Mesoporous Ultrathin In2O3 Nanosheet Cocatalysts on a Silicon Nanowire Photoanode for Efficient Photoelectrochemical Water Splitting

Vertical Si nanowire (NW) arrays are a promising photoanode material in the photoelectrochemical (PEC) water splitting field because of their highly efficient light absorption capability and large surface areas for PEC reactions. However, Si NW arrays always suffer from high overpotential, low photocurrent density, and low applied bias photon-to-current efficiency (ABPE) due to their low surface catalytic activity and intense charge recombination. Here, we report an efficient oxygen evolution cocatalyst of optically transparent, mesoporous ultrathin (2.47 nm thick) In₂O₃ nanosheets, which are coupled on the top of Si NW arrays. Combined with a conformal TiO₂ thin film as an intermediate protective layer, this Si NW/TiO₂/In₂O₃ (2.47 nm) heterostructured photoanode exhibited an extremely low onset potential of 0.6 V vs reversible hydrogen electrode (RHE). The Si NW/TiO₂/In₂O₃ (2.47 nm) photoanode also showed a high photocurrent density of 27 mA cm^-2 at 1.23 V vs RHE, more than 1 order of magnitude higher than that of the Si NW/TiO₂ photoanodes. This improvement in solar water splitting performance was attributed to the significantly promoted charge injection efficiency as a result of the In₂O₃ nanosheet coupling. This work presents a promising pathway for developing efficient Si-based photoanodes by coupling ultrathin 2D cocatalysts.