Spinel oxide modified FeCoNi alloy composites prepared with one-step pyrolytic reduction as bifunctional catalyst for ORR/OER

The development of low-cost and highly efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) is a challenging topic in the fuel cells and metal-air batteries field. Herein, a noble metal-free composite consisting of nano-FeCoNi alloy and spinel oxide was successfully prepared through a simple one-step pyrolytic reduction strategy as identified by XRD, TEM, HRTEM, XPS, and other techniques. The effect of the reduction temperatures (700, 850, and 950 °C) on the composite structure as well as its OER/ORR performances was further investigated. It was observed that FeCoNi@Mn ₂AlO ₄ was harvested at the temperature of 700 °C, while FeCoNi@MnAl ₂O ₄ was finally formed when the reduction temperature was 850 °C and 950 °C. The composites showed comparable electrocatalytic performance to Pt/C in ORR as well as RuO ₂ in OER. Moreover, all three catalysts showed great potential for bifunctional catalysis while FeCoNi@MnAl ₂O ₄-850 with a ΔEgap of 0.75 V, FeCoNi@MnAl ₂O ₄-950 with a ΔEgap of 0.77 V, and FeCoNi@Mn ₂AlO ₄-700 with a ΔEgap of 0.83 V. Density functional theory (DFT) computations further confirmed the synergistic effect between FeCoNi and MnAl ₂O ₄. This work provides a facile approach to prepare an alternative bifunctional composite electrocatalyst for ORR/OER with deep understanding on the structure-performance relationship.