Partially carbonized tungsten oxide as electrode material for asymmetric supercapacitors

Synthesis of partially carbonized tungsten oxide employing a simple, one-step, and scalable in-situ reduction/carbonization process is reported along with its electrochemical performance as electrode material in an asymmetric supercapacitor. The synthesis produces a WO 2 /W 2 C composite where the carbide part is introduced to enhance the electronic conductivity of redox-active tungsten oxide. Electrochemical performance and charge storage mechanism of WO 2 /W 2 C heterostructure is elucidated in detail. The electrode material exhibits compelling areal capacitance within −0.3 to −1 V window in half-cell configuration. Notably, both surface-controlled and diffusion-controlled processes govern the charge storage behavior, with the former dominating at higher scan rates. An asymmetric supercapacitor assembled with WO 2 /W 2 C composite as a negative electrode and activated charcoal (AC) as a positive electrode exhibits good cycling stability within a stable voltage window of 0.2 to 1.4 V and could deliver an energy density of 0.6 mWh/cm 3 at a power density of 9 mW/cm 3 in aqueous electrolyte. This study thus provides a fundamental understanding of the charge storage mechanism in WO 2 /W 2 C composite electrode which is required for realizing futuristic energy storage devices with low cost but efficient electroactive materials.