Filling Octahedral Interstices by Building Geometrical Defects to Construct Active Sites for Boosting the Oxygen Evolution Reaction on NiFe 2 O 4

Owing to the faster kinetics and outstanding catalytic performance, spinel oxides are regarded as a potential non‐precious metal electrocatalyst for oxygen evolution reaction (OER). Regulation of the geometrical structures of the spinel oxides is one of the most effective approaches for enhancing their OER performance. However, more wide and deep investigations remain because of the structural complexity of spinel oxides, for example, how to fill the unoccupied octahedral interstices to construct a large number of active sites for boosting the OER. Herein, iron foam (IF) supported NiFe 2 O 4 nanocubes with high occupancy at octahedral sites (HO oct ‐NFO NC/IF) are synthesized by hydrothermal method followed by anchoring and annealing. Detailed structural characterizations indicate that the foreign Fe cations can be filled into the octahedral interstices along the geometrical defects channel of transition metal cations coordinated with six oxygen anions (TMO 6 ) by etching TMO 6 units with an anchoring agent. As a result of the increasing of TMO 5 sites with better activity and tuning of the electronic structures, the as‐fabricated HO oct ‐NFO NC/IF electrocatalysts exhibit excellent performance for OER with overpotentials of 260 and 310 mV to reach 10 and 400 mA cm −2 , respectively. Meanwhile, the catalysts show faster kinetics and superior stability.