Negative electrodes oxygen recombination

The principle of the sealed battery is based on the ability of the negative electrode to recombine this oxygen gas and prevent the buildup of internal gas pressure. The capacity for this recombination is limited. Hence the maximum charge rate that can be tolerated is the one that keeps the rate of oxygen generation below the gas recombination rate so that the internal gas pressure does not build up excessively. 

Some battery designs have a one-way valve for pressure rehef and operate on an oxygen cycle. In these systems the oxygen gas formed at the positive electrode is transported to the negative electrode where it reacts to reform water. Hydrogen evolution at the negative electrode is normally suppressed by this reaction. The extent to which this process occurs in these valve regulated lead —acid batteries is called the recombination-efficiency. These processes are reviewed in the Hterature (50—52). 

Similar reactions can be writteu for other metallic additives. At the negative electrode two more reactions can occur, hydrogen evolution and oxygen recombination. 

The chemistry of these batteries is that of conventional lead-acid batteries. However, they have a unique characteristics. The oxygen generated on overcharge is recombined in the cell and there is no water loss. Indeed, oxygen reacts at the negative electrode ... 

The oxygen recombination reaction in negative electrode 2Cd+02+2H20 ----------- > 2Cd(OH)2... 

An oxygen gas recombination reaction occurs on the negative electrode. 

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