Continuous Electrosynthesis of Pure H₂O₂ Solution with Medical-Grade Concentration by a Conductive Ni-Phthalocyanine-Based Covalent Organic Framework

Abstract

Electrosynthesis of H₂O₂ provides an environmentally friendly alternative to the traditional anthraquinone method employed in industry, but suffers from impurities and restricted yield rate and concentration of H₂O₂. Herein, we demonstrated a Ni-phthalocyanine-based covalent-organic framework (COF, denoted as <b>BBL-PcNi</b>) with a higher inherent conductivity of 1.14 × 10^-5 S m^-1, which exhibited an ultrahigh current density of 530 mA cm^-2 with a Faradaic efficiency (H₂O₂) of ∼100% at a low cell voltage of 3.5 V. Notably, this high level of performance is maintained over a continuous operation of 200 h without noticeable degradation. When integrated into a scale-up membrane electrode assembly electrolyzer and operated at ∼3300 mA at a very low cell voltage of 2 V, <b>BBL-PcNi</b> continuously yielded a pure H₂O₂ solution with medical-grade concentration (3.5 wt %), which is at least 3.5 times higher than previously reported catalysts and 1.5 times the output of the traditional anthraquinone process. A mechanistic study revealed that enhancing the π-conjugation to reduce the band gap of the molecular catalytic sites integrated into a COF is more effective to enhance its inherent electron transport ability, thereby significantly improving the electrocatalytic performance for H₂O₂ generation.