larger than that of undoped ZnO films; the blue emission was due to the transition from an unknown donor level by indium doping to the valance band; and the orange-green emission originated from acceptor defects (OZn) formed in the O-rich plasma. Meanwhile, the current- voltage characteristics and persistent photoconductivity phenomenon also could be explained by the increased acceptor defects (OZn) that formed when the substrate temperature was increased.

We have combined radio frequency (RF) plasma with hot filament (HF) chemical vapor deposition (CVD) together to investigate diamond growth. By modifying the conventional RF apparatus and tungsten arrangement in RF system, we systematically investigated the process of nucleation, interlayer formation and growth by atom force microscopy (AFM), X-ray diffraction (XRD) and Raman spectra. The experimental results showed that at low substrate temperature, nano-crystal diamond and other non-diamond carbons formed. The interface between the film and the substrate contained four components: SiC, tungsten (W), W/WC or W2C, W–δ-WB and W/Si2W. High-quality diamond film can only be prepared at Ts>700 °C by RF+HF-CVD and the contamination from tungsten filaments has been remarkably reduced by pre-heating the filament in CH4+H2 atmosphere and placing it as near the upper electrode as possible. Furthermore, large area diamond film can be easily synthesized by HF+RF-CVD method, which has more advantages than other methods.

β-SiC films were prepared on crystalline silicon substrates by radio-frequency sputtering method. High-resolution X-ray diffraction (XRD), infrared absorption spectroscopy (IR) and atomic force microscopy (AFM) measurements were employed to characterize the crystal structure, bonding feature and surface morphology of the films. Porous β-SiC (PSC) films were fabricated using these β-SiC films by electrochemical anodization in the HF-ethanolic solution. Fluorescence photospectrometer, scanning electron microscope (SEM) and AFM were employed to characterize the samples’ photoluminescence (PL) and surface morphology. Intense blue luminescence with a peak at 2.8 eV has been observed at room temperature. Another peak at about 770 nm (1.61 eV) appears when changing the etching time and vanishes when decreasing the HF concentration in the electrolyte. The luminescence mechanism and structure of the porous β-SiC films were discussed also.

Silicon carbon nitride (SiCN) films were deposited on Si(1 0 0) substrates by radio-frequency sputtering method. High-resolution X-ray diffraction, infrared absorption spectroscopy and X-ray photoelectron spectroscopy were used to investigate the composition and bonding structures of the SiCN films. The analysis indicated that Si–C, Si–N and CN bonds were formed in the SiCN films deposited at room temperature. The films grown at high temperature were found to consist of SiCN crystallites. Furthermore, atomic force microscopy was used to examine the surface morphology of the SiCN films. The field emission properties of the films were also studied.

•The resultant CoSx/C hybrid electrodes exhibit a superior rate capability of 66.1% when the current density increased to 100 A g−1, and good cycling stability with over 89.0% specific capacitance remained after 2000 cycles.•The onion-like carbon layer covering the hollow CoSx NPs increases the conductivity of the CoSx/C hybrid electrode.•The 1D PCNFs confined the conversion reaction of TMSs particles to prevent them from aggregating.•The hollow structured of TMSs NPs provide more space to accommodate volume changes during charge/discharge cycles.Transition metal sulfides coupled with carbon materials hold a promising application platform for high-performance supercapacitors. Herein, we report a strategy to fabricate a type of integrated CoSx hollow nanoparticles (HNPs)/C hybrid nanofibers via electrospinning technique combining with hydrothermal method. Results show that the in-situ formed CoSx HNPs were completely covered by a layer of onion-like carbon, which can not only increase their conductivity but also buffer their volume changes during the charging/discharging processes. Interestingly, this type of unique configuration will raise the synergistic effect from excellent electrical conductivity of porous carbon nanofibers (PCNFs) and high specific capacitance of CoSx, endowing the hybrids to be an excellent electrode for high-rate performance supercapacitors. The resultant CoSx/C hybrid electrodes exhibit a high specific capacitance (496.8 F g−1 at 0.5 A g−1), superior rate capability (remaining 66.1% at 100 A g−1), and good cycling stability (over 89.0% after 2000 cycles). Besides, the assembled asymmetric supercapacitors of CoSx/C hybrids//PCNFs show high energy density (15.0 W h kg−1 at power density of 413 kW kg−1) and high cycling stability (over 80% after 2000 cycles).

It was demonstrated that suitable interfaces between two materials can enhance the separation of photogenerated carriers. In this study, ZrO2/ZnO interfaces with type I structure were designed and prepared by the electrospinning technique. The obtained ZrO2/ZnO:Eu3+ (ZZOE) composites are highly porous in the form of nanobelts with width of 600–700 nm, comprising ZnO and ZrO2 nanocrystals, and the Eu doping can hinder the t–m phase transition of ZrO2. By tuning the annealing temperature, the inner stress and defects can be well controlled to improve the photoluminescence (PL) of the ZZOE porous nanobelts. Macro- and micro-PL spectra indicated that the body oxygen vacancies benefit the PL from Eu3+ ions, whereas the surficial ones do not. The optimal parameters for the preparation of ZZOE porous nanobelts were also investigated. Finally, a charge transfer mechanism was proposed to illuminate the PLs from the ZZOE porous nanobelts.

Nanostructured photocatalysts are often attractive due to their enhanced photocatalytic performance by the quantization effect. In this study, BiVO4 quantum dots were decorated on the surface of screw-like SnO2 nanostructures by successive ionic layer absorption and reaction method. The distinctions from bulk materials and the role of BiVO4 quantum dots were investigated in their function as a water splitting photoanode. It was demonstrated that the band-gap of BiVO4 could increase to 2.6 eV when the particle size decreased to about 5 nm, but the band gap of the bulk was only 2.4 eV. Moreover, the decrease in particle size and the coupling with screw-like SnO2 nanostructures enhanced the photocurrent density up to two times under visible light irradiation. The incident photon to current conversion efficiency also increased up to 13.47% at 400 nm. Furthermore, by depositing Pt as cocatalyst, splitting water into hydrogen was realized on the BiVO4 quantum dot/screw-like SnO2 nanostructures under visible light irradiation, and the generation rate is up to 1.16 μmol h−1 cm−2. The improved photoelectrochemical properties and the enhanced photocatalytic activity for hydrogen evolution are attributed to the effective electron-transfer between BiVO4 quantum dots and screw-like SnO2 nanostructures, and the accordingly prolonged photogenerated charge carrier lifetime, as well as the elevated conduction band bottom level of BiVO4 and SnO2 due to the band-gap widening and energy level realignment.

We report the fabrication of cadmium sulfide (CdS) quantum dot-decorated barium stannate (BaSnO3) nanowires and their application as photoanodes for photoelectrochemical water splitting. First, polycrystalline BaSnO3 nanowires, which have a perovskite structure, were prepared by electrospinning their polyvinylpyrrolidone polymer precursors and calcining the resultant polymer fibres. Then, CdS quantum dots were decorated onto the BaSnO3 nanowires by a wet-chemical method. Our results show that the hybrid photoanode made of the CdS quantum dot-decorated BaSnO3 nanowires exhibits a high photocurrent density up to 4.8 mA cm−2 at 0 V (vs. saturated calomel electrode), which corresponds to a hydrogen generation rate of 71.8 μmol (h cm2)−1 with a faradaic efficiency of around 80%. Its favourable performance was attributed to the effective charge separation at the type II staggered gap heterojunction formed at the BaSnO3/CdS interface, and the low charge recombination in BaSnO3 nanowires during transport. Our findings indicate that the water splitting performance of photoelectrochemical cells can be highly improved by rationally building a type II band alignment heterojunction with sensitizing quantum dots and wide band gap semiconductor nanowires which have a low charge recombination rate during transport.

Porous Co3O4 nanonetworks (NNWs), converted from precursor CoOOH nanosheets, have been synthesized via a controllable chemical reaction route followed by calcination at 400 °C in air. The morphologies and microstructures of the precursor nanosheets and the final products were characterized by high-resolution transmission electron microscopy and X-ray diffraction, respectively. The growth mechanism of CoOOH nanosheets and the structural transformation processes of NNWs were investigated in detail. Significantly, the porous Co3O4 NNW based sensor showed an enhanced response to toluene gas at low concentration, which was mainly due to its porous neck-connected networks.

Silica nanotubes were fabricated via single-nozzle electrospinning based on phase separation effect. TEM and SEM results showed that the diameter of silica nanotubes ranged from 150 nm to 350 nm. The diameter and wall thickness of silica nanotubes could be tuned by different molar ratios of H2O to tetraethyl orthosilicate (TEOS). Based on phase separation effect, a mechanism was proposed to explain the formation of the tubes. The photoluminescence (PL) properties of these silica nanotubes were also discussed.

A simple procedure for preparing highly porous TiO2 nanotubes is reported. The nanotubes were prepared in the form of a nonwoven mat by emulsion electrospinning a solution containing poly(vinyl pyrrolidone), titanium tetraisopropoxide and oil, followed by calcination in air at 500 °C. The mixed crystalline material comprised anatase and rutile TiO2 particles, whose diameters were about 11 nm and 21 nm, respectively. The highly porous TiO2 nanotube membranes, which had large specific surface areas and excellent ratios of anatase phase to rutile phase, were shown to have excellent catalytic activities. Also the mixture of crystal forms improved the efficiency of photocatalysis because at the mixed interface electrons and holes are separated effectively. The new method for producing highly porous TiO2 nanotubes is versatile and could be extended to the fabrication of various types of highly porous nanotubes.

Hierarchical hybrid electrodes were successfully fabricated by electrodeposition of ultrathin cobalt sulfide (CoSx) nanosheets on NiCo2S4 nanotube arrays grown on Ni foam for high-performance supercapacitors. The hierarchical NiCo2S4@CoSx core/shell nanotube arrays exhibit a high areal capacitance (4.74 F cm−2 at a current density of 5 mA cm−2), a good rate capability (2.26 F cm−2 at 50 mA cm−2) and cycle stability (76.1% capacitance retention after 1500 cycles at a high current density of 50 mA cm−2), which are much better than those of NiCo2S4 nanotubes. Such superior electrochemical performance could be attributed to the smart configuration of the two electroactive materials, which can provide more pathways for electron transport and improve the utilization rate of the electrode materials. This effective strategy shows the feasibility of designing and fabricating metal sulfides with core/shell hybrid structures as electrode materials for high-performance supercapacitors.

Rational design and synthesis of core/shell nanostructures as binder-free electrodes has been believed to be an effective strategy to improve the electrochemical performance of supercapacitors. In this work, hierarchical ZnCo2O4@NixCo2x(OH)6x core/shell nanowire arrays (NWAs) have been successfully constructed by electrodepositing NixCo2x(OH)6x nanosheets onto hydrothermally grown ZnCo2O4 nanowires and investigated as a battery-type electrode for hybrid supercapacitors. Taking advantage of the hierarchical core/shell structures and the synergetic effect between ZnCo2O4 nanowires and NixCo2x(OH)6x nanosheets, the optimised core/shell electrode exhibits remarkable electrochemical performance with a high areal capacity (419.1 μA h cm−2), good rate capability and cycling stability. Moreover, the assembled ZnCo2O4@NixCo2x(OH)6x//activated carbon (AC) hybrid device can be reversibly cycled in a large potential range of 0–1.7 V and deliver a maximum energy density of 26.2 W h kg−1 at 511.8 W kg−1. Our findings indicate that the hierarchical ZnCo2O4@NixCo2x(OH)6x core/shell NWAs have great potential for applications in energy storage devices.