Theoretical study on double-atom catalysts supported with graphene for electroreduction of nitrogen into ammonia

Developing electrocatalyst with high catalytic activity for the nitrogen reduction reaction (NRR) is the key step to accelerate the application of electrocatalytic nitrogen fixation. Eight kinds of double-atom Fe catalysts supported with graphene-based substrate (Fe-TMDA/GS, TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) were constructed for electroreduction of nitrogen into ammonia. The bonding mechanism of Fe-transition metal dimer on substrates was studied from the perspectives of orbital hybridization and electron transfer. Based on the analysis of reaction paths and Gibbs free energy variation, the potential determining step of the NRR is the transfer process of the first H+/e− pair. Fe-TiDA/GS has the highest NRR catalytic activity among the eight kinds of Fe-TMDA/GS, with a Gibbs energy variation of 0.88 eV. Based on the analysis of electron density difference, band structure and work function, electron transfer is the main factor affecting nitrogen adsorption, and the second metal atom improves the catalytic activity of NRR through promoting electron transfer between N2 and the graphene surface. This theoretical research provides new insights into developing highly efficient electrocatalyst for NRR.