Browsing by Author "Hamza, Andrea"

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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.
N-Alkylated Pyridoxal Derivatives as Negative Electrolyte Materials for Aqueous Organic Flow Batteries: Computational Screening
(2023-08-04) Hamza, Andrea; Németh, Flóra B.; Madarász, Ádám; Nechaev, Anton; Pihko, Petri M.; Peljo, Pekka; Pápai, Imre
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
N-functionalized pyridinium frameworks derived from the three major vitamers of vitamin B6, pyridoxal, pyridoxamine and pyridoxine, have been screened computationally for consideration as negative electrode materials in aqueous organic flow batteries. A molecular database including the structure and the one-electron standard reduction potential of related pyridinium derivatives has been generated using a computational protocol that combines semiempirical and DFT quantum chemical methods. The predicted reduction potentials span a broad range for the investigated pyridinium frameworks, but pyridoxal derivatives, particularly those involving electron withdrawing substituents, have potentials compatible with the electrochemical stability window of aqueous electrolytes. The stability of radicals formed upon one-electron reduction has been analyzed by a new computational tool proposed recently for large-scale computational screening.