Transition metal oxynitride catalysts for electrochemical reduction of nitrogen to ammonia

Electrochemical nitrogen reduction reaction (ENRR) under ambient conditions is beneficial compared to the energy intensive thermochemical Haber-Bosch process for NH3 production. Here, periodic density functional theory (DFT) calculations are carried out to study the ENRR on transition metal oxynitride (TMNO) catalysts. Our calculations show that the ENRR occurs at thermodynamically more favorable surface nitrogen vacancy (N-vac) sites compared to surface oxygen vacancy (O-vac) sites. The DFT results show that TiNO efficiently catalyzes the ENRR at a low applied potential (U) and its ENRR activity is predicted to be similar to that of VNO, a previously identified excellent ENRR catalyst. We observed a volcano like relationship between the DFT calculated nitrogen binding energy (NBE) and the limiting potential (U-L), which suggests that the NBE can be used as a descriptor of the ENRR activity on TMNO based catalysts.