Novel three-dimensional (3D) island-chain structured vanadium pentoxide (V2O5)/graphene (GN)/multiwalled carbon nanotube (MWCNT) hybrid aerogels (VGMA) are synthesized by a sol–gel method. In this process, V2O5 in situ grows along the surface of both MWCNT and GN by the coordination effect. These two kinds of one-dimensional fibers (V2O5 nanofibers and V2O5 coated MWCNT) and one kind of two-dimensional sheets (GN) co-assemble into a 3D porous island-chain structure. VGMA exhibit enhanced specific capacitance (504 F g−1), large energy density (70 W h kg−1) and outstanding cyclic property (82.9% retention after 32 500 cycles). All these excellent electrochemical properties of ternary VGMA can be attributed to the well-designed nanostructure and synergistic effect of the individual components. This also demonstrates that the unique island-chain nanostructured VGMA can be a good candidate for supercapacitors.

The carbon nanotubes/vanadium oxide composites have been prepared through a facile hydrothermal method. Morphology features of the samples are investigated by field-emission scanning electron microscope. Raman and X-ray diffraction patterns confirm the formation of phase structure. Thermogravimetric analysis was used to quantify the content of carbon nanotube in the composites. When used as cathode materials for lithium-ion batteries, the composites exhibit improved electrochemical performance compared to electrode materials free of carbon nanotubes. V2O5/carbon nanotubes can deliver a good capacity of 196.8 mA h g−1 at a current density of 100 mA g−1 after 50 cycles. However, the electrode materials free of carbon nanotubes (V2O5) can reach a capacity of 171 mA h g−1 at the same conditions. Moreover, V2O5/carbon nanotubes present a higher capacity than that of V2O5 under the same rate conditions. The improved electrochemical performance can be attributed to the fact that the carbon nanotubes in the V2O5/carbon nanotube composites can effectively facilitate ionic diffusion by raising the electrical conductivity.Open image in new window

•Unbroken Fe-doped vanadium oxide nanorods were synthesized by a simple hydrothermal method.•Metal ions can enhance the electrical conductivity of electrodes and ion diffusion coefficient.•Fe-doped nanorods (0.15Fe-V2O5) can deliver a good capacity retention rate of 82.2% at 1 A g−1 after 50 cycles.Fe-doped vanadium oxide nanorods were synthesized by a simple hydrothermal method. Experimental results demonstrate that doping moderate amount of metal ions can inhibit the breakage of the morphology structure during phase transition and enhance the structure stability of vanadium oxide nanorods after calcination. Meanwhile, metal ions can enhance the electrical conductivity of electrodes and ion diffusion coefficient, but doping more metal ions can reduce ion diffusion coefficient due to ions block Li+ diffusion path. The unbroken Fe-doped vanadium oxide nanorods play an important role in improving the electrochemical performance of electrodes. Fe-doped nanorods (0.15Fe-V2O5) can deliver a high initial capacity of 271 mA h g−1, and a good capacity retention of 82.2% at a current density of 1 A g−1 after 50 cycles, while un-doped V2O5 electrode materials show a low capacity retention of ∼65.6% under the same condition. Improved performance of Fe-doped vanadium oxides is mainly attributed to the enhancement of electrical conductivity and the maintenance of nanorods structure during electrochemical cycling.

Herein, thick tungsten–silicon films with long-term gasochromic performance were synthesized from methyltrimethoxysilane (MTMS) and tungsten oxide sols. Via the addition of MTMS, the thickness of WO3/SiO2 films was largely increased to nearly 3 μm without any cracks. Moreover, the transmittance difference between coloring and bleaching status reached over 97% in the near-infrared region. Different ratios of WO3–MTMS compound films were prepared to confirm that the proper proportion of WO3 : MTMS was 1 : 2, and WO3–TEOS films were also prepared for comparisons. FT-IR and Raman spectra were obtained to characterize the structure of W–O and the existence of –CH3 bonds. SEM and TEM images revealed the thickness of compound films and cross-links of the microstructure. The results showed that the WO3–MTMS films exhibited a stable network with tungsten and silicon bonds, and the methyl group derived from MTMS hydrolysate played a positive role in gel and drying processes.

•A novel hierarchical starfish-like vanadium oxide are synthesized by a simple hydrothermal method.•The functional V2O5 sol plays a crucial role for formation hierarchical starfish-like structure.•Starfish-like vanadium oxide grown along the (1 1 0) plane and four oblique sheets grown on the flanking of (1 1 0) plane, respectively.•Hierarchical starfish-like V2O5 cathode materials can deliver discharge capacity of approximately 163 mA h g−1 at high current density of 1000 mA g−1 (5C) after 50 cyclesA novel hierarchical starfish-like vanadium oxide is synthesized by a simple and direct hydrothermal method using a functional V2O5 sol as a vanadium source. The formation mechanism of hierarchical starfish-like structure is discussed. Results demonstrate that the functional V2O5 sol plays a crucial role in the formation of a hierarchical starfish-like structure. Starfish-like vanadium oxide is composed of single crystals of a metastable VO2 (B) phase that grow along the (1 1 0) plane and four oblique sheets growing on the flanks of the (1 1 0) plane. The starfish-like structure can be preserved and undergoes phase transition to the orthorhombic V2O5 phase when calcined at 350 °C. Hierarchical starfish-like V2O5 displays higher electrochemical performance than pristine V2O5 powder as a cathode material for LIBs. This improved performance could be attributed to the shortened diffusion path of lithium ions in the former; a large electrode/electrolyte contact area resulting from the unique hierarchical starfish-like structure composed of nanosheets also offers better electrolyte wetting and alleviates the structural degradation upon cycling. The hierarchical starfish-like V2O5 can deliver a discharge capacity of approximately 163 mA h g−1 at a high current density of 1000 mA g−1 (5C) even after 50 cycles.

Vanadium pentoxide (V2O5)/multiwalled carbon nanotube (MWCNT) core/shell hybrid aerogels with different MWCNT contents are controlled synthesized through a facile mixed growth and self-assembly methodology. V2O5 coated MWCNTs from the in situ growth of V2O5 on the surface of acid-treated MWCNTs incorporate with V2O5 nanofibers from the preferred orientation growth of V2O5 in a one-step sol–gel process. These two kinds of one-dimensional fibers self-assemble into a three-dimensional monolithic porous hybrid aerogel. Owing to its high specific surface area, favorable electrical conductivity and unique three-dimensional and core/shell structures, the light weight hybrid aerogel (about 30 mg cm−3) exhibits excellent specific capacitance (625 F g−1), high energy density (86.8 W h kg−1) and outstanding cycle performance (>20000 cycles). And the optimal content of MWCNTs in hybrid aerogels for the highest-performance supercapacitor is 7.6%.

This paper describes the synthesis of a hierarchical porous vanadium pentoxide (V2O5)/graphene hybrid aerogel through a low-cost and facile sol–gel method. The V2O5/graphene hybrid aerogel is synthesized through the in situ growth of V2O5 nanofibers on graphene sheets. The V2O5/graphene hybrid aerogel-based supercapacitors exhibit enhanced specific capacitance (486 F g−1), high energy density (68 W h kg−1) and outstanding cycle performance. These effects are attributed to the unique hierarchical porous structure of the hybrid aerogel.

Urchin-like vanadium oxide nanotube clusters, abbreviated to VOx-NUs, were synthesized using a new method. Vanadium pentoxide, having a layered structure, was modified by lithium fluoride (LiF) and transformed into bi-phase lithium vanadate as the inorganic precursor. Then, VOx-NUs were prepared by hydrothermal reaction with dodecylamine as a template. This is different from other molecular assembly methods reported. VOx-NUs-350 nano clusters were obtained by annealing VOx-NUs at a temperature of 350 °C in air. Both samples were identified as three dimensional urchin-like nano clusters. Based on the characterization data obtained, a formation mechanism was established. By simply varying the LiF stoichiometric ratio, the nano tube density of the VOx-NUs could be controlled. VOx-NUs presented a higher initial rate capacity of 400 mA h g−1 and VOx-NUs-350 maintained a better capacity of 150 mA h g−1 after 50 cycles at a 100 mA g−1 current density between 1.5 and 4 V versus Li/Li+.

Vanadium pentoxide (V2O5) nanosheet thin film without conductive additives and binders has been synthesized via sol–gel and liquid phase deposition methods on ITO glass substrate followed by heat treatment at 450 °C. The SEM and TEM results showed that the as-deposited film presents an intertwined nanowire structure with a length of several micrometers and a width of dozens of nanometers, and it transformed into nanosheet-like crystalline orthorhombic V2O5 after annealing. Possible formation process of the nanowired structure is briefly discussed. The analysis of XRD confirmed that the film exhibits a strong preferred orientation along c-axis. The Raman spectrum verified the layered structure of the film. The corresponding electrochemical performance tests indicated that the binder- and carbon-free film possesses comparable high specific capacity and good cyclic stability to the conventional electrodes, which manifests that this facile synthesized material is quite promising and it provides a low-cost alternative for lithium-ion battery applications.

Highly ordered mesoporous WO3 film was synthesized by employing a template-assisted peroxopolytungstic acid sol–gel method and applied for the first time in gasochromic smart windows. The results demonstrated that this mesoporous microstructured sample with semicrystalline pore walls exhibits excellent performance, including wide optical modulation ability, fast coloring/bleaching response and reliable cyclic stability.

The electrochemical and Mg ion diffusion properties of tavorite-Mg0.5FeSO4F were studied by using first principles calculations. A discharge voltage of about 2.52 V versus Mg/Mg2+ corresponding to the redox couples of Fe3+/Fe2+ was predicted for tavorite-Mg0.5FeSO4F, and the experimental diffusion coefficient for the Mg-vacancy in Mg0.5−xFeSO4F is expected to be of the same order of magnitude as that of the Li-vacancy in Li1−xFeSO4F.

Carbon black (CB) anchored vanadium oxide (C-VOx) nanobelts are successfully prepared by a simple sol–gel route and subsequent hydrothermal treatment. The synthesized C-VOx nanobelts display high specific capacity and good cycling stability as a cathode material for lithium ion batteries (LIBs) (232 mA h g−1 at initial discharge and 195 mA h g−1 during 50th discharge at a current density of 100 mA g−1 between 1.5–4 V versus Li) due to the nano-belted morphology and closely attached CB. The orthorhombic V2O5 nanobelts can be obtained by post-sintering of C-VOx nanobelts in air. These V2O5 nanobelts, which maintain their previous belted morphology and possess higher vanadium valence, exhibit superior electrochemical properties, especially the higher specific capacity (406 mA h g−1 and 220 mA h g−1 during the 1st and 50th discharge at a current density of 100 mA g−1, and 146 mA h g−1 at a current density of 1000 mA g−1 between 1.5–4 V versus Li). Both of them can be used as high performance cathode materials for LIB application. Furthermore, a full-cell using V2O5 nanobelts as the cathode and lithiated graphite as the anode is assembled and its electrochemical performance is measured in the voltage range of 1.5–3.8 V.

The coloration response of gasochromic films is crucial for gas sensors and solar energy cells. Based on a comparison of different post-treatments of WO3 gasochromic films, UV irradiation is found useful for fast coloration, in which fast exponential optical changes can be detected instead of a long activation delay process. Infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy studies show that the gasochromic response of WO3 films depends on the ion and electron diffusion velocities, which can be engineered by altering the film porosities and conductivities. A new gasochromic model is proposed based on a resistor and capacitor (RC) circuit and the double-injection theory. According to this model, the slow coloration delay and fast exponential coloration should result from thermodynamic and electrochemical reactions, respectively. Our new model is also successfully used to build a link between two well-identified theoretical models.

MgVPO4F is proposed as a cathode material for rechargeable Mg ion batteries for the first time. First principles calculations were performed to study the electrochemical properties of MgVPO4F as a positive electrode material for rechargeable Mg ion batteries. Our theoretical study gives an expectation of good battery performance by MgVPO4F.

Bi-crystal lithium vanadate is synthesized with starting materials of V2O5 and LiF by one-step solid-state reaction. Since fluorine reacts with crucible made of silica, Li0.3V2O5-liked and LiV3O8-liked phases without F coexist in the produces. The stoichiometric proportion of two phases depends on the amount of dopant LiF. These are confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and transmission electron microscopy (TEM). Charge and discharge curves of bi-crystal materials present better reversibility of voltage plateaus than that of pure V2O5. The initial discharge capacity of Li0.3V2O5-liked phase dominated bi-crystal material is higher than pure V2O5. LiV3O8-liked phase dominated bi-crystal material has lower initial discharge capacity but delivers better cycling performance. Electrochemical impedance spectroscopy (EIS) measurements are performed to evaluate electrochemical kinetics of the bi-crystal materials. The results indicate that bi-crystal phase benefit the transfer resistance, interior diffusion resistance, and structure stability. Cathodes with different bi-phase structures have variable charge transfer resistance and lithium-ion diffusion speed due to this special structure.

Multiwalled carbon nanotubes (MWCNTs)–V2O5 integrated composite with nanosized architecture has been synthesized through hydrothermal treatment combined with a post-sintering process. During the hydrothermal reaction, protonated hexadecylamine (C16H33NH3+) acts as an intermediator, which links the negatively charged vanadium oxide layer with the mixed-acid pretreated MWCNTs by weak electrostatic forces to form a three-phase hybrid (MWCNTs–C16–VOx). MWCNT–V2O5 composite and V2O5 nanoparticles can be obtained by sintering MWCNTs–C16–VOx at 400 and 550 °C in air, respectively. Among them, MWCNTs–V2O5 possesses better electrochemical performance as a cathode material for lithium ion batteries (LIBs). The unique porous nanoarchitecture of MWCNTs–V2O5 provides a large specific surface area and a good conductive network, which facilitates fast lithium ion diffusion and electron transfer. Additionally, the uniformly dispersed MWCNTs conducting network also behaves as an effective buffer which can relax the strain generated during charge–discharge cycles. Electrochemical tests reveal that MWCNTs–V2O5 could deliver a superior specific capacity (402 mA h g−1 during initial discharge at a current density of 100 mA g−1 between 1.5 and 4 V versus Li/Li+), good cycling stability (222 mA h g−1 after 50 cycles) and high rate capability (194 mA h g−1 at a current density of 800 mA g−1).

In this paper, MWCNT (Multi-Wall Carbon Nanotube)-induced vanadium oxide nanosheet composite is synthesized via sol–gel method and subsequent hydrothermal treatment process. TEM and SEM tests confirmed that the synthesized product shows a rectangular sheet-like nanostructure with the length of several micrometers, width of a few hundred nanometers and thickness of dozens of nanometers. The analysis of XRD verified the monoclinic crystal structure of the vanadium oxide nanosheet. The XPS results manifested that V4+ is predominant in the V element of vanadium oxide nanosheet. The corresponding electrochemical performance examinations indicated this nanosheet-MWCNT composite with distinct single phase transition feature exhibits high specific capacity and good cycling stability due to its sheet-like nanostructure and uniform adding of MWCNTs, which makes this novel vanadium oxide nanosheet-MWCNT composite quite suitable and promising as cathode material for Li+ ion batteries applications.

This paper describes the synthesis of a hierarchical porous vanadium pentoxide (V2O5)/graphene hybrid aerogel through a low-cost and facile sol–gel method. The V2O5/graphene hybrid aerogel is synthesized through the in situ growth of V2O5 nanofibers on graphene sheets. The V2O5/graphene hybrid aerogel-based supercapacitors exhibit enhanced specific capacitance (486 F g−1), high energy density (68 W h kg−1) and outstanding cycle performance. These effects are attributed to the unique hierarchical porous structure of the hybrid aerogel.

Multiwalled carbon nanotubes (MWCNTs)–V2O5 integrated composite with nanosized architecture has been synthesized through hydrothermal treatment combined with a post-sintering process. During the hydrothermal reaction, protonated hexadecylamine (C16H33NH3+) acts as an intermediator, which links the negatively charged vanadium oxide layer with the mixed-acid pretreated MWCNTs by weak electrostatic forces to form a three-phase hybrid (MWCNTs–C16–VOx). MWCNT–V2O5 composite and V2O5 nanoparticles can be obtained by sintering MWCNTs–C16–VOx at 400 and 550 °C in air, respectively. Among them, MWCNTs–V2O5 possesses better electrochemical performance as a cathode material for lithium ion batteries (LIBs). The unique porous nanoarchitecture of MWCNTs–V2O5 provides a large specific surface area and a good conductive network, which facilitates fast lithium ion diffusion and electron transfer. Additionally, the uniformly dispersed MWCNTs conducting network also behaves as an effective buffer which can relax the strain generated during charge–discharge cycles. Electrochemical tests reveal that MWCNTs–V2O5 could deliver a superior specific capacity (402 mA h g−1 during initial discharge at a current density of 100 mA g−1 between 1.5 and 4 V versus Li/Li+), good cycling stability (222 mA h g−1 after 50 cycles) and high rate capability (194 mA h g−1 at a current density of 800 mA g−1).

Vanadium pentoxide (V2O5)/multiwalled carbon nanotube (MWCNT) core/shell hybrid aerogels with different MWCNT contents are controlled synthesized through a facile mixed growth and self-assembly methodology. V2O5 coated MWCNTs from the in situ growth of V2O5 on the surface of acid-treated MWCNTs incorporate with V2O5 nanofibers from the preferred orientation growth of V2O5 in a one-step sol–gel process. These two kinds of one-dimensional fibers self-assemble into a three-dimensional monolithic porous hybrid aerogel. Owing to its high specific surface area, favorable electrical conductivity and unique three-dimensional and core/shell structures, the light weight hybrid aerogel (about 30 mg cm−3) exhibits excellent specific capacitance (625 F g−1), high energy density (86.8 W h kg−1) and outstanding cycle performance (>20000 cycles). And the optimal content of MWCNTs in hybrid aerogels for the highest-performance supercapacitor is 7.6%.

Highly ordered mesoporous WO3 film was synthesized by employing a template-assisted peroxopolytungstic acid sol–gel method and applied for the first time in gasochromic smart windows. The results demonstrated that this mesoporous microstructured sample with semicrystalline pore walls exhibits excellent performance, including wide optical modulation ability, fast coloring/bleaching response and reliable cyclic stability.

Carbon black (CB) anchored vanadium oxide (C-VOx) nanobelts are successfully prepared by a simple sol–gel route and subsequent hydrothermal treatment. The synthesized C-VOx nanobelts display high specific capacity and good cycling stability as a cathode material for lithium ion batteries (LIBs) (232 mA h g−1 at initial discharge and 195 mA h g−1 during 50th discharge at a current density of 100 mA g−1 between 1.5–4 V versus Li) due to the nano-belted morphology and closely attached CB. The orthorhombic V2O5 nanobelts can be obtained by post-sintering of C-VOx nanobelts in air. These V2O5 nanobelts, which maintain their previous belted morphology and possess higher vanadium valence, exhibit superior electrochemical properties, especially the higher specific capacity (406 mA h g−1 and 220 mA h g−1 during the 1st and 50th discharge at a current density of 100 mA g−1, and 146 mA h g−1 at a current density of 1000 mA g−1 between 1.5–4 V versus Li). Both of them can be used as high performance cathode materials for LIB application. Furthermore, a full-cell using V2O5 nanobelts as the cathode and lithiated graphite as the anode is assembled and its electrochemical performance is measured in the voltage range of 1.5–3.8 V.