Departments of Chemistry and Chemical & Biological Engineering, The University of British Columbia , 2036 Main Mall, Vancouver, British Columbia V6T1Z1, Canada.
J Am Chem Soc. 2016 Feb 10;138(5):1561-7. doi: 10.1021/jacs.5b10728. Epub 2016 Feb 1.
The dynamic behavior of the anodic peak for amorphous nickel oxy/hydroxide (a-NiOx) films in basic media was investigated. Chronocoulometry of films with known nickel concentrations reveals that a total of four electrons per nickel site comprise the signature anodic peak at 1.32 V during the first oxidative scan, and two electrons are passed through the associated cathodic peak on the reverse scan. The anodic and cathodic signals each contain two electrons on the successive scans. Catalytic oxygen evolution reaction (OER) was detected within the anodic peak, which is at a lower potential than is widely assumed. In order to rationalize these experimental results, we propose that the four-electron oxidation event is the conversion of the film from nickel(II) hydroxide (Ni(II)-OH) to a higher valent nickel peroxide species (e.g., Ni(IV)-OO or Ni(III)-OO·). The subsequent reduction of the nickel peroxide species is confined by a chemical step resulting in the accumulation of Ni(II)-OOH, which is then oxidized by two electrons to form Ni(IV)-OO during the subsequent oxidative scan on the time scale of a cyclic voltammetric experiment. Our proposed mechanism and the experimental determination that each nickel site is oxidized by four electrons helps link the myriad of seemingly disparate literature data related to OER catalysis by nickel electrodes. The faster catalysis that occurs at higher oxidative potentials is derived from a minority species and is not elaborated here.
研究了碱性介质中无定形镍氧/氢氧化物(a-NiOx)薄膜阳极峰的动力学行为。具有已知镍浓度的薄膜的计时库仑法表明，在第一次氧化扫描中，每个镍位总共包含四个电子，形成了 1.32V 的特征阳极峰，而在反向扫描中通过相关的阴极峰传递两个电子。在连续扫描中，阳极和阴极信号各包含两个电子。在阳极峰内检测到了催化氧气析出反应（OER），其电位低于广泛假设的电位。为了使这些实验结果合理化，我们提出四电子氧化事件是薄膜从镍(II)氢氧化物(Ni(II)-OH)转化为高价镍过氧化物物种（例如，Ni(IV)-OO 或 Ni(III)-OO·）。随后，镍过氧化物物种的还原受到化学步骤的限制，导致Ni(II)-OOH的积累，然后在随后的循环伏安实验时间尺度上通过两个电子氧化形成 Ni(IV)-OO。我们提出的机制和每个镍位被氧化为四个电子的实验确定有助于将与镍电极 OER 催化相关的众多看似不同的文献数据联系起来。在更高的氧化电位下发生的更快催化来自于少数物种，这里不做详细阐述。
