Transition metal-based composites are one of the most important electrocatalysts because of their rich redox chemistry. The reaction kinetics of a redox couple is dependent on the chemical valence and is a key issue in electrocatalytic performance. In this study, a metallic Co catalyst was synthesized by pyrolyzing Co(OH)₂. The effect of the chemical valence of Co on the oxygen reduction reaction (ORR) was investigated by comparing the electrocatalytic properties of three Co-based catalysts containing Co⁰, Co²⁺, and Co³⁺. The electrocatalytic properties were evaluated mainly by linear scan voltammetry (LSV) and a direct borohydride fuel cell (DBFC) where the Co-based catalysts were used as cathodes. The LSV results show that the ORR peak current density increases with a decrease in chemical valence. The DBFC with the Co⁰ cathode exhibits highest power density and good durability. In situ X-ray diffraction combined with in situ X-ray absorption fine structure tests was carried out to reveal the dynamic microstructure evolution of the Co⁰ cathode during ORR. The in situ results clearly demonstrate the evolution of metallic Co to Co(OH)₂ and then to CoOOH during the ORR.

中文翻译：

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高性能钴催化剂对氧还原反应的同步辐射原位X射线吸收精细结构及原位X射线衍射分析

过渡金属基复合材料由于其丰富的氧化还原化学性质而成为最重要的电催化剂之一。氧化还原对的反应动力学取决于化学价，并且是电催化性能中的关键问题。在这项研究中，通过热解Co（OH）₂合成了金属Co催化剂。通过比较三种含有Co ⁰，Co ²⁺和Co ^3+的Co基催化剂的电催化性能，研究了Co的化学价对氧还原反应（ORR）的影响。。电催化性能主要通过线性扫描伏安法（LSV）和直接硼氢化物燃料电池（DBFC）进行评估，其中钴基催化剂用作阴极。LSV结果表明，ORR峰值电流密度随着化学价的降低而增加。带有Co ⁰阴极的DBFC具有最高的功率密度和良好的耐久性。进行了原位X射线衍射与原位X射线吸收相结合的精细结构测试，以揭示ORR期间Co ⁰阴极的动态微观结构演变。该原位结果清楚地表明金属Co的演变对Co（OH）₂的ORR期间，然后到的CoOOH。