An electrochemical sensor for hydrogen peroxide (H2O2) has been fabricated by electrodepositing gold nanoparticles (AuNPs) on an indium tin oxide (ITO) electrode modified with cobalt and manganese-layered double hydroxides (CoMn-LDHs). Scanning electron microscopy images reveal well-dispersed AuNPs with a typical size of 12 nm on the surface of the layered double hydroxides. Electrochemical characterizations show that the introduction of the LDH support significantly enhances the voltammetric response to H2O2. This is underpinned by a comparative study that uses single transition metal-LDHs (CoAl-LDHs or MgMn-LDHs) as supports. The results indicate that the presence of binary transition metals in the LDH layer may result in multiple interaction and interfacial effects between AuNPs and the support. At an optimal working voltage of +0.55 V (vs. Ag/AgCl), the sensor displays a wide linear range (0.1 μM to 1.27 mM), low detection limit (0.06 μM) and high sensitivity (125.0 μA∙mM−1∙cm−2), which are characteristics superior to those of most previously reported AuNP-based composite-modified electrodes. The sensor has good reproducibility and storage stability. In our view, this sensor represents a valuable tool for advanced sensing of H2O2.

A Si/C composite with Si nanoparticles (nSi) uniformly dispersed in the interlayers of reduced graphene oxide scrolls (rGS) is successfully developed for high–performance Li–ion battery anodes. The rGS can deform reversibly with the repeated expansion/contraction of nSi to maintain contact between the nSi and the conductive rGS network, which can effectively buffer large volume changes and maintain continuous large–area core–shell electrical contact. Additionally, the continuous electrical network of rGS greatly enhances the electrical conductivity, and the open structures at the ends and sides of rGS provide paths for rapid diffusion of Li ions, thus enhancing the rate performance. By virtue of the rational design, the composite shows a high reversible specific capacity of 2030 mA h g−1 at 0.2 A g−1, high cycling stability of 1200 mA h g−1 at 4 A g−1 with 99.2% capacity retention after 200 cycles, and an excellent rate performance of 1000 mA h g−1 even at 8 A g−1.Download high-res image (334KB)Download full-size image

Cobalt sulfides are considered as one of the most promising alternative anode materials for high-performance lithium-ion batteries by virtue of their remarkable electrical conductivity and high theoretical capacity. However, the volume expansion of cobalt sulfides and polysulfide shuttling effect during the discharge/charge process result in a poor cycling stability and low rate capability. Herein, we report the designed synthesis of a flower-like structure, including cobalt sulfide nanoparticles with a small particle size partially embedded within the nitrogen-doped carbon nanosheets and few-layer graphene covering the external surface of cobalt sulfides (Co9S8/Co1−xS@NC), by simultaneous decomposition and sulfidation of a metanilic anion intercalated Co(OH)2 precursor. Through adjusting the annealed temperature and the mass ratio of the precursor and S powders, the composition of cobalt sulfides could be easily controlled. Co9S8/Co1−xS@NC prepared under optimized conditions exhibits a high reversible capacity of 1230 mA h g−1 after 110 cycles, excellent rate capability (≈1016, 979, 931, 813 mA h g−1 at the current densities of 200, 500, 1000, and 2000 mA g−1, respectively), and stable cycling performance (≈98.4% capacity retention after 110 cycles). Significantly, this intercalated Co(OH)2-derived strategy can be expanded to the preparation of other metal sulfides and carbon composites for application in other energy conversion and storage devices.

Transition-metal-coordinating nitrogen-doped carbon catalysts (M-N/C, M = Co, Fe, Mn, Ni, etc.) are considered one of the most promising nonprecious-metal electrocatalysts for the oxygen reduction reaction (ORR). However, they suffer from low ORR catalytic activity, and their active sites have not been fully identified. Herein, we report the synthesis of a porous Co-N/C hollow-sphere electrocatalyst by carbonization of metanilic anions between the layers of a Co-Al layered double hydroxide. The as-prepared Co-N/C catalyst exhibited excellent ORR catalytic activity with a high half-wave potential and a large diffusion-limited current in alkaline and neutral solutions. The performance of the catalyst was comparable to those of commercial Pt/C electrocatalysts. Through investigating the effects of mask ions (SCN− and F−) on the ORR activity of the Co-N/C catalyst, and comparing the ORR activity before and after the destruction of Co-Nx sites in different pH media, we concluded that the Co-Nx sites act directly as the ORR active sites in acidic and neutral solutions, but have a negligible effect on the ORR activity in alkaline conditions.

Unique hollow hybrid structures composed of well-dispersed catalyst nanoparticles embedded in a carbon matrix offer great advantages for constructing advanced supported catalysts. Herein, we report the designed synthesis of Co9S8 and nitrogen doped hollow carbon sphere (Co9S8/NHCS) composites by carbonization of metanilic anions within the confinement of two-dimensional galleries of hollow spherical cobalt–aluminum layered double hydroxides. The Co9S8/NHCS composites are composed of numerous porous carbon nanoflakes, and monodisperse Co9S8 nanoparticles are embedded within the carbon nanoflakes. Electrochemical measurements show that the Co9S8/NHCS catalysts prepared at 900 °C exhibit superior oxygen reduction reaction (ORR) activity, resulting in the highest ORR performance to date among all transition metal sulfide-based ORR catalysts in both alkaline and acidic electrolytes. This interlayer confined reaction approach may provide an efficient platform for the synthesis of other functional materials for alternative applications.

A self-assembled peptide nanofibrous hydrogel composed of N-fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) was used to construct a smart biointerface. This biointerface was then used for enzyme-based electrochemical biosensing and cell monitoring. The Fmoc-FF hydrogel had two functions. One was as a matrix to embed an enzyme model, horseradish peroxidase (HRP), during the self-assembly of Fmoc-FF peptides. The other was use as a robust substrate for cell adhesion. Experimental data demonstrated that HRP was immobilized in a stable manner within the peptide hydrogel, and that HRP retained its inherent bioactivity toward H2O2. The HRP also can realize direct electron transfer in the Fmoc-FF hydrogel. The resulting third-generation electrochemical H2O2 biosensor exhibited good analytical performance, including a low limit of detection of 18 nM, satisfactory reproducibility, and high stability and selectivity. HeLa cells were then adhered to the HRP/Fmoc-FF hydrogel-modified electrode. The sensitive in situ monitoring of H2O2 released from HeLa cells was realized. This biointerface based on the Fmoc-FF hydrogel was easily prepared, environmentally friendly, and also versatile for integration of other cells and recognized molecules for the monitoring of various cellular biomolecules. The smart biointerface has potential application in broad physiological and pathological investigations.Keywords: cell monitoring; electrochemical biosensing; H2O2; peptide hydrogel; self-assembly

•Non-enzymatic ACh biosensor was constructed based on flower-like NiAl-LDHs decorated with CDs.•The biosensor exhibited a wide linear range, high sensitivity, low LOD, and good stability and selectivity.•Good performance was attributed to the synergistic effect between NiAl-LDHs and CDs.•NiAl-LDHs with a cross-linking nanosheet structure were hydrothermally fabricated.A non-enzymatic acetylcholine (ACh) electrochemical biosensor was constructed based on flower-like NiAl layered double hydroxides (NiAl-LDHs) decorated with carbon dots (CDs). The flower-like NiAl-LDHs with a cross-linking nanosheet structure and high specific surface area were hydrothermally fabricated. Then CDs with negative surface charge were decorated on the NiAl-LDHs with positively charged brucite-like layers to obtain NiAl-LDH/CD composites. Compared with the NiAl-LDHs, the NiAl-LDH/CD composites exhibited enhanced electroconductivity and electrocatalytic performance for ACh oxidation. The NiAl-LDH/CD composites modified glassy carbon electrode had a wide linear response range of 5–6885 μM, high sensitivity of 133.20 ± 0.03 mA M−1 cm−2 and low limit of detection of 1.7 μM, which are superior among the non-enzymatic ACh electrochemical biosensors. The biosensor also exhibited a good durability and long-term stability, and an excellent selectivity for ACh detection. The good performance in the non-enzymatic detection of ACh could be attributed to the synergistic effect between NiAl-LDHs and CDs.Flower-like NiAl layered double hydroxides decorated with carbon dots are synthesized, which exhibit a wide linear response range, high sensitivity, low limit of detection, good durability and long-term stability, and excellent selectivity for ACh detection.

•N–C@Ni–Al2O3@GO, a nanosheet array@graphene oxide composite is synthesized.•N–C@Ni–Al2O3@GO exhibits high activity for HER with low onset overpotential.•High HER activity arises from the synergistic effect between Ni and N–C.•High HER activity arises from the formation of an electrically conductive network.An NiAl-layered double-hydroxide (NiAl-LDH) nanosheet array is grown on a graphene oxide (GO) substrate (NiAl-LDH@GO) by the hydrothermal method. The NiAl-LDH@GO is used as the precursor to synthetize an N-doped carbon@Ni–Al2O3 nanosheet array@GO composite (N–C@Ni–Al2O3@GO) by coating with dopamine followed by calcination. The N–C@Ni–Al2O3@GO is used as a non-noble metal electrocatalyst for hydrogen evolution reaction in alkaline medium, and exhibits high electrocatalytic activity with low onset overpotential (−75 mV). The improved electrocatalytic performance of N–C@Ni–Al2O3@GO arises from its intrinsic features. First, it has a high specific surface area with the Ni nanoparticles in the composite dispersed well and the sizes of Ni nanoparticles are small, which lead to the exposure of more active sites for electrocatalysis. Second, there is a synergistic effect between the Ni nanoparticles and the N–C coating layer, which is beneficial to reduce the activation energy of the Volmer step and improve the electrocatalytic activity. Third, the N–C coating layer and the XC-72 additive can form an electrically conductive network, which serves as a bridge for the transfer of electrons from the electrode to the Ni nanoparticles.

Carbon quantum dots (CQDs) with multiple surface states were prepared by high-energy ball milling a mixture of activated carbon and KOH, followed by ultrafiltration purification. The as-prepared CQDs exhibit dual-wavelength photoluminescence emission peaks. Most interestingly, the first emission peak is independent of excitation wavelength (λex) and the second one is dependent on λex and red shifts monotonically with increasing λex. Meanwhile, the as-prepared CQDs also present dual-wavelength electrochemiluminescence property.

Layered double hydroxides (LDHs) have been widely investigated in the past years because of their unique physicochemical properties and promising applications in chemical power sources. In this article, we review the current work on applications in areas such as supercapacitors, fuel cells, metal-air batteries, Li-ion batteries based on various LDH materials, such as LDH powder, LDH nanosheet, LDH film, or their composites, and offer some perspectives for the future application and development direction of LDHs.

High specific capacity battery electrode materials have attracted great research attention. Phosphorus as a low-cost abundant material has a high theoretical specific capacity of 2596 mAh/g with most of its capacity at the discharge potential range of 0.4–1.2 V, suitable as anodes. Although numerous research progress have shown other high capacity anodes such as Si, Ge, Sn, and SnO2, there are only a few studies on phosphorus anodes despite its high theoretical capacity. Successful applications of phosphorus anodes have been impeded by rapid capacity fading, mainly caused by large volume change (around 300%) upon lithiation and thus loss of electrical contact. Using the conducting allotrope of phosphorus, “black phosphorus” as starting materials, here we fabricated composites of black phosphorus nanoparticle-graphite by mechanochemical reaction in a high energy mechanical milling process. This process produces phosphorus–carbon bonds, which are stable during lithium insertion/extraction, maintaining excellent electrical connection between phosphorus and carbon. We demonstrated high initial discharge capacity of 2786 mAh·g–1 at 0.2 C and an excellent cycle life of 100 cycles with 80% capacity retention. High specific discharge capacities are maintained at fast C rates (2270, 1750, 1500, and 1240 mAh·g–1 at C/5, 1, 2, and 4.5 C, respectively).

•Hierarchical hollow urchin-like NiCo2O4 (HU-NiCo2O4) is facilely synthesized.•HU-NiCo2O4 shows high activity and stability for oxygen evolution reaction.•High stability of HU-NiCo2O4 electrode is due to abundant diffusion paths of gas.Hierarchical hollow urchins of NiCo2O4 (HU-NiCo2O4) were synthesized by a hard templating method followed by thermal decomposition. The structure consists of three levels of hierarchy i.e., zero-dimensional nanoparticle with a diameter of about 6 nm, one-dimensional chain, and three-dimensional hollow urchin, respectively. Nanoparticle aggregates of NiCo2O4 (NA-NiCo2O4) were also synthesized by the same procedure in the absence of the hard template. Relative to NA-NiCo2O4, HU-NiCo2O4 features a well-connected three-dimensional porous structure, which is beneficial for diffusion of oxygen. Consequently, HU-NiCo2O4 displayed superior electrocatalytic activity towards oxygen evolution processes with lower overpotential, higher current density, and higher stability than NA-NiCo2O4.

In this work, we successfully developed a novel wet chemical method to prepare LiNi0.5Mn1.5O4 coated LiMn2O4 (LMO@LNMO), in which commercial LiMn2O4 produced by solid state reaction method was used as the starting material and a nitrate precursor containing Li, Ni and Mn was used to form LiNi0.5Mn1.5O4 coating layer. There is no precipitant, chelating agent and washing process needed. The effect of the calcination temperature and the mass ratio of LiMn2O4 and LiNi0.5Mn1.5O4 (mLMO:mLNMO) were systematically studied. LMO@LNMO was investigated by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), which showed that a completed coating layer was formed via the wet chemical method and some Ni2+ in LiNi0.5Mn1.5O4 were diffused to LiMn2O4 to form a Ni concentration-gradient structure after calcination. Typically, LMO@LNMO with the calcination temperature of 800 °C and the mass ratio of 9:1 (mLMO:mLNMO) showed an initial discharge specific capacity of ∼100 mAh·g−1 between 3.0 and 4.3 V vs. Li+/Li at 55 °C, and greatly improved cyclic performance with a capacity retention of 81.9% over 400 cycles. The thermal safety of LMO@LNMO was also enhanced according to the differential scanning calorimetry (DSC) results.

Yolk–shell structured porous Si–C microspheres have been fabricated by magnesiothermic reduction of silica spheres inside carbon shells and exhibit excellent electrochemical performance due to the porous yolk–shell structure.

Chinese lantern-like MnO coated with N-doped C (MnO@N–C) was fabricated from Chinese lantern-like MnCO3 coated with polydopamine (MnCO3@PDA) precursor that was calcined at 600 °C for 5 h under an N2 atmosphere. MnO@N–C was then investigated as an anode for lithium-ion batteries. Structural characterization results indicate that MnO@N–C comprised numerous nanoplates with a thickness of ∼35 nm. The nanoplates consisted of MnO nanoparticles (∼15 nm) that were homogeneously embedded within the N-doped C (N–C) matrix. The uniformly embedded MnO nanoparticles can realize a high electrochemical utilization of the material to generate a high specific capacity. The N–C matrix and voids between the nanoplates can minimize strain, thereby maintaining the structural stability of the MnO@N–C electrode during the discharge/charge process, enabling improved cyclic performance. Additionally, the MnO@N–C nanoplates with high specific surface area in the Chinese lantern-like framework can shorten the path diffusing length of the lithium ions and the N–C matrix can provide efficient electrical integrity to the electrode, which can enhance the rate capability. Consequently, the obtained MnO@N–C exhibits a high reversible specific capacity of 810 mA h g−1 at 0.2 A g−1, favorable cyclic stability of 640 mA h g−1 after 400 cycles, and excellent rate capability of 451 mA h g−1 at 1 A g−1 and 285 mA h g−1 at 4 A g−1.

The spinel Li4Ti5O12 with a core–shell hierarchical macro–mesoporous structure has been synthesized via a hydrothermal reaction followed by a subsequent calcination step. Scanning electron microscopy and transmission electron microscopy show that the hydrothermal reaction time greatly influences the structure of the spinel Li4Ti5O12 through the Ostwald ripening process. An N2 adsorption–desorption study and mercury intrusion porosimetry measurements show that the optimized product has a high specific surface area of 77.14 m2 g−1 with meso- and macropores. Used as the anode material for lithium-ion batteries, the spinel Li4Ti5O12 exhibits an excellent high-rate performance with a discharge specific capacity of 117.9 mA h g−1 at a rate of 10 C (1700 mA g−1).

Superposed cobalt(II)–cobalt(III) layered double hydroxide (CoII–CoIII-LDH) nanoplates were synthesized by an oil droplet template method, in which the main steps are as follows: LDH nanosheets were first assembled on an oil droplet template to form a multishell sphere, and then the oil droplet was easily removed under centrifugal force due to its very different density from that of the assembled LDH shell. This resulted in the multishell spheres being split open to create superposed LDH nanoplates. The resulting material has a three-stage architecture, namely, the primary building blocks of nanosheets, the secondary architecture of shells derived from the nanosheets, and the long-range architecture of superposed nanoplates assembled from the vertically stacked shells. Most importantly, the as-fabricated LDH-based hierarchical structure can be readily converted to a Co3O4/C composite via calcination, without obvious structural alteration, where the residual surfactant is the source of the carbon. When used as an anode material for Li-ion batteries, the Co3O4/C electrode exhibits an excellent electrochemical performance, which is attributed to the unique hierarchically porous structure.

The improvement of the electrochemical properties of electrode materials with large capacity and good capacity retention is becoming an important task in the field of lithium ion batteries (LIBs). We designed a function-oriented hybrid material consisting of silver vanadium oxide (β-AgVO3) nanowires modified with uniform Ag nanoparticles and multi-walled carbon nanotubes (CNTs) as a high-performance cathode material for LIBs. The Ag nanoparticles which precipitated automatically in the synthetic process act as a bridge between the β-AgVO3 nanowires and CNTs, creating a self-bridged network structure. The Ag particles at the junction of the nanowires and CNTs facilitate electron transport from the CNTs to the nanowires, and thereby improve the electrical conductivity of the β-AgVO3 nanowires and the composite. Moreover, the self-bridged network is hierarchically porous with a high surface area. When used as a cathode material, this composite electrode reveals high discharge capacities, excellent rate capability, and good cycling stability. The improved performance of the composite arises from its unique nanosized β-AgVO3 nanowires with short diffusion pathway for lithium ions, efficient electron collection and transfer in the presence of Ag nanoparticles, together with excellent electrical conductivity of CNTs.

In this work, the cubic polymorph of (NH4)3FeF6 has been obtained at room temperature via a precipitation reaction within 2 min by a phase-transfer method. The structural properties of the sample were investigated by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). This is the very first time to report that iron-based fluoride has been prepared without using hydrofluoric acid or at high temperature, and give an application of (NH4)3FeF6 as a novel anode material for lithium-ion batteries. (NH4)3FeF6 exhibits decent first discharge and reversible specific capacities of 1035 mA h g−1 and 555 mA h g−1 at room temperature, respectively.Graphical abstractHighlights► A phase-transfer method to synthesize cubic (NH4)3FeF6. ► Quick, easy and safe synthesis procedure at room temperature without HF acid. ► (NH4)3FeF6 as a novel anode material for lithium-ion batteries. ► First discharge specific capacity of 1035 mA h g−1. ► Reversible specific capacity of 555 mA h g−1.

A homogeneous core–shell structured Li3V2(PO4)3@C cathode material of lithium-ion batteries was synthesized by a momentary freeze-drying method and exhibited good electrochemical properties, particularly its rate capability, for lithium ion storage.

Graphene nanosheets have been generated in the confined space of the two-dimensional galleries of a layered double hydroxide (LDH) and good control over the number of graphene layers can be achieved by adjusting the amounts of intercalated carbon source.

A manganese dioxide (MnO2) nanosheet-based thin film deposited on a conductive Ni substrate has been synthesized via a hydrothermal route. Field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) showed that the as-prepared thin film had a porous network structure, which consisted of interlaced MnO2 nanosheets oriented perpendicular to the substrate. Electrochemical tests demonstrated that the MnO2 nanosheet-based thin-film electrode exhibited excellent capacitance performance with high rate properties and good cycling stability. A specific capacitance of 385 F g−1 was obtained at a current density of 0.5 A g−1, with a capacitance retention of about 81% when the current density was increased from 0.5 to 5 A g−1. When cycled at a higher current density of 1.25 A g−1, 93% of the initial specific capacitance was retained over 5000 cycles. The excellent electrochemical properties of this MnO2 thin-film electrode can be attributed to its thin-sheet morphology, porous structure and the good contact between the MnO2 active material and the Ni substrate. Considering the excellent performance and facile preparation, this thin-film electrode should have great potential for application in energy storage and conversion devices.Highlights► A flexible porous MnO2 nanosheet-based thin-film electrode has been fabricated. ► The MnO2 thin-film electrode exhibited excellent capacitance performance. ► The fabrication process may be extended to the preparation of other metal oxide films.

Hemoglobin (Hb) has been successfully immobilized on a glassy carbon (GC) electrode modified by an interlaced Co(OH)2 nanosheet-based three-dimensional (3D) macroporous film prepared by a cathodic electrodeposition method. The surface morphology of the Co(OH)2 film was examined by scanning electron microscopy. UV–vis spectra revealed that the Hb immobilized on the Co(OH)2 film retained its native structure. A fast direct electron transfer was achieved between Hb and the underlying electrode, with an average electron transfer rate of 7.8 s−1. The resulting biosensor exhibited good performance for the detection of H2O2, with a wide linear range from 0.4 to 200 μM, low detection limit of 0.2 μM, high sensitivity of 744 μA mM−1 cm−2, excellent stability and reproducibility. The cathodic electrodeposition method provides a simple and efficient way to prepare a 3D nanostructured film for immobilizing protein or enzyme, and the resulting film has potential applications in biosensors, catalytic bioreactors, and biomedical devices.

A novel hybrid material constructed from 2D graphene nanosheets (GNS) and 1D vanadium pentoxide (V2O5) nanowires was successfully fabricated via a very simple green approach. The ultralong V2O5 single crystalline nanowires were supported on the transparent GNS substrate and exhibited excellent electrochemical properties. When used as a cathode material of lithium-ion batteries, the composite material revealed high initial discharge capacities and exceptional rate capacities. For instance, at the lower current density of 50 mA g−1, an initial specific discharge capacity of 412 mAh g−1 could be achieved; when the current density was increased to 1600 mA g−1, the composite still delivered 316 mAh g−1lithium ions. The good performance of the composite resulted from its unique nano-scaled V2O5 wires with short diffusion pathway for lithium ions and the excellent electrical conductivity of GNS. Note that the fabrication approach in the present work is environmental friendly without any strong reduction and oxidation reagents, or causing the generation of toxic gas during the fabrication process. We believe that this green approach may open up the possibility of fabricating more novel structured graphene-based functional materials.

A well defined nano-structured material, NaV6O15 nanorods, was synthesized by a facile low temperature hydrothermal method. It can perform well as the cathode material of rechargeable sodium batteries. It was found that the NaV6O15 nanorods exhibited stable sodium-ion insertion/deinsertion reversibility and delivered 142 mAh g−1 sodium ions when worked at a current density of 0.02 A g−1. In galvanostatic cycling test, a specific discharge capacity of around 75 mAh g−1 could be obtained after 30 cycles under 0.05 A g−1 current density. Concerned to its good electrochemical performance for reversible delivery of sodium ions, it is thus expected that NaV6O15 may be used as cathode material for rechargeable sodium batteries with highly environmental friendship and low cost.

PEO16–LiClO4–ZnAl2O4 nanocomposite polymer electrolyte (NCPE) films prepared by hot-pressing method have been investigated. In order to compare with the hot-pressed NCPEs, the NCPE films have also been prepared using the conventional solution-casting method. Field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), conductivity (σ) and interface property studies have been carried out on above two kinds of films. The results show that the NCPE film prepared by hot-pressing method has smoother surface, higher interface stability, lower crystallization and melting temperature values than that prepared by solution-casting method. An all-solid-state lithium polymer battery using the hot-pressed NCPE film as electrolyte, lithium metal and LiFePO4 as anode and cathode respectively, shows high discharge specific capacity, good rate capacity, high coulombic efficiency, and excellent cycling stability as revealed by galvanostatical charge/discharge cycling tests.

The composite material of polyaniline (PANI)/layered manganese oxide film electrode was prepared by the layer-by-layer adsorption technique. The corresponding photoelectrocatalytic activity was studied for the degradation of Rhodamine B (RhB) under visible light irradiation (λ > 400 nm). The efficiency of the self-assembled film to assist photodegradation of RhB improved significantly with an applied potential of 0.9 V vs. standard calomel electrode. The results showed that PANI could enhance the efficiency of photon harvesting, and the impressed current could reduce the chance of electron-hole recombination. A synergetic effect was found between PANI and MnO2. This study proposed an effective material for the photoelectrocatalytic degradation of RhB under visible light irradiation.

The synthesis of p-type polyaniline (PAN) by the in situ polymerization of aniline in the confined interlamellar galleries of an n-type semiconducting layered protonic titanate (LPT) affords an intercalated PAN/LPT nanocomposite. The in situ polymerization of aniline can be initiated by oxygen in the air. The resulting nanocomposites have been characterized by XRD, FTIR, UV−visible spectroscopy, TG−DTG, SEM, and elemental analysis. The PAN/LPT nanocomposites show significant absorption in the visible region, whereas the pristine LPT absorbs only in the ultraviolet region. Under visible irradiation, the PAN π−π* transition delivers excited electrons into the conduction band of LPT, and the subsequent electron transfer to a substrate electrode contributes to the photocurrent. The PAN/LPT nanocomposites exhibit much higher photocatalytic activities for the degradation of methylene blue in aqueous solution under visible light irradiation than LPT itself.

Co–Al mixed metal oxide (CoAl-MMO) has been used for surface modification of LiMn2O4 spinel by means of a co-precipitation method in an attempt to improve the electrochemical performance of LiMn2O4 at elevated temperature. The surface modified materials were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometry (EDS), Auger electron spectroscopy (AES) and galvanostatic charge–discharge cycling. After heat-treatment at 400 °C, the CoAl-MMO coated LiMn2O4 shows better capacity retention at both 25 °C and 55 °C than the pristine LiMn2O4. The enhancement in electrochemical performance is mainly attributed to the CoAl-MMO coating layer which has the synergistic effect of cobalt and aluminum oxide species and could block the direct contact between the spinel cathode material and electrolyte resulting in Mn dissolution decrease.

Graphite nanosheet (GNS)–Nafion composites were prepared for the immobilization of hemoglobin (Hb) to construct a mediator-free H2O2 biosensor. Scanning electron microscopy (SEM), UV-vis spectroscopy and Fourier transform infrared spectroscopy were used to characterize the Hb–GNS–Nafion composite film. Due to good biocompatibility of the composite film, immobilized Hb retained its native structure. The Hb–GNS–Nafion composite film-modified electrodes showed direct electrochemistry with a fast electron-transfer rate (6.63 s−1) and high electrocatalytic activity to the reduction of hydrogen peroxide (H2O2). The resulting biosensor exhibited a high sensitivity of 412.7 mA M−1 cm−2, a low detection limit of 2.0 × 10−7 M, and a small apparent Michaelis–Menten constant of 37 µM. These results were comparable or superior to the biosensors based on the carbon nanofiber (CNF)- and carbon nanotube (CNT)-based biosensors. Due to the lower cost of GNSs, the GNS-based composite can combine with other redox proteins and widely apply in mediator-free biosensors, bioelectronics and biofuel cells.

A novel poly(ethylene oxide) (PEO)-based nanocomposite polymer electrolyte (NCPE) has been developed by using nanosized, high surface area ZnAl2O4 with a mesopore network as the filler. X-ray diffraction (XRD), differential scanning calorimetry (DSC), and field emission scanning electron microscopy (FESEM) were used to characterize the NCPE. The results showed that the presence of the nanosized ZnAl2O4 powder leads to a reduction in the crystallinity of the PEO phase. The ionic conductivity and lithium ion transference number of the PEO-based polymer electrolyte were enhanced by the addition of the nanosized ZnAl2O4 powder. A broad electrochemical stability window suggests that the PEO-LiClO4-ZnAl2O4 NCPE is a viable candidate for the electrolyte material in lithium polymer batteries.

A simple method has been employed to prepare pillared layered Li1−2xCaxCoO2 cathode materials by cationic exchange under hydrothermal conditions. The synthesized materials were characterized by means of X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), field emission scanning electron microscope (FE-SEM) and galvanostatic charge–discharge cycling. The XRD data of the products show that they are single phases and retain the layered α-NaFeO2 type structure. The FE-SEM images of the materials prepared by hydrothermal method show uniform small particles, and the particle size of the materials is about 200 nm. The initial discharge specific capacities of layered LiCoO2 and pillared layered Li0.946Ca0.027CoO2 cathode materials calcined at 800 °C for 5 h within the potential range of 3.0–4.3 V (vs. Li+/Li) are 144.6 and 142.3 mAh g−1, respectively, and both materials retain good charge–discharge cycling performance. However, with increasing upper cutoff voltage, the pillar effect of Ca2+ in Li1−2xCaxCoO2 becomes more significant. The pillared layered Li0.946Ca0.027CoO2 has a higher capacity with an initial discharge specific capacity of 177.9 and 215.8 mAh g−1 within the potential range of 3.0–4.5 and 4.7 V (vs. Li+/Li), respectively, and retains good charge–discharge cycling performance.

LiCoO2 was surface modified by a coprecipitation method followed by a high-temperature treatment in air. FePO4-coated LiCoO2 was characterized with various techniques such as X-ray diffraction (XRD), auger electron spectroscopy (AES), field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), 3 C overcharge and hot-box safety experiments. For the 14500R-type cell, under a high charge cutoff voltage of 4.3 and 4.4 V, 3 wt.% FePO4-coated LiCoO2 exhibits good electrochemical properties with initial discharge specific capacities of 146 and 155 mAh g−1 and capacity retention ratios of 88.7 and 82.5% after 400 cycles, respectively. Moreover, the anti-overcharge and thermal safety performance of LiCoO2 is greatly enhanced. These improvements are attributed to the FePO4 coating layer that hinders interaction between LiCoO2 and electrolyte and stabilizes the structure of LiCoO2. The FePO4-coated LiCoO2 could be a high performance cathode material for lithium-ion battery.

Multilayer thin films of manganese oxide nanosheets (MNSs) and polyethylenimine (PEI) polyelectrolyte have been fabricated onto various substrates via layer-by-layer self-assembly technique. UV–vis absorption spectra showed that the absorbance values at the characteristic wavelength of the multilayer films increased almost linearly with the number of PEI/MNS bilayers. Field emission scanning electron microscope (FESEM) images indicated that the surface of the multilayer film was rather smooth and dense. The electrochemical performances of (PEI/MNS)n films on indium–tin oxide (ITO)-coated glass substrates were investigated by cyclic voltammetry and constant current charge–discharge test from 0 to 0.9 V in a 2 M KCl aqueous solution. The multilayer films showed excellent electrochemical activity, high reversibility and high power density. A specific capacitance value of 288 F g−1 was obtained at a current density of 1.25 A g−1 for (PEI/MNS)10 film in 2 M KCl aqueous solution. The specific capacitance decreased 9.5% of initial capacity over 1000 cycles at a high current density of 2.5 A g−1. These good electrochemical properties could be attributed to the special microstructure of the electrode.

A continuous cobalt-based layered double hydroxide (LDH) nanosheet thin-film electrode has been fabricated by drying a nearly transparent colloidal solution of cobalt-based LDH nanosheets on an indium tin oxide (ITO)-coated glass plate substrate. The effects of varying the Al content, the film thickness, and the heating temperature on the electrochemical properties of the as-deposited thin-film electrode have been investigated. A thin-film electrode with a Co/Al molar ratio of 3:1, which has a large specific capacitance of 2500 F cm−3 (833 F g−1) and a good high-rate capability, shows the best performance when used as an electrode in thin-film supercapacitors (TFSCs). As the thickness of the thin film was increased from 100 to 500 nm, the specific capacitance of the thin-film electrode remained essentially unchanged, which is due to the porous microstructure generated in the original electrochemical process and the low internal resistance of the thin-film electrode. The specific capacitance of the thin-film electrode showed no observable change after heating at 160 °C, but decreased on further heating to 200 °C, indicating that the electrochemically active Co sites inside the thin-film nanosheet electrode are already essentially fully exposed in the as-prepared material and hence cannot be further exposed through heating. Such a thin-film electrode made up of nanosheets may be a potential economical alternative electrode for use in TFSCs.

Multilayer thin films comprising negatively charged MnO2 sheets and positively charged Mg–Al LDHs sheets have been prepared by the electrostatic layer-by-layer adsorption technique. The resulting films were characterized by UV–vis spectra, scanning electron microscope (SEM), X-ray photoelectron spectra (XPS), and so on. UV–vis spectra show that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of LDHs/MnO2 bilayers. SEM images indicate that the surface of the multilayer films is rather smooth and dense. XPS spectra confirm the incorporation of MnO2 and Mg–Al LDHs into the films.

A novel biocompatible polyquaternium (QY)-manganese oxide nanosheet (MNS) nanocomposite has been prepared and shown to be a promising matrix for horseradish peroxidase (HRP) immobilization. The resulting HRP-QY-MNS film was characterized by Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy, which indicated that HRP retained its native structure in the nanocomposite film. An HRP-QY-MNS film-modified glassy carbon electrode exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks centered at −0.272 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solution. The direct electrochemical behavior of HRP was greatly enhanced in the QY-MNS nanocomposite film compared with that in single-component QY or MNS films. The immobilized HRP showed excellent electrocatalysis in the reduction of hydrogen peroxide (H2O2), which was exploited in the construction of an H2O2 biosensor. The linear range of the biosensor for H2O2 was found to be from 1.0 × 10−7 to 3.2 × 10−5 M with a correlation coefficient of 0.998. The detection limit was 7.8 × 10−8 M at a signal-to-noise ratio of 3. The biosensor exhibited rapid response and good long-term stability.

A novel material MnO2 nanosheet has been used as the support matrix for the immobilization of horseradish peroxidase (HRP). HRP entrapped in MnO2 nanosheet film exhibits facile direct electron transfer with the electron transfer rate constant of 6.86 s−1. The HRP/MnO2 nanosheet film gives a reversible redox couple with the apparent formal peak potential (E0) of −0.315 V (vs. Ag/AgCl) in pH 6.5 phosphate buffer solution (PBS). The formal potential E0 of HRP shifts linearly with pH with a slope of −53.75 mV · pH−1, denoting that an electron transfer accompanies single-proton transportation. The immobilized HRP shows an electrocatalytic activity to the reduction of H2O2. The response time of the biosensor for H2O2 is less than 3 s, and the detection limit is 0.21 μmol · L−1 based on signal/noise = 3.

Polyaniline-intercalated layered manganese oxide (PANI-MnO2) nanocomposite was synthesized via exchange reaction of polyaniline (PANI) with n-octadecyltrimethylammonium-intercalated manganese oxide in N-methyl-2-pyrrolidone solvent. The PANI-MnO2 nanocomposite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and so on. XRD analysis showed that the basal spacing was 1.47 nm, corresponding to the benzene rings of PANI were arranged in a zigzag conformation and located perpendicular to the inorganic layers. The CN stretching vibration (νCN) which appeared with PANI at 1293 cm−1 shifted to 1306 cm−1 for PANI-MnO2 nanocomposite, indicating the existence of interactions between intercalated PANI and manganese oxide layers. The XPS results showed that PANI was still in the conductive form after inserting the polymer into layered manganese oxide. The electrochemical properties as electrode materials for electrochemical capacitors were examined by cyclic voltammetry and galvanostatic charge/discharge test in 0.1 M Na2SO4 solution. The maximum specific capacitance of 330 F g−1 was obtained from galvanostatic charge/discharge at a constant current density of 1 A g−1. The specific capacitance of PANI-MnO2 nanocomposite had improvement values of 76 and 59% compared to those of PANI (187 F g−1) and manganese oxide (208 F g−1) components, respectively, which was due to synergic effects from each pristine component.

A homogeneous core–shell structured Li3V2(PO4)3@C cathode material of lithium-ion batteries was synthesized by a momentary freeze-drying method and exhibited good electrochemical properties, particularly its rate capability, for lithium ion storage.

Unique hollow hybrid structures composed of well-dispersed catalyst nanoparticles embedded in a carbon matrix offer great advantages for constructing advanced supported catalysts. Herein, we report the designed synthesis of Co9S8 and nitrogen doped hollow carbon sphere (Co9S8/NHCS) composites by carbonization of metanilic anions within the confinement of two-dimensional galleries of hollow spherical cobalt–aluminum layered double hydroxides. The Co9S8/NHCS composites are composed of numerous porous carbon nanoflakes, and monodisperse Co9S8 nanoparticles are embedded within the carbon nanoflakes. Electrochemical measurements show that the Co9S8/NHCS catalysts prepared at 900 °C exhibit superior oxygen reduction reaction (ORR) activity, resulting in the highest ORR performance to date among all transition metal sulfide-based ORR catalysts in both alkaline and acidic electrolytes. This interlayer confined reaction approach may provide an efficient platform for the synthesis of other functional materials for alternative applications.

Graphene nanosheets have been generated in the confined space of the two-dimensional galleries of a layered double hydroxide (LDH) and good control over the number of graphene layers can be achieved by adjusting the amounts of intercalated carbon source.

Cobalt sulfides are considered as one of the most promising alternative anode materials for high-performance lithium-ion batteries by virtue of their remarkable electrical conductivity and high theoretical capacity. However, the volume expansion of cobalt sulfides and polysulfide shuttling effect during the discharge/charge process result in a poor cycling stability and low rate capability. Herein, we report the designed synthesis of a flower-like structure, including cobalt sulfide nanoparticles with a small particle size partially embedded within the nitrogen-doped carbon nanosheets and few-layer graphene covering the external surface of cobalt sulfides (Co9S8/Co1−xS@NC), by simultaneous decomposition and sulfidation of a metanilic anion intercalated Co(OH)2 precursor. Through adjusting the annealed temperature and the mass ratio of the precursor and S powders, the composition of cobalt sulfides could be easily controlled. Co9S8/Co1−xS@NC prepared under optimized conditions exhibits a high reversible capacity of 1230 mA h g−1 after 110 cycles, excellent rate capability (≈1016, 979, 931, 813 mA h g−1 at the current densities of 200, 500, 1000, and 2000 mA g−1, respectively), and stable cycling performance (≈98.4% capacity retention after 110 cycles). Significantly, this intercalated Co(OH)2-derived strategy can be expanded to the preparation of other metal sulfides and carbon composites for application in other energy conversion and storage devices.