pH Effects on Electrocatalytic H2O2 Production and Flooding in Gas-Diffusion Electrodes for Oxygen Reduction Reaction

Electrocatalytic two-electron oxygen reduction reaction (2e– ORR) is a crucial process for on-site and on-demand H2O2 production. Evaluating the impact of the medium’s pH is essential for achieving selective H2O2 production at higher current density through continuous O2 supply to gas diffusion electrodes (GDEs) in membrane electrolyzers. We investigated the effect of electrolyte pH on both H2O2 production and the flooding behavior of GDEs loaded with a cobalt single-atom catalyst in a typical H-type cell. The electrocatalyst was prepared by heating cobalt(II) tetraphenylporphyrin loaded on Ketjen Black (CoTPP/KB) at 750 °C. Remarkably, the cobalt single-atom catalyst exhibited high current density when the top of the hydrophobic gas-diffusion layer was exposed to the gas phase, facilitating efficient O2 diffusion within the GDE. Potential–time curves at −40 mA cm–2 showed stable potentials and Faradaic efficiencies (>80%) over 5 h across a pH range from 1 to 10, with the H2O2 concentration reaching approximately 100 mmol L–1 at pH 1.0. In contrast, the potential at pH 13 decreased abruptly in 3 h due to the flooding of GDE. Long-term tests demonstrated stable electrocatalytic H2O2 production only in the acidic electrolytes for 24 h, attributed to reduced flooding with decreasing pH. These findings underscore the impact of electrolyte pH on GDE performance during H2O2 production via the 2e– ORR, with acidity favoring the mitigation of undesirable flooding behavior.