Transition metal oxynitrides have been promising as supercapacitor (SC) electrode active material due to their higher electrical conductivity and good corrosion resistance than oxide compounds. These excellent features are due to the bonding of nitride groups with metallic atoms. Tungsten oxynitride W(O,N) compound has been proven to be a proper choice for SC electrodes. A novel one-step combustion reaction strategy followed by an ammonia gas nitriding process is provided for binder-free W(O,N)|nickel foam electrode preparation. Structural measurements, including X-ray photoelectron spectroscopy, confrm the coexistence of oxygen and nitrogenbased redox groups for different nitriding temperatures ranging from 550 to 800 ◦C. The W(O,N)-800|NF electrode exhibits a maximum specifc capacitance of 478 F g− 1 (1848.9 mF cm− 2) at 1 A g− 1 in 1 M KOH aqueous electrolyte. Density functional theory simulations show that this high capacitance can be attributed to the presence of N atoms. In-depth investigations suggest that the capacitive-controlled process governs the charge storage mechanism at all scan rates in the compound. The designed asymmetric supercapacitor device can deliver a high energy density of 16.52 Wh kg− 1 and a high-power density of 3650.67 W kg− 1 in 6 M KOH aqueous electrolyte and retain 86.04 % of the capacitance after 10,000 cycles. Moreover, providing deep insight into the charge-storage process and representing the importance of nitrogen tuning by studying the electronic structure suggests a promising capacitive material for the next-generation energy storage device.

Keywords