Efficient Photoelectrochemical Hydrogen Evolution on Silicon Photocathodes Interfaced with Nanostructured NiP₂ Cocatalyst Films

Increasing attention has now been focused on the photoelectrochemical (PEC) hydrogen evolution as a promising route to transforming solar energy into chemical fuels. Silicon is one of the most studied PEC electrode materials, but its performance is still limited by its inherent PEC instability and electrochemical inertness toward water splitting. To achieve significant PEC activities, silicon-based photoelectrodes usually have to be coupled with proper cocatalysts, and thus, the formed semiconductor–cocatalyst interface presents a critical structural parameter in the rational design of efficient PEC devices. In this study, we directly grow nanostructured pyrite-phase nickel phosphide (NiP 2 ) cocatalyst films on textured pn + -Si photocathodes via on-surface reaction at high temperatures. The areal loading of the cocatalyst film can be tailored to achieve an optimal balance between its optical transparency and electrocatalytic activity. As a result, our pn + -Si/Ti/NiP 2 photocathodes demonstrate a great PEC onset potential of 0.41 V versus reversible hydrogen electrode (RHE), a decent photocurrent density of ∼12 mA/cm 2 at the thermodynamic potential of hydrogen evolution, and an impressive operation durability for at least 6 h in 0.5 M H 2 SO 4 . Comparable PEC performance is also observed in 1 M potassium borate buffer (pH = 9.5) using this device.