Split net response

The split net response may also appear if square-wave voltammogram of irreversible electrode reaction (1.1) is recorded starting from low potential, at which the reduction is diffusion controlled [22,23]. This is shown in Fig. 2.16b. If the starting potential is 0.3 V vs. E, a single net peak appears and the backward component of the response does not indicate the re-oxidation of the product (see Fig. 2.16a). If the reverse scan is applied (Fst = -0.8 V, Fig. 2.16b), the forward, mainly oxidative component f is in maximum at 0.190 V, while the backward, partly reductive... 

Similar to the pure surface electrode reaction, the response of reaction (2.146) is characterized by splitting of the net peak under appropriate conditions. The splitting occurs for an electrochemically quasireversible reaction and vanishes for the pure reversible reaction. Typical regions where the splitting emerges are 3 < m < 10 and 0.1 < r < 10 for a = 0.5 and i sw = 50 mV. Contrary to the surface electrode reaction where the ratio of the split peak currents is solely sensitive to a, in the present system this ratio depends additionally on r. For instance, if a = 0.5 and r = 1 the ratio is = 1 for r = 10, > 1 and r = 0.1, < 1. Finally it is worth mentioning when experimentally possible, the electrode mechanism represented by (2.145) to (2.147) has to be simplified to a simple surface reaction (Sect. 2.5.1) in order to avoid the complexity arising from the effect of diffusion mass transport. 

Secondly, selectivity is not always achievable. For example, permselectivity of ion-exchanging polymer films fails at high electrolyte concentration. We have shown that even if permselectivity is not thermodynamically found, measurements on appropriate time scales in transient experiments can lead to kinetic permselectivity. To rationalise this behaviour we recall that the thermodynamic restraint, electrochemical potential, can be split into two components the electrical and chemical terms. These conditions may be satisfied on different time scales. Dependent on the relative transfer rates of ions and net neutral species, transient responses may be under electroneutrality or activity control. 

The broadening of both valence and conduction band due to spin-orbit splitting of levels, and the net upward shift and broadening of the W 5d component of the VB are largely responsible for the differences seen in comparing NR and R DOS in Fig. 12. 

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