Potential-Dependent Free Energy Relationship in Interpreting theElectrochemical Performance of CO2Reduction on Single AtomCatalysts

Acquiring the fundamental understanding ofelectrochemical processes occurring at the complex electrode-liquid interface is a grand challenge in catalysis. Herein, to gaintheoretical insights into the experimentally observed potential-dependent activity and selectivity for the CO2reduction reaction(CO2RR) on the popular single-iron-atom catalyst, we performedab initio molecular dynamics (AIMD) simulation, constrained MDsampling, and thermodynamic integration to acquire the freeenergy profiles for the proton and electron transfer processes ofCO2at different potentials. We have demonstrated that theadsorption of CO2is significantly coupled with the electrontransfer from the substrate while the further protonation does notshow distinct charge variation. This strongly suggests that CO2adsorption is potential-dependent and optimizing the electrodepotential is vital to achieve the efficient activated adsorption of CO2. We further identified a linear scaling relationship between thereaction free energy (Delta G) and the potential for key elementary steps of CO2RR and HER, of which the slope is adsorbate-specificand not as simple as 1 eV per volt as suggested by the traditional computational hydrogen electrode (CHE) model. The derivedscaling relationship can reproduce the experimental onset potential (Uonset)ofCO2RR, potential of the maximal CO2-to-CO Faradayefficiency (FECO), and potential where FECO=FEH2. This suggests that our state-of-the-art model could precisely interpret theactivity and selectivity of CO2RR/HER on the Fe-N4-C catalyst under different electrode potentials. In general, our study not onlyprovides an innovative insight into the theoretical explanation of the origin of the solvation effect from the perspective of chargetransfer but also emphasizes the critical role of electrode potential in the theoretical consideration of catalytic activity, which offers aprofound understanding of the electrochemical environment and bridges the gap between theoretical predictions and experimentalresults