Bimetallic doped graphite carbon nitride electrocatalyst for efficient urea synthesis

Urea is an important nitrogen fertilizer and chemical raw material. Nowadays, searching for a harmless direct urea synthesis catalyst to electrochemically co-reduce N2 and CO2 gas for green urea synthesis under environmental conditions and avoiding the traditional ammonia synthesis pathway is a challenging research area. Here, a density functional theory (DFT) study was performed to investigate the catalytic activity of bimetallic doped graphite carbon nitride electrocatalysts (M2@g-C6N6, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Hf, Ta, W) for the urea synthesis by reducing N2 and CO2 (NCR). The preference of CO2 adsorption and the co-adsorption of CO and N2, which then the key intermediate *NCON is generated through the C-N coupling process. Three possible limiting steps are revealed, then the surface oxidation or hydroxylation and the competitive side reactions of NRR and HER were compared. The calculated results indicate that Ta2@g-C6N6 could be one of most promising catalysts for electrocatalytic NCR activity with limiting potentials of −1.01 V, which could effectively restrict surface oxidation or hydroxylation and suppress the competitive side reactions of the nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER).