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.