Multifunctional inorganic electrode materials for high-performance rechargeable metal–air batteries
This paper reports the application of Ni–Fe layered double hydroxides (LDHs) intercalated with CO32− (Ni–Fe CO32− LDH) to a catalyst layer of a rechargeable metal–air battery using an alkaline electrolyte. Ni–Fe CO32− LDH is found to play multifunctional roles in the catalyst layer as a mixed conductor with hydroxide ions and electrons, and also as an electrocatalyst. The air electrode with Ni–Fe CO32− LDH shows superior performance to all electrodes with other LDHs, indicating that Ni–Fe CO32− LDH forms more favorable triple-phase boundary regions in the catalyst layer of the air electrode. The Ni–Fe CO32− LDH addition to the catalyst layer of the reversible air electrode using α-MnO2 also improves the performance of a rechargeable zinc–air battery. The reversible air electrode with α-MnO2 shows good cycle stability during 40 cycles, indicating that Ni–Fe LDH as an ionomer remains stable in the reversible air electrode after cycles. There must be a limited influence of CO2 on Ni–Fe CO32− LDH which can exist stably in air. Consequently, these results demonstrate that Ni–Fe CO32− LDHs are promising materials for use as multifunctional ionomers with high durability. They are widely applicable to rechargeable metal–air batteries using alkaline electrolytes.