Towards Sustainable Hydrogen Peroxide Electroproduction: Activated Carbon from Sewage Sludge As an Eco-Friendly Electrode Material

Hydrogen peroxide (H 2 O 2 ) has emerged as a chemical of paramount importance, finding diverse applications as a bleaching agent, medical disinfectant, and environmentally benign oxidant [1]. The industrial production of H 2 O 2 currently relies on the anthraquinone oxidation process, primarily executed within large-scale industrial plants [1]. Herein lies a challenge— H 2 O 2 , typically concentrated to an 80% level, introduces inherent hazards concerning storage and transportation, prompting a quest for a safer alternative. One way to overcome such problems is by the in-situ electrogeneration of H 2 O 2 , which would allow an adjustable production of the chemical on demand directly for its application, avoiding storing costs and safety issues. The in-situ electrogeneration can be done by using a gaseous-diffusion electrode (GDE), which typically enables the application of elevated current densities or substantial overpotentials, consequently facilitating the generation of high concentrations of H 2 O 2 , since there is less limitation due to O 2 mass transport to the electrode surface [2]. Commonly, these electrodes are constructed from amorphous carbon materials, due to their highly active surface area with oxygenated functional groups, excellent conductivity, and innate selectivity for H 2 O 2 electroproduction. However, a notable challenge emerges – bare carbon's selectivity for H 2 O 2 presents its highest response at high overpotentials, entailing heightened energy consumption. The studies in this field are currently focused on using these types of carbon as support for other catalytic materials that are more active and selective towards H 2 O 2 electroproduction [3, 4]. Numerous studies in the literature have explored the use of carbon materials, with the most commonly employed carbon supports for such applications being Printex 6L (Orion) and Vulcan XC 72R (Cabot). These materials are obtained from the incomplete combustion of heavy petroleum products at high temperatures, being non-sustainable and environmentally unfriendly. A potential solution lies in the use of environmentally conscious carbon sources. While amorphous carbon can be obtained from various carbon-rich wastes through an activation process, their utility in H 2 O 2 electrogeneration remains underexplored. This study sought to obtain activated carbon from sewage sludge, focusing on its efficacy in H 2 O 2 electrogeneration. Acid (H 3 PO 4 ) and alkaline (KOH/NaOH mixture) carbon ac