Coupling of oxygen vacancies and an anatase/TiO2 (B) phase junction for promoting photocatalytic performance of platinum toward ammonia synthesis

Abstract

Photocatalytic ammonia synthesis under ambient conditions represents a sustainable pathway compared to the Haber–Bosch process, but its efficiency is very limited by poor charge separation and the weak capability to simultaneously activate N₂ and H₂. In this study, we demonstrate that platinum-loaded defective anatase/TiO₂ (B) phase-junction photocatalysts provide a viable route for simultaneous N₂ and H₂ activation, while enabling efficient electron separation. Under visible light irradiation, the optimized catalyst achieves an NH₃ production rate of 5114 μg g⁻¹ h⁻¹, surpassing that of most reported TiO₂-based systems. The phase-junction interface creates an intrinsic electric field to drive electron–hole separation and provide more activated electrons. Meanwhile, oxygen vacancies play a crucial role in nitrogen activation owing to the excellent electron back-donation ability and strong nitrogen chemisorption, which is conducive to electron transfer from the active sites to nitrogen molecules. More specifically, a small number of surface-loaded Pt nanoparticles dynamically mediate hydrogen spillover from Pt to oxygen vacancies, facilitating efficient N₂ protonation via hydrogen species (H*). As a result of these factors, the phase junction remarkably promotes interfacial charge separation and transformation capacity. The synergistic effect as a result of oxygen vacancies and loaded Pt species can simultaneously create an efficient catalytic pathway for visible-light-driven NN bond cleavage and hydrogen oxidation. This work lays the foundation for constructing multifunctional catalysts in the field of photocatalytic ammonia synthesis.