NiOOH Exfoliation-Free Nickel Octahedra as Highly Active and Durable Electrocatalysts Toward the Oxygen Evolution Reaction in an Alkaline Electrolyte

Abstract

A layered beta-NiOOH crystal with undercoordinated facets is an active and economically viable nonnoble catalyst for the oxygen evolution reaction (OER) in alkaline electrolytes. However, it is extremely difficult to enclose the beta-NiOOH crystal with undercoordinated facets because of its inevitable crystal transformation to gamma-NiOOH, resulting in the exfoliation of the catalytic surfaces. Herein, we demonstrate {111}-faceted Ni octahedra as the parent substrates whose surfaces are easily transformed to catalytically active beta-NiOOH during the alkaline OER. Electron microscopic measurements 1.2 demonstrate that the horizontally stacked beta-NiOOH on the surfaces of Ni octahedra has resistance to further oxidation to gamma-NiOOH. By contrast, significant crystal transformation and thus the exfoliation of the gamma-NiOOH sheets can be observed on the surfaces of Ni cubes and rhombic dodecahedra (RDs). Electrocatalytic measurements show that the beta-NiOOH formed on Ni octahedra exhibits highly enhanced OER durability compared to the Ni cubes, Ni RDs, and the state-of-the-art Ir/C catalysts.