Sulfur Defect Tuning of CuS/BiVO₄ and Understanding the Function of Hydrogen Radicals for Photoelectrochemical Ammonia Production

Photoelectrochemical nitrate reduction has been a promising method for ammonia (NH₃) production under normal temperatures and neutral conditions. However, hydrogenation is a key process in the selective production of NH₃ during nitrate reduction; therefore, inducing the active hydrogen for nitrate hydrogenation and inhibiting hydrogen production are a noteworthy problem. In this study, BiVO₄/CuS (BVO/CS) heterostructure has been constructed for a photoelectrochemical nitrate reduction reaction (PEC NIRR). The introduction of CuS optimizes the electron-transfer ability and enhances the surface catalytic kinetics of BVO/CS. At the same time, the presence of sulfur vacancies on the surface promotes the adsorption and activation of nitrate, realizes the splitting of H₂O, and successfully generates abundant hydrogen radicals (H*). The generated H* is effectively utilized in the hydrogenation of NIRR. The NH₃ yield and selectivity of optimal BVO/CS reach 30.55 μg h^-1 cm^-2 and 43.8%, respectively, which are 2.65 and 2.39 times that of bare BVO. Therefore, this work determines the key role of H* for nitrate hydrogenation, providing a novel strategy for boosting PEC NIRR. CuS/BiVO₄ was successfully fabricated for photoelectrochemical nitrate reduction. Sulfur defects enabled the generation of hydrogen radicals, which effectively promoted nitrate hydrogenation and NH₃ production.