Electrochemical synthesis of urea at cooperative active sites on Mo2C grain boundary

Abstract

The design of multiple types of active sites with cooperative functions on catalyst surface holds great promise for urea synthesis, yet forming these specific sites and ensuring their functionality remain a prominent challenge. Here, we propose two types of Mo₂C grain boundaries (GBs) that feature intrinsic cooperative active sites, facilitating the coupling of C and N species and achieving efficient urea synthesis. By density-functional theory (DFT) calculations, we verify that positively charged Mo atoms on the GBs exhibit high adsorption and reduction activity for CO₂, whereas adjacent Mo atoms contribute to the activation of N₂ or NO. The cooperative effects of these active sites enables C-N coupling to proceed spontaneously on the GBs with ultralow limiting potentials (−0.24 ∼ −0.42 V). Furthermore, analysis of the competing hydrogen evolution reaction and nitrogen reduction reaction confirms the high selectivity to generate urea on Mo₂C GBs. Our work demonstrates GB engineering as a promising strategy for urea generation through the synergistic cooperation between multiple active sites, thus paving the way towards the rational design of effective catalysts for urea electrosynthesis.