Understanding catalytic activity trends of atomic pairs in single-atom catalysts towards oxygen reduction reactions

Single-atom catalysts are regarded as the most promising materials for oxygen electroreduction reactions. However, their rational development is hindered by challenges such as determining the reaction mechanism and modulating the electronic configuration at the orbital level. Using density functional theory (DFT) calculations, in this work we investigate the catalytic activities of 13 transition metal single-atom (TM1)-doped titanium dioxide (TM1@TiO2) nanosheets toward the oxygen reduction reaction (ORR). Based on the scaling relationships between ORR intermediates, the number of theoretical d-valence electrons of TM1 atoms could be used to directly predict the ORR activities. The overall synergy of TM1 and Ti active sites (TM1-Ti1 atomic pairs) can effectively decrease the theoretical overpotential by reducing the bonding contribution of dz2-sp orbital pairs in TM1-OH bonds. This work paves the way toward a better understanding of orbital interactions between active sites and adsorbates, which will promote the discovery and design of candidate materials with desirable catalytic activities.