Bifunctional Mn-Fe Oxide Catalysts for Zn-Air Battery Air Electrodes Fabricated Through Atomic Layer Deposition

Abstract

Zinc-air batteries (ZABs) are one of many energy storage technologies that can help integrate renewable energy into the power grid. A key developmental goal for ZABs is replacing the precious metal catalysts at the air electrode with more abundant and inexpensive materials. In this work, a MnFe_xO_y bifunctional catalyst is directly deposited on a ZAB air electrode using atomic layer deposition (ALD). With ALD, the atomic composition of the air electrode coating can be finely tuned based on catalytic activity. Characterization through electron microscopy, photoelectron spectroscopy and diffraction techniques indicate that the novel ALD film deposits as a nanocrystalline (Mn,Fe)₃O₄ cubic spinel. The mixed oxide catalyst outperforms its individual binary MnO_x or FeO_x constituents, operating at 52.5 % bifunctional efficiency at 20 mA cm⁻². Moreover, the long term stability of the ALD catalyst is showcased by 600 h (1565 cycles) of ZAB cycling at 10 mA cm⁻². The efficiency retention of the bifunctional transition metal oxide catalyst is superior to a precious metal benchmark of Pt−Ru−C, with 84.7 % efficiency retention after more than 1500 cycles versus only 66.2 % retention for the precious metal catalyst. The ALD technique enables deep penetration of catalyst material into the air electrode structure, improving the cycling behaviour.