Synergistic Effects of the Ni₃B Cocatalyst and N Vacancy on g-C₃N₄ for Effectively Enhanced Photocatalytic N₂ Fixation

Abstract

The photocatalytic fixation of N₂ is a promising technology for sustainable production of ammonia, while the unsatisfactory efficiency resulting from the low electron-transfer rate, narrow light absorption range, and limited active sites of the photocatalyst seriously hinder its application. Herein, we designed a noble metal-free Schottky junction photocatalyst constructed by g-C₃N₄ nanosheets with N vacancies (V_N-CN) and metallic Ni₃B nanoparticles (Ni₃B/V_N-CN) for N₂ reduction to ammonia. The ammonia yield rate over the optimized Ni₃B/V_N-CN is 7.68 mM g^-1 h^-1, which is 6.7 times higher than that of pristine CN (1.15 mM g^-1 h^-1). The superior photocatalytic N₂ fixation performance of Ni₃B/V_N-CN can be attributed not only to the formation of Schottky junctions between Ni₃B and V_N-CN, which facilitates the migration and separation of photogenerated electrons, but also to the incorporation of V_N into g-C₃N₄, which enhances visible light absorption and improves electrical conductivity. More importantly, Ni₃B nanoparticles can act as the cocatalyst, which provide more active sites for the adsorption and activation of N₂, thereby improving the N₂ reduction activity. This work provides an effective strategy of designing noble metal-free-based cocatalyst photocatalyst for sustainable and economic N₂ fixation.