Activity and selectivity of N2 fixation on B doped g-C9N10: a density functional theory study

Abstract

N₂ fixation driven by photocatalysis or electrocatalysis to produce ammonia under mild conditions is a promising method to replace the industrial Haber–Bosch process. Inspired by recent studies, which showed that the boron atom can effectively activate N₂ due to its Lewis-acid characteristics, we herein investigate the mechanism of N₂ adsorption and fixation on B doped g-C₉N₁₀, a new carbon nitride material, with three different doping configurations, namely substitutions of B at C (B_C1) and N (B_N1) sites and B anchored g-C₉N₁₀ (B_A) by density functional theory calculations. We found that the nitrogen reduction reaction (N₂RR) can only proceed on B_N1 and B_A due to N₂ chemisorption ability. The optimal N₂RR mechanism of the B_N1 and B_A doped g-C₉N₁₀ is the mix I mechanism with mix I low limiting potential of −0.62 V and −0.44 V, respectively. However, the H poisoning effect at B_A doped g-C₉N₁₀ due to stronger H adsorption than N₂ adsorption will suppress N₂RR selectivity. In contrast, H poisoning at B_N1 doped g-C₉N₁₀ can be effectively inhibited due to weaker H adsorption ability, thereby improving the selectivity for the N₂RR. The electronic structure analysis indicates that the H–B interaction arises from hybridization between B 2p_y and H 1s orbitals, which is suppressed in the case of B_N1 because the 2p_y orbital of is less populated B_N1. Our work provides useful guidance for more experimental works to explore more B doped carbon nitride materials for the N₂ fixation field.