Facile synthesis approach of bifunctional Co-Ni-Fe oxyhydroxide and spinel oxide composite electrocatalysts from hydroxide and layered double hydroxide composite precursors

Zinc-air batteries (ZABs) are promising candidates for the next-generation energy storage systems, however, their further development is severely hindered by kinetically sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Facile synthesis approaches of highly active bifunctional electrocatalysts for OER and ORR are required for their practical applications. Herein, we develop a facile synthesis procedure for composite electrocatalysts composed of OER-active metal oxyhydroxide and ORR-active spinel oxide containing Co, Ni and Fe from composite precursors consisting of metal hydroxide and layered double hydroxide (LDH). Both hydroxide and LDH are simultaneously produced by a precipitation method with a controlled molar ratio of Co2+, Ni2+ and Fe3+ in the reaction solution, and calcination of the precursor at a moderate temperature provides composite catalysts of metal oxyhydroxides and spinel oxides. The composite catalyst shows superb bifunctional performances with a small potential difference of 0.64 V between a potential of 1.51 V vs. RHE at 10 mA cm(-2) for OER and a half-wave potential of 0.87 V vs. RHE for ORR. The rechargeable ZAB assembled with the composite catalyst as an air-electrode exhibits a power density of 195 mA cm(-2) and excellent durability of 430 hours (1270 cycles) of a charge-discharge cycle test.

Automated summary

This study presents a facile synthesis method for composite electrocatalysts with highly active performance for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The composite catalyst is composed of metal oxyhydroxides and spinel oxides containing Co, Ni, and Fe, and is synthesized by simultaneous production of metal hydroxide and layered double hydroxide (LDH) through precipitation method with controlled molar ratio, followed by moderate temperature calcination. The composite catalyst exhibits superb bifunctional performances and shows high power density and excellent durability when assembled in zinc-air batteries.