Redox Electrode Kinetics at Membrane Bielectrodes

The first workers to carry out such experiments (Crane and Davies ) found current-potential curves that were not linear. They interpreted it as a result of membrane breakdown (electrostriction ). Mandel, developing a suggestion due to Bockris, took data for currents caused to pass across pig s bladder membranes by means of the bielectrode technique and found that the logarithm of current varies linearly with the potential applied across the membrane. 

FIGURE 2. Experimental setup for the measurement of potentials across a membrane/  

Habib and Bockris examined systems in which the redox couple on each side of a BLM was systematically varied. They showed that the relation between the current passing across the membrane and the total potential difference across it is Tafelian/ and this means that the condition for electron transfer as the rate-determining step prevails at the membrane/solution interfaces. 

For a system of membranes with solution on either side, one has two the membrane/solution interfaces, one side being anodic and the other cathodic. If and E2 are the potentials of the corresponding surfaces on the same potential scale, then the p.d. across the membrane is  

The above Eq. (5.3) is a pseudo-Tafel equation for the system of membrane-solution interfaces and is diagnostic for electron transfer to occur across membrane-solution interfaces. The logarithm of the current should vary linearly with p.d. across the membrane, provided the p.d. is not too small ( 20 mV). 

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