Chemistry Reference
In-Depth Information
•A measurement of the current at any level of the cell shows how much
reacting substance is transformed at both electrodes.
•To retain the neutrality of charge in the solution, ions should move
between the electrodes.
Besides charge transfer, the transport of electroactive substance towards
the electrode and the transport of reaction product away from the electrode
also play an important role
3
. It is clear that an electrochemical reaction can
only occur if the electroactive species is in the vicinity of the electrode
surface. However, due to the continuous transformation of electroactive
species, this also means that fresh species should be transported towards
the electrode surface and that the formed reaction product must be trans-
ported away from the surface. The transport conditions and properties will
be discussed more in detail in section 1.7.
Furthermore, it should be noted that the electroactive species taking part
in an electrochemical reaction at an interface can be:
•
organic, inorganic or bio-organic;
•
solid (inclusive of the electrode material itself), a dissolved product, the
solvent itself or a gas;
•
neutral, negatively or positively charged.
The electrode involved in the reaction can be:
• metal or other type of conductor, semi-conductor or insulator;
• homogeneous or heterogeneous;
•a large surface (industrial applications, electrolysis) or a very small
surface (sensing);
•a simple configuration (disc, sheet,...) or complex.
Finally, the advantages (1-3) and disadvantages (4-6) of electrochemistry
are:
1.
The methods are well established, and are supported by a well-defined
theory, and the equipment used is relatively inexpensive for obtaining
information concerning molecules in solution, thermodynamic data and
insight in kinetics of reactions.
2.
Detection limits are low; with electrochemical methods, it is possible to
detect concentrations at nanolevel.
3.
These methods are also selective because of control of the electro-
chemical spectrum through selection of applied potential range. In
addition, selectivity can be improved by modification of the electrode
surface with membranes, electrocatalysts, etc.
4.
All the disadvantages are related to the electrical double layer, which
in fact is the region at the electrode-electrolyte interface in which the
electrochemical reactions occur. Such a layer behaves like a capacitor.
