Browsing by Author "Gonzalez, Gabriel"

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Experimental Set-Up for Measurement of Half-Cell- and Over-Potentials of Flow Batteries During Operation
(2024-11-14) Gonzalez, Gabriel; Peljo, Pekka
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The study of flow batteries (FBs) requires the development of tools able to evaluate their performance during operation in a reliable and simple way. In this work, we present an experimental set-up that allows the on-line monitoring of the half-cells state of charge and apparent overpotentials on the positive and negative electrodes during battery operation. These measurements are feasible by using additional flow cells that include a reference electrode on each side. We used the experimental set-up to study the performance of the vanadium system as well as a previously reported stable organic couple. The studies consisted on short cycling operation at different current densities and polarization curves at different flow rates and states of charge. By confirming previous results obtained for vanadium-FBs and extending the analysis to further systems, we demonstrated that this approach provides a reliable deeper insight into the battery performance and the processes taking place during operation.
Exploration of Vitamin B6-Based Redox-Active Pyridinium Salts Towards the Application in Aqueous Organic Flow Batteries
(2024-06-25) Nechaev, Anton A.; Gonzalez, Gabriel; Verma, Prachi; Peshkov, Vsevolod A.; Bannykh, Anton; Hashemi, Arsalan; Hannonen, Jenna; Hamza, Andrea; Pápai, Imre; Laasonen, Kari; Peljo, Pekka; Pihko, Petri M.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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 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.