What are Electrochemical Cells?

Typical electrochemical cells are batteries, accumulators, fuel cells or electrolytic cells. An electrochemical cell consists of two so-called half-cells, each half-cell consisting of an electrode immersed in an electrolyte. Both half-cells can be immersed in the same electrolyte or in different electrolytes.
Two half-cells in different electrolytes must be ionically connected via an electrolyte bridge, also known as a salt bridge. The easiest variant is a filter paper soaked in KNO₃ or KCI. Others are made of glass. A special form of salt bridge is the Haber-Luggin capillary. Every reference electrode with an interior electrolyte operates with a salt bridge. And by the way: every reference electrode is a half-cell.
The chemical reactions in a half-cell can affect the electrolyte, the electrode, or components supplied from outside such as hydrogen gas in fuel cells. Two half-cells that are connected ionically and electrically form a full cell. One of the half-cells emits electrons (oxidation). These electrons flow through the outer circuit into the second half-cell, where corresponding reductions processes take place. The salt bridge allows a flow of anions and cations of the electrolyte so that an equilibrium between the half-cells can occur. Without this ionic connection, the load difference caused by the electron flow would bring the reactions to a standstill.
A typical half-cell which is known in the electrochemistry is the so-called Daniell cell. It consists of a zinc rod in a zinc sulphate solution and a copper rod in a copper sulphate solution. For the ion exchange, both half-cells are connected via a salt bridge. If a multimeter is interposed between the half-cells, a cell voltage of approximately 1.1 Volt can be read off. On each half-cell (often referred to as a half-element), a potential sets, which can be measured by means of a reference electrode.

Reference Electrode – but which one?

To measure electrochemical potentials, you need the object to be studied as well as a second electrode with a known and constant potential, a so-called reference electrode. In this case, you have a simple two electrodes set-up, and the measurement happens quasi currentless.
If you want to measure the potential and the current, you have to choose a three-electrode set-up. The third electrode is the so-called counter electrode which is used to detect the electrical current. In this set-up, you must insert the reference electrode with a Haber-Luggin capillary to minimize the voltage drop between the working electrode and the counter electrode and to avoid disruptions which are caused by the current flowing between the working and the counter electrode.
In both cases, it is important to choose the right reference electrode – a large number of reference electrodes is available. Most of them work with an interior electrolyte which contains chlorides, such as potassium chloride. In that case, you will contaminate your measuring solution with potassium chloride. This can cause major problems, especially if you want to study corrosion processes, because chloride can strengthen the corrosion of your material. It is best to work with an electrolyte-free reference electrode (indicator electrode). We recommend the hydrogen reference electrode HydroFlex since it works without an interior electrolyte and every electrochemist should work with it. There are no mistakes caused by diffusion voltages.