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.

中文翻译：

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pH 对氧还原反应气体扩散电极中电催化 H2O2 生成和溢流的影响


电催化双电子氧还原反应（2e ^– ORR）是现场按需生产 H ₂ O ₂ 的关键过程。评估介质 pH 值的影响对于通过向气体扩散电极 (GDE) 连续供应 O ₂ 在较高电流密度下实现选择性 H ₂ O ₂ 生产至关重要）在膜电解槽中。我们研究了电解质 pH 值对 H ₂ O ₂ 产生的影响以及在典型 H 型电池中负载钴单原子催化剂的 GDE 的驱替行为。该电催化剂是通过在 750 °C 下加热负载在科琴黑 (CoTPP/KB) 上的四苯基卟啉钴 (II) 来制备的。值得注意的是，当疏水性气体扩散层的顶部暴露于气相时，钴单原子催化剂表现出高电流密度，促进 O ₂ 在 GDE 内有效扩散。 -40 mA cm ^–2 下的电位-时间曲线显示出在 1 至 10 的 pH 范围内 5 小时内稳定的电位和法拉第效率 (>80%)，其中 H ₂ O ₂ 浓度在 pH 1.0 时达到约 100 mmol L ^–1 。相反，由于 GDE 的淹没，pH 13 时的电位在 3 小时内突然下降。长期测试表明，电催化 H ₂ O ₂ 仅在酸性电解质中稳定生产 24 小时，这归因于随着 pH 值降低而减少了水淹。这些发现强调了通过 2e ^– ORR 生产 H ₂ O ₂ 过程中电解质 pH 值对 GDE 性能的影响，酸度有利于减轻不良的溢流行为。