Oxygen-Vacancy–Driven Reactivity in Nanocrystal-Assembled NiFe2O4 Toward Efficient Oxygen Evolution
ChemSusChem, (2026), Vol. 19, No. 9
Dieu Minh Ngo
a
,
Paula Marielle S. Ababao
a,b
,
Farkhod Azimov
a,c
,
Changjoon Park
a
,
Siyoon Yang
a
,
Ilwhan Oh
a
,
Hyun Min Jung
a
a Department of Applied Chemistry, Kumoh National Institute of Technology, Gumi, Republic of Korea
b Mathematics and Physical Sciences Department, FEU Institute of Technology, Manila, Philippines
c R&D Park, Uzbekistan Technological Metals Complex, Chirchik City, Republic of Uzbekistan
Abstract: Developing highly active electrocatalysts for the oxygen evolution reaction is a pivotal challenge in sustainable water electrolysis. Herein, we report a novel in situ oxidative phase-restructuring strategy to fabricate oxygen vacancy-rich NiFe2O4 (NFO) directly on nickel foam. Distinct from conventional hydrothermal methods that typically yield thermodynamically stable crystals with limited intrinsic defects, our unique one-pot process involves the formation of a reduced metallic intermediate. The subsequent drastic phase transformation from this metallic state to a spinel oxide thermodynamically enforces the generation of abundant oxygen vacancies to relieve lattice stress, resulting in unique polycrystalline nanocrystal assemblies (NFO-1). Electrochemical evaluations reveal that NFO-1 significantly outperforms its thermodynamically equilibrated counterpart (NFO-2), exhibiting a low overpotential of 330 mV at 20 mA cm−2 and a remarkable mass activity of 6.78 A g−1. This superior performance is primarily attributed to intrinsic oxygen vacancies generated during the oxidative phase evolution, which optimize the active-site electronic structure and enhance charge–transfer kinetics. Furthermore, the catalyst demonstrates excellent durability over 1200 cycles. This work highlights oxidative phase restructuring as a powerful pathway to engineer intrinsic defects for high-efficiency energy-conversion applications.