Electrochemistry studies and develops applications by controlling a single type of chemical reaction and measuring the many physical phenomena it produces. For its part, a large variety of experiments have been conducted over the years to benefit such research. Experiments range from simple potentiostats (timing currents) to cyclic voltammetry (dynamic potentials) to complex AC techniques such as impedance spectroscopy. Not only that, but each independent technology has many possible experimental settings, all of which have one of the best options. This technical report discusses a portion of the experimental setup: the number of electrodes used.
Gamry potentiostats are all 4-electrode systems. This means that four related electrodes need to be placed in a given experiment. The working electrode (green) and the auxiliary electrode (red) are used to load the current, and the working sensing electrode (blue) and the reference electrode (white) measure the potential (potential).
The four-electrode instrument can be easily changed to achieve 2-electrode, 3-electrode and 4-electrode testing. Understand why, how to use different modes is confusing.
The discussion of several electrode experiments needs to figure out what the electrodes are. The electrode is a conductor or semiconductor and contacts the solution to form an interface. The usual design is the working electrode, the reference electrode and the counter electrode (or auxiliary electrode).
The working electrode is connected to the electrode under investigation. It may be an electrode material in the battery test, and in the corrosion test, it is likely to be a corrosive metal material. In physical analysis experiments, often inert materials - usually gold, platinum or graphite - can transfer current to other molecules without being affected by themselves.
The counter electrode or auxiliary electrode is the current path in the battery. All electrochemical experiments have a pair of working and counter electrodes. In most experiments, the counter electrode is a simple conductor, and a relatively inert material such as graphite or platinum is the ideal electrode, although it is not necessary. In some experiments, the counter electrode is also part of the study, and its material composition and design will be different.
This way of separating the reference electrode and the counter electrode is a more accurate study of the electrochemical reaction. Therefore, the three-electrode system is the most commonly used method in electrochemical tests.
The four-electrode system separates WS from W and is similar to the reference electrode. The four-electrode system is shown in Figure 5.
The four-electrode system measures the potential drop between B and D in Figure 3, and that point C has the potential to affect. This system is relatively less used in electrochemical tests, but still useful. The potential drop caused by the electrochemical reaction occurring at the working electrode or the counter electrode surface in the four-electrode system is not detected. Only the current drawn through the solution or the potential drop caused by the obstacle in the solution is measured.
Figure 5 Four-electrode system diagram The four-electrode system is typically used to measure the impedance of the solution phase interface. Such as membrane or liquid-liquid phase boundaries. Can also be used to accurately measure solution resistance, or metal surface resistance (solid state battery)
Special case settings: ZRA mode
A zero resistance galvanometer test is a special case. Briefly mention it. In ZRA mode, the working electrode and the counter electrode are short-circuited, such as the entire battery has no potential drop. In the Gamry instrument, this mode is similar to the 3-electrode system, with an orange CS end connected to the counter electrode. The reference electrode is not important in this test, but the potential can be applied to the working and counter electrode.
The ZRA mode is Figure 3 re-displayed in accordance with Figure 6. The potential at point A is equal to point E. The reference electrode can be connected at point B, C or D. The reference electrode in the solution measures the potential drop caused by the position, current and solution resistance.
The ZRA mode is used for galvanic corrosion, electrochemical noise and a few special tests.