Potential Driven Spin-Crossover Synergized with Hydrogen-Bond Engineering in a Molecular Catalyst for Selective H2O2 Electrosynthesis

Abstract

The electrochemical two-electron oxygen reduction reaction (2e– ORR) provides a sustainable route for hydrogen peroxide (H2O2) production. However, its efficiency is fundamentally constrained by the spin-forbidden activation of triplet O2 and the subsequent proton-coupled electron-transfer steps required to form singlet H2O2. Herein, we report a pyrazine-functionalized nickel phthalocyanine catalyst (NiPNPC) that overcomes these constraints and achieves exceptional selectivity for H2O2 (up to 97.15%). In situ spectroscopic and computational studies reveal that the pyrazine units within the macrocyclic ligand promote a dynamic spin-crossover at the Ni center from a low-spin to a high-spin under cathodic polarization for O2 activation, thereby resolving the intrinsic spin mismatch. Concurrently, the pyrazine units facilitate the reorganization of a well-defined hydrogen-bonding network at the electrolyte-catalyst interface. This network ensures efficient proton delivery to the active center and thereby efficient H2O2 formation. The synergy between dynamic spin-state modulation and interfacial hydrogen-bond engineering provides a mechanistic understanding for selective H2O2 formation and establishes a new design paradigm for advanced molecular electrocatalysts in sustainable synthesis.