Defect-Rich CoNi Prussian Blue Analogues Enable Highly Selective Electrochemical Hydrogen Peroxide Production

Decentralized electrosynthesis of hydrogen peroxide (H₂O₂) via the two-electron oxygen reduction reaction (2e^- ORR) offers a promising alternative to the traditional anthraquinone process, though developing non-precious metal electrocatalysts with high activity, selectivity, and industrial durability remains challenging. Herein, we report a defect-engineering strategy to synthesize CoNi Prussian blue analogues (PBAs) with precisely tunable [Co(CN)₆]^3- vacancy concentrations via kinetic trapping. Advanced synchrotron X-ray diffraction and absorption spectroscopy (EXAFS) reveal that these vacancies transform the local coordination of adjacent nickel atoms from saturated octahedral geometries to unsaturated square-planar Ni-N₄ motifs. This structural modulation triggers a fundamental shift in the ORR pathway, delivering an H₂O₂ selectivity exceeding 97% and a remarkable production rate of 6.2 $mol{g}_{cat.}^{-1}{h}^{-1}$ in a flow-cell device. Crucially, our defect-rich catalyst demonstrates exceptional durability under a rigorous 120-h variable-current stability test. Density functional theory (DFT) calculations identify the coordinatively unsaturated Ni-N₄ sites as the intrinsic active centers, which optimize the binding energy of the *OOH intermediate and suppress the four-electron ORR pathway. This work identifies a robust H₂O₂ synthesis electrocatalyst and establishes a validated protocol for defect engineering in coordination frameworks.