Active Motif Change of Ni‐Fe Spinel Oxide by Ir Doping for Highly Durable and Facile Oxygen Evolution Reaction

• Published in: Advanced functional materials Vol. 33; no. 1
• Main Authors: Hong, Sukhwa, Ham, Kahyun, Hwang, Jeemin, Kang, Sinwoo, Seo, Min Ho, Choi, Young‐Woo, Han, Byungchan, Lee, Jaeyoung, Cho, Kangwoo
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.01.2023
• Subjects: Absorption spectroscopy; Density functional theory; density functional theory calculation; Doping; doping effect; Electrocatalysts; in situ X‐ray absorption spectroscopy; Iron; Materials science; Metal foams; Nanoparticles; Nickel ferrites; Oxidation; oxygen evolution reaction; Oxygen evolution reactions; Spinel; spinel oxide; Switches
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202209543

The oxygen evolution reaction (OER) is crucial for producing sustainable energy carriers. Herein, Ir (5 mol.%) doped inverse‐spinel NiFe2O4 (Ir‐NFO) nanoparticles deposited on Ni foam (NF) by scalable solution casting are considered a promising OER electrocatalyst for industrial deployments. The Ir‐NFO/NF (with minimal lattice distortion by uniform Ir doping) provides an OER overpotential of 251 mV (intrinsically outperforming NFO/NF and benchmarking IrO2/NF) and extraordinary robustness over 130 days at 100 mA cm−2. In situ X‐ray absorption spectroscopy reveals oxidation only for Fe on NFO, whereas concurrent generation of higher‐valent Ni and Fe occurs on Ir‐NFO during OER. Density functional theory calculations further demonstrate that Ir substitutes the sublayer Ni octahedral site and switches the main active reaction center from FeOhFeTd bridge site (FeOFe) on NFO to NiOh–FeTd bridge site (NiOFe active motif) on Ir‐NFO for a co‐catalytic OER. This study sheds new light on precious‐metal doped Ni‐Fe oxides, which may be applicable to other binary/ternary oxide electrocatalysts. The Ir (5 mol.%) doped inverse‐spinel NiFe2O4 (Ir‐NFO) nanoparticles deposited on Ni foam provide oxygen evolution reaction overpotential of 251 mV and unprecedented robustness over 130 days at 100 mA cm−2. In situ X‐ray absorption spectroscopy and density functional theory calculations reveal that the Ir switches the main active reaction center of Ir‐NFO into a NiOh‐FeTd bridge site.