1. Electron conductor in an electrochemical cell connected to the external circuit.
2. Half-cell consisting of at least one electron conductor and at least one ionic conductor (electrolyte).

Notes:

1. The current flow through electrochemical cells may be zero or non-zero. An electrochemical cell with current flow can operate either as a galvanic cell or an electrolytic cell.
2. In some electroanalytical techniques (conductometry and differential potentiometry), two indicator electrodes are used. For many analytical measurements in cells with current flow, a three-electrode cell is used.
3. Many types of electrodes are used. These may be classified into groups according to their composition, form and size, and according to their operating mode.