Browsing by Author "Recio, F. Javier"

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    Elucidating the electronic synergetic effects in heteroatomic doped FeN4-C-N-R (R= -F, -Cl, -Br) oxygen reduction catalysts
    (2023) Escobar, Gonzalo; Venegas, Ricardo; Ponce, Ingrid; Toro-Labbe, Alejandro; Zagal, Jose H.; Recio, F. Javier; Munoz-Becerra, Karina
    The structural and electronic characteristics of FeN4 are the determining factors in the catalytic performance of heat-treated Fe-N-C materials, as they serve as active sites. The insertion of heteroatoms as co-dopants (B, S, halogens) can induce electronic effects in the carbon matrix that improves their ORR catalytic activity. Therefore, it has become essential to combine experimental studies with DFT approaches to rationally design this type of catalyst. In this work, we evaluated by means of first principle DFT approaches, the ORR activity for the Fe (phen)2N2 moiety including atoms/functionalities with different atomic radii and electronegativity, to resemble co-doped Fe-N-C-R catalysts. The results showed that the inclusion of halogens heteroatoms (-F, -Cl, and -Br) in the graphitic N-C surrounding the FeN4 core could improve its ORR activity in terms of Fe-O2 binding energy that is related to the Fe(III)/Fe(II) formal potential and, in consequence, with the on-set potential for the ORR. The high expected ORR activity is obtained for bromide co-doped FeN4 catalyst (FeN4-C-Br) since -Br atoms act synergistically, inducing long- and short-range electronic effects over both the FeN4 unit and N-pyridinic-like functions that change the electronic distribution over the aromatic N-C structure modulating the Fe acidity, FeO2 binding, and Fe-O2 orbital interaction.
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    Nanostructured Fe-N-C pyrolyzed catalyst for the H2O2 electrochemical sensing
    (2021) Candia-Onfray, Christian; Bollo, Soledad; Yanez, Claudia; Escalona, Nestor; Marco, Jose F.; Menendez, Nieves; Salazar, Ricardo; Recio, F. Javier
    Fe-N-C pyrolyzed materials have been proposed as substitutes of the noble-based catalyst for energy conversion reactions. However, their use as electrochemical sensors has not been deeply explored. In the present work, different Fe-N-C pyrolyzed catalysts were synthesized for the amperometric sensing of the H2O2 reduction in neutral media. The catalysts were characterized by BET, TEM, FESEM, XPS, Mossbauer spectroscopy, and cyclic voltammetry. The catalysts present an N-doped graphitic matrix with a macroporous structure and mesoporous contribution. Different amounts of N-pyridinic, N-pyrrolic, N-graphitic, N-oxides, and FeN4 sites have been detected on the catalysts. Among the different active sites present in the catalysts, the FeN4 structure is proposed as the most catalytic active site for the hydrogen peroxide reduction reaction (HPRR). Under optimal conditions (0.61 V vs. NHE, 0.00 V vs. Ag/AgCl), the materials show a lineal amperometric response in the range of 0.08 and 14 mu M, with a sensitivity of 31.3 mu A mu M-1 cm(-2), and a detection and quantification limits of 0.25 mu M and 0.75 mu M respectively. The amperometric results indicate that the best performance is reached when increasing the amount of FeN4 active sites, and the redox potential of the FeN4 species becomes more positive. The Fe-N-C catalyst stands out for the more positive working potential than other materials proposed in the literature. (C) 2021 Elsevier Ltd. All rights reserved.