Oriented-growth Ta3N5/SrTaO2N array heterojunction with extended depletion region for improved water oxidation

Depletion region at solid-solid or solid-liquid interface is mainly responsible for separating charge. Extending depletion region is an effective strategy to promote charge separation, and thus improving photoelectrochemical (PEC) performance. Herein, we designed an array heterojunction photoanode consisting of a-axis oriented-growth Ta3N5 nanorod arrays coated by SrTaO2N shell. This array heterojunction with a contiguous Ta3N5/SrTaO2N solid-solid and SrTaO2N/electrolyte solid-liquid junctions maximizes the charge separation and light absorption in depletion layer, shortens the hole diffusion distance to electrolyte, and effectively transfers electrons along the a-axis (light electron effective mass) of Ta3N5 to conductive substrate. As a result, compared with Ta3N5, Ta3N5/SrTaO2N array heterojunction exhibits more excellent PEC performance. Our results demonstrated a potential crystal oriented growth strategy of nanostructured heterojunctions with extended depletion region for promoting charge separation and overcoming the short carrier diffusion distance.