Operando Fe dissolution in Fe-N-C electrocatalysts during acidic oxygen reduction: impact of local pH change.

Autor: Pedersen A; Imperial College London, Department of Materials, Royal School of Mines London SW7 2AZ UK i.stephens@imperial.ac.uk.; Imperial College London, Department of Chemical Engineering London SW7 2AZ UK.; Univ. Grenoble Alpes, Univ. Savoie-Mont-Blanc, CNRS, Grenoble-INP, LEPMI 38000 Grenoble France frederic.maillard@grenoble-inp.fr., Kumar K; Forschungszentrum Jülich GmbH, Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (HI ERN) Cauerstraße 1 91058 Erlangen Germany., Ku YP; Forschungszentrum Jülich GmbH, Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (HI ERN) Cauerstraße 1 91058 Erlangen Germany.; Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Chemical and Biological Engineering Cauerstraße 1 91058 Erlangen Germany., Martin V; Univ. Grenoble Alpes, Univ. Savoie-Mont-Blanc, CNRS, Grenoble-INP, LEPMI 38000 Grenoble France frederic.maillard@grenoble-inp.fr., Dubau L; Univ. Grenoble Alpes, Univ. Savoie-Mont-Blanc, CNRS, Grenoble-INP, LEPMI 38000 Grenoble France frederic.maillard@grenoble-inp.fr., Santos KT; Univ. Grenoble Alpes, Univ. Savoie-Mont-Blanc, CNRS, Grenoble-INP, LEPMI 38000 Grenoble France frederic.maillard@grenoble-inp.fr., Barrio J; Imperial College London, Department of Materials, Royal School of Mines London SW7 2AZ UK i.stephens@imperial.ac.uk.; Imperial College London, Department of Chemical Engineering London SW7 2AZ UK., Saveleva VA; ESRF, The European Synchrotron 71 Avenue des Martyrs, CS40220 38043 Grenoble Cedex 9 France., Glatzel P; ESRF, The European Synchrotron 71 Avenue des Martyrs, CS40220 38043 Grenoble Cedex 9 France., Paidi VK; ESRF, The European Synchrotron 71 Avenue des Martyrs, CS40220 38043 Grenoble Cedex 9 France., Li X; Laboratoire de Physique des Solides CNRS, Université Paris Sud 91405 Orsay France., Hutzler A; Forschungszentrum Jülich GmbH, Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (HI ERN) Cauerstraße 1 91058 Erlangen Germany., Titirici MM; Imperial College London, Department of Chemical Engineering London SW7 2AZ UK., Bonnefont A; Univ. Grenoble Alpes, Univ. Savoie-Mont-Blanc, CNRS, Grenoble-INP, LEPMI 38000 Grenoble France frederic.maillard@grenoble-inp.fr., Cherevko S; Forschungszentrum Jülich GmbH, Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (HI ERN) Cauerstraße 1 91058 Erlangen Germany., Stephens IEL; Imperial College London, Department of Materials, Royal School of Mines London SW7 2AZ UK i.stephens@imperial.ac.uk., Maillard F; Univ. Grenoble Alpes, Univ. Savoie-Mont-Blanc, CNRS, Grenoble-INP, LEPMI 38000 Grenoble France frederic.maillard@grenoble-inp.fr.
Jazyk: angličtina
Zdroj: Energy & environmental science [Energy Environ Sci] 2024 Jul 30; Vol. 17 (17), pp. 6323-6337. Date of Electronic Publication: 2024 Jul 30 (Print Publication: 2024).
DOI: 10.1039/d4ee01995d
Abstrakt: Atomic Fe in N-doped C (Fe-N-C) catalysts provide the most promising non-precious metal O 2 reduction activity at the cathodes of proton exchange membrane fuel cells. However, one of the biggest remaining challenges to address towards their implementation in fuel cells is their limited durability. Fe demetallation has been suggested as the primary initial degradation mechanism. However, the fate of Fe under different operating conditions varies. Here, we monitor operando Fe dissolution of a highly porous and >50% FeN x electrochemical utilization Fe-N-C catalyst in 0.1 M HClO 4 , under O 2 and Ar at different temperatures, in both flow cell and gas diffusion electrode (GDE) half-cell coupled to inductively coupled plasma mass spectrometry (ICP-MS). By combining these results with pre - and post-mortem analyses, we demonstrate that in the absence of oxygen, Fe cations diffuse away within the liquid phase. Conversely, at -15 mA cm -2 geo and more negative O 2 reduction currents, the Fe cations reprecipitate as Fe-oxides. We support our conclusions with a microkinetic model, revealing that the local pH in the catalyst layer predominantly accounts for the observed trend. Even at a moderate O 2 reduction current density of -15 mA cm -2 geo at 25 °C, a significant H + consumption and therefore pH increase (pH = 8-9) within the bulk Fe-N-C layer facilitate precipitation of Fe cations. This work provides a unified view on the Fe dissolution degradation mechanism for a model Fe-N-C in both high-throughput flow cell and practical operating GDE conditions, underscoring the crucial role of local pH in regulating the stability of the active sites.
Competing Interests: There are no conflicts to declare.
(This journal is © The Royal Society of Chemistry.)
Databáze: MEDLINE
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