Strongly Facet-Dependent Activity of Iron-Doped β-Nickel Oxyhydroxide for the Oxygen Evolution Reaction

Journal Article · 11 April 2024 · Physical Chemistry Chemical Physics. PCCP

DOI: https://doi.org/10.1039/d4cp00315b · OSTI ID:2341802

Rajan, Ananth Govind ^[1]; Martirez, John P. ^[2]; Carter, Emily Ann ^[3]

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1. Indian Institute of Science (IISC), Bengaluru (India); Princeton Univ., NJ (United States)
2. Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
3. Princeton Univ., NJ (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Iron(Fe)-doped β-nickel oxyhydroxide (β-NiOOH) is a highly active, noble-metal-free electrocatalyst for the oxygen evolution reaction (OER), with the latter being the bottleneck in electrochemical water splitting for sustainable hydrogen production. The mechanisms underlying how the Fe dopant modulates this host material’s water electro-oxidation activity are still not entirely clear. Here, we combine hybrid density functional theory (DFT) and Hubbard-corrected DFT to investigate the OER activity of the most thermodynamically favorable (and therefore, 2 expected to be the majority) crystallographic facets of β-NiOOH, namely ($0001$) and ($10$$$$\overline{1}$$$$0$). By considering active sites involving both oxidation and reduction of the transition-metal active center during the redox cycle on these two different facets, we show that six-fold-lattice coordinated Fe in β-NiOOH is redox inactive towards both oxidation and reduction while five-fold -lattice-coordinated Fe in β-NiOOH does exhibit redox activity. However, the determined redox activity of Fe (or lack of it) is not indicative of good (or bad) performance as a dopant on these two facets. Three of the four active sites investigated (oxo and hydroxo sites on ($0001$) and a hydrated site on ($10$$$$\overline{1}$$$$0$)) exhibit only a marginal (< 0.1 V) decrease or increase in the thermodynamic overpotential upon doping with Fe. Only one of the redox-active sites investigated, the hydroxo site on ($10$$$$\overline{1}$$$$0$), exhibits a large attenuation in the thermodynamic overpotential upon doping (to ~0.52 V from 0.86 V), although the doped overpotential is larger than that observed experimentally for Fe-doped NiOOH. Thus, although pure β-NiOOH facets containing four-, five-, or six-fold lattice-coordinated Ni sites have roughly equal OER activities, yielding similar OER onset potentials, only those facets containing four-fold lattice-coordinated Fe would be active under analogous conditions for the Fe-doped material. It follows that, while undoped β- NiOOH demonstrates a roughly facet-independent oxygen evolution activity, the activity of Fe doped β-NiOOH strongly depends on the crystallographic facet. Our study further motivates the investigation of strategies for the selective growth of facets with low iron coordination number to enhance the water splitting activity of Fe-doped β-NiOOH.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE Laboratory Directed Research and Development (LDRD) Program; US Air Force Office of Scientific Research (AFOSR)
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 2341802
• Alternate ID(s): OSTI ID: 2346275
• Journal Information: Physical Chemistry Chemical Physics. PCCP, Journal Name: Physical Chemistry Chemical Physics. PCCP Journal Issue: 20 Vol. 26; ISSN 1463-9076
• Publisher: Royal Society of ChemistryCopyright Statement
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY