Coulometric Titration of Active Sites at Mesostructured Cobalt Oxide Spinel by Surface Interrogation Mode of Scanning Electrochemical Microscopy,The Journal of Physical Chemistry C

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Coulometric Titration of Active Sites at Mesostructured Cobalt Oxide Spinel by Surface Interrogation Mode of Scanning Electrochemical Microscopy
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-03-30 , DOI: 10.1021/acs.jpcc.9b11114
Julian Lorenz _{1,

2} , Mingquan Yu ₃ , Harun Tüysüz ₃ , Corinna Harms ₁ , Alexander Dyck ₁ , Gunther Wittstock ₂

Affiliation

Cobalt-based transition-metal oxides are promising candidates for the oxygen evolution reaction (OER). However, a complex interplay between the catalyst crystal structures and material morphologies as well as the surface reactions hampers a comprehensive understanding of the electrocatalytic OER at those materials. Here, we investigate the amount and reactivity of specific surface sites of a mesostructured cobalt oxide spinel powder by surface interrogation mode of scanning electrochemical microscopy (SI-SECM). The powder material was supplied in cavity microelectrodes and efficiently titrated with an Fe(II)-triethanolamine redox mediator generated at a gold microelectrode in an alkaline electrolyte. Thus, quantification of different surface sites was achieved, and their reactivity showed dependence on the cobalt oxidation state. Titration experiments after adjustable time delays with respect to the generation of the different surface sites indicated that these surface sites are active for the OER. Kinetic analysis revealed two pseudo-first-order decay constants that were related to fast and slow surface sites for the OER. Rate constants were determined for potentials where predominantly a mixed-valence Co^III/IV state might be present as the most active species. These results expand the great potential of the surface interrogation mode on studying the reaction kinetics of distinct surface sites for practically relevant powdered, nonprecious metal catalysts to address a highly relevant challenge in electrocatalysis.

中文翻译：

扫描电化学显微镜的表面询问模式库仑滴定中晶结构氧化钴尖晶石上的活性位

钴基过渡金属氧化物是氧释放反应（OER）的有希望的候选者。然而，催化剂晶体结构和材料形态之间以及表面反应之间的复杂相互作用阻碍了对这些材料上电催化OER的全面理解。在这里，我们通过扫描电化学显微镜（SI-SECM）的表面询问模式研究介孔结构的氧化钴尖晶石粉末的比表面积的数量和反应性。将粉末材料装入空腔微电极中，并用碱性电解质中金微电极上生成的Fe（II）-三乙醇胺氧化还原介体有效滴定。因此，实现了对不同表面位点的定量，并且它们的反应性显示出对钴氧化态的依赖性。关于不同表面位点的产生在可调节的时间延迟之后的滴定实验表明，这些表面位点对于OER是活性的。动力学分析揭示了两个伪一阶衰减常数，它们与OER的快速和慢速表面位置有关。确定电位常数的速率常数，主要是混合价Co^{III / IV}状态可能是最活跃的物种。这些结果扩展了表面询问模式的巨大潜力，可用于研究实际相关的粉末状非贵金属催化剂在不同表面部位的反应动力学，从而解决电催化中高度相关的挑战。

更新日期：2020-03-30

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