Tuning the electrochemical properties of tungsten oxide nanoplates via Sn doping and mixed-phase formation for superior quasi-solid-state asymmetric supercapacitors

Abstract

The development of high-performance electrode materials remains a critical challenge in advancing next-generation pseudocapacitors due to their low electrical conductivity, slow ion diffusion, and structural instability during long-term cycling. The hydrated tungsten oxide (WO₃·H₂O) has emerged as a promising candidate owing to its layered structure and abundant interlayer water. However, its electrochemical performance is still constrained by limited active sites and inefficient charge-transfer kinetics. To overcome these limitations, Sn doping and controlled phase engineering of WO₃·H₂O were implemented to enhance the intrinsic electrochemical properties. Sn-doped WO₃·H₂O was synthesized at different doping concentrations via a simple wet chemical method, followed by annealing to achieve mixed phases of Sn-doped WO₃·H₂O and WO₃. Furthermore, the electrochemical measurements exhibited a significant enhancement in specific capacitance with the doping concentration, i.e., W0, SnW5, and SnW25 delivering specific capacitances of 115 F g⁻¹, 146 F g⁻¹, and 182 F g⁻¹, respectively, at 1 A g⁻¹. Similarly, among the annealed samples (SnW200, SnW400 and SnW600), SnW200 exhibited the highest capacitance of 323 F g⁻¹, demonstrating the synergistic effect of defect modulation and mixed-phase interaction. Eventually, the fabricated quasi-solid-state asymmetric supercapacitor (QSSAS) device achieved 36 F g⁻¹, an energy density of 11 W h kg⁻¹, and a power density of 5795 W kg⁻¹ while retaining 72% capacitance after 10 000 cycles. This work highlights the Sn doping of tungsten oxides as a promising and scalable route for developing durable, high-energy-density pseudocapacitors.