Excess heat production in the redox couple reaction of ferricyanide and ferrocyanide

• Published in: Scientific reports 2020-11, Vol.10 (1), p.20072-20072, Article 20072
• Main Authors: Sugiyama, Atsushi, Miura, Makoto, Oshikiri, Yoshinobu, Kim, Yena, Morimoto, Ryoichi, Miura, Miki, Osaka, Tetsuya, Mogi, Iwao, Yamauchi, Yusuke, Aogaki, Ryoichi
• Format: Article
• Language: English
• Subjects: 639/166; 639/638; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-76611-3

In order to establish the universality of the excess heat production in electrochemical reaction, under a high magnetic field, as one of the most fundamental electrochemical reactions, the case of ferricyanide-ferrocyanide redox reaction was examined, where ionic vacancies with ± 1 unit charge were collided by means of magnetohydrodynamic (MHD) flow. As a result, from the pair annihilation of the vacancies with opposite signs, beyond 7 T, excess heat production up to 25 kJ·mol −1 in average at 15 T was observed, which was attributed to the liberation of the solvation energy stored in a pair of the vacancy cores with a 0.32 nm radius, i.e., 112 kJ·mol −1 . Difference between the observed and expected energies comes from the small collision efficiency of 0.22 due to small radius of the vacancy core. Ionic vacancy initially created as a by-product of electrode reaction is unstable in solution phase, stabilized by releasing solvation energy. Ionic vacancy utilizes the energy to enlarge the core and stores the energy in it. As a result, solvated ionic vacancy consists of a polarized free space of the enlarged core surrounded by oppositely charged ionic cloud. The accuracy and precision of the measured values were ascertained by in situ standard additive method.