Tungsten oxide nanopowders: pulse alternating current electrosynthesis, structure optimization and performance in a flow photocatalytic fuel cell

Photocatalytic fuel cell (PFC) is a promising technology to produce electrical energy from transformation of both light and chemical energy of waste products/biomass. Tungsten oxide (WO3) nanopowder is synthesized via a facile and ecologically sound top-down approach using pulse alternating current as an oxidant and aqueous ammonium chloride solution as an electrolyte without any surfactants and organic solvents. The large photocurrent density enhancement for WO3 nanopowder annealed at 500 °C demonstrates the importance of WO3 crystallinity in governing its photo-assisted water oxidation. The improved photoactivity of WO3-500 photoanode is due to reduction of the density of deep trap states boosting the charge transfer efficiency. The optimized WO3 photoanode was used to build up a solar light responsive PFC system with a Pt/C air-breathing cathode and the organic electron donors with different functional groups acting as fuels. The maximum power density value increases in the order of formic acid, glycerol, ethanol, and glucose. When glucose was used as the fuel, the WO3-Pt/C PFC obtained the highest power density (Pmax) and current density (Jmax) of 140.8 μW cm−2 and 704 μA cm−2, respectively. This study provides an efficient way for large-scale electrochemical preparation of WO3 nanopowders from bulk tungsten for solar light responsive waste products/biomass-fueled PFC system.