Govind Rajan Ananth, Martirez John Mark P, Carter Emily A
Department of Mechanical and Aerospace Engineering , Princeton University , Princeton , New Jersey 08544-5263 , United States.
Department of Chemical and Biomolecular Engineering , University of California, Los Angeles , Los Angeles , California 90095-1592 , United States.
J Am Chem Soc. 2020 Feb 19;142(7):3600-3612. doi: 10.1021/jacs.9b13708. Epub 2020 Feb 4.
β-Nickel oxyhydroxide (β-NiOOH) is a promising electrocatalyst for the oxygen evolution reaction (OER), which is the more difficult half-reaction involved in water splitting. In this study, we revisit the OER activities of the two most abundant crystallographic facets of pristine β-NiOOH, the (0001) and (1010) facets, which expose 6-fold-lattice-oxygen-coordinated and 5-fold-lattice-oxygen-coordinated Ni sites, respectively. To this end, we model various active sites on these two facets using hybrid density functional theory, which includes a fraction of the exact nonlocal Fock exchange in the electronic description of the system. By evaluating thermodynamic OER overpotentials, we show that the two active sites considered on each crystallographic facet demonstrate OER activities remarkably different from each other. However, the lowest OER overpotentials calculated for the two facets were found to be similar to each other and comparable to the overpotential for the 4-fold-lattice-oxygen-coordinated Ni site on the (1211) facet of β-NiOOH previously examined in 2019 , 141 , 1 , 693 - 705 . This finding shows that all of the low-index facets investigated so far could be responsible for the experimentally observed OER activity of pristine β-NiOOH. However, the lowest overpotential active sites on these three crystallographic facets operate via different mechanisms, underscoring the importance of considering multiple OER pathways and intermediates on each crystallographic facet of a potential electrocatalyst. Specifically, our work demonstrates that consideration of previously overlooked active sites, transition-metal-ion oxidation states, reaction intermediates, and lattice-oxygen-stabilization are critical to reveal the lowest overpotential OER pathways on pristine β-NiOOH.
β-羟基氧化镍（β-NiOOH）是一种很有前景的用于析氧反应（OER）的电催化剂，析氧反应是水分解中较难的半反应。在本研究中，我们重新审视了原始β-NiOOH的两个最丰富的晶体学面，即（0001）面和（1010）面的OER活性，这两个面分别暴露了6重晶格氧配位和5重晶格氧配位的镍位点。为此，我们使用杂化密度泛函理论对这两个面上的各种活性位点进行建模，该理论在系统的电子描述中包含了一部分精确的非局部福克交换。通过评估热力学OER过电位，我们表明在每个晶体学面上考虑的两个活性位点表现出彼此显著不同的OER活性。然而，发现为这两个面计算出的最低OER过电位彼此相似，并且与2019年在文献141, 1, 693 - 705中先前研究的β-NiOOH的（1211）面上4重晶格氧配位的镍位点的过电位相当。这一发现表明，到目前为止研究的所有低指数面都可能是原始β-NiOOH实验观察到的OER活性的原因。然而，这三个晶体学面上最低过电位活性位点通过不同的机制起作用，强调了在潜在电催化剂的每个晶体学面上考虑多种OER途径和中间体的重要性。具体而言，我们的工作表明，考虑先前被忽视的活性位点、过渡金属离子氧化态、反应中间体和晶格氧稳定性对于揭示原始β-NiOOH上最低过电位的OER途径至关重要。
