Size−selected Cu4 cluster anchored on C2N monolayer for efficient nitrite electroreduction to ammonia: a computational study

Abstract

The electrochemical reduction of nitrite (NO2ER) to ammonia (NH3) at ambient conditions is of great significance for environmental remediation and energy conservation. However, developing the promising electrocatalysts with high activity, selectivity, and stability still remains a huge challenge. Herein, by means of density functional theory (DFT) computations, we proposed a series of sub−nano transition metal−based tetrahedral clusters anchored on C2N monolayer (TM4/C2N) as NO2ER catalysts for NH3 synthesis. Our results revealed that the strong hybridization between TM−d orbitals and N−2p orbitals guarantees the high stability of these candidates, endowing the top TM sites lower oxidation state valence and thus leading to their stronger ability to capture the adsorbates. Interestingly, according to the computed free energy changes, Cu4/C2N was identified as the most promising NO2ER catalyst with an ultra−low limiting potential of −0.14 eV due to its optimal binding strength with NO2– reactant. In addition, Cu4/C2N can greatly suppress the generation of NO, N2O, and N2 byproducts, as well as the competing hydrogen evolution reaction, boosting its extreme selectivity for NH3 production from NO2ER. Our simulations may provide a promising size−selected cluster for NO2ER to resolve the environmental pollution and the sustainable ammonia production simultaneously.