One approach is to contrast those electrochemical systems involving desirable reactions from those involving undesirable reactions. Synthetic electrolysis is an example of a desirable reaction because the chemical process is promoted to generate a desired product. Or, in designing a battery, for example, we might want to set up conditions to promote an electrochemical reaction in order to extract useful energy.

Corrosion is an example of undesirable electrochemistry because in this case spontaneous electrochemical reactions destroy structural materials and so harm the integrity of a system: we aim to minimize the rate of these reactions.

Electrochemical systems can also be classified into systems that output energy or systems that consume energy. Batteries and fuel cells are energy extraction devices — an electrochemical reaction is used to convert the energy in chemical system into a voltage. Such cells are also called galvanic cells. By contrast, in electrolysis, the system consumes energy to promote an electrochemical reaction for synthesis. Similar electrochemical systems needing energy input include manufacturing processes such as electroplating. Electrochemical reactions may also be driven for electroanalysis, to quantify or otherwise explore the chemical constituents or reactivity of a system.