Tensile Strain-Mediated Spinel Ferrites Enable Superior Oxygen Evolution Activity.

Exploring efficient strategies to overcome the performance constraints of oxygen evolution reaction (OER) electrocatalysts is vital for electrocatalytic applications such as H 2 O splitting, CO 2 reduction, N 2 reduction, etc . Herein, tunable, wide-range strain engineering of spinel oxides, such as NiFe 2 O 4 , is proposed to enhance the OER activity. The lattice strain is regulated by interfacial thermal mismatch during the bonding process between thermally expanding NiFe 2 O 4 nanoparticles and the nonexpanding carbon fiber substrate. The tensile lattice strain causes energy bands to flatten near the Fermi level, lowering e g orbital occupancy, effectively increasing the number of electronic states near the Fermi level, and reducing the pseudoenergy gap. Consequently, the energy barrier of the rate-determining step for strained NiFe 2 O 4 is reduced, achieving a low overpotential of 180 mV at 10 mA/cm 2 . A total water decomposition voltage range of 1.52-1.56 V at 10 mA/cm 2 (without iR correction) was achieved in an asymmetric alkaline electrolytic cell with strained NiFe 2 O 4 nanoparticles, and its robust stability was verified with a voltage retention of approximately 99.4% after 100 h. Furthermore, the current work demonstrates the universality of tuning OER performance with other spinel ferrite systems, including cobalt, manganese, and zinc ferrites.