Decomposition potentials and overvoltage

A graph of current, or current density, versus potential gives a decomposition curve and allows decomposition potentials to be determined (Fig. 8.10). Decomposition potentials are never well-defined and can only be obtained approximately by extrapolation of the rising part of the curve to the potential axis. Nevertheless the value of approximately 1 -7 V for the electrolysis of water is sufficiently different from the theoretical value for it to be apparent that there is a large cell overvoltage even when resistance and concentration 

Decomposition curve, decomp the minimum potential difference which must be applied between a pair of electrodes before decomposition occurs and a current flows, decomp tittle theoretical signiflcance since it is made up of two individual electrode potentials and their associated overvoltages. 

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