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improved by controlling current density and the
amount of electricity passed. Since current
density is correlated to applied potential,
changing the current density creates a potential
shift. The current density should be selected
depending on the concentration of the starting
substrate. When the concentration of the
substrate is low, the current density should be
low and vice versa. The electricity passed is
readily calculated according to the following
equation: current (
A
) × time (
s
) = electricity
(
C
). For instance, when the desired electrolytic
reaction is a two-electron reaction, the
theoretical amount of electricity is 2 F (2 ×
96480 C). When this electricity is divided by
applied current (
A
), one can easily calculate for
how many hours the electrolysis must be
carried out. As shown in
Figure 3.5a
, the
electrode potential changes with the
consumption of the starting substrate (positive
shift in case of oxidation or negative shift in
case of reduction), therefore the product
selectivity and current efficiency sometimes
decrease, particularly in the late stage of
electrolysis. However, highly selective and
efficient organic electrosynthesis can often be
achieved even at constant current electrolysis,
hence commercialized electrode processes are
operated mainly by constant current
electrolysis. Nevertheless, a constant potential
electrolysis is suitable for achieving high
selectivity and clarification of the reaction
mechanisms. Moreover, based on constant
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