Theoretical understanding of CO2 reduction products on nitrogen-doped graphene supported dual-atom catalysts.

In recent years, nitrogen-doped graphene supported dual-atom catalysts (DAC@NC) for the CO2 reduction reaction (CO2RR) have attracted widespread research interest. Although some DAC structures for deep reduction C1 products and C2 products have been proposed in previous theoretical calculations, the desired products are still difficult to be realized in experiments. This work systematically investigates the reaction pathways and products of CO2 reduction on bimetallic DAC@NC (M1-M2@NC, M1, M2 = Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, and Pt) by first-principles calculations. After excluding improper M1-M2@NC due to catalyst poisoning and hydrogen evolution competition, C-C coupling processes always have much higher free-energy increments than the corresponding hydrogenation, making it difficult to form multi-carbon structures. For most of the C1 intermediates on M1-M2@NC, the free-energy increments of C-C coupling are higher than 0.8 eV. Some C1 intermediates could couple with a second carbon, but this process is much more difficult than hydrogenation toward C1 products. This work reveals why C2 products are still difficult to be achieved for the CO2RR on M1-M2@NC and identifies the M1-M2 combinations for deep reduction C1 products (methane and methanol), which is inspiring for the future design of CO2RR catalysts.