Material design for converting an oxidative-type BiVO4 catalyst into a reductive BiV(S,O)4−x sulfo-oxide catalyst for nitrogen photoreduction to ammonia

Abstract

Herein, we demonstrated S²⁻ anion incorporation into BiVO₄ for converting an oxidative-type BiVO₄ photocatalyst into a reductive-type BiV(S,O)_4−x (labeled BiVOS) sulfo-oxide photocatalyst for efficient N₂ fixation under an ambient environment. BiVOS-2 not only exhibited the highest NH₃ production rate of 563.6 μmol g⁻¹ h⁻¹ without sacrificial agents and with durable stability but also had an apparent quantum efficiency (AQE) of 2.18% at 420 nm and a solar-to-ammonia (STA) conversion efficiency of 0.071% in pure water under AM1.5G light irradiation. At the same time, the sulfur-free BiVO₄ can't realize N₂ to NH₃ conversion. The S²⁻ doping introduced Vo, which converted V⁵⁺ around Vo into V⁴⁺ to keep the electrical neutrality. The active atoms V⁴⁺ were exposed and activated N₂, and the electron hopping between V⁵⁺ and V⁴⁺ improved electron transfer. Density functional theory (DFT) calculation indicates that S²⁻ anion doping can enhance adsorption energy, elongate the NN bond of the adsorbed N₂ molecule, and facilitate electron transfer to the antibonding orbital of the N₂ molecule, leading the BiVOS sulfo-oxide catalyst to have excellent N₂ fixation activity. This study provides a promising method for converting an oxidative-type catalyst into a reductive catalyst to extend material applications.