Amorphous Ni–Fe Phosphide @ 2D WS2 as Bifunctional Electrocatalyst for Unassisted Solar-Driven Overall Water Splitting

Utilizing solar-cell-assisted water splitting has emerged as a promising strategy for producing clean hydrogen energy and addressing the energy crisis. Nevertheless, the efficiency of solar to hydrogen (STH) remains hindered by the sluggish reaction kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Two-dimensional (2D) WS2, while featuring abundant exposed reaction sites, suffers from inadequate intrinsic activity, limiting its practical application. In this work, we develop an innovative covalent doping approach to modify the electronic structure and adjust the free-energy barrier from O* to OOH* by growing amorphous Ni–Fe phosphide on WS2 nanosheets (NSs). Consequently, the overpotentials for the OER and HER at 10 mA/cm2 are reduced by 7% and 15%, respectively, in comparison to pure Ni–Fe phosphide. Furthermore, the bifunctional electrocatalyst, Ni–Fe phosphide @ WS2, can deliver a current density of 10 mA/cm2 at a low voltage of 1.67 V. When coupled with an a-Si:H/a-SiGe:H/a-SiGe:H triple-junction solar cell, it attains a substantial STH efficiency of 8.49%.