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The stability of bifunctional oxygen electrodes used in electrically rechargeable zinc/air batteries was investigated as a function of the concentration in the feed gas. Using pure oxygen as feed gas, the oxygen CO 2 evolving electrode was life limiting being stable up to 2500 h. However, by increasing the in CO 2 -concentration synthetic air up to 10 000 ppm, the life limiting electrode is changed to the oxygen reducing electrode and the lifetime is reduced due to poisoning by carbonate precipitation inside the pores of the gas di †usion electrode. Furthermore, the Ðltering efficiency of several alkaline Ðlter materials has been tested. It has been found CO 2 that the Ðlter capacity was strongly dependent on the humidity ratio of the feed gas. 9.2 g of LiOHÈCa(OH) 2 mixture were able to Ðlter 2500 l ambient air (90% RH, 409 ppm with a rest concentration of less than 20 CO 2 ) ppm.

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Metal/air batteries provide high specific energy and consist of inexpensive and environmentally benign materials. They have begun to penetrate the market of portable power sources and offer great promise for transportation applications. In this review, we first discuss the basic aspects of metal/air batteries, then concentrate on the Zn/air system as the most promising metal/air battery. The Zn/air systems have important advantages due to the excellent electrochemical properties of metallic zinc, which include a high overpotential towards hydrogen evolution. This implies that Zn/air batteries with aqueous electrolytes can be electrically recharged, that zinc from spent batteries can be regenerated by electrolysis in aqueous systems, and that mechanically rechargeable Zn/air batteries (arrangements resembling fuel cells) can be realized with aqueous electrolytes. Advances in the development of Zn/air battery components are reviewed and the state of the art of electrically and mechanically rechargeable Zn/air systems is described in detail. An overview of industrial developments in zinc/air battery systems and the nominal performance of available products is included. Practical specific energies in the range of 90–120 Wh kg −1 have been reported for electrically rechargeable Zn/air batteries, about twice as much for mechanically rechargeable systems. Significant progress has been made concerning the cyclability of the electrically rechargeable Zn/air system, by utilizing pasted zinc electrodes and graphitized carbon for the bifunctional oxygen diffusion electrodes. Cycle lives in the range of 200–450 cycles have been achieved.