Abstract:

Oxygen evolution reaction (OER) is the rate-determining step for water electrolysis. Manganese oxides (MnO_x) possess five valence states, hence with multiple steps to reduce the activation energy, and semiconductor titanium dioxide (TiO₂) exhibits corrosion resistance. Here we demonstrate OER performance over three catalysts, of MnO_x synthesized by gliding arc plasma (pM) and commercial MnO_x (cM), and commercial TiO₂ (cT). Of non- Faradiac process, using ideal polarized electrode (IPE), it expresses the electrode-solution interface, hence reveals the association between triple phase boundary (TPB) and activity. It suggests that, the MnO_xof pM shows better activity than cM. In alkali, the former has 180 mV lower potential vs RHE, and nearly half Tafel slope. In acid, both the MnO_x catalysts show step-current polarization with similar activity. Moreover, cM shows higher activity than cT, e.g., 420 mV lower potential. The revealed solution resistance, R_s is consistent with activity. For the same catalyst, the fraction in voltage drop of capacitance f_Cd, is also in accordance with the activity in terms of ionomer to catalyst ratio (I/C), loading and single/double layer(s). However, for the varied catalysts, e.g., cM versus cT, or pM versus cM, the f_Cd is inconsistent with the activity, which might result from involving the non-Faradiac process of MnO_x.

Key words: MnO_x, TiO₂, gliding arc plasma, oxygen evolution reaction, electrode-solution interface

摘要：

析氧半反应是速控步骤。氧化锰（MnO_x）具有多价态，可形成多个子步骤降低活化能。二氧化钛（TiO₂）是抗氧化性半导体。考察两种氧化锰催化剂析氧性能，即滑动弧等离子体合成MnO_x（pM）和商业化（cM），与商业化TiO₂ （cT）比较。通过理想极化电极系统（IPE）解析，表达电极界面特性，揭示三相界面与活性的关联。结果表明：对两种MnO_x 催化剂，pM比cM性能更优。碱性环境中，前者起始电位低180 mV，Tafel斜率近半。酸性中，均表现阶跃式极化，析氧性能相近。cM比cT催化剂析氧性能更优，起始电位低420 mV。溶液电阻R_s与活性变化趋势一致。对相同催化剂，考察I/C、担量、单双层结构，电容压降占比f_Cd与活性一致。对不同催化剂，考察cM， cT或pM， cM，f_Cd与活性不一致，这与多价态锰参与非法拉第过程有关。

关键词: 氧化锰, 二氧化钛, 滑动弧等离子体, 析氧反应, 电极-溶液界面