Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA.
J Am Chem Soc. 2011 Apr 13;133(14):5587-93. doi: 10.1021/ja200559j. Epub 2011 Mar 17.
Scanning electron microscopy, linear sweep voltammetry, chronoamperometry, and in situ surface-enhanced Raman spectroscopy were used to investigate the electrochemical oxygen evolution reaction (OER) occurring on cobalt oxide films deposited on Au and other metal substrates. All experiments were carried out in 0.1 M KOH. A remarkable finding is that the turnover frequency for the OER exhibited by ∼0.4 ML of cobalt oxide deposited on Au is 40 times higher than that of bulk cobalt oxide. The activity of small amounts of cobalt oxide deposited on Pt, Pd, Cu, and Co decreased monotonically in the order Au > Pt > Pd > Cu > Co, paralleling the decreasing electronegativity of the substrate metal. Another notable finding is that the OER turnover frequency for ∼0.4 ML of cobalt oxide deposited on Au is nearly three times higher than that for bulk Ir. Raman spectroscopy revealed that the as-deposited cobalt oxide is present as Co(3)O(4) but undergoes progressive oxidation to CoO(OH) with increasing anodic potential. The higher OER activity of cobalt oxide deposited on Au is attributed to an increase in fraction of the Co sites present as Co(IV) cations, a state of cobalt believed to be essential for OER to occur. A hypothesis for how Co(IV) cations contribute to OER is proposed and discussed.
扫描电子显微镜、线性扫描伏安法、计时安培法和原位表面增强拉曼光谱用于研究沉积在 Au 和其他金属基底上的氧化钴薄膜的电化学氧气析出反应（OER）。所有实验均在 0.1 M KOH 中进行。一个显著的发现是，沉积在 Au 上的约 0.4 ML 氧化钴表现出的 OER 的转换频率比体相氧化钴高 40 倍。沉积在 Pt、Pd、Cu 和 Co 上的少量氧化钴的活性按 Au > Pt > Pd > Cu > Co 的顺序单调递减，与基底金属的电负性递减平行。另一个显著的发现是，沉积在 Au 上的约 0.4 ML 氧化钴的 OER 转换频率比体相 Ir 高近 3 倍。拉曼光谱表明，沉积的氧化钴最初为 Co(3)O(4)，但随着阳极电势的增加，逐渐氧化为 CoO(OH)。沉积在 Au 上的氧化钴具有更高的 OER 活性归因于 Co(IV)阳离子存在的 Co 位分数增加，这种钴的状态被认为对于 OER 的发生是必不可少的。提出并讨论了一种关于 Co(IV)阳离子如何促进 OER 的假设。
