Microkinetic assessment of electrocatalytic oxygen evolution reaction over iridium oxide in unbuffered conditions
Microkinetic assessment of electrocatalytic oxygen evolution reaction over iridium oxide in unbuffered conditions
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DOI：
10.1016/j.jcat.2020.09.007
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发表时间：
2020-11-01
影响因子：
7.3
通讯作者：
Takanabe, Kazuhiro
中科院分区：
文献类型：
--
作者：
Nishimoto, Takeshi;Shinagawa, Tatsuya;Takanabe, Kazuhiro
由可再生能源产生的电力驱动的水电解将在未来的可持续社会中发挥关键作用，这需要适应各种反应条件以及电解质特性。无论如何，析氧反应（OER）的阳极半反应被认为是动力学瓶颈。这项研究提供了OER动力学的定量描述的基础上严格的微观动力学分析，包括塔菲尔分析，同位素效应和温度依赖性，使用IrOx电催化剂在不同pH值的非缓冲溶液中。H+/OH的扩散限制决定了pH-电位-电流关系中三种不同的动力学状态：pH 5以下，pH 5 - 10之间，以及pH 10以上，电流密度约为1 mA cm（-2）。当从碱性溶液转变为酸性溶液时，电极表面附近的局部OH的完全消耗将OER转换为OH氧化为pH 11下的水分子的OER，而与电极身份无关。在pH 5-10时，通过氧化反应产生的H+的扩散约束甚至在OER之前在电极表面附近产生pH 4的环境，导致OER性能的本体pH独立区域。在这种无缓冲的近中性pH条件下，OER催化的同位素效应减弱，这与速率决定步骤（rds）是通过形成O-O键的唯一电子转移步骤一致，与质子转移解耦。这种反应机理与在更酸性的条件下（pH < 4）的反应机理不同，尽管水分子是相同的反应物。在酸性条件下，可观察到明显的同位素效应，这与O-O键的形成是一致的，O-O键是未配位的裸Ir位点上的rds作为最丰富的表面物种。这项研究提供了反应物和机械切换的定量描述，指出电极材料和电解质的同时优化，以提高近中性pH水平下的OER性能。(c)2020作者（S）爱思唯尔公司出版这是一个在CC BY-NC-ND许可证下的开放获取文章（http：//creativecommons.org/licenses/by-nc-nd/4.0/）。
Water electrolysis driven by electrical power generated from renewable energy sources will play a piv-otal role in future sustainable societies, which requires adaptation of various reaction conditions as well as electrolyte identities. Regardless, the anodic half-reaction of the oxygen evolution reaction (OER) is considered a kinetic bottleneck. This study provides quantitative description of the OER kinetics based on rigorous microkinetic analyses including Tafel analysis, isotope effects and temperature dependence using an IrOx electrocatalyst in unbuffered solution at varying pH levels. The diffusional constraints of H+/OHdetermine three distinctive kinetic regimes in the pH-potential-current relationships: below pH 5, between pH 5 and 10, and above pH 10 at appreciable current densities on the order of 1 mA cm(-2). When shifting from alkaline to acidic solution, the complete consumption of local OHnear the electrode surface switches the OER proceeding as the oxidation of OHto that of the water molecule at pH 11 irrespective of the electrode identity. At pH 5-10, the diffusional constraints of H+ generated via oxidation reaction yield an environment with pH 4 near the electrode surface even prior to the OER, resulting in a bulk pH-independent region for the OER performance. Under this unbuffered near-neutral pH condition, the isotope effect was diminished for the OER catalysis, which is consistent with the rate determining step (rds) being the sole electron-transfer step via the formation of O-O bonds, decoupled from proton transfer. This reaction mechanism is distinct from that under more acidic conditions (pH < 4), although the water molecule is the same reactant. Under acidic conditions, noticeable isotope effects were observable, which is consistent with the formation of O-O bonds being the rds on uncoordinated bare Ir sites as the most abundant surface species. This study provides a quantitative description of the reactantand mechanistic-switching that points to concurrent optimization of both electrode materials and electrolyte for improved OER performance at near-neutral pH levels. (c) 2020 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).