Amorphous oxides are one of the most active catalysts for the oxygen evolution reaction (OER). However, very little is known about the structure of the amorphous oxide catalyst during OER, especially the structural detail of the low-atomic number groups (e.g., O, P-containing species). Herein, we report in situ stimulated Raman spectroscopy (SRS) of an amorphous cobalt oxide deposited in phosphate electrolyte (CoPi), one of the most active OER catalysts in neutral pH. In situ SRS reveals the presence of orthophosphates (PO₄^3–) in CoPi, despite the species being unstable at the studied pH. ¹⁸O labeling of water during the CoPi electrodeposition substantially shifts the vibrational spectra of the phosphate bands, even though the phosphate groups were not labeled. The new vibrational positions match best to the phosphate network, for example, pyrophosphates (P₂O₇^4–), implying that the phosphates polymerize like a phosphate glass. We propose that the CoPi formation starts by electro-generating high-valence Co that subsequently react with water and phosphate to form CoPi. In ¹⁸O water, the kinetic isotope effect slows down the Co reactivity toward water. As a result, the high-valence Co reacts preferably with phosphates, polymerizing them into a phosphate network. Our finding provides a mechanistic view of how the buffer ions affect the structure of an amorphous oxide, which may explain why the activity is sensitive to the deposition procedure.

中文翻译：

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原位激发拉曼光谱揭示了非晶氧化钴催化剂中的磷酸盐网络及其在催化剂形成中的作用

非晶态氧化物是氧释放反应（OER）活性最高的催化剂之一。然而，关于OER期间的无定形氧化物催化剂的结构，特别是低原子序数基团（例如，含O，P的物质）的结构细节知之甚少。本文中，我们报告了沉积在磷酸盐电解质（CoPi）中的无定形氧化钴的原位激发拉曼光谱（SRS），磷酸盐电解质是中性pH值中最活跃的OER催化剂之一。原位SRS揭示了CoPi中存在正磷酸盐（PO ₄ ^3–），尽管该物种在所研究的pH下不稳定。^18岁即使未标记磷酸酯基团，在CoPi电沉积过程中水的O标记基团也会大大改变磷酸盐带的振动光谱。新的振动位置最适合磷酸盐网络，例如焦磷酸盐（P ₂ O ₇ ^4–），这意味着磷酸盐像磷酸盐玻璃一样聚合。我们建议，通过电生成高价钴开始CoPi的形成，高价钴随后与水和磷酸盐反应形成CoPi。在¹⁸在水中，动力学同位素效应减慢了Co对水的反应性。结果，高价Co优选与磷酸盐反应，使它们聚合成磷酸盐网络。我们的发现为缓冲离子如何影响非晶氧化物的结构提供了一种机械的观点，这可以解释为什么活性对沉积过程敏感。