Designing Nonheme Single Atom Catalysts for Oxygen Reduction Reaction by High-Throughput Screening

Heme-based single-atom catalysts (SACs) have attracted significant interest for the oxygen reduction reaction (ORR). However, their poor electrochemical stability limits catalytic performance. Inspired by reports of nonheme-based SACs in electrocatalysis, we perform a density functional theory (DFT) study of 112 heme and nonheme SACs comprising corrole, confused porphyrin, and salen frameworks with different transition metals (Sc, Ti, V, Cr, Mo, W, Mn, Fe, Ru, Os, Co, Rh, Ir, Ni, Cu, Zn) adsorbed on a graphene surface. We employ a five-step high-throughput screening framework to assess the activity and stability of the SACs. In the first step, analyzing the thermodynamic stability, two candidates with endothermic formation energies are removed. The next step involves determining the binding energies of the reaction intermediates following a four-step reaction pathway on the 110 candidates. O* and HOO* follow a linear scaling relation with HO* intermediates resembling the metal(111) surfaces. Around 47 SACs showing very strong or weak intermediate binding are eliminated from the 110 SACs. In the third step, mean-field microkinetic modeling is performed. We identify 19 SACs with activity for the 4-electron ORR comparable to that of the Pt(111) surface. The Pourbaix stability analysis for the active catalysts highlights 18 stable combinations. Fe, Rh, and Ir embedded in corrole, salen, and confused porphyrin frameworks exhibit greater stability than other metal dopants. In the final step, by incorporating electric-field effects into the microkinetic model, we obtain 14 SACs that exhibit activity comparable to that of the Pt(111) surface under alkaline conditions.