| Increasing energy density is very important for the improvement of supercapacitor which is a new kind of energy storage device with high power density. It is crucial to expand the energy storage potential window of electrode materials of supercapacitor, which can increase the operational voltage of the capacitor and its energy density as well. In this work, organic-inorganic composites with wide energy storage potential window were synthesized through electrochemical codeposition of vanadium oxide (V2O5) and conducting polymers. Symmetric and asymmetric model supercapacitors were assembled to study the energy storage applications of the obtained composites. Advantages of both of the organic and inorganic components can be combined in the composites, synergetic effects can be induced as well.Electrochemical codeposition of vanadium oxide and polyaniline (PANI) was first tried through electrodeposition of V2O5 and electropolymerization of aniline in solutions of 0.1 M aniline containing 0.05,0.1,0.2,0.3,0.4 and 0.5 M vanadyl sulfate (VOSO4), respectively to get V2O5-PANI composites VP-0.5, VP-1, VP-2, VP-3, VP-4, and VP-5. The crystal structure of V2O5 was studied by X-ray diffraction (XRD), well the vibration absorptions of V2O5 and PANI were characterized by Fourier transform infrared spectroscopy (FT-IR). The morphologies of V2O5-PANI composites were investigated by scanning electron microscopy (SEM), the influence of VOSO4 concentration on morphologies of the obtained composites was studied. It was found that one-dimensional growth of PANI was directed by the incorporation of V2O5. Pseudocapacitive behaviors of composite films were investigated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Benefits from organic-inorganic composition, the V2O5-PANI composites exhibited a large energy storage potential window of 1.6 V from-0.9 to 0.7 V vs. SCE. Attributed to the nanorod structure of V2O5-PANI composite which is helpful for the effect conctact of reactive centers on the composite with electrolyte, the V2O5-PANI composite VP-1 displayed a high specific capacitance of 443 F/g at the current density of 0.5 mA/cm2 in 5 M LiCl aqueous electrolyte. This value is higher than those of similarly prepared V2O5 (217 F/g) and PANI (241 F/g).Then electrochemical codeposition of vanadium oxide and polypyrrole (PPy) was conducted at 0.7 V through electrodeposition of V2O5 and electropolymerization of pyrrole in solutions of 0.1 M phosphate buffer solution (PBS, pH=6.864) containing 0.1 M LiClO4,0.1 M VOSO4 and 0.1,0.05,0.03.0.025,0.02 M pyrrole, respectively to get V2O5-PPy composite films VPy-1, VPy-2, VPy-4 and VPy-5. The crystal structure of V2O5 was studied by XRD, well the vibration absorptions of V2O5 and PPy were characterized by FT-IR. The morphologies of V2O5-PPy were investigated by SEM which revealed that one-dimensional growth of PPy was also induced by the incorporation of V2O5. Pseudocapacitive behaviors of V2O5-PPy composite films were investigated by CV, CP and EIS. The V2O5-PPy composites exhibited an exceptional wide energy stroge potential window of 2.0 V from-1.4 to 0.6 V due to the cation-anion dual doping of PPy. The one-dimensional structure of V2O5-PPy composites can facilitate the contact of their reactive centers with electrolyte and so improve their energy storage performance. The V2O5-PPy composite VPy-3 displayed a specific capacitance of 412 F/g at the current density of 4.5 mA/cm2 in 5 M LiCl aqueous electrolyte, which is higer than those of similarly prepared V2O5 (181 F/g) and PPy (257 F/g).Symmetric supercapacitors VP-1//VP-1 and VPy-3//VPy-3 were fabricated by using VP-1 and VPy-3 as electrode materials, repectively in which two identical pieces of VP-1 or VPy-3 electrodes were assembled together with a piece of filter paper as separator and LiCl/PVA as electrolyte. Pseudocapacitive behaviors of the model supercapacitor were investigated by CV and CP. The VP-1//VP-1 achieved a high energy density of 69.2 Wh/kg due to the high operating voltage of 1.6 V with an excellent cycling stability,92% of its capacitance can be retented after 5000 charge-discharge cycles. The VPy-3//VPy-3 achieved an excellent energy density of 82 Wh/kg attributed to its exceptional high operating voltage of 2.0 V.80% of the capacitance can be maintained for VPy-3//VPy-3 after 5000 charge-discharge cycles. Both of VP-1//VP-1 and VPy-3//VPy-3 are highly flexible. The devices exhibited similar electrochemical performance at different bend angles of 0°,60°,120° and 180°.Electrochemical deposition of ruthenium oxide was conducted from a solution of 0.05 M rutheniumchloride hydrate RuCl3·H2O containing 0.1 M KCl,0.01 M HCl and 0.05 M NH4Ac. Asymmetric supercapacitors VP-1//RuO2 and VPy-3//RuO2RuO2 were assembled by using RuO2 as anode and VP-1 and VPy-3 as cathode. The VP-1//RuO2 and VPy-3//RuO2 displayed high energy density of 83.3 Wh/kg and 91 Wh/kg, respectively with a high operating voltage of 2.0 V for both. After 5000 charge-discharge cycles, the capacitance retentions are 90% and 86% for VP-1//RuO2 and VPy-3//RuO2, respectively. |
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