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Papanikolaou M, Hadjithoma S, Keramidas O, Drouza C, Amoiridis A, Themistokleous A, Hayes SC, Miras HN, Lianos P, Tsipis AC, Kabanos TA, Keramidas AD. Experimental and Theoretical Investigation of the Mechanism of the Reduction of O 2 from Air to O 22- by V IVO 2+- N, N, N-Amidate Compounds and Their Potential Use in Fuel Cells. Inorg Chem 2024; 63:3229-3249. [PMID: 38317481 PMCID: PMC10880062 DOI: 10.1021/acs.inorgchem.3c03272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 01/08/2024] [Accepted: 01/09/2024] [Indexed: 02/07/2024]
Abstract
The two-electron reductive activation of O2 to O22- is of particular interest to the scientific community mainly due to the use of peroxides as green oxidants and in powerful fuel cells. Despite of the great importance of vanadium(IV) species to activate the two-electron reductive activation of O2, the mechanism is still unclear. Reaction of VIVO2+ species with the tridentate-planar N,N,N-carboxamide (ΗL) ligands in solution (CH3OH:H2O) under atmospheric O2, at room temperature, resulted in the quick formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] and cis-[VV(═O)2(κ3-L)] compounds. Oxidation of the VIVO2+ complexes with the sterically hindered tridentate-planar N,N,N-carboxamide ligands by atmospheric O2 gave only cis-[VV(═O)2(κ3-L)] compounds. The mechanism of formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] (I) and cis-[VV(═O)2(κ3-L)] (II) complexes vs time, from the interaction of [VIV(═O)(κ3-L)(Η2Ο)2]+ with atmospheric O2, was investigated with 51V, 1H NMR, UV-vis, cw-X-band EPR, and 18O2 labeling IR and resonance Raman spectroscopies revealing the formation of a stable intermediate (Id). EPR, MS, and theoretical calculations of the mechanism of the formation of I and II revealed a pathway, through a binuclear [VIV(═O)(κ3-L)(H2O)(η1,η1-O2)VIV(═O)(κ3-L)(H2O)]2+ intermediate. The results from cw-EPR, 1H NMR spectroscopies, cyclic voltammetry, and the reactivity of the complexes [VIV(═O)(κ3-L)(Η2Ο)2]+ toward O2 reduction fit better to an intermediate with a binuclear nature. Dynamic experiments in combination with computational calculations were undertaken to fully elucidate the mechanism of the O2 reduction to O22- by [VIV(═O)(κ3-L)(Η2Ο)2]+. The galvanic cell {Zn|VIII,VII||Id, [VIVO(κ3-L)(H2O)2]+|O2|C(s)} was manufactured, demonstrating the important applicability of this new chemistry to Zn|H2O2 fuel cells technology generating H2O2 in situ from the atmospheric O2.
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Affiliation(s)
| | - Sofia Hadjithoma
- Department
of Chemistry, University of Cyprus, Nicosia 2109, Cyprus
| | | | - Chryssoula Drouza
- Department
of Agricultural Sciences, Biotechnology and Food Science, Cyprus University of Technology, Limassol 3036, Cyprus
| | | | | | - Sofia C. Hayes
- Department
of Chemistry, University of Cyprus, Nicosia 2109, Cyprus
| | - Haralampos N. Miras
- School
of Chemistry, The University of Glasgow, Glasgow G12 8QQ, U.K.
- Department
of Chemical Engineering, University of Patras, 26500 Patras, Greece
| | - Panagiotis Lianos
- Department
of Chemical Engineering, University of Patras, 26500 Patras, Greece
| | - Athanassios C. Tsipis
- Section
of Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
| | - Themistoklis A. Kabanos
- Section
of Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
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