Exploration of Vitamin B6-Based Redox-Active Pyridinium Salts towards the Application in Aqueous Organic Flow Batteries
: Nechaev Anton A., Gonzalez Gabriel, Verma Prachi, Peshkov Vsevolod A., Bannykh Anton, Hashemi Arsalan, Hannonen Jenna, Hamza Andrea, Papai Imre, Laasonen Kari, Peljo Pekka, Pihko Petri M.
Publisher: Wiley-VCH
: 2024
: Chemistry - A European Journal
: Chemistry (Weinheim an der Bergstrasse, Germany)
: Chemistry
: e202400828
: 30
: 36
: 0947-6539
: 1521-3765
DOI: https://doi.org/10.1002/chem.202400828
: https://doi.org/10.1002/chem.202400828
: https://research.utu.fi/converis/portal/detail/Publication/387767512
Pyridoxal hydrochloride, a vitamin B6 vitamer, was synthetically converted to a series of diverse redox-active benzoyl pyridinium salts. Cyclic voltammetry studies demonstrated redox reversibility under basic conditions, and two of the most promising salts were subjected to laboratory-scale redox flow battery tests involving galvanostatic cycling at 10 mM in 0.1 M NaOH. In these tests, the battery was charged completely, corresponding to the transfer of two electrons to the electrolyte, but no discharge was observed. Both CV analysis and electrochemical simulations confirmed that the redox wave observed in the experimental voltammograms corresponds to a two-electron process. To explain the irreversibility in the battery tests, we conducted bulk electrolysis with the benzoyl pyridinium salts, affording the corresponding benzylic secondary alcohols. Computational studies suggest that the reduction proceeds in three consecutive steps: first electron transfer (ET), then proton-coupled electron transfer (PCET) and finally proton transfer (PT) to give the secondary alcohol. 1H NMR deuterium exchange studies indicated that the last PT step is not reversible in 0.1 M NaOH, rendering the entire redox process irreversible. The apparent reversibility observed in CV at the basic media likely arises from the slow rate of the PT step at the timescale of the measurement.
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This project has received funding from the European Union's Horizon2020 Research and Innovation programme under grant agreement No 875565 (Project CompBat). Support from Research Council Finland (projects 322899 and 348328 – via European Union – NextGenerationEU instrument – to P. M. P.) and 346895 (to A. N.), as well as project DIGIPOWER (Technology Industries of Finland Centennial Foundation and Jane & Aatos Erkko Foundation) is also acknowledged. A. B. thanks the Chemistry Department of University of Jyväskylä for funding, Prof. Kari Rissanen for training in crystallography and assistance in measurement of the structures 5 b and 11 a. The organizing committee of Zürich Summer School of Crystallography is thanked for assistance in measuring and solving the structure 11 b (in particular Dr. Michael D. Wörle, Dr. Nils Trapp and Dr. Farzaneh Fadaei-Tirani). We also thank Dr. Elina Kalenius and Dr. Anniina Kiesilä for assistance with mass spectrometry, Dr. Esa Haapaniemi for NMR assistance, and Doc. Elina Sievänen (all at Jyväskylä) for assistance with CompBat project management. P. P. gratefully acknowledges the Academy Research Fellow funding (grant no. 315739, 343791, 320071 and 343794) and BioFlow project (grant no. 343493) from Research Council Finland, and European Research Council through a Starting grant (agreement no. 950038).
