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Fink, Michael ; Helling, T. ; Eckhardt, J. ; Gerdes, Thorsten ; Jess, Andreas:
Development of a MnO2-based bifunctional oxygen electrocatalyst and its application in zinc/air battery air-cathodes.
2018
Veranstaltung: 2nd International Zinc-Air Battery Workshop
, 10.-12.04.2018
, Trondheim, Norwegen.
(Veranstaltungsbeitrag: Workshop
,
Vortrag
)
Abstract
Reliable and economical battery technologies are gaining a growing importance due to current energy policy reasons e.g. regarding an increasing electrification of road transportation and storage of renewable electricity. While lithium-ion (LIB) and lead-acid batteries (LAB) are currently used in these fields of applications, electrically rechargeable zinc-air batteries (ZAB) are a very promising alternative. ZAB mainly consist of a metal zinc anode, separator and a breathable porous air-cathode in a aqueous potassium hydroxide (KOH) electrolyte. They provide several advantages such as a higher theoretical energy density, sufficient material availability, enhanced operational safety, environmental compatibility and cost effectiveness as compared with LIB and LAB. However, ZAB still exhibit limited electrochemical reversibility of the zinc anode as well as the air-cathode and thus the introduction as electrically rechargeable systems[1, 2]. Initial results show how the reversibility of the zinc anode can be improved[3]. In contrast, suitable and affordable bifunctional electrocatalysts providing fast kinetics/low overpotentials for the oxygen electrochemical reactions at the air-cathode, namely the Oxygen Reduction (ORR) and Oxygen Evolution Reaction (OER), still have to be developed in order to ensure efficient charge and discharge reactions. Current commercially available electrocatalysts for the ORR and OER often include precious metals such as platinum and iridium. However, due to high costs, limited availability and poor electrochemical stability in aqueous KOH electrolyte they are not applicable in electrically rechargeable ZAB. In contrast to precious metals, transition metal oxides (TMOs) are inexpensive, readily available, electrochemically stable und catalytically active in aqueous KOH electrolyte. The combination of two or more TMOs, e.g. manganese oxide (MnO2) and cobalt oxide (Co3O4), while one being active for the ORR and the other one for the OER, provides a promising bifunctional electrocatalyst material. Besides catalytic activity and (electro-)chemical stability of the catalyst materials, its electrochemical performance in air-cathodes under practical charge/discharge conditions is crucial for its application in electrically rechargeable ZAB[4-7].
We present a stable and active bifunctional oxygen electrocatalyst containing MnO2 and Co3O4 and its application in air-cathodes of electrically rechargeable ZAB. The electrocatalytic activity and (electro-)chemical stability with respect to the ORR and OER in aqueous KOH electrolyte of the as-synthesised catalyst materials are investigated using the Thin-Film Rotating Disk Electrode (TF-RDE) technique. Bifunctional air-cathodes (gas diffusion electrodes) containing the as-synthesised catalysts are prepared through electrode slurries, which are printed on commercially available gas diffusion layers using a blade coating technique. The electrochemical performance of the bifunctional air-cathodes under practical charge/discharge conditions is evaluated in full cell ZAB configurations using El-Cell® ECC Air test cells.