CoFeNiCuMn layered double hydroxide as a bifunctional electrocatalyst for rechargeable zinc-air batteries

Abstract

In this work, the CoFe, CoFeNi, CoFeNiMn, CoFeNiCu, and CoFeNiCuMn layered double hydroxides (LDHs) were synthesized by a hydrothermal method for catalyzing the oxygen evolution (OER) and oxygen reduction (ORR) reactions. According to X-ray diffraction and X-ray photoelectron spectroscopy, the crystallinity of LDHs decreased, and distinct oxidation states emerged with increasing transition-metal (TM) content. The electrodes exhibited a sheet- and nanoneedle-like morphology arranged in a flower-like pattern, as observed by scanning and transmission electron microscopy. Among the compositions, the CoFeNiCuMn LDH showed the highest OER and ORR electroactivity, including a low overpotential of 240 mV (at 10 mA cm −2 ), a high half-wave potential of 0.73 V vs. RHE, and low Tafel slopes of 93 and 128 mV dec −1 . The assembled zinc-air battery, using CoFeNiCuMn LDH as the air electrode, stored electrochemical energy with a high maximum power density of 147 mW cm −2 and demonstrated long-term cycling stability.