pH Effects on Electrocatalytic H<sub>2</sub>O<sub>2</sub> Production and Flooding in Gas-Diffusion Electrodes for Oxygen Reduction Reaction
Takuya Okazaki, Kento Shibata, Chihiro Tateishi, Kazuma Enomoto, Kosuke Beppu, Fumiaki Amano
Abstract
Electrocatalytic two-electron oxygen reduction reaction (2e – ORR) is a crucial process for on-site and on-demand H 2 O 2 production. Evaluating the impact of the medium’s pH is essential for achieving selective H 2 O 2 production at higher current density through continuous O 2 supply to gas diffusion electrodes (GDEs) in membrane electrolyzers. We investigated the effect of electrolyte pH on both H 2 O 2 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 O 2 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 H 2 O 2 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 H 2 O 2 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 H 2 O 2 production via the 2e – ORR, with acidity favoring the mitigation of undesirable flooding behavior.