Catalysts in metal-air batteries

Air or oxygen batteries can be classified as primary batteries or as mechanically or electrically rechargeable batteries. Battery types and applicable electrolytes are shown in Table 23.2 [3]. 

Anode Primary batteries Mechanically rechargeable batteries Electrically rechargeable batteries 

Electrically rechargeable batteries, like other conventional secondary batteries, can be recharged by electricity. Mechanically rechargeable batteries require the mechanical replacement of spent anode with fresh electrode. 

In air electrodes, the reduction of oxygen proceeds via a four-electron reaction that produces water and a two-electron reaction that produces hydrogen peroxide 

the desirable reaction is four-electron reduction, which requires that oxygen adsorbs with the rupture of the 0=0 bond. Since the traditional electrode materials such as pyrolytic graphite or activated carbon do not facilitate 0=0 bond rupture, a catalyst is needed to accelerate oxygen adsorption with 0=0 bond rupture, the four-electron reduction, or the hydrogen peroxide decomposition. A variety of catalysts have been examined for their activity, stability, and cost (Table 23.3). These catalysts can be divided into three categories  

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The future of catalysts in metal-air batteries is very exciting and interesting. As the world increases its demand for energy storage, metal-air batteries and the catalysts, they depend upon, will gain interest. Metal-air batteries that use oxygen from the air to produce electricity are interesting in themselves. Hopefully new catalysts will be developed to improve these batteries. 

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