Boosting Unassisted Alkaline Solar Water Splitting Using Silicon Photocathode with TiO Nanorods Decorated by Edge-Rich MoS Nanoplates.

To construct a highly efficient photoelectrochemical tandem device with silicon photocathode operating in alkaline conditions, it is desirable to develop stable and active catalysts which enable the photocathode to reliably perform under an alkaline environment. With nanostructured passivation layer and edge-exposed transition metal disulfides, silicon photocathode provides new opportunities for achieving unbiased alkaline solar water splitting. Here, the TiO nanorod arrays decorated by edge-rich MoS nanoplates are elaborately synthesized and deposited on p-Si. The vertically aligned TiO nanorods fully stabilize the Si surface and improve anti-reflectance. Moreover, MoS nanoplates with exposed edge sites provide catalytically active regions resulting in the kinetically favored hydrogen evolution under an alkaline environment. Interfacial energy band bending between p-Si and catalyst layers facilitates the transport of photogenerated electrons under steady-state illumination. Consequently, the MoS nanoplates/TiO nanorods/p-Si photocathode exhibits significantly improved photoelectrochemical-hydrogen evolution reaction (PEC-HER) performance in alkaline media with a high photocurrent density of 10 mA cm at 0 V versus RHE and high stability. By integrating rationally designed photocathode with earth-abundant Fe (NiCo) Cr anode and perovskite/Si tandem photovoltaic cell, an unassisted alkaline solar water splitting is accomplished with a current density of 5.4 mA cm corresponding to 6.6% solar-to-hydrogen efficiency, which is the highest among p-Si photocathodes.