The Need to Measure Fast Transients

So far, we have concentrated our attention on activation-controlled processes. Since the rate of such processes increases exponentially with potential, it is usually possible to drive them at a rate sufficiently high, so that mass transport becomes the limiting 

To maintain the ratio jac/ji small (say, 0.05) over a wide range of potentials, we would like to find ways of increasing jl without changing jac- The best way to achieve this is to decrease the diffusion-layer thickness, 6. This can be done by improving the efficiency of stirring, or by taking measurements in unstirred solutions at short times. As stated earlier, in quiescent solutions, in which diffusion is the only mode of mass transport, the diffusion-layer thickness is given by  

Taking measurements at short times increases the value ofJl allowing us to study jac over a wider range of potentials. 

Equation (4.12) is strictly applicable only in imstirred solutions, but as long as the value of 6 calculated from it for a purely diffusion-controlled process is small compared to the thickness of the diffusion layer set up by stirring, the latter will have no effect on ji. 

Now that the importance of transient measurements in electrode kinetics has been established, it is of interest to discuss the effect of the residual jRs potential drop in solution on the analysis of such transients. 

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