Higher-valent nickel oxides with enhanced two-electron oxygen reduction in advanced electro-Fenton system for organic pollutants degradation

Abstract

A higher-valent NiO catalyst, enriched with trivalent Ni (Ni 3+ ) and exposed {111} crystal facets, was developed to enhance selective two-electron oxygen reduction (2e – ORR) for electrochemical hydrogen peroxide (H 2 O 2 ) production, leading to highly efficient organic pollutant removal. The catalyst was synthesized via a precipitation method, incorporating crystal facet and cation vacancy engineering to expose active sites. It demonstrated 96 % selectivity and 59 A g −1 mass activity, attributed to weakened *OOH binding, as shown by density functional theory. Integrated into an advanced electro-Fenton (EF) flow cell, the system achieved 100 % removal of 200 mL of 50 ppm bisphenol A (BPA) in 4 minutes, with 93 % total organic carbon removal within 2 hours. This study provides a scalable and efficient solution for decentralized environmental remediation and wastewater treatment. • A novel {111}-NiO catalyst with Ni vacancies shows 96% selectivity and 59 A g −1 mass activity for H 2 O 2 electrosynthesis. • The catalyst achieves over 85 % Faradaic efficiency for H 2 O 2 production across various pH conditions. • Combining a flow cell and electro-Fenton process enables fast and complete BPA removal, outperforming conventional methods.