Development of carbon electrodes with high volumetric electrochemical performance is challenging for high-performance energy storage devices. In this work, we demonstrate a novel sucrose-derived porous carbon monolith (NPC-m) constructed by holey carbon nanosheets for super-high volumetric energy storages.NPC-m, derived from sucrose via a facile yet scalable and economic “bottom-up” synthesis route, exhibits a high specific surface area of 1376 m2 g−1, a narrow hole size distribution, and a high N content (∼6.65 at. %). Most importantly, a self-stacking density as high as 1.26 g cm−3 can be achieved via simple drying processes. The electrodes based on NPC-m in carbon electrodes deliver super-high volumetric capacities of 1385 mAh cm−3 (0.1 A g−1) for Li-ion batteries and 380 F cm−3 (0.5 A g−1) for supercapcacitors, highlighting their great potentials for high-performance energy storages.

Graphene is an ideal candidate for gas sensing due to its excellent conductivity and large specific surface areas. However, it usually suffers from sheet stacking, which seriously debilitates its sensing performance. Herein, we demonstrate a three-dimensional conductive network based on stacked SiO2@graphene core–shell hybrid frameworks for enhanced gas sensing. SiO2 spheres are uniformly encapsulated by graphene oxide (GO) through an electrostatic self-assembly approach to form SiO2@GO core–shell hybrid frameworks, which are reduced through thermal annealing to establish three-dimensional (3D) conductive sensing networks. The SiO2 supported 3D conductive graphene frameworks reveal superior sensing performance to bare reduced graphene oxide (RGO) films, which can be attributed to their less agglomeration and larger surface area. The response value of the 3D framework based sensor for 50 ppm NH3 and 50 ppm NO2 increased 8 times and 5 times, respectively. Additionally, the sensing performance degradation caused by the stacking of the sensing materials is significantly suppressed because the graphene layers are separated by the SiO2 spheres. The sensing performance decays by 92% for the bare RGO films when the concentration of the sensing material increases 8 times, while there is only a decay of 25% for that of the SiO2@graphene core–shell hybrid frameworks. This work provides an insight into 3D frameworks of hybrid materials for effectively improving gas sensing performance.

•Structures of RGO-PANI films were regulated by MnO2-templated polymerization.•Porous RGO-PANI nanotube papers had capacitances of 956 F g−1 and 172 F cm−3.•Volumetric capacitance of PANI nanotube-anchored graphene papers was 722 F cm−3.•PANI nanotube-anchored graphene papers had a gravimetric capacitance of 363 F g−1.The adjustment and optimization of graphene-based electrode structures are crucial to achieve both high volumetric and gravimetric capacitances for portable energy storage devices. Structures of reduced graphene oxide (RGO)-polyaniline (PANI) nanotube hybrid electrodes were facilely regulated and rationally designed by in-situ MnO2 nanowire-templated polymerization. Typically, two different architectures of RGO-PANI composites were obtained by controlling the content of MnO2 nanowires in graphene papers. The assembled symmetric device based on the porous RGO-PANI nanotube papers (0.18 mg cm−2, 20.0 μm), showed a high gravimetric specific capacitance of 956 F g−1 (against the mass of single electrode) at 1 A g−1 with excellent rate capability of 74.3% from 1 A g−1 to 10 A g−1. In addition, another symmetric device based on the sandwiched polyaniline nanotube/layered graphene/polyaniline nanotube papers (0.80 mg cm−2, 4.02 μm), provided an ultrahigh volumetric capacitance (722 F cm−3 at 2 A cm−3) and a decent gravimetric capacitance (363 F g−1 at 1 A g−1) calculated against the volume and mass of single electrode. With these excellent volumetric and gravimetric capacitive performances, this polyaniline nanotube/layered graphene/polyaniline nanotube supercapacitor holds the potential for high-volumetric and gravimetric-performance energy storages.Download high-res image (311KB)Download full-size image

Three-dimensional free-standing film electrodes have aroused great interest for energy storage devices. However, small volumetric capacity and low operating voltage limit their practical application for large energy storage applications. Herein, a facile and novel nanofoaming process was demonstrated to boost the volumetric electrochemical capacitance of the devices via activation of Ni nanowires to form ultrathin nanosheets and porous nanostructures. The as-designed free-standing Ni@Ni(OH)2 film electrodes display a significantly enhanced volumetric capacity (462 C/cm3 at 0.5 A/cm3) and excellent cycle stability. Moreover, the as-developed hybrid supercapacitor employed Ni@Ni(OH)2 film as positive electrode and graphene-carbon nanotube film as negative electrode exhibits a high volumetric capacitance of 95 F/cm3 (at 0.25 A/cm3) and excellent cycle performance (only 14% capacitance reduction for 4500 cycles). Furthermore, the volumetric energy density can reach 33.9 mWh/cm3, which is much higher than that of most thin film lithium batteries (1–10 mWh/cm3). This work gives an insight for designing high-volume three-dimensional electrodes and paves a new way to construct binder-free film electrode for high-performance hybrid supercapacitor applications.Keywords: energy storage; nanofoaming; nickel nanowire; supercapacitor; volumetric capacity

•The structure of the rGO/PPy NT paper is incompact and hierarchical.•The addition of rGO can improve the cycling stability of PPy NT paper electrode.•The ASSSC device exhibits 86.3% capacitance retention from 1 to 10 mA/cm2.•The device has an areal energy density of 61.4 μWh/cm2 at 10 mW/cm2.•The device provides a volumetric energy density of 7.18 mWh/cm3 at 1.17 W/cm3.Pseudocapacitive materials are known to suffer from severe capacitance loss during charging/discharging cycling. Here we report flexible all-solid-state supercapacitors (ASSSCs) based on reduced graphene oxide (rGO)/polypyrrole nanotube (PPy NT) papers prepared by a facile vacuum filtration method. It is revealed that the incorporation of rGO nanosheets can improve the electrochemical stability of PPy NT paper electrodes for pseudocapacitors. The hybrid paper electrode shows a high areal specific capacitance of 807 mF/cm2 at 1 mA/cm2 and a large volumetric specific capacitance of 94.3 F/cm3 at 0.1 A/cm3. The assembled ASSSC possesses a maximum areal specific capacitance of 512 mF/cm2 at 1 mA/cm2 and a maximum volumetric specific capacitance of 59.9 F/cm3 at 0.1 A/cm3. Moreover, it also exhibits excellent rate capability (86.3% capacitance retention from 1 to 10 mA/cm2) and cycling stability, little capacitance deviation under different bending states, a small leakage current and a low self-discharge characteristic. The device can provide an areal energy density of 61.4 μWh/cm2 at 10 mW/cm2 and a volumetric energy density of 7.18 mWh/cm3 at 1.17 W/cm3, indicating this high-performance ASSSC is a promising candidate for flexible high-power supply devices.

Metal-semiconductor-based photocatalysts show high efficiencies and catalytic activities in the photocatalysis process. Herein, the magnetic and one-dimensional Ni–Cu2O heteronanowires have been fabricated via in situ reduction of pre-adsorbed Cu2+ on the surface of prickly Ni nanowires in an ethanol solution for photocatalysis application. The resultant Ni–Cu2O heteronanowires show higher photocatalytic ability than pure Cu2O nanoparticles in the degradation of methyl orange. The enhancement of photocatalytic efficiency can be ascribed to the unique one-dimensional nanostructure and the electron sink effect of Ni nanowires in the heterostructure. It is believed that the low-cost metal Ni is an alternative candidate for substituting the costly metals (Au, Ag and Pt) to improve the photocatalytic ability of semiconductor-based photocatalysts.

•Engineering graphene films was achieved by steamed water regulation techniques.•Gravimetric specific capacitance of tailored graphene films can reach 340 F/g.•A highest specific capacitance of 326 F/cm3 or 915 mF/cm2 can be achieved.•Assembly of high-performance flexible solid-state supercapacitor was achieved.Developing versatile methods to fabricate flexible graphene film electrodes with favorable mechanical strength and desirably tailored areal and volumetric capacitances are very challenging for high-performance capacitive energy storages. Here, we present a simple yet versatile method to regulate the structures of scalable free-standing reduced graphene oxide (rGO) films for high-performance flexible supercapacitors. Steamed water with a high pressure and a moderately high temperature in closed vessels was used to prepare reduced graphene oxide with regulated structures, and the resultant rGO films exhibited favorable mechanical robustness (with modulus and tensile strength higher than 0.28 GPa and 5.9 MPa respectively) as well as excellently controllable areal and volumetric capacitances (with a highest gravimetric specific capacitance, a highest areal specific capacitance, and a highest volumetric capacitance up to 340 F/g, 915 mF/cm2, and 326 F/cm3, respectively), revealing the versatile behavior of this regulation technique for high-performance flexible energy storage. In addition, a typical assembled all-solid-state supercapacitor based on as-fabricated graphene films shows large gravimetric and areal specific capacitances, high energy density and power density, as well as excellent capacitance stability, highlighting its great potential for high-performance flexible energy storage devices.This work demonstrates a simple yet versatile method to regulate the structures of scalable free-standing reduced graphene oxide (rGO) films for high-performance flexible supercapacitors. Steamed water with a high pressure and a moderately high temperature in closed vessels was used to prepare rGO films with regulated structures, and the resultant rGO films exhibited favorable mechanical robustness as well as excellently controllable areal and volumetric capacitances, revealing the versatile behavior of this fabrication method for high-performance flexible energy storage.

•Ni@Ni(OH)2 core-sheath nanowire structure is constructed for energy storage.•The active material layer is obtained by a facile electrochemical treatment.•A high volumetric capacity of 111.1 C cm−3 is obtained at 0.12 A cm−3.•The electrode exhibits excellent rate capability and cycle stability.We report a facile approach to fabricate a novel membrane electrode based on unique Ni@Ni(OH)2 coaxial core-sheath structures for electrochemical energy storage application in this work. The Ni nanowire membranes, prepared from vacuum filtration of Ni nanowires with unique embossments, can be used as excellent precursors for preparing Ni@Ni(OH)2 membranes by an electrochemical cyclic voltammetry method. After electrochemical treatment, a layer of amorphous Ni(OH)2 was obtained on the surface of Ni nanowires. An important property of the as-synthesized Ni@Ni(OH)2 membranes is that it can be directly utilized for electrochemical energy storage applications without the need for binders or additional conducting additives. The Ni@Ni(OH)2 electrode demonstrates a high volumetric capacity (111.1 C cm−3 at 0.12 A cm−3), excellent rate capability (83.1 C cm−3 at 1.92 A cm−3), and cycling stability at a high current density (78% capacity retention after 1500 cycles at 1.92 A cm−3). This fabrication method is very simple and paves a new route for designing membrane electrodes based on similar structures for high-performance electrochemical energy storage electrodes.

In this work, we reported a simple method to fabricate novel free-standing stiff carbon-based composite films with excellent mechanical properties and superhydrophobic behaviors. The free-standing stiff carbon composite films based on reduced graphene oxide/glassy carbon (rGO/GC) were prepared by the combination of in-situ polymerization and carbonization process. The obtained composite films exhibited excellent mechanical properties by the addition of rGO nanosheets. It was found that incorporating 0.5 wt.% of rGO sheets in GC precursors resulted in enhancements of 99% in strength (202.6 MPa) and 184% in modulus (33.8 GPa), respectively. More interestingly, carbon nanoarrays were uniformly grown on the surface of composite films by the incorporation of rGO sheets. Superhydrophobic surfaces of carbon films were subsequently formed through functionalizing carbon nanoarrays with Trichloro(1H, 1H, 2H, 2H-perfluorodecyl)silane. Contact angle (CA) analysis suggested that superhydrophobic surfaces with a CA as high as 155° could be formed through optimizing the fabrication process.

•The sensing properties of different aniline reduced graphene oxides were studied.•We contrast the sensing response of three products to NH3 gas.•Free CRG shows the excellent sensing response, recovery to NH3 gas.•Free CRG exhibits the excellent repeatability, selectivity to NH3 gas.In this work, the NH3 gas sensors based on chemically reduced graphene oxide (CRG) have been fabricated and studied. Aniline was used to reduce graphene oxide (GO) in order to obtain CRGs attached with different states of polyaniline (PANI), i.e., acid-doped PANI attached CRG, de-doped PANI attached CRG and free CRG. These various products were characterized by scanning electron microscopy, transmittance electron microscopy, infrared spectroscopy and UV–Vis spectroscopy. Furthermore, gas sensing properties of gas sensors based on these CRGs were studied. And the results suggested that free CRG exhibited excellent response to NH3 and showed high sensitivity to NH3 with the concentrations at parts-per-million (ppm) level. The sensors based on free CRG exhibited a response of 37.1% when exposure to 50 ppm of NH3. And they showed excellent recovery in comparison with the acid-doped CRG, as well. Above all, free CRG can be considered as an excellent sensing material for the detection of NH3. In addition, the sensing device can be easily fabricated by drop drying method, which holds great potential in various gas sensing fields, due to its miniature, low cost and portable characteristics.Novel ammonia gas sensing devices based on aniline reduced graphene oxide (CRG), which exhibit great sensing response, recovery, repeatability and selectivity to NH3 gas, have been reported.

Here we present a useful ammonia (NH3) gas sensor based on reduced graphene oxide (RGO)–polyaniline (PANI) hybrids. PANI nanoparticles were successfully anchored on the surface of RGO sheets by using RGO–MnO2 hybrids as both of the templates and oxidants for aniline monomer during the process of polymerization. The resultant RGO–PANI hybrids were characterized by transmittance electron microscopy, infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and scanning electron microscopy. The NH3 gas sensing performance of the hybrids was also investigated and compared with those of the sensors based on bare PANI nanofibers and bare RGO sheets. It was revealed that the synergetic behavior between both of the candidates allowed excellent sensitivity and selectivity to NH3 gas. The RGO–PANI hybrid device exhibited much better (3.4 and 10.4 times, respectively, with the concentration of NH3 gas at 50 ppm) response to NH3 gas than those of the bare PANI nanofiber sensor and bare graphene device. The combination of the RGO sheets and PANI nanoparticles facilitated the enhancement of the sensing properties of the final hybrids, and pave a new avenue for the application of RGO–PANI hybrids in the gas sensing field.

We present a useful gas sensor based on chemically reduced graphene oxide (CRG) by drop drying method to create conductive networks between interdigitated electrode arrays. CRG, which is formed from the reduction of graphene oxide by p-phenylenediamine (PPD), can be used as an excellent sensing material. Its efficient dispersion in organic solvents (i.e., ethanol) benefits the formation of conductive circuits between electrode arrays through drop drying method. Preliminary results, which have been presented on the detection of dimethyl methylphosphonate (DMMP) using this simple and scalable fabrication method for practical devices, suggest that PPD reduced CRG exhibits much better (5.7 times with the concentration of DMMP at 30 ppm) response to DMMP than that of CRG reduced from hydrazine. Furthermore, this novel gas sensor based on CRG reduced from PPD shows excellent responsive repeatability to DMMP. Overall, the efficient dispersibility of CRG reduced from PPD in organic solvents facilitates the device fabrication through drop drying method, the resultant CRG-based sensing devices, with miniature, low cost, portable characteristics, as well as outstanding sensing performances, can ensure its potential application in gas sensing fields.

A novel hybrid material composed of single-walled carbon nanotubes (SWNTs) and cobalt phthalocyanine (CoPc) derivatives have been obtained. The resultant hybrid has been confirmed by infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy and X-ray photoelectron spectrometry. The results revealed that the CoPc derivatives had been successfully anchored on the surface of nanotubes through π–π stacking. The quantitatively determination of the CoPc derivatives have also been carried out through characterization by thermogravimetric analysis. Furthermore, the morphology of the resultant SWNT-CoPc derivative hybrids has been observed by transmission electron microscopy and scanning electron microscopy. Finally, gas sensor tests were performed to check the potential of this hybrid material while the sensing devices have been fabricated. The synergetic behavior between both of the candidates allows an excellent sensitivity and selectivity to dimethyl methylphosphonate (DMMP) (stimulant of nerve agent sarin). Overall, we present the advantages of combining metallophthalocyanine (MPc) with SWNTs in enhancing the properties of the final product, and pave a new avenue for the application of SWNT-MPc hybrids in the gas sensing field.

•Magnetically separable catalyst is synthesized in an energy-efficient strategy.•High stability and efficiency is observed for 4-nitrophenol reduction with NaBH4.•Improvement relies on accelerated electron transfer and strong synergistic effect.Design supported bimetallic nanoparticles is an interesting and important strategy for developing new catalysts with enhanced activity and selectivity. Herein the magnetically separable reduced graphene oxide supported Ni-Au (RGO-Ni-Au) nanocatalysts were prepared by an in situ co-reduction and surfactant-free method, which exhibited excellent performance both in the catalytic reduction of 4-nitrophenol and degradation of environmentally polluting dyes with NaBH4. The best activity parameters of RGO-Ni-Au-6h nanocomposites for 4-nitrophenol reduction is 36.77 s−1 g−1 with an apparent rate constant of 11.03 × 10−3 s−1. Additionally, the prepared catalyst could be recycled over 6 times without obvious performance decay or even a morphology change. The enhancement in catalytic capability can be ascribed to the electron-enhanced effect of graphene support and strong synergistic effect between noble metal and magnetic transition metal. It is believed that such desirable catalyst with magnetic properties, high activity, and long-life stability make it promising in retrievable catalysis.

Here we present a useful ammonia (NH3) gas sensor based on reduced graphene oxide (RGO)–polyaniline (PANI) hybrids. PANI nanoparticles were successfully anchored on the surface of RGO sheets by using RGO–MnO2 hybrids as both of the templates and oxidants for aniline monomer during the process of polymerization. The resultant RGO–PANI hybrids were characterized by transmittance electron microscopy, infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and scanning electron microscopy. The NH3 gas sensing performance of the hybrids was also investigated and compared with those of the sensors based on bare PANI nanofibers and bare RGO sheets. It was revealed that the synergetic behavior between both of the candidates allowed excellent sensitivity and selectivity to NH3 gas. The RGO–PANI hybrid device exhibited much better (3.4 and 10.4 times, respectively, with the concentration of NH3 gas at 50 ppm) response to NH3 gas than those of the bare PANI nanofiber sensor and bare graphene device. The combination of the RGO sheets and PANI nanoparticles facilitated the enhancement of the sensing properties of the final hybrids, and pave a new avenue for the application of RGO–PANI hybrids in the gas sensing field.

A novel hybrid material composed of single-walled carbon nanotubes (SWNTs) and cobalt phthalocyanine (CoPc) derivatives have been obtained. The resultant hybrid has been confirmed by infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy and X-ray photoelectron spectrometry. The results revealed that the CoPc derivatives had been successfully anchored on the surface of nanotubes through π–π stacking. The quantitatively determination of the CoPc derivatives have also been carried out through characterization by thermogravimetric analysis. Furthermore, the morphology of the resultant SWNT-CoPc derivative hybrids has been observed by transmission electron microscopy and scanning electron microscopy. Finally, gas sensor tests were performed to check the potential of this hybrid material while the sensing devices have been fabricated. The synergetic behavior between both of the candidates allows an excellent sensitivity and selectivity to dimethyl methylphosphonate (DMMP) (stimulant of nerve agent sarin). Overall, we present the advantages of combining metallophthalocyanine (MPc) with SWNTs in enhancing the properties of the final product, and pave a new avenue for the application of SWNT-MPc hybrids in the gas sensing field.

Metal-semiconductor-based photocatalysts show high efficiencies and catalytic activities in the photocatalysis process. Herein, the magnetic and one-dimensional Ni–Cu2O heteronanowires have been fabricated via in situ reduction of pre-adsorbed Cu2+ on the surface of prickly Ni nanowires in an ethanol solution for photocatalysis application. The resultant Ni–Cu2O heteronanowires show higher photocatalytic ability than pure Cu2O nanoparticles in the degradation of methyl orange. The enhancement of photocatalytic efficiency can be ascribed to the unique one-dimensional nanostructure and the electron sink effect of Ni nanowires in the heterostructure. It is believed that the low-cost metal Ni is an alternative candidate for substituting the costly metals (Au, Ag and Pt) to improve the photocatalytic ability of semiconductor-based photocatalysts.