Carbon-free bifunctional cathodes for the use in Lithium - Air Batteries with an aqueous alkaline electrolyte

Kurzfassung

Carbon materials are widely used in gas diffusion electrodes due to their high electronic conductivity, relatively low costs and catalytic activity towards oxygen reduction reaction (ORR), the cathodic reaction during discharging. During charging a lithium-air battery the cathode is operated in oxygen evolution reaction (OER) mode. Carbon materials corrode in OER mode, this leads to degradation and a power loss of the electrode. To improve long-term stability and reduce side reactions as H2 and CO2 evolution in OER operation mode carbon-free bi-functional cathodes for aqueous alkaline lithium-air batteries were prepared [1-4]. Gas diffusion electrodes with silver catalysts show a high activity towards oxygen reduction reaction in alkaline media but a rather poor activity towards oxygen evolution reaction. For the use in future lithium-air batteries with an aqueous alkaline electrolyte the activity of such electrodes must be improved significantly. Combinations of silver with promising oxide catalysts [5] show a significant improvement in OER performance and also long-term stability. Gas diffusion electrodes were electrochemically investigated in a half cell. In addition to cyclic voltammograms electrochemical impedance spectroscopy (EIS) [6] was carried out. SEM and XRD were used for the physical and morphological investigations. [1] H. Ohkuma, I. Uechi, M. Matsui, Y. Takeda, O. Yamamoto, N. Imanishi, J. Power Sources 245 (2014) 947 [2] P. N. Ross, M. Sattler, J. Electrochem. Soc. 135 (1988) 1464 [3] H. Arai, S. Müller, O. Haas, J. Electrochem. Soc. 147 (2000) 3584 [4] P. N. Ross, H. Sokol, J. Electrochem. Soc. 131 (1984) 1742 [5] D. Wittmaier, T. Danner, N. Wagner, K.A. Friedrich, J. Appl. Electrochem., (2013) in press, (DOI: 10.1007/s10800-013-0602-x) [6] N. Wagner, “Electrochemical power sources – Fuel cells” in Impedance Spectroscopy: Theory, Experiment and Applications”, 2nd Edition, Edited by Evgenij Barsoukov and J. Ross Macdonald, John Wiley&Sons, Inc., ISBN: 0-471-64749-7, pp.497-537, 2005