Self-Nanocavity-Confined Halogen Anions Boosting the High Selectivity of the Two-Electron Oxygen Reduction Pathway over Ni-Based MOFs

We present a strategy of self-nanocavity confinement for substantially boosting the superior electrochemical hydrogen peroxide (H 2 O 2 ) selectivity for conductive metal–organic framework (MOF) materials. By using operando synchrotron radiation X-ray adsorption fine structure and Fourier transform infrared spectroscopy analyses, the dissociation of key *OOH intermediates during the oxygen reduction reaction (ORR) is effectively suppressed over the self-nanocavity-confined X-Ni MOF (X = F, Cl, Br, or I) catalysts, contributing to a favorable two-electron ORR pathway for highly efficient H 2 O 2 production. As a result, the as-prepared Br-confined Ni MOF catalyst significantly promotes H 2 O 2 selectivity up to 90% in an alkaline solution, evidently outperforming the pristine Ni MOF catalyst (40%). Moreover, a maximal faradic efficiency of 86% with a high cumulative H 2 O 2 yield rate of 596 mmol g catalyst –1 h –1 for electrochemical H 2 O 2 generation is achieved by the Br-confined Ni MOF catalyst.