Defect-engineered WO3-x/WO3 pseudocapacitive proton storage electrode with enhanced capacity and lowered impedance via vacancy doping and hydrothermal-assisted electro-coating

Proton batteries are a promising, sustainable alternative to lithium-ion batteries due to the abundance of hydrogen and its smaller ionic radius, which facilitates its seamless intercalation in electroactive materials. However, their progress depends on the development of cost-effective, high-capacity electrode materials. Herein, we report the successful fabrication of a binder-less, defect-engineered WO_3-x/WO₃ pseudocapacitive proton storage electrode (HTT_WO_3-x) through scavenging of atomic sub-surface oxygen from hydrothermal-treated electro-coated WO₃ films (HTT_WO₃). The defect-engineered electrode (HTT_WO_3-x) combined improved mass load with enhanced electronic and ionic transport behaviour. The electrode achieved an areal capacitance of 42.13 mF∙cm⁻² at 5.00 mV∙s⁻¹, approximately 300 % higher than the electro-coated WO₃ seed electrode. The hydrothermal treatment yielded an increased mass load and areal capacity, further improved through lowered impedance parameters and better interfacial characteristics by defect engineering. This study offered a facile method for achieving binder-free coating of high-mass load proton storage active materials without compromising their ionic and electronic transport.