B modulating MXene/Graphene heterojunction catalyst for highly efficient NO electrochemical synthesis of ammonia

The electrochemical nitric oxide reduction reaction (NORR) is deemed to be a promising alternative to remove atmospheric pollutant NO and produce ammonia simultaneously. In this work, we systematically study the NORR catalytic performance of 9 different-ordered Mo₂MC₂O₂-v (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) coupling Graphene (Gr) monolayer forming the 2D/2D heterojunctions by first-principle calculations. The results demonstrated that B@Mo₂MC₂O₂-v/Gr (M = Zr, Hf, Nb, Ta, and W) exhibit excellent NORR activity and selectivity to synthesize NH₃ occurring spontaneously under low nitric oxide coverage compared to Mo₂MC₂O₂-v/Gr heterojunctions. This phenomenon can be attributed to the synergetic effect between the interface interaction and the B atom doping suppressing the competitive hydrogen evolution reaction (HER). The interface interaction between B@Mo₂MC₂O₂-v and Graphene enhanced the charge transfer from the Graphene to the MXene surface. The B atom doping provides the active site and acts as an electronic transmitter for rapid electron transfer to the adsorbed NO molecules promoting the cleavage of N=O and further interacting with the H⁺ to generate NH₃. We introduce the △G(_*NH2O) as an efficient descriptor to predict the NORR performance. Moreover, DOS, CDD and COHP analysis reveal the electron “donation/back-donation” mechanism between NO molecules and the B atom, which elaborates the activation effect of NO molecules. Furthermore, the key function of the p-band center (ε_p) was emphasized in characterizing the activation degree of NO, which can be regulated by the chemical environment around the B atom. Finally, we testified the stability of catalysts using AIMD simulation. In addition, this work provides a theoretical foundation for future experimental research on NORR electrocatalysts to produce renewable fuels from pollutant NO molecules.