Cycle hydrogen electrode reaction

If the discharge step in the hydrogen electrode reaction, as discussed earlier, really is Reaction 13 then for platinum black electrode this would represent the step e (Pt) —> e aq. The following cycle is thus worth considering... 

Oxidation-reduction potentials are expressed in volts relative to the standard hydrogen electrode at 0 volts, and represent the tendency of a compound to lose electrons (oxidation) or gain electrons (reduction). Various enzyme systems in respiration reactions (e.g., the cytochromes) utilizing ascorbic acid, hemoglobin, as well as reactions in the Krebs cycle (succinic and fumaric acids) involve electron transfers. Drugs can affect all these systems, and the consequences must be taken into account. 

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). 

These equations are based on the thermodynamically stable species. Further research is needed to clarify the actual intermediate formed during overcharge. In reahty, the oxygen cycle can not be fully balanced because of other side reactions, that include gtid corrosion, formation of residual lead oxides in the positive electrode, and oxidation of organic materials in the cell. As a result, some gases, primarily hydrogen and carbon dioxide (53), are vented. 

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