ZnO monolayer supported single atom catalysts for efficient nitrogen electroreduction to ammonia

Efficient and sustainable ammonia production via electrochemical nitrogen reduction reaction (eNRR) requires low-cost catalysts with high stability, high selectivity, and high activity. Using first-principles calculations, we assessed the eNRR activities of single atom catalysts (SACs) constructed with a transition metal atom TM substituting a Zn atom in ZnO monolayer (TM/ZnO). Three criteria, the SACs' stability, the selectivity of eNRR relative to hydrogen evolution, and the limiting potential, were adopted to screen efficient eNRR SACs among 17 different models. Two SACs, V/ZnO and Mo/ZnO, survived the screening. eNRR on both SACs proceeds along the distal pathway, with limiting potentials −0.26 and −0.65 V, at the first and last hydrogenation step, respectively. Electronic structure analysis demonstrated that the stable NN triple bond was activated by the back-donation mechanism. Our results illustrate that ZnO monolayer is a non-toxic and low-cost SAC support for eNRR, while V/ZnO and Mo/ZnO are promising electrochemical catalysts to produce ammonia.