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. Here, we will present results of quantum calculations assessing the OER activities of various active sites on two of the most abundant crystallographic facets of this oxide, namely, the six-fold-Ni-coordinated (0001) plane and the five-fold-Ni-coordinated (10-10) plane. To properly describe oxidation state changes during redox reactions, we use hybrid density functional theory that includes a fraction of exact Hartree-Fock exchange. By evaluating thermodynamic OER overpotentials, we show that the two distinct active sites considered on each facet demonstrate OER activities remarkably different from each other. Surprisingly, the active sites with the lower OER overpotential on each facet were found to demonstrate overpotentials similar to each other and to the four-fold-lattice-O-coordinated Ni site on the (-12-11) facet of β-NiOOH investigated previously (J. Am. Chem. Soc. 2019, 141, 1, 693-705). These calculated lower overpotentials are among the lowest computationally determined values for undoped β-NiOOH. Accordingly, our findings indicate that various low-index facets could be responsible for the experimentally observed OER activity of undoped, pristine β-NiOOH. Nevertheless, the lowest-overpotential active sites on these three crystallographic facets operate via different local chemistries, underscoring the importance of considering multiple OER mechanisms on each crystallographic facet of a potential electrocatalyst. Specifically, our work reveals that the consideration of lattice-oxygen-stabilization, as well as previously overlooked active sites, metal oxidation states (e.g., +4 for Ni), and reaction intermediates (e.g., adsorbed hydrogen peroxide), are promising strategies to identify lower overpotential OER pathways.

Revealing the facet-independent oxygen evolution activity of pure β-NiOOH using hybrid density functional theory: Different chemistries leading to similar overpotentials

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.