Phase-dependent optical, photocatalytic and capacitive properties of tungsten oxide nanowires

Transition metal oxides hold great promise across a wide range of applications due to favorable properties such as high abundance, low toxicity, and excellent stability. Nanoengineering approaches are essential for controlling the structural, optical, and electronic properties of these materials, enabling the achievement of desired characteristics in a cost-effective and environmentally friendly manner. In this study, we synthesize stoichiometric (WO₃) and sub-stoichiometric (WO_3-) tungsten oxide nanowires by controlling their phases and morphologies through the hydrothermal method. This approach allows us to systematically investigate the effects of different phases and oxygen vacancies on the optical properties, as well as on photocatalytic and supercapacitance applications. We use the photodegradation of RhB as a benchmark for photocatalytic activity under various experimental conditions, revealing that oxygen vacancies significantly influence photocatalytic behavior. For example, WO_3- nanowires adsorb/degrade a substantial amount of RhB within short durations under ambient conditions, where WO₃ nanowires are mostly inactive. The addition of H₂O₂ enhances the photocatalytic performance of WO₃ nanowires over 30 minutes, with even better results under low pH conditions with H₂O₂. This study also explores the phase-dependent electrochemical properties of WO₃ and WO_3- nanowires, providing insights into their potential for improved supercapacitor performance by leveraging their complementary properties in symmetric and asymmetric configurations. WO_3-, with a higher density of oxygen vacancies and thinner structure, offers enhanced conductivity and increased active sites for charge storage, resulting in superior specific capacitance and charge retention.