Electrochemical contributions: Tatyana Aleksandrovna Kryukova (1906–1987)

Tatyana Alexandrovna Kryukova (Figure 1), a Russian scientist and electrochemist, made important contributions to electroanalytical chemistry (Figure 2), particularly working in close collaboration with Professor Aleksandr Naumovich Frumkin, who was the greatest Russian scientist in the area of electrochemistry. Kryukova is particularly remembered for developing the theory of polarographic maxima, which were observed as a sharp increase in the current produced upon polarographic measurements under some conditions (Figure 3). These current peaks originated from tangential movements (rotation) of a mercury droplet electrode, then stimulating diffusion in the depletion layer and current increase. Kryukova experimentally observed and theoretically explained the formation and then inhibition of these peaks upon adsorption of organic substances (mostly surfactants) on a mercury droplet electrode. It should be noted that for the first time, the effect of surfactants on polarographic measurements was reported in the 1920s in the laboratory of Professor Jaroslav Heyrovský (polarography inventor and Nobel Prize laureate in 1959), and the study of this effect was published in 1931. However, the study of the surfactant effect performed by Heyrovský was only fragmental. Then, the credit for a detailed explanation of the reasons for the polarographic maxima origin and a systematic study of this effect belongs to Kryukova.

In 1949, Kryukova discovered another very unusual phenomenon, later named as “Kryukova effect” (Figure 4). This effect was observed as a sudden decrease in the current at very negative potentials upon polarographic reduction of anionic species, for example, persulfate or dichromate anions, particularly when a very diluted supporting electrolyte was present in the analyte solution. This current minimum disappeared when the electrolyte concentration was increased. Later, in 1952, Frumkin and G. M. Florianovich (a graduate student at that time) theoretically explained the effect observed by Kryukova as the repulsion of redox anions from the negatively charged electrode surface, as predicted by the Frumkin theory of 1933. This is exactly why the effect was only observed for anionic redox species particularly with very negative potentials, providing a negative charge at the working electrode. As expected, the high concentration of the supporting electrolyte was screening the electrostatic interaction between the negative Hg droplet electrode and the negative redox-anions, then eliminating the current decrease.

It should be noted that the electrochemical study of persulfate ions when the “Kryukova effect” was observed, had not only gained theoretical interest demonstrating a fundamental electrostatic effect at polarized electrodes, but it was also practically important as a part of the Russian uranium project because they were used as a reagent in the separation of uranium isotopes.

Kryukova published many important research papers and her 800-page textbook Polarographic Analysis written in collaboration with a few other scientists and published in Russian in 1959 was one of the most important educational materials and a reference guide on polarography in the USSR for many years.

The author declares no conflict of interest.