Details

Autor(en) / Beteiligte

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

Titel

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

Ist Teil von

• Energy & environmental science, 2018-01, Vol.11 (11), p.3176-3182

Ort / Verlag

Cambridge: Royal Society of Chemistry

Erscheinungsjahr

2018

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• For catalysing 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 FeN x C y moieties in a representative Fe–N–C catalyst are structurally stable but electrochemically unstable when exposed in an acidic medium to H 2 O 2 , the main oxygen reduction reaction (ORR) byproduct. We reveal that exposure to H 2 O 2 leaves iron-based catalytic sites untouched but decreases their turnover frequency (TOF) via oxidation of the carbon surface, leading to weakened O 2 -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 the ORR in an acidic medium. This study identifies the N-doped carbon surface as the Achilles' heel during ORR catalysis in PEMFCs. Observed in acidic but not in alkaline electrolytes, these insights suggest that durable Fe–N–C catalysts are within reach for PEMFCs if rational strategies minimizing the amount of H 2 O 2 or reactive oxygen species (ROS) produced during the ORR are developed.