Tensile Strain-Mediated Spinel Ferrites Enable Superior Oxygen Evolution Activity

Abstract

Exploring efficient strategies to overcome the performance constraints of oxygen evolution reaction (OER) electrocatalysts is vital for electrocatalytic applications such as H₂O splitting, CO₂ reduction, N₂ reduction, <i>etc</i>. Herein, tunable, wide-range strain engineering of spinel oxides, such as NiFe₂O₄, is proposed to enhance the OER activity. The lattice strain is regulated by interfacial thermal mismatch during the bonding process between thermally expanding NiFe₂O₄ 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 NiFe₂O₄ is reduced, achieving a low overpotential of 180 mV at 10 mA/cm². A total water decomposition voltage range of 1.52-1.56 V at 10 mA/cm² (without <i>iR</i> correction) was achieved in an asymmetric alkaline electrolytic cell with strained NiFe₂O₄ 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.