Aqueous-Phase and End-Group Engineering Synergistically Modulate CO2 Reduction on Porphyrin Single-Atom Catalysts: Mechanistic Insights.

Practical application has been limited by the scarcity of highly efficient catalysts. Porphyrin-based single-atom catalysts (SACs) have emerged as particularly attractive candidates for CO2RR. In this work, we systematically evaluated the CO2RR performance of 14 metal-based porphyrin SACs under aqueous conditions. We used density functional theory (DFT) calculations combined with a computational hydrogen electrode (CHE) model. Our results show that these catalysts exhibit outstanding selectivity in reducing CO2 to CO. Both aqueous solvation effects and strategic end-group modifications significantly enhance catalytic efficiency. Notably, the aqueous environment strengthens the adsorption of all of the key reaction intermediates. When the potential-determining step (PDS) is CO2 → COOH, aqueous solvation greatly improves catalytic activity. Conversely, when CO desorption is the PDS, solvation has a negative effect. For systems where the COOH → CO conversion is the PDS, the influence is more complex. Here, activity changes depend on the specific metal center and end-group configuration. Detailed electronic structure analysis, especially for Cu and Ni systems, reveals that solvation and end-group modifications work together to tune the d-electron configuration of the active metal centers. This electronic modulation plays a critical role in governing the catalytic activity. This study underscores the importance of aqueous-phase end-group regulation in optimizing the catalyst performance. It also offers fundamental theoretical guidance for designing high-efficiency CO2RR catalysts. These insights contribute meaningfully to the advancement of sustainable energy technologies.