Anthraquinone-catalyzed H2O2 electrosynthesis coupled with an advanced oxidation process for water treatment

Abstract

Advanced oxidation processes (AOPs) coupled with in situ H₂O₂ electrosynthesis are highly desirable and safe as they do not involve H₂O₂ storage and transportation, and therefore, developing highly robust cathodic electrocatalysts is especially important. In this work, we developed a series of anthraquinone molecules as metal-free electrocatalysts to accelerate H₂O₂ production. The electrocatalytic performance, mechanism, and enhancement of these anthraquinone molecules were studied and compared to those of traditional thermal catalysts. It was found that the electrochemical hydrogenation and chemical dehydrogenation processes on anthraquinones are important to accelerate H₂O₂ electrosynthesis. To increase the materials' applicability in chemical engineering, we assembled anthraquinone-derived gas diffusion electrodes (GDEs). Owing to the strong electron donation property of amino groups, amino-anthraquinone-derived GDEs exhibited high performance for H₂O₂ electrosynthesis in electrolytes of various pH values (H₂O₂ productivity of 0.25 mg cm⁻² min⁻¹ at 30 mA cm⁻², and the cumulative amount of 1077 mg L⁻¹ during 150 min in a static electrolyzer without a membrane separator) and long-term durability (stable operation for 120 h). The in situ H₂O₂ electrosynthesis coupled with electro-peroxone was further employed for the degradation of various phenolic compounds, where the chemical oxygen demand (COD) removal reached above 90% in 120 min with ultra-low energy consumption (below 15 W h g_COD⁻¹). The treatment of practical petrochemical wastewater was also evaluated. This work provides valuable insights into using metal-free catalysts for high-performance electrochemical applications.