To further rationalize the superior activity of Fe-O single-atom catalysts Gibbs free energy diagrams were calculated for the oxidation of AA to DHA for four different metal single-atoms at U = 0 V an

In summary, the superior activity of Fe-O single-atom catalysts in the oxidation of ascorbic acid to dehydroascorbic acid can be attributed to the strong adsorption of metal cations with HA- anions, leading to a weaker p-π conjugation effect of C-O in the enol structure and a weaker polarization of the hydroxyl group on the other side. This makes the -OH group in the enol structure of the adsorbed HA- more difficult to hydrolyze, making the electron transfer process the rate-determining step of the overall reaction. These findings provide important insights into the design and development of highly efficient single-atom catalysts for various catalytic reactions.