From high loading to high activity: unraveling the correlation in high-performance single-atom catalyst design

Single-atom catalysts (SACs) have shown great promise for electrocatalytic applications such as the oxygen evolution reaction (OER). However, the high surface free energy of the isolated metal sites in SACs results in a generally low metal loading, which limits the density of active sites. Herein, we constructed low- and high-loading SACs on a γ-graphyne (GY) support using a series of transition metals (Fe, Co, Ni, Cu, Rh, Pd, Ag, Ir, and Pt) to study their OER performance. Calculations demonstrate that a high metal loading reduces the OER overpotential of Fe- and Co-GY catalysts, especially for Fe-GY, which shows exceptional activity with an overpotential of only 0.39 V. Notably, the bonding and anti-bonding stabilized energy difference (BASED) analysis indicates that the high loading Fe-GY optimizes the binding strength of *OH and *O intermediates, thereby lowering the overpotential of the rate-determining step (*OH → *O). This change is attributed to the synergy between adjacent Fe atoms, which modifies the charge distribution at the Fe sites, as shown by differential charge and density of states (DOS) analyses. Our findings help pave the way for the rational design of high-loading SACs for electrocatalysis.