Revealing electrocatalytic C-N coupling for urea synthesis with metal-free electrocatalyst

Urea is ubiquitous in agriculture and industry, but its production consumes a lot of energy. The conversion of nitrogen (N2) and carbon dioxide (CO2) into urea via an electrocatalytic C-N coupling reaction under ambient conditions would be a major boon to sustainable development. However, designing a metal - free catalyst with high activity and selectivity for urea remains a major challenge. Herein, by means of density functional theory (DFT) and ab - initio molecular dynamics (AIMD) computations, the B12 cluster doped on nitrogenated graphene (C2N) substrate catalyst (B12@C2N) with superior stability was designed for electrocatalytic urea synthesis starting from the CO2 and N2 through four reaction mechanisms. The nature of the co-adsorption activation of CO2 and N2 on the B12@C2N catalyst was investigated, the electrochemical proton - electron transfer steps and the C-N thermochemical coupling led to the synthesis of urea. The study showed that the B12@C2N catalyst exhibited high catalytic activity for urea synthesis with the lowest limiting potential of -1.01 V following the *HNNH mechanism compared with other mechanisms. The potential - determining step (PDS) is the formation of the *CO+*NH2NH2 species. However, the two - step C-N coupling barriers of *NCON species are 0.13 eV and 0.60 eV using AIMD and a slow - growth sampling approach in an explicit water molecules model. Calculations also showed that the byproducts of carbon monoxide (CO), methane (CH4), methanol (CH3OH), ammonia (NH3), and hydrogen (H2) can be inhibited on the B12@C2N catalyst. Therefore, the metal - free catalyst not only has a good performance for the hydrogenation of CO2 and N2 promoting the electrochemical

Automated summary

A metal-free catalyst, B12@C2N, was designed for the electrocatalytic synthesis of urea from CO2 and N2. The catalyst showed excellent stability and high activity, with efficient inhibition of byproduct formation.