Water Spillover to Expedite Two‐Electron Oxygen Reduction

Abstract

Limited by the activity-selectivity trade-off relationship, the electrochemical activation of small molecules (like O₂, N_2, and CO₂) rapidly diminishes Faradaic efficiencies with elevated current densities (particularly at ampere levels). Nevertheless, some catalysts can circumvent this restriction in a two-electron oxygen reduction reaction (2e^- ORR), a sustainable pathway for activating O₂ to hydrogen peroxide (H₂O₂). Here we report 2e^- ORR expedited in a fluorine-bridged copper metal-organic framework catalyst, arising from the water spillover effect. Through operando spectroscopies, kinetic and theoretical characterizations, it demonstrates that under neutral conditions, water spillover plays a dual role in accelerating water dissociation and stabilizing the key ^*OOH intermediate. Benefiting from water spillover, the catalyst can expedite 2e^- ORR in the current density range of 0.1-2.0 A cm^-2 with both high Faradaic efficiencies (99-84.9%) and H₂O₂ yield rates (63.17-1082.26 mg h^-1 cm^-2). Further, the feasibility of the present system has been demonstrated by scaling up to a unit module cell of 25 cm², in combination with techno-economics simulations showing H₂O₂ production cost strongly dependent on current densities, giving the lowest H₂O₂ price of $0.50 kg^-1 at 2.0 A cm^-2. This work is expected to provide an additional dimension to leverage systems independent oftraditional rules.