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both substrate and mediator, and ex-cell, where
electrolysis is used for only regeneration of the
mediator. In the former case, the redox
potential of the mediator should be lower than
that of the substrate. When the redox potential
of the mediator is higher than that of the
substrate, the latter type is employed. In the
former case a catalytic amount of mediator
should be enough, while in the latter case a
quantitative or excess amount of mediator is
necessary. When the heterogeneous electron
transfer between mediator and electrode, as
well as the redox reaction with the substrate, is
fast enough ( Figure 3.7b ), a significantly
enhanced catalytic current can be obtained due
to decreased electrolysis potential (decreased
activation energy), as shown in Figure 3.8 . In
other word, a large electrocatalytic current can
be obtained.
Figure 3.7 Principle of indirect electrolysis
using a mediator
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