Unlocking the Potential of Mn-based Catalyst for Durable Two-electron Oxygen Reduction in Acid at High Current Densities.

Electrochemical synthesis of HO by two-electron oxygen reduction (2e ORR) often shows limited stability at high current densities in acidic media. Mn-based catalysts have been demonstrated highly stable for four-electron ORR thanks to their intrinsically low rate constant for Fenton-like reactions. However, their activity toward acidic 2e ORR remains low because of too strong adsorption to *OOH. Here, we report a diatomic Mn catalyst with high-spin Mn centers to enable high onset potential (0.69 V), high selectivity (>90%), and outstanding stability (240 h under 300 mA cm) toward HO electrosynthesis in acid. Theoretical calculations and in situ spectroscopies reveal that the diatomic Mn sites have downshifted d-band center and thus weakened adsorption strength for *OOH. Moreover, the inertia of the Mn sites toward the troublesome Fenton-like reactions leads to the long-term stability at high current densities. We further demonstrate the functionalization of waste polyethylene (PE) using the high-concentration HO as produced, which provides a sustainable route toward on-site upcycling of plastic waste.