Research Article


2019, 12(9): 2288–2295


Ternary Ni-Co-Fe oxyhydroxide oxygen evolution catalysts: Intrinsic activity trends, electrical conductivity, and electronic band structure

Michaela Burke Stevens1,§, Lisa J. Enman1,§, Ester Hamal Korkus2, Jeremie Zaffran2, Christina D. M. Trang1, James Asbury1, Matthew G. Kast1, Maytal Caspary Toroker2 (*), and Shannon W. Boettcher1 (*)

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1 Department of Chemistry & Biochemistry and the Materials Science Institute, University of Oregon Eugene, OR 97403, USA
2 Department of Materials Science & Engineering and The Nancy & Stephen Grand Technion Energy Program Technion, Israel Institute of Technology, Haifa 3200003, Israel
§ Michaela Burke Stevens and Lisa J. Enman contributed equally to this work.

Keywords: electrocatalysis, heterogeneous catalysis, water electrolysis, oxygen evolution, density functional theory
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Nickel-, cobalt-, and iron-based (oxy)hydroxides comprise the most-commonly studied electrocatalysts for the oxygen-evolution reaction (OER) in alkaline solution. A fundamental understanding of composition–structure–activity relationships for mixed-metal Ni-Co and Ni-Co-Fe (oxy)hydroxides is important to guide the design of advanced OER catalysts. Here we use cyclic voltammetry, chronopotentiometry, inductively-coupled plasma-optical emission spectroscopy, and in situ electrical conductivity measurements to characterize the properties and activity of various compositions of Ni-Co-Fe (oxy)hydroxides prepared by cathodic co-electrodeposition. Consistent with previous studies, we find Fe is essential for the mixed-metal (oxy)hydroxides to achieve high OER activity. In the rigorous absence of Fe (achieved by using specially cleaned electrolytes), the most-active Ni-Co (oxy)hydroxide composition has an OER turn-over frequency only twice that of pure Co (oxy)hydroxide, suggesting minimal synergism between the two metals. The addition of Co to Ni-Fe (oxy)hydroxides shifts the onset of electrical conductivity to lower potentials, but has little effect on the intrinsic OER activity, with the most-active Ni-Co-Fe (oxy)hydroxide having an OER turn-over frequency only ~ 1.5 times that of the Ni-Fe (oxy)hydroxides. The magnitudes of the electrical conductivities are similar for all the compositions measured. Density-functional-theory-calculated projected density of states show a significant contribution of all chemical elements at the valence band edge of the mixed-metal oxyhydroxide electronic structure, demonstrating significant electronic hybridization between the elements. The calculations suggest the involvement of all the elements in modulating the electronic structure at putative Fe-based active sites that are probably located at edges or defects in the two-dimensional oxyhydroxide sheets.
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Ternary Ni-Co-Fe oxyhydroxide oxygen evolution catalysts: Intrinsic activity trends, electrical conductivity, and electronic band structure. Nano Res. 2019, 12(9): 2288–2295

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