The oxygen evolution reaction (OER) is the performance-limiting half reaction of water splitting, which can be used to produce hydrogen fuel using renewable energies. Whereas a number of transition metal oxide and oxyhydroxide have been developed as promising OER catalysts in alkaline medium, the mechanisms of OER on these catalysts are not well understood. Here we combine electrochemical and in-situ spectroscopic methods, particularly operando X-ray absorption and Raman spectroscopy, to study the mechanism of OER on cobalt oxyhydroxide (CoOOH), an archetypi-cal unary OER catalyst. We find the dominating resting state of the catalyst as a Co(IV) species CoO2. Through oxygen isotope exchange experiments, we discover a cobalt superoxide species as an active intermediate in the OER. This intermediate is formed concurrently to the oxidation of CoOOH to CoO2. Combing spectroscopic and electrokinetic data, we identify the rate-determining step of the OER as the release of dioxygen from the superoxide intermediate. The work provides important experimental fingerprints and new mechanistic perspectives for OER catalysts.

中文翻译：

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羟基氧化钴催化析氧机理：钴超氧化物物种作为关键中间体和分子氧释放作为速率决定步骤

析氧反应 (OER) 是水分解的性能限制半反应，可用于使用可再生能源生产氢燃料。尽管已经开发了许多过渡金属氧化物和羟基氧化物作为碱性介质中很有前景的 OER 催化剂，但 OER 在这些催化剂上的机制尚不清楚。在这里，我们结合电化学和原位光谱方法，特别是原位 X 射线吸收和拉曼光谱，研究 OER 在羟基氧化钴 (CoOOH) 上的机理，这是一种典型的一元 OER 催化剂。我们发现催化剂的主要静止状态为 Co(IV) 物种 CoO2。通过氧同位素交换实验，我们发现了一种钴超氧化物物质作为 OER 中的活性中间体。该中间体与 CoOOH 氧化成 CoO2 同时形成。结合光谱和电动数据，我们将 OER 的速率决定步骤确定为从超氧化物中间体释放分子氧。该工作为 OER 催化剂提供了重要的实验指纹和新的机理观点。