Electrochemical contributions: Hans Wenking (1923–2007)

Hans Wenking (Figure 1) was a German electrical engineer, physicist and inventor who devoted his lifetime to the development of electronic equipment for chemistry and physics, particularly constructing the first potentiostats, which became major parts of modern electrochemical instruments. He was the first who described the basic principles of potentiostats.

In 1952, Hans Wenking constructed an electronic amplifier for controlling an oscilloscope using a mirror galvanometer with the signals recorded on photographic paper. This amplifier was later used as a core of a new potentiostat with only a power supplier added. This potentiostat, being an important instrument for electrochemical investigations, was designed by Wenking during his work at the Max Plank Institute in Göttingen, Germany. At that time Hans Wenking was working in a group with Professor Karl Friedrich Bonhoeffer where he was appointed to develop a potentiostat that was needed for electrochemical experiments, particularly, for studying corrosion.

Until 1957, Wenking's potentiostat was manufactured only for the internal use of the Max Planck Institute in Göttingen. Later Hans Wenking together with Gerhard Bank established “Elektronische Werkstatt Göttingen” to commercialize the potentiostats. From 1959, the company operated under the name “Gerhard Bank Electronik”. Wenking designed the instruments as a freelance, but the brand “Wenking potentiostat” (Figure 2) soon became a famous trademark. The consequence of the potentiostat development was a rush in the development of electrochemical science. The phenomena of metal passivity could be better explained, including mechanisms of oxide layer formation, and far beyond the materials science. The potentiostat became a standard instrument for most electrochemical investigations, particularly for electroanalytical measurements.

Independent of Wenking's work, similar instruments were designed by other companies. Tacussel was one of those companies which came to a similar design as Wenking's potentiostats and started manufacturing potentiostats in France. In the USA, Wenking's potentiostats were leading on the market and became standard instruments in electrochemical labs.

Wenking has never published his results in scientific papers. On the other hand, Wenking never concealed the technical details of his instruments. The circuits and layouts designed by him were included in the operation manuals for the instruments, and even in some manuals, a detailed theoretical treatise was given. Wenking's instruments were always state-of-the-art and electrochemists of the 1950s–70s used them for many different applications.

In the 1920s–50s many polarographic and later voltammetric (e.g., cyclic voltammetry) measurements were performed using a two-electrode configuration composed of a dropping mercury electrode or any other small working electrode and a counter electrode, also serving as a reference. The two-electrode configuration provided reasonable quality of the electrochemical measurements as long as the working electrode was small, the potential sweep was not fast and the background solution included a high concentration of an electrolyte in an aqueous solution, then providing a small current over small resistance in a liquid phase. In other words, the potential drop in the electrolyte solution was not significant to affect the potential measurement precision, so, the applied voltage was close to the actual potential of the working electrode. However, when the analytical measurements started to be performed in non-aqueous solvents with much higher resistance or/and the potential scan rates were much faster (particularly in cyclic voltammetry), then resulting in larger currents, the potential drop in the liquid phase became significant, thus requiring its compensation. At this time, the standard electrochemical/electroanalytical configuration included a three-electrode configuration with a reference electrode added. The three electrodes, working, counter and reference have operated with a potentiostat having more sophisticated electronic circuitry than previously used two-electrode polarographs. While sometimes the reference electrode is not really needed or difficult to be used, particularly in micro-sized electrochemical cells or in implantable electrochemical devices operating in biological fluids, modern electroanalytical devices have always the circuit allowing their operation with three electrodes. The change of the electrochemical instruments operating with two electrodes to three electrodes, thus operating as potentiostats, occurred in approximately the 1950s when numerous potentiostats became commercially available (Figures 3 and 4); many of them were based on the fundamental design of Hans Wenking. Some of these devices were used for control-potential electrolyzers rather than electroanalytical applications. Notably, the electrolysis was conducted with large area electrodes, thus operated with large currents that required very powerful electrical devices. It should be also mentioned that many polarographs produced in 1950 and later have already included potentiostat electrical circuits.

A multipurpose electroanalytical instrument constructed by Lingane (Figure 4a) was operating with various functions, including the potentiostat function maintaining the potential of a working electrode constant during electrolysis, in electrogravimetric analysis of metals, electrolytic separations of metals prior to final determinations by other methods, coulometric analysis, and electrolytic preparations by the controlled potential technique. Electrolysis at constant total applied voltage, or with constant current (i.e., operating in potentiostatic or galvanostatic regimes) was also possible.

The author declares that he has no conflict of interest.