WO3 homojunction photoanode: Integrating the advantages of WO3 different facets for efficient water oxidation

The manipulation of the surface property of WO3 photoanode is the main breakthrough direction to improve its solar water oxidation performance both in thermodynamics and kinetics. Here, we report a WO3(002)/m-WO3 homojunction film that is composed of an upper WO3 layer with predominant (002) facet (WO3(002)) and a lower WO3 layer with multi-crystal facets (m-WO3) as a photoanode for solar water oxidation. Due to the synergistic effect of WO3(002) layer and m-WO3 layer, better water oxidation activity and stability are achieved on the WO3(002)/m-WO3 homojunction film relative to the m-WO3 and WO3(002) film. Specifically, the improved water oxidation performance on the WO3(002)/m-WO3 homojunction film is attributed to the followings. In thermodynamics, the band position differences between WO3(002) layer and m-WO3 layer lead to the formation of WO3(002)/m-WO3 homojunction, which has positive function of improving their charge separation and transfer. In kinetics, the upper WO3(002) layer of the WO3(002)/m-WO3 film has superior activity in the adsorption and activation of water molecules, water oxidation on this homojunction film photoanode is inclined to follow the four-holes pathway, and the corrosion of photoanode from the H2O2 intermediate is restrained. The present work provides a new strategy to modify the WO3 photoanodes for thermodynamically and kinetically efficient water oxidation.