Transfert d'électron et bouleversement moléculaire (réduction électrochimique et photoinduite de liaisons carbone-halogène et carbone-soufre)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Cyclic Voltammetry Analysis of Electrocatalytic Films

Contemporary energy challenges require the catalytic activation of small molecules such as H₂O, H⁺, O₂, and CO₂ in view of their electrochemical reduction or oxidation. Mesoporous films containing the catalyst, conductive of electron or holes and permeable by the substrate appearance, when coated onto the electrode surface, as a convenient means of carrying out such reactions. Cyclic voltammetry then offers a suitable way of investigating mechanistically the interplay between catalytic reaction, mass, and charge transport, forming the basis of rational strategies for optimization of the film performances and for benchmarking catalysts. Systematic analysis of the cyclic voltammetric responses of catalytic films reflecting the various mechanistic scenarios has been lacking so far. It is provided here, starting with simple reaction schemes, which provides the occasion of introducing the basic concepts and relationships that will serve to the future resolution of more complex cases. Appropriate normalizations and dimensionless formulations allow the definition of actual governing parameters. The use of kinetic zone diagrams provides a precious tool for understanding the functioning of the catalytic film

Attempts To Catalyze the Electrochemical CO₂‑to-Methanol Conversion by Biomimetic 2e^– + 2H⁺ Transferring Molecules

In the context of the electrochemical and photochemical conversion of CO₂ to liquid fuels, one of the most important issues of contemporary energy and environmental issues, the possibility of pushing the reduction beyond the CO and formate level and catalytically generate products such as methanol is particularly attractive. Biomimetic 2e^– + 2H⁺ is often viewed as a potential hydride donor. This has been the object of a recent interesting attempt (<i>J. Am. Chem. Soc</i>. <b>2014</b>, <i>136</i>, 14007) in which 6,7-dimethyl-4-hydroxy-2-mercaptopteridine was reported as a catalyst of the electrochemical conversion of CO₂ to methanol and formate, based on cyclic voltammetric, ¹³C NMR, IR, and GC analyses. After checking electrolysis at the reported potential and at a more negative potential to speed up the reaction, it appears, on ¹H NMR and gas chromatographic grounds, that there is neither catalysis nor methanol and nor formate production. ¹H NMR (with H₂O presaturation) brings about an unambiguous answer to the eventual production of methanol and formate, much more so than ¹³C NMR, which can even be misleading when no internal standard is used as in the above-mentioned paper. IR analysis is even less conclusive. Use of a GC technique with sufficient sensitivity confirmed the lack of methanol formation. The direct or indirect hydride transfer electrochemical reduction of CO₂ to formate and to methanol remains an open question. Original ideas and efforts such as those discussed here are certainly worth tempting. However, in view of the importance of the stakes, it appears necessary to carefully check reports in this area