Oxygen‐Deficient NiFe₂O₄ Spinel Nanoparticles as an Enhanced Electrocatalyst for the Oxygen Evolution Reaction

Abstract Herein, mesoporous NiFe₂O₄ spinel nanoparticles with abundant oxygen vacancies are successfully prepared by a simple hydrothermal method followed by mild H₂ reduction and used as catalysts for the oxygen evolution reaction. Compared with the pristine and air‐treated NiFe₂O₄, the H₂‐treated NiFe₂O₄ shows a much lower overpotential of 389 mV at a current density of 10 mA cm⁻². The H₂‐treated NiFe₂O₄ also indicates substantial long‐term stability even after 1000 cyclic tests. This outstanding electrochemical activity and stability can be attributed to the improved physicochemical properties by H₂ treatment: small nanoparticles with well‐developed mesoporous structures, a high ratio of Ni²⁺/Ni³⁺ cations, and abundant oxygen vacancies. These properties can significantly improve charge transfer kinetics and increase the number of active sites on the catalyst. The results demonstrate that this facile fabrication method is a promising route for developing cost‐effective and high‐performance catalysts to be used in electrochemical applications.