Highly efficient production of hydroxyl radicals from oxygen reduction over Ni-Fe dual atom electrocatalysts for removing emerging contaminants in wastewater

Advanced oxidation process (AOP) based on hydroxyl radicals (•OH) produced from electrocatalytic oxygen reduction reaction (ORR) is regarded as a promising technique for treating industrial wastewater. However, the poor efficiency of •OH production considerably limits the •OH-based AOP efficiency. In this study, a high-efficiency production of •OH from oxygen reduction is realized over Ni-Fe dual atom supported on nitrogen-doped carbon electrocatalysts (Ni0.5–Fe0.5–NC), where the O2 is preferentially adsorbed onto Ni sites. With the aid of neighboring electron-rich Fe atoms, the 2-electron intermediate *H2O2 over Ni sites is inclined to gain one electron to produce •OH (ΔG = -2.69 eV) rather than desorb to form H2O2 (ΔG = -1.05 eV). Even when hydrogen peroxide is produced by desorption, it is quickly activated to generate •OH by neighboring electron-rich Fe atoms. The in-situ produced •OH on Ni0.5–Fe0.5–NC reaches up to 4.61 mmol L−1 min−1 gcat−1, presenting the state-of-the-art AOP. Some emerging refractory contaminants (florfenicol, thiamphenicol, bisphenol A, phenol, sulfamethoxazole, and tetracycline hydrochloride) in wastewater can be fast and deep removed in the proposed AOP system based on ORR (C0 = 20 mgL−1, pH 7, −0.5 V vs SCE, working electrode: 6 cm2 carbon paper loading 6.0 mg catalyst). This study provides an ORR catalyst design inspiration for energetic and green generation of •OH, which would supply a reliable method for the development of wastewater treatment technology.