Synergistic Effects of the Ni 3 B Cocatalyst and N Vacancy on g-C 3 N 4 for Effectively Enhanced Photocatalytic N 2 Fixation

The photocatalytic fixation of N 2 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-C 3 N 4 nanosheets with N vacancies (V N -CN) and metallic Ni 3 B nanoparticles (Ni 3 B/V N -CN) for N 2 reduction to ammonia. The ammonia yield rate over the optimized Ni 3 B/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 N 2 fixation performance of Ni 3 B/V N -CN can be attributed not only to the formation of Schottky junctions between Ni 3 B and V N -CN, which facilitates the migration and separation of photogenerated electrons, but also to the incorporation of V N into g-C 3 N 4, which enhances visible light absorption and improves electrical conductivity. More importantly, Ni 3 B nanoparticles can act as the cocatalyst, which provide more active sites for the adsorption and activation of N 2, thereby improving the N 2 reduction activity. This work provides an effective strategy of designing noble metal-free-based cocatalyst photocatalyst for sustainable and economic N 2 fixation.