Restructuring hydrogen-bonding networks via hydroxyl-functionalized covalent organic frameworks for efficient nitrate electroreduction.

Abstract

Electrocatalytic nitrate reduction reaction (NO3RR) is a promising strategy for nitrate removal and ammonia synthesis, but its efficiency is largely limited by sluggish proton transfer kinetics and poor reaction selectivity. Herein, we rationally design a series of hydroxyl-functionalized copper phthalocyanine-based covalent organic frameworks (Cu-COF-nOH) to regulate interfacial proton transfer via restructuring hydrogen-bonding networks. The hydroxyl functional groups in Cu-COF-nOH enhance water adsorption and dissociation to enrich interfacial proton supply. Optimized hydroxyl loading further induces the formation of continuous hydrogen-bond chains, enabling oriented and accelerated proton shuttling toward Cu active centers instead of stochastic diffusion. Electrocatalytic tests in 0.5 M nitrate electrolyte show that the optimal Cu-COF-4OH catalyst achieves an ammonia Faradaic efficiency of 93.20% and an NH3 yield rate of 65.84 mg·h-1, along with excellent long-term stability, outperforming most state-of-the-art NO3RR electrocatalysts. Combined with in situ characterizations and theoretical calculations, we clearly clarify that hydroxyl-mediated hydrogen-bonding restructuring plays a critical role in boosting proton transfer kinetics and reaction selectivity. This work provides a versatile interface engineering strategy for efficient multiproton/electron-coupled electrocatalytic reactions, offering insights into the design of high-performance NO3RR catalysts.