Compressively Strained Fe₃O₄ in Core-Shell Oxygen Reduction Electrocatalyst Boosts Zinc-Air Battery Performance

Fe₃O₄ is barely taken into account as an electrocatalyst for oxygen reduction reaction (ORR), an important reaction for metal-air batteries and fuel cells, due to its sluggish catalytic kinetics and poor electron conductivity. Herein, how strain engineering can be employed to regulate the local electronic structure of Fe₃O₄ for high ORR activity is reported. Compressively strained Fe₃O₄ shells with 2.0% shortened Fe─O bond are gained on the Fe/Fe₄N cores as a result of lattice mismatch at the interface. A downshift of the d-band center occurs for compressed Fe₃O₄, leading to weakened chemisorption energy of oxygenated intermediates, and lower reaction overpotential. The compressed Fe₃O₄ exhibits greatly enhanced electrocatalytic ORR activity with a kinetic current density of 27 times higher than that of pristine one at 0.80 V (vs reversible hydrogen electrode), as well as potential application in zinc-air batteries. The findings provide a new strategy for tuning electronic structures and improving the catalytic activity of other metal catalysts.