Chemistry Reference
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electrode material is not chosen, the desired
electrolytic reaction does not proceed, therefore
a suitable electrode material must be selected
carefully. In an aqueous solution, oxygen gas
and hydrogen gas are generated competitively
due to discharge of water during the electrolytic
reaction. In order to avoid such undesirable
reactions, cathode materials with high
hydrogen overpotential or anode materials with
high oxygen overpotential should be used. The
order of oxygen overpotential is Au > Pt, Pd,
Cd, Ag > PbO 2 > Cu > Fe > Co > Ni, and the
order of hydrogen overvoltage is Hg > Zn, Pb,
Cd > graphite > Cu > Fe, Ni > Ag, Co > Pt, Pd. A
mercury cathode was very often used for
electroreductive organic synthesis, but it is no
longer used except for electrochemical
measurements because of its toxicity. A
platinum electrode is the first choice in aprotic
organic solvents. Although various kinds of
cathode materials are available, usable anode
materials are limited. Most metals are easily
oxidized apart from noble metals like platinum
and gold. Carbon, graphite and metal oxides
like PbO 2 are commonly used as anodes.
Carbon electrodes generally include a trace
amount of metals like iron, therefore their
surface is paramagnetic. Hence, such carbon
anodes easily capture anodically generated
radicals to enhance further oxidation to form
cationic intermediates. On the other hand,
platinum anodes generally tend to generate
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