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Microwave-assisted synthesis of a nanoamorphous (Ni0.8,Fe0.2) oxide oxygen-evolving electrocatalyst containing only “fast” sites

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Abstract

Nickel–iron oxyhydroxides (Ni1−xFexOOH) are non-precious metal electrocatalysts for the oxygen evolution reaction (OER) that have high efficiency in alkaline media. It has been suggested that the layered-double hydroxide (LDH) crystal structure of Ni0.8Fe0.2OOH contains two types of catalytic sites, “fast” Fe sites and “slow” Ni sites, which may limit the overall activity because only 20% of the catalytic surface is highly active. Herein, we report a facile microwave-assisted synthesis route of creating a nanoamorphous nickel–iron oxide electrocatalyst that contains only “fast” catalytic sites. Benchmarking experiments on flat electrodes (roughness factors <1.4) showed that the microwave-assisted, nanoamorphous (Ni0.8,Fe0.2) oxide had a low OER overpotential of 286 mV at a current density of 10 mA cm−2. We measured the kinetic rate constant of the active sites directly with the surface interrogation mode of scanning electrochemical microscopy (SI-SECM). We show that the microwave-assisted, nanoamorphous (Ni0.8,Fe0.2) oxide has only one type of catalytic site with an OER kinetic rate constant of 1.9 s−1 per site. We compared this to a crystalline Ni0.8Fe0.2OOH that was synthesized via electrochemical conditioning of crystalline Ni0.8:Fe0.2 oxide, and verified that the Ni0.8Fe0.2OOH contained two types of catalytic sites – “fast” sites with an OER rate constant of 1.3 s−1 per site and “slow” sites with an OER rate constant of 0.05 s−1 per site. The percentage of “fast” sites in the crystalline Ni0.8Fe0.2OOH was well matched to the total iron atom content, while 100% of the sites were “fast” in the microwave-assisted, nanoamorphous (Ni0.8,Fe0.2) oxide.

Graphical abstract: Microwave-assisted synthesis of a nanoamorphous (Ni0.8,Fe0.2) oxide oxygen-evolving electrocatalyst containing only “fast” sites

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Publication details

The article was received on 05 Jan 2017, accepted on 14 Mar 2017 and first published on 14 Mar 2017


Article type: Paper
DOI: 10.1039/C7TA00151G
Citation: J. Mater. Chem. A, 2017, Advance Article
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    Microwave-assisted synthesis of a nanoamorphous (Ni0.8,Fe0.2) oxide oxygen-evolving electrocatalyst containing only “fast” sites

    J. M. Barforoush, D. T. Jantz, T. E. Seuferling, K. R. Song, L. C. Cummings and K. C. Leonard, J. Mater. Chem. A, 2017, Advance Article , DOI: 10.1039/C7TA00151G

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