The importance of nickel oxyhydroxide deprotonation on its activity towards electrochemical water oxidation.
The importance of nickel oxyhydroxide deprotonation on its activity towards electrochemical water oxidation.
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DOI：
10.1039/c5sc04486c
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发表时间：
2016-04-21
期刊：
影响因子：
8.4
通讯作者：
Koper MTM
中科院分区：
文献类型：
--
作者：
Diaz-Morales O;Ferrus-Suspedra D;Koper MTM
在pH > 11时，NiOOH的OER活性增强，这是由于在其表面形成了类超氧物种。羟基氧化镍（NiOOH）是一种广泛应用于能量储存的催化剂，是一种很有前途的析氧反应催化剂。然而，在电荷积累和OER期间在NiOOH表面上发生的过程还没有很好地理解。本工作提出了一种原位表面增强拉曼光谱（Sers）研究的pH值依赖的界面变化的NiOOH催化剂的工作条件下用于OER。我们证明了NiOOH的表面去质子化的程度上的电解质pH值的重要影响，这至关重要地影响其OER活性。我们的研究结果表明，NiOOH的去质子化产生带负电荷（或质子缺乏）的表面物种，这是负责增强OER活性的NiOOH在高碱性pH值。此外，我们提供了光谱证据中获得的18 O-标记的电解质，使我们能够分配这种表面物种的superoxo型物种（镍OO-）。此外，我们提出了NiOOH上的OER的机制，这与观察到的pH敏感性一致，并且这也解释了为什么NiOOH不是用于中性或中等碱性pH（在7-11的范围内）的应用的合适催化剂，除了在这些条件下催化剂的较低稳定性之外。
The OER activity of NiOOH enhances at pH > 11 due to formation of superoxo-like species on its surface. Nickel oxyhydroxide (NiOOH) is extensively used for energy storage and it is a very promising catalyst for the oxygen evolution reaction (OER). However, the processes occurring on the NiOOH surface during charge accumulation and OER are not well understood. This work presents an in situ Surface Enhanced Raman Spectroscopy (SERS) study of the pH dependent interfacial changes of the NiOOH catalyst under the working conditions used for OER. We demonstrate the important effect of the electrolyte pH on the degree of surface deprotonation of NiOOH, which crucially affects its OER activity. Our results show that the deprotonation of NiOOH produces negatively charged (or proton-deficient) surface species, which are responsible for the enhanced OER activity of NiOOH in highly alkaline pH. Moreover, we provide spectroscopic evidence obtained in an 18O-labeled electrolyte that allows us to assign this surface species to a superoxo-type species (Ni–OO–). Furthermore, we propose a mechanism for the OER on NiOOH which is consistent with the observed pH-sensitivity, and that also explains why NiOOH is not a suitable catalyst for applications in neutral or moderately alkaline pH (in the range 7–11), apart from the lower stability of the catalyst under these conditions.