# Stabilization of Fe-N4 sites by platinum during oxygen reduction reaction in acid medium

Nicolas Ishiki, Keyla Teixeira Santos, Nicolas Bibent, Kavita Kumar, Ina Reichmann, Yu-Ping Ku, Tristan Asset, Laetitia Dubau, Michel Mermoux, Hongxin Ge, et al.

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## ► To cite this version:

Nicolas Ishiki, Keyla Teixeira Santos, Nicolas Bibent, Kavita Kumar, Ina Reichmann, et al. Stabilization of Fe-N4 sites by platinum during oxygen reduction reaction in acid medium. 247th ECS Meeting, The Electrochemical Society, May 2025, Montréal (Québec), Canada. pp.2653-2653, 10.1149/MA2025-01552653mtgabs. hal-05253226

HAL Id: hal-05253226

https://hal.science/hal-05253226v1

Submitted on 13 Sep 2025

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STABILIZATION OF FE-N₄ SITES BY PLATINUM DURING OXYGEN REDUCTION IN ACID MEDIUM

Nicolas A. ISHIKI,<fnref n="1" />,<fnref n="2" /> Keyla T. SANTOS,<fnref n="1" /> Nicolas BIBENT,<fnref n="3" /> Kavita KUMAR,<fnref n="1" /> Ina REICHMANN,<fnref n="4" /> Yu-
Ping KU,<fnref n="4" /> Tristan ASSET,<fnref n="3" />,<fnref n="5" /> Laetitia DUBAU,<fnref n="1" /> Michel MERMOUX,<fnref n="1" /> Hongxin GE,<fnref n="6" /> Sandrine
BERTHON-FABRY,<fnref n="6" /> Tzonka MINEVA,<fnref n="1" /> Hazar GUESMI,<fnref n="1" /> Viktoriia A. SAVELEVA,<fnref n="7" /> Vinod PAIDI,<fnref n="7" />
Pieter GLATZEL,<fnref n="7" /> Andrea ZITOLO,<fnref n="8" /> Serhiy CHEREVKO,<fnref n="4" /> Edson A. TICIANELLI,<fnref n="2" /> Frédéric
MAILLARD,<fnref n="1" /> Frédéric JAOUEN<fnref n="3" />

frederic.jaouen@umontpellier.fr

**Keywords:** proton exchange membrane fuel cells, iron-nitrogen-carbon, durability, platinum

The deployment of proton-exchange-membrane fuel cells is hindered by the large amount of Pt required for anode and cathode electrocatalysis. While Fe-N-C materials have shown promising initial oxygen reduction reaction (ORR) activity, they lack durability. Key degradation mechanisms include direct demetallation of FeN₄ sites and indirect deactivation caused by reactive oxygen species. Enhanced durability of Fe-N-C materials can be achieved by interfacing them with a low amount of Pt nanoparticles (NPs) or even Pt single atoms.<sup>1-2</sup> The original idea was to lean on the known activity of bulk Pt and Pt NPs towards H<sub>2</sub>O<sub>2</sub> electroreduction. However, different Pt and Fe active sites can emerge in the current process for preparing Pt/Fe-N-C hybrid materials due to a relatively high-temperature step needed to reduce the Pt salt, leading to the transformation of some Fe-N<sub>4</sub> sites into Pt@FeO<sub>x</sub> core-shell structures, etc.

The presentation will show that it is possible to add controlled amounts of Pt NPs (0.25-2.0 wt. %) via a soft polyol method, resulting in unmodified Fe coordination, well-defined Pt structures and stable Pt/Fe-N-C hybrids. The approach is first validated for various mainstream Fe-N-Cs, including ZIF-8-derived Fe-N-C, aerogel derived Fe-N-C and silica-templated Fe-N-C.

With *operando* techniques, we demonstrate that the Pt addition nearly suppresses H₂O₂ production during ORR and strongly reduces the Fe leaching rate during ORR, while *post mortem* Mössbauer spectroscopy reveals that the highly active but unstable Fe(III)N₄ site is partially stabilized.

The similar H₂O₂ electroreduction activity of Pt/Fe-N-C and Fe-N-C and other analyses point toward a long-distance electronic effect of Pt NPs in stabilizing FeN₄ sites. This key stability property of Fe-N₄ sites during ORR brought by a low amount of Pt is experimentally elusive to understand. Possible synergistic effects between Pt and FeN₄ sites were further studied with density functional theory and a proposed mechanism will be presented that could explain the experimental observations.

<footnote n="1">¹Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, L'ÉPMI, Grenoble, France</footnote>

<footnote n="2">² Instituto de Química de São Carlos (IQSC), Universidade de São Paulo, São Carlos, SP, Brazil.</footnote>

<footnote n="3">³ ICGM, Univ. Montpellier, CNRS, ENSCM, Montpellier, France</footnote>

<footnote n="4">⁴ Forschungszentrum Jülich GmbH, Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (IET-2),
Erlangen, Germany.</footnote>

<footnote n="5">⁵ Institut de Chimie et Procédés pour l'Energie, l'Environnement et la Santé, UMR 7515, Strasbourg, France.</footnote>

<footnote n="6">⁶ MINES Paris, PSL University PERSEE - Centre procédés, énergies renouvelables et systèmes énergétiques,
Sophia Antipolis Cedex, France.</footnote>

<footnote n="7">⁷ ESRF, The European Synchrotron, 38000, Grenoble, France.</footnote>

<footnote n="8">⁸ Synchrotron SOLEIL, L'orme des Merisiers, 91192 Gif-sur-Yvette, France</footnote>
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Characterization of catalysts in PEMFC or in gas diffusion electrode (GDE) setup. a) Chronoamperometry at $U = 0.5$ V, b) Online ICP-MS results conducted in a GDE setup in $O_2$-saturated 0.1 M $HClO_4$ electrolyte, the Fe dissolution rates of Fe-N-C$_{Aero}$ and Pt/Fe-N-C$_{Aero}$ were normalized to catalyst loading during an accelerated stress test consisting of 200 square cycles of 3.2 s at -49.7 mA·cm$^{-2}$ and 2.1 s at -0.1 mA·cm$^{-2}$. The aerogel-derived Fe-N-C catalyst (Fe-N-C$_{Aero}$) has an Fe content of 1.25 wt. %, and 1 wt.% Pt nanoparticles was deposited onto it to form the Pt/Fe-N-C$_{Aero}$ hybrid.</figcaption></figure>

**References:**

1. Mechler, A. K.; Sahraie, N. R.; Armel, V.; Zitolo, A.; Sougrati, M. T.; Schwämmlein, J. N.; Jones, D. J.; Jaouen, F.; *J. Electrochem. Soc.* **2018**, *165*, F1084.

2. Bae, G.; Kim, M. M.; Han, M. H.; Cho, J.; Sougrati, M-T.; Kim, J.; Lee, K-S.; Joo, S. H.; Goddard, W. A.; Oh, H-S.; Kim, H.; Jaouen, F.; Choi, C. H.; *Nature Catal.* **2023**, *6*, 1140-1150.