(671a) Hydrogen Peroxide Electrosynthesis in a Strong Acidic Environment Using Cationic Surfactants

Hydrogen peroxide (H₂O₂) is an essential chemical utilized in disinfection, water treatment, chemical synthesis, and the paper and pulp manufacturing industry. Our group produces H₂O₂ via the two-electron oxygen reduction reaction (2e^-­-ORR), which utilizes electricity from renewable resources. This technique has several advantages over the current industrial method for H₂O₂ synthesis, the anthraquinone process. No organic waste is produced; the infrastructure is not limited to a centralized location, reducing transportation costs; and the emissions are clean. Much of the H₂O₂ literature has focused on electrosynthesis in alkaline electrolytes as the higher pH environment favors the ORR over the hydrogen evolution reaction (HER). However, the implementation of H₂O₂ electrosynthesis in an acidic environment could help with the commercialization of practical H₂O₂ electrolyzers due to the superior stability of the in-situ generated H₂O₂ in low pH solutions and the compatibility with commercially-available proton-exchange membranes (PEMs). In order to exploit both high selectivity toward H₂O₂ product and high stability of the generated H₂O₂, we introduced cationic surfactants to a strongly acidic solution, which increased the H₂O₂ selectivity at low pH from 12% to 95% Faradaic efficiency (FE) under a current density of 200 mA cm^-2. We employed in-situ surface enhanced Raman spectroscopy (SERS) and optical microscopy (OM) in order to understand the behavior of the electrode-electrolyte interface under electrolysis operating conditions. The results from our experiments demonstrate that the surfactant molecules become attracted to the electrode surface, likely displacing protons at the electrode-electrolyte interface, and thus promoting the ORR over HER. We also detected micelles in solution under OM imaging, which can facilitate O₂ gas transport to the electrode surface, further favoring ORR conditions to produce H₂O₂.

Figure 1. Schematic portraying hypothetical electric double layer at cathode interface (a.) without CTAB and (b.) with CTAB.