Measurements of the Steady‐State Activation Overpotential of Chlorine Evolving Electrodes

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Abstract
Detailed measurements of interfacial concentration and concentration overpotential of chlorine evolving platinized platinum electrodes were performed in , at 25°C and 1 atm chlorine or 1 atm nitrogen in the cell. Based on these and electrode polarization measurements, steady‐state activation overpotential curves were obtained. The applied method enabled for the first time in this field, development of true steady‐state activation overpotential curves. Our findings indicated that 30–40 mV/decade slopes typically obtained in nitrogen atmosphere were essentially a sequence of quasi equilibria at the electrode interface. Also, micropolarization data obtained near the open circuit with chlorine atmosphere in the cell were found to be a concentration overpotential phenomenon. The true activation overpotential was found to become a significant part of the electrode polarization only after it exceeded several millivolts in chlorine saturated brine. In nitrogen saturated brine, where the open circuit was undefined, the activation overpotential became significant for polarizations that exceeded two decades of steady‐state low current density polarization. In this case, the activation overpotential was observable as a departure from a 32 mV/decade slope. The obtained activation overpotential curves can be used as a base for developing kinetic parameters, however, a considerably greater emphasis than in the past must be given to the corresponding interfacial conditions.
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