Development of Bifunctional Catalysts/Electrodes for Rechargeable Zn-Air Batteries in Alkaline and Near-Neutral Electrolyte

Abstract

In the framework of the EU funded project ZAS (Zinc Air Secondary innovative nanotech based batteries for efficient energy storage); we aim at improving the cycle life performance of secondary Zn-air batteries using low cost nanostructured materials and production methods. However, the goal is challenging due to the degradation of electrodes during cycling, which results in a rapid reduction in (storage) capacity. Furthermore, in order to improve the overall reversibility of the zinc-air battery it is necessary to understand the current limitations, requirements and challenges for each cell component (viz. anode, electrolyte, and cathode) and their interaction. Through close interaction between computer simulations and experimental testing, ZAS will select and develop electrodes to achieve its targets. For rechargeable metal-air batteries, bifunctional air electrodes should be capable of catalyzing both the oxygen reduction and oxygen evolution reaction (ORR and OER, respectively) efficiently. In Zn-Air systems where aqueous alkaline and near-neutral electrolyte is used, it is not necessary to use a pure noble metal catalyst; instead it is possible to implement typical transition metal oxides such as perovskites, pyrochlores and spinels, individual oxides, and their mixture. This presentation will describe the achievements in the development of nanostructure bifunctional catalysts/electrodes in ZAS so far. Oxide materials of spinel and perovskite structures is being synthesized and electrochemically assessed in both alkaline and near-neutral electrolyte. The catalyst synthesis methods have comprised of a modified Pechini route, flame spray pyrolysis and regular spray pyrolysis. Physical methods such as specific surface area (BET), XRD and SEM have been used to characterize the catalysts. The electrocatalytic activity of the bifunctional catalysts is determined by polarization measurements through rotating disk electrodes and a lab-scale screening method. Promising catalysts were further tested through half-cell and full-cell setups to systematically investigate the performance and lifetime. By constructing a database of the results, comparison of the relationship among the physicochemical and electrochemical characteristics from the different synthesis routes has been benchmarked. Figure 1