Activation of ferrocene-based coordination compounds for oxygen evolution and the application in zinc-air battery

Rational reconstruction of oxygen evolution reaction (OER) pre-catalysts and the performance index is crucial but still challenging. Herein, a coordination compound composed by ferrocenedicarboxylic acid and Co2+ was prepared, which was then treated by NaBH4 solution for the rational reconstruction. The electrochemical activation of the treated product results in the generation of oxyhydroxides with unique microstructure acting as the catalytic active phase, which exhibits excellent electrocatalytic activity with a low overpotential of 256 mV for 10 mA cm−2 towards OER and a half-wave potential of 0.69 V (vs RHE) for oxygen reduction (ORR). Ru species was then loaded on the treated product to further improve the catalytic activity for oxygen reduction. The annealed product (Ru-CoFe/C) presents a core-shell structure with carbon layer on the surface. The product presents an increased half-wave potential of 0.744 V (vs RHE) for ORR with the OER/ORR overpotential gap of 0.776 V for 10 and 1 mA cm−2, respectively, showing the bifunctional catalytic activity. Ru species with small size improves the catalytic activity for ORR; the carbon shell provides the high stability. A Zn-air battery was then fabricated with the Ru-CoFe/C catalyst, which delivers a high power density of 88 mW cm−2 and a large specific capacity of 709 mAh g−1, as well as an excellent cycling stability over 65 h, surpassing commercial Pt/C + RuO2 based counterpart, demonstrating its feasibility in the field of renewable electronic devices. This work affords valuable guidelines for the application of ferrocene-based materials in OER and for the exploring of advanced bifunctional ORR/OER catalysts in rational construction of high-quality Zn-air batteries.