Exposure of V Sites on InVO₄ via Rapid Joule-Heating for Highly Efficient Photocatalytic N2 Fixation

Abstract

The photocatalytic nitrogen reduction reaction (NRR) is a sustainable green alternative to the Haber-Bosch process for ammonia production. However, due to the inert properties of dinitrogen, the photocatalytic activity in N2 reduction is still pretty low. Based on density functional theory calculations, this study finds that the formation energy of oxygen vacancies around the V site in InVO4 was significantly lower than that around the In site. This indicated that the V-O bond was thermodynamically less stable and tends to break preferentially. Therefore, selective cleavage of the V–O bond was achieved by subjecting InVO4 to transient high-temperature treatment via rapid Joule heating technology. This resulted in the directed construction of an InVO4-JH catalyst enriched with oxygen vacancies and exposing coordination-unsaturated V sites. The resulting InVO4-JH catalyst delivered a photocatalytic ammonia production rate of up to 35.28 μmol g-1 h-1 under ambient conditions without any sacrificial agent, while exhibiting excellent stability and reaction selectivity. Mechanistic studies and structural characterization confirmed that the formation of oxygen vacancies via V–O bond cleavage releases electrons, which reduce adjacent V5+ to V4+. This created localized electron-rich regions at exposed V sites. Theoretical calculations further confirmed that these exposed V sites act as the active center of the reaction, not only significantly enhancing nitrogen adsorption but also substantially lowering the energy barrier of the hydrogenation step through alternative reaction pathways. This work provides a novel strategy for the rational design of highly efficient defect-engineered catalysts via targeted bond cleavage.