Electrochemical contributions: John Edward Brough Randles (1912–1998)

Abstract

John Edward Brough Randles (Figure 1) was an English electrochemist who made important contributions to the theoretical background of polarography, cyclic voltammetry, and electrochemical impedance spectroscopy. Many modern techniques of electrochemistry are descended from his work, including cyclic voltammetry, anodic stripping voltammetry, and various types of hydrodynamic voltammetry. The Randles-Ševčík equation applied on linear sweep voltammetry and cyclic voltammetry, and the Randles equivalent circuit used in the modeling of impedance spectra are named after him. The earliest electrochemical work of Randles performed with an oscillopolarograph (cathode ray polarograph) resulted in the development of linear sweep voltammetry.[1, 2] In addition to the experimental work, Randles solved a theoretical problem for expressing the current for diffusion-controlled electrochemical reactions by applying an ingenious graphical method.[3] Another important contribution of Randles to electrochemistry was in the theoretical analysis of Faraday impedance spectra published in 1947.[4] The Randles equivalent circuit has been applied to the analysis of the impedance spectra including interfacial electron transfer (Faradaic component), capacitance and diffusion contributions to the impedance. It became the most frequently used theoretical treatment of impedance spectra. It should be noted that similar results were obtained by Russian scientists Dolin and Erschler in 1940, but the papers published in the Russian language have not been seen by the electrochemical community. The Randles equivalent circuit (Figure 2) is one of the simplest and most common circuit models of electrochemical impedance. It includes a solution resistance, a double-layer capacitor, and a charge transfer or polarization resistance. While the Randles equivalent circuit is frequently sufficient for modeling simple electrochemical systems, it can be used as a starting point for more sophisticated models, for example, based on more resistances and capacitances organized in parallel or in a sequence. It should be noted that John Randles was not only working on solving theoretical problems in electrochemistry, but he was a very good experimentalist. As an example of his experimental work, the Volta potential difference between a mercury droplet and an electrolyte solution measured by Randles can be mentioned.[5] Notably, the great Russian electrochemist Alexander Frumkin had failed to obtain a stable and reproducible result for this kind of measurement. Randles published relatively few papers, but many of them are of great importance and his theoretical treatments of electrochemical systems have been included in all electrochemistry textbooks. The author declares that he has no conflict of interest.