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

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. Less is more: Oxygen vacancies on NiFe2O4 correlate with enhanced electrocatalytic performance for oxygen evolution reaction. Hydrogen‐treated NiFe2O4 exhibited a high performance and substantial long‐term stability, which was attributed to abundant oxygen vacancies.