Self-adjusting Cr−N4 sites with peripheral engineering: diversifying catalyst library for selective O2 reduction to H2O2 in acidic media

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 gcat−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.