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‐SnO 2 /n‐Fe 2 O 3 core/shell/shell nanowire (css‐NW) arrays, consisting of vertical Si NW cores coated with a thin SnO 2 layer and a dense Fe 2 O 3 nanocrystals (NCs) shell, and their application for significantly enhanced solar water reduction in a neutral medium is reported. The p‐Si/n‐SnO 2 /n‐Fe 2 O 3 css‐NW structure is characterized in detail using scanning, transmission, and scanning transmission electron microscopes. The p‐Si/n‐SnO 2 /n‐Fe 2 O 3 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‐SnO 2 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‐SnO 2 /n‐Fe 2 O 3 css‐NWs exhibit long‐term photoelectrochemical stability due to the Fe 2 O 3 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.