Achilles' heel of iron-based catalysts during oxygen reduction in acidic medium

Chang Hyuck Choi; Hyung-Kyu Lim; Min Wook Chung; Gajeon Chon; Nastaran Ranjbar Sahraie; Abdulrahman Altin; Moulay Tahar Sougrati; Lorenzo Stievano; Hyun Seok Oh; Eun-Soo Park; Fang Luo; Peter Strasser; Goran Dražić; Karl Mayrhofer; Hyungjun Kim; Frederic Jaouen

doi:10.1039/C8EE01855C

Achilles' heel of iron-based catalysts during oxygen reduction in acidic medium

Chang Hyuck Choi ¹ Hyung-Kyu Lim ² Min Wook Chung ¹ Gajeon Chon ¹ Nastaran Ranjbar Sahraie ³ Abdulrahman Altin ⁴ Moulay Tahar Sougrati ³ Lorenzo Stievano ³ Hyun Seok Oh ⁵ Eun-Soo Park ⁵ Fang Luo ⁶ Peter Strasser ⁶ Goran Dražić ⁷ Karl Mayrhofer ⁸ Hyungjun Kim ² Frederic Jaouen ³

1 GIST - Gwangju Institute of Science and Technology

2 KAIST - Korea Advanced Institute of Science and Technology

3 ICGM ICMMM - Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier

4 Max-Planck-Gesellschaft

5 Seoul National University [Seoul]

6 TUB - Technische Universität Berlin

7 National Institute of Chemistry

8 IEK-11 - Helmholtz Institute Erlangen Nürnberg for Renewable Energy

Abstract : For catalyzing dioxygen reduction, iron-nitrogen-carbon (Fe-N-C) materials are today the best candidates to replace platinum in proton-exchange membrane fuel cell (PEMFC) cathodes. Despite tremendous progress in their activity and site-structure understanding, improved durability is critically needed but challenged by insufficient understanding of their degradation mechanisms during operation. Here, we show that FeNxCy moieties in a representative Fe-N-C catalyst are structurally stable but electrochemically unstable when exposed in acidic medium to H2O2, the main oxygen reduction reaction (ORR) byproduct. We reveal that exposure to H2O2 leaves iron-based catalytic sites untouched but decreases their turnover frequency (TOF) via oxidation of the carbon surface, leading to weakened O2-binding on iron-based sites. Their TOF is recovered upon electrochemical reduction of the carbon surface, demonstrating the proposed deactivation mechanism. Our results reveal for the first time a hitherto unsuspected key deactivation mechanism during ORR in acidic medium. This study identifies the N-doped carbon surface as Achilles' heel during ORR catalysis in PEMFCs. Observed in acidic but not in alkaline electrolyte, these insights suggest that durable Fe-N-C catalysts are within reach for PEMFCs if rational strategies minimizing the amount of H2O2 or reactive oxygen species (ROS) produced during ORR are developed.

Document type :

Journal articles

Domain :

Chemical Sciences / Catalysis

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https://hal.archives-ouvertes.fr/hal-01887695
Contributor : Frederic Jaouen <>
Submitted on : Thursday, October 4, 2018 - 1:33:11 PM
Last modification on : Thursday, November 15, 2018 - 2:23:03 PM

Achilles' heel of iron-based catalysts during oxygen reduction in acidic medium

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Achilles' heel of iron-based catalysts during oxygen reduction in acidic medium

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