Local reaction microenvironment impacts on H2O2 electrosynthesis in a dual membrane electrode assembly solid electrolyte electrolyzer

Abstract

Hydrogen peroxide (H2O2) synthesis via the electrocatalytic reduction of oxygen is a sustainable alternative to the energy-intensive anthraquinone oxidation process. The use of gas diffusion electrodes in dual membrane electrode assembly (MEA) solid electrolyte (SE) electrolyzers has substantially improved H2O2 production, but the influence of mass transport and local reaction environment on H2O2 performance in these cell architectures is still unclear and unoptimized. Herein, we investigate the impacts of electrode components and reactor operating conditions on the H2O2 performance and cell potential required to reach current densities up to 400 mA cm−2. Results show an intermediate catalyst loading of 2 mg cm−2 improves H2O2 production through balancing O2 diffusion and active site exposure. Hydrophobic treatment via fluoropolymer improves electrode stability, but addition of >15 wt% fluoropolymer worsens performance, likely by limiting active site accessibility at the catalyst-membrane interface. Moreover, decreasing O2 concentration from typical pure streams to match the composition of air has a negligible effect at moderate current densities (∼50 mA cm−2), but significantly impacts overall performance at higher current densities (∼200 mA cm−2). This work also highlights benefits of operating the reactor with a recycled product stream rather than tuning the flow rate of water over the SE to extremely low values to obtain high H2O2 concentrations, as the latter likely contributes to exacerbated H2O2 degradation in the electrolyzer. This work provides insights into how macroscale system properties in flow cell electrolyzers impact the local reaction environment and mass transport, which in turn dictate overall catalytic performance.