Selective nitrogen reduction reaction on single-atom centers of molybdenum-based MXenes by pulsing the electrochemical potential

Abstract

Electrocatalytic reduction of dinitrogen is a promising route for sustainable production of ammonia, although the selectivity challenge of the competing nitrogen reduction (NRR) and hydrogen evolution reactions in aqueous electrolytes has not yet been solved. Single-atom catalysts (SACs) offer the hope of bridging this gap because they exhibit unique electronic structure and reactivity in catalytic transformations compared to conventional bulk materials. In addition, potential pulse experiments have shown that they promote the formation of kinetically unfavorable products by efficiently modulating the electrolyte structure at the solid–liquid interface. So far, a combination of SACs and potential pulse experiments for the NRR is mutually exclusive, since SACs are likely to be degraded during the anodic potential pulse due to metal dissolution. Using density functional theory calculations in a grand canonical framework, we demonstrate in the present communication that molybdenum-based MXenes are able to overcome this limitation: compared to traditional SACs, MXenes form single-atom centers during the anodic potential pulse, and their SAC-like structure allows the selectivity to be directed to ammonia instead of gaseous hydrogen during the cathodic pulse. Our study paves the way for the development of high-performance materials with in-situ formed SAC-like sites to enable advances in selective catalytic transformations under applied bias.