Dual Regulation of Molecular Orbital and Interfacial Water on Nickel Phthalocyanine for Highly Selective H₂O₂...

Hydrogen peroxide (H₂O₂) electrosynthesis via the two-electron oxygen reduction reaction (2e^- ORR) is fundamentally challenged by both spin-forbidden O₂ activation and sluggish proton-coupled electron transfer. Herein, we move beyond conventional metal-centered design and propose a dual-regulation strategy that integrates molecular orbital engineering with control of the interfacial water network. Using nickel phthalocyanines as a platform, extended π-conjugation combined with polar methoxy (-OCH₃) groups was introduced. It narrows the HOMO-LUMO gap and facilitates potential-driven formation of a paramagnetic superoxide intermediate, while the methoxy groups further reorganize the interfacial water layer with moderate hydrogen-bonding strength that enables efficient proton delivery for subsequent hydrogenation steps. This led to high H₂O₂ selectivity (up to 96.49%) over a wide potential range, with stable performance in both flow cell and porous state electrolyte reactors for over 50 h. In situ spectroscopy and simulations reveal how molecular orbital regulation contributes to the catalytic process, and how the interfacial water layer facilitates hydrogenation. Our work provides a molecular orbital perspective on the cooperative roles of metal and ligand, establishing a design strategy that co-regulates electronic and interfacial determinants for selective multi-electron electrocatalysis.