Transition metals anchored diphenyl porphyrin complexes as single atom catalysts toward CO₂ reduction to CO versus HER

Efficient single atom electrocatalysis is backbone in advancing sustainable electrocatalytic reduction of CO₂ to CO. Herein, density functional theory (DFT) calculations are employed systematically to investigate the CO₂ reduction to CO along with competitive hydrogen evolution reaction (HER) efficiency of Ni, Pd, and Pt anchored on 5,15-diphenylporphyrin (DPP) framework. Structural optimization and spin multiplicity analysis confirmed the formation of stable planar TM-N coordination environments with singlet ground state. Electronic structure analysis revealed that metal incorporation significantly alters the frontier orbitals and work function, governing charge transfer characteristics. These TM@DPP complexes emerged as the most viable single atom catalysts for electrocatalytic reduction of CO₂ to CO because of lower barrier. HER activity is evaluated using the hydrogen electrode model, where all SACs exhibit low hydrogen adsorption Gibbs free energy indicating a balanced hydrogen interaction and inferior HER thermodynamics. These results indicate that CO₂ adsorption is more favorable than hydrogen on TM@DPP SACs, making them promising surfaces for the reduction of CO₂ to CO. Overall, this study establishes a clear structure activity relationship of porphyrin supported single atom catalysts by corelating TM-N₄ coordination environment and electronic properties with CO₂ reduction energetics. The favorable CO₂ reduction energetics together with suppressed HER activity demonstrates the ability of the TM-N₄ sites to selectively promote CO₂ to CO conversion under intrinsic catalytic conditions. These findings provide fundamental designing principles for developing sustainable and economical electrocatalysts with maximized metal utilization efficiency.