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

N-2 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 N-2 due to its Lewis-acid characteristics, we herein investigate the mechanism of N-2 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 BA due to N-2 chemisorption ability. The optimal N2RR mechanism of the B-N1 and BA doped g-C9N10 is the mix I mechanism N-2*-> NNH*-> NH2N*-> NH2NH*-> NH2NH2*-> NH2* -> NH3*) with mix I low limiting potential of -0.62 V and -0.44 V, respectively. However, the H poisoning effect at BA doped g-C9N10 due to stronger H adsorption than N-2 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 BN1 because the 2py 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 N-2 fixation field.

Automated summary

The study investigates the mechanism of N-2 adsorption and fixation on B doped g-C9N10 material by density functional theory calculations. It is found that nitrogen reduction reaction can only proceed on B-N1 and BA due to their strong N-2 chemisorption ability. The optimal N2RR mechanism for B-N1 and BA doped g-C9N10 is the mix I mechanism, with H poisoning effect at BA doped g-C9N10 suppressing N2RR selectivity.