Title: Characterization of NiFe oxyhydroxide electrocatalysts by integrated electronic structure calculations and spectroelectrochemistry

Abstract

NiFe oxyhydroxide materials are highly active electrocatalysts for the oxygen evolution reaction (OER), an important process for carbon-neutral energy storage. Recent spectroscopic and computational studies increasingly support iron as the site of catalytic activity but differ with respect to the relevant iron redox state. A combination of hybrid periodic density functional theory calculations and spectroelectrochemical experiments elucidate the electronic structure and redox thermodynamics of Ni-only and mixed NiFe oxyhydroxide thin-film electrocatalysts. The UV/visible light absorbance of the Ni-only catalyst depends on the applied potential as metal ions in the film are oxidized before the onset of OER activity. In contrast, absorbance changes are negligible in a 25% Fe-doped catalyst up to the onset of OER activity. First-principles calculations of proton-coupled redox potentials and magnetizations reveal that the Ni-only system features oxidation of Ni2+ to Ni3+, followed by oxidation to a mixed Ni3+/4+ state at a potential coincident with the onset of OER activity. Calculations on the 25% Fedoped system show the catalyst is redox inert before the onset of catalysis, which coincides with the formation of Fe4+ and mixed Ni oxidation states. The calculations indicate that introduction of Fe dopants changes the character of the conduction band minimum from Ni-oxidemore » in the Ni-only to predominantly Fe-oxide in the NiFe electrocatalyst. These findings provide a unified experimental and theoretical description of the electrochemical and optical properties of Ni and NiFe oxyhydroxide electrocatalysts and serve as an important benchmark for computational characterization of mixedmetal oxidation states in heterogeneous catalysts.« less

Authors:

Goldsmith, Zachary K. ^[1]; Harshan, Aparna K. ^[1]; Gerken, James B. ^[2]; Vörös, Márton  ^[3];

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• Search OSTI.GOV for ORCID "0000-0003-1321-9207"
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Galli, Giulia ^[3]; Stahl, Shannon S. ^[2]; Hammes-Schiffer, Sharon  ^[1]

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• Search OSTI.GOV for ORCID "0000-0002-3782-6995"
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+ Show Author Affiliations

1. Univ. of Illinois at Urbana-Champaign, IL (United States)
2. Univ. of Wisconsin, Madison, WI (United States)
3. Univ. of Chicago, IL (United States); Argonne National Lab. (ANL), Lemont, IL (United States)

Publication Date:

2017-03-06

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

National Science Foundation (NSF)

OSTI Identifier:

1367202

Grant/Contract Number:  

AC02-06CH11357; CHE-1305124; 1545907.

Resource Type:

Journal Article: Accepted Manuscript

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Volume: 114; Journal Issue: 12; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; NiFe oxyhydroxide; oxygen evolution reaction; electrocatalysis; spectroelectrochemistry; density functional theory