p-Si/SnO2/Fe2O3 Core/Shell/Shell Nanowire Photocathodes for Neutral pH Water Splitting

Silicon is one of the promising materials for solar water splitting and hydrogen production; however, it suffers from two key factors, including the large external potential required to drive water splitting reactions at its surface and its instability in the electrolyte. In this study, a successful fabrication of novel p-Si/n-SnO2/n-Fe2O3 core/shell/shell nanowire (css-NW) arrays, consisting of vertical Si NW cores coated with a thin SnO2 layer and a dense Fe2O3 nanocrystals (NCs) shell, and their application for significantly enhanced solar water reduction in a neutral medium is reported. The p-Si/n-SnO2 /n-Fe2O3 css-NW structure is characterized in detail using scanning, transmission, and scanning transmission electron microscopes. The p-Si/n-SnO2 /n-Fe2O3 css-NWs show considerably improved photocathodic performances, including higher photocurrent and lower photocathodic turn-on potential, compared to the bare p-Si NWs or p-Si/n-SnO2 core/shell NWs (cs-NWs), due to increased optical absorption, enhanced charge separation, and improved gas evolution. As a result, photoactivity at 0 V versus reversible hydrogen electrode and a low onset potential in the neutral solution are achieved. Moreover, p-Si/n-SnO2 /n-Fe2O3 css-NWs exhibit long-term photoelectrochemical stability due to the Fe2O3 NCs shell well protection. These results reveal promising css-NW photoelectrodes from cost-effective materials by facile fabrication with simultaneously improved photocathodic performance and stability.