| Summary: | Tuning the coordination environment centering metal atoms has been regarded as a promising strategy to promote the activities of noble metal single-atom catalysts (SACs). In the present work, first-principle calculations are employed to explore the oxygen evolution reaction (OER) performance of Ir and Ru SACs with chemical coordination being nitrogen (M-N<sub>4</sub>-C), oxygen (M-O<sub>4</sub>-C), and carbon (M-C<sub>4</sub>-C) in graphene, respectively. A “three-step” strategy was implemented by progressively investigating these metrics (stability, catalytic activity, structure–activity relationship). A volcano plot of reactivity is established by using the adsorption-free energy of O* (∆G<sub>O*</sub>) as a theoretical descriptor. The intrinsic OER activity is IrN<sub>4</sub>-C > IrO<sub>4</sub>-C > RuO<sub>4</sub>-C > RuN<sub>4</sub>-C > IrC<sub>4</sub>-C > RuC<sub>4</sub>-C. The in-depth tuning mechanism of ∆G<sub>O*</sub> can be indicated and interpreted by the <i>d</i>-band centers of the active sites and the crystal orbital Hamilton population analysis of metal-oxygen bonds, respectively.
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