Controlled Growth of WO Photoanode under Various pH Conditions for Efficient Photoelectrochemical Performance.

Herein, the effects of the precursor solution's acidity level on the crystal structure, morphology, nucleation, and growth of WO·nHO and WO nanostructures are reported. Structural investigations on WO·nHO using X-ray diffraction and Fourier-transform infrared spectroscopy confirm that the quantity of hydrate groups increases due to the interaction between H and water molecules with increasing HCl volume. Surface analysis results support our claim that the evolution of grain size, surface roughness, and growth direction on WO·nHO and WO nanostructures rely on the precursor solution's pH value. Consequently, the photocurrent density of a WO photoanode using a HCl-5 mL sample achieves the best results with 0.9 mA/cm at 1.23 V vs. a reversible hydrogen electrode (RHE). We suggest that the improved photocurrent density of the HCl-5 mL sample is due to the efficient light absorption from the densely grown WO nanoplates on a substrate and that its excellent charge transport kinetics originate from the large surface area, low charge transfer resistance, and fast ion diffusion through the photoanode/electrolyte interface.