Syntheses And Property Studies Of High Mass Loading Pseudocapacitive Materials With High Cycling Stability For Supercapacitors

Pseudocapacitive materials,including transition metal oxides and conducting polymers,are one of the most promising energy storage materials due to its abundant resources,environmental friendliness and high energy density.However,the poor structure stability and low conductivity of pseudocapacitive electrodes resulting in severe capacitance loss and poor rate capability.In addition,a small active material loading is generally required for the pseudocapacitive electrodes to achieve satisfactory electrochemical performance.The amount of energy stored in the low mass loading materials are,in fact,small,which limits their practical application for high energy systems.In this paper,we aim to improve the energy storage ability of high mass loading pseudocapacitive materials,and open up new opportunities in their practical application.Oxygen-deficient WO_3-x(WO_3-x NW)was prepared by a hydrothermal synthesis with the mass loading of 7.7 mg cm^-2.Meanwhile,a fully oxided tungsten oxide（WO₃ NW）electrode was obtained by calcining WO_3-x NW at high temperature as the control sample.The crystalline structure and oxygen defects of the WO_3-x were characterized by various structural characterization methods.To explore the influence of oxygen defects relevant to the electrochemical properties of WO₃ NW,the capacitance performance,rate performance and cycle stability of WO_3-x NW and WO₃NW were studied by various electrochemical analysis methods.The results show that the electrochemical performance of WO_3-x NW with much oxygen defects is significantly superior to that of the WO₃ electrode.The area capacitance of WO_3-xNW is 4761.4 m F cm^-2(gravimetric capacitance equal to 618.3 F g^-1),which is higher than WO₃ NW(2490 m F cm^-2,359.8 F g^-1).After 30000 cycles,the WO_3-x NW electrode retains 113.08%of its capacitance,which is significantly higher than that of WO₃ NW electrode（76.18%）.In addition,a high mass loading of 24.69 mg cm^-2 and high-performance polypyrrole was grown on the surface of functionalized partially exfoliated graphite substrate by a facile pulse electrodeposition technique（denoted as FEG@PPy-P）.Polypyrrole electrode was also prepared by a traditional potentiostatic method with similar mass loading（denoted as FEG@PPy-C）.Subsequently,the structural properties and electrochemical performance of these two electrodes were analyzed by variety of structural characterization and electrochemical technology.The FEG@PPy-P electrode exhibits an ultra-high area capacitance of 7249.57 m F cm^-2 at a current density of 3 m A cm^-2 and maintaining a high gravimetric capacitance of293.62 F g^-1.These properties were much higher than that of FEG@PPy-P under the same conditions.More importantly,the FEG@PPy-P delivers a high capacitance retention rate of 90.45%after 20,000 charging and discharging cycles,which is higher than 79.83%of FEG@PPy-C.This result shows that the polypyrrole electrode obtained by pulse electrodeposition method is expected to break the inherent bottleneck of the poor cycle performance of conducting polymer-based supercapacitors,and promotes its practical applicantion process.