Self-adjusting Cr-N₄ sites with peripheral engineering: diversifying catalyst library for selective O₂ reduction to...

Electrochemical two-electron oxygen reduction reaction (2e^- ORR) serves as an appealing approach for green hydrogen peroxide (H₂O₂) production. However, the corresponding progress in efficient non-precious metal catalysts for acidic 2e^- ORR has not kept pace, with the research model being almost confined to Co-based system. Here, guided by molecular dynamics simulations, the active nature and origin of pyrolyzed Cr-N₄ catalysts for ORR are unveiled, wherein the over-strong oxygen affinity of the Cr center is counterbalanced by a spontaneous axial O-coordination. By creating an oxidation-induced electron-deficient environment, the Cr-N₄ can be flexibly tailored for selective H₂O₂ formation. A single-atom Cr-N₄/C(O) catalyst is developed experimentally, which rivals and even slightly outperforms its Co-based counterpart in terms of selectivity (92% versus 71%) and productivity (202 versus 145 mmol g_cat^-1 h^-1) for H₂O₂. More encouragingly, the Cr-based catalysts exhibit minimal reactivity towards H₂O₂-related side reactions, with the metal component being robust against leaching. This research marks the first identification of pyrolyzed Cr-N₄ catalysts as competent for acidic two-electron O₂ reduction to H₂O₂. The innovative models and insights offer profound guidance for the design of future-generation catalysts for electrochemical H₂O₂ synthesis.