Metal-air cell

Metal acetylides Metal-air cells Metal alcoholates Metal alkoxides Metal alloys Metal amalgams... 

CARBON MATERIALS FOR GAS DIFFUSION ELECTRODES, METAL AIR CELLS AND BATTERIES... 

Metal-air cells are developed with air gas-diffusion cathodes and Mg-anodes. Non-aggressive NaCl-solution is used as electrolyte. Carbon based catalysts for the oxygen reduction are selected and tested in the air gas-diffusion electrodes. Various Mg-alloys are tested as anodes. The V-A, power and discharge characteristics of the Mg-air cells are investigated. 

Various metals can be used as an anode in metal-air cells, the amperhour capacity of the cell being determined by the type of metal anode. 

Magnesium is a reactive metal with relatively high electrochemical equivalent of 2.2 Ah/g and low specific gravity 1.74 g/cm3 its price is not high. This makes magnesium suitable for use as anode in metal-air cells. 

Gas-diffusion electrode metal-air cells gas-transport in porous media carbon-based catalysts. 

The theoretical data [1] shows that Li and Ca possess very high energy density (13172 and 4560 Ah/kg respectively) but these metals are not suitable to be used as anodes because of their instability in aqueous electrolytes. The theoretical energy densities of Mg and A1 are also high (6846 Wh/kg and 8212 Wh/kg). It is shown that some alloys of Mg and A1 can be successfully used as anodes, especially in metal-air cells with neutral electrolytes. The theoretical energy density of Zn is much lower than that of Li and Ca, but the self-discharge of Zn can be effectively suppressed by the use of suitable inhibitors. That s why the zinc-air batteries with KOH electrolyte are the first metal-air system brought into service. 

One of the main problems in the development of air gas-diffusion electrodes for metal-air cells is to find active and stable catalysts for the electrochemical reduction of oxygen. Carbon-based catalysts are mostly used, because of their highly developed surface area and capability for adsorption of 02, suitable morphology, chemical stability, good electric conductivity and comparatively low price. 

Various types of metal-air cells are developed using the described air gas-diffusion electrodes. In the most cases zinc is used as an anode [13]. 

Air gas-diffusion electrodes with similar overall structure suitable for operation in neutral electrolytes are developed. On the basis of these air electrodes metal-air cells are developed using aluminum and magnesium as an anode. 

Air gas-diffusion electrodes were developed, suitable for use in metal-air cell with alkaline or with saline electrolytes. A variety of carbon-based catalysts are used in these air electrodes. Methods for the estimation of the activity and the transport hindrances are proposed and used successfully for the optimization of the carbon-based catalysts. 

Many scientists deeply investigated the processes of oxygen reduction in metal-air cells [9 - 11]. The process in question is very complicated. Products of the oxygen reduction usually contain hydrogen peroxide. Therefore, the oxygen reduction can proceed by a two-electron scheme ... 

A number of cylindrical and flat magnesium-based cells have been developed on a commercial scale, mainly for military applications where high discharge currents and low unit weight are important. However, for most of these applications, magnesium batteries have now been replaced by various lithium/organic systems. There are no commercial aluminium-based Leclanchd cells. Magnesium and aluminium are both exploited as anodes in metal-air cells which are considered below. 

The pros and cons of aluminium and magnesium anodes were discussed in Section 3.5. The corrosion problem is even more serious in metal-air cells since the electrolyte may be saturated with oxygen. 

Metal-air cells have a very favourable energy density which is achieved through not requiring to incorporate the positive active component within... 

The oxygen electrode suffers from considerable polarization losses on discharge, largely due to mass transport limitations. Metal-air cells have... 

One of the most extensively examined gas evolution reactions, next only to the H2 evolution reaction, is the O2 evolution reaction (OER) (209) as it is one of the main electrochemical reactions in water electrolysis, metal electrowinning, and recharging of metal-air cells. The standard electrode potential for the oxygen evolution reaction at 25°C calculated from the standard Gibbs energy of formation of H2O and OH ions (/) is 1.299 V [versus normal H2 electrode (NHE)] and 0.401 V (versus NHE) in alkaline media. The oxygen evolution reactions are... 

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