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The Achilles' heel of iron-based catalysts during oxygen reduction in an acidic medium†
Energy & Environmental Science ( IF 32.4 ) Pub Date : 2018-10-04 00:00:00 , DOI: 10.1039/c8ee01855c Chang Hyuck Choi 1, 2, 3, 4 , Hyung-Kyu Lim 4, 5, 6, 7, 8 , Min Wook Chung 1, 2, 3, 4 , Gajeon Chon 1, 2, 3, 4 , Nastaran Ranjbar Sahraie 9, 10, 11, 12, 13 , Abdulrahman Altin 14, 15, 16, 17 , Moulay-Tahar Sougrati 9, 10, 11, 12, 13 , Lorenzo Stievano 9, 10, 11, 12, 13 , Hyun Seok Oh 4, 18, 19, 20 , Eun Soo Park 4, 18, 19, 20 , Fang Luo 5, 17, 21, 22, 23 , Peter Strasser 5, 17, 21, 22, 23 , Goran Dražić 24, 25, 26, 27 , Karl J. J. Mayrhofer 14, 15, 16, 17, 28 , Hyungjun Kim 4, 5, 6, 7, 8 , Frédéric Jaouen 9, 10, 11, 12, 13
Energy & Environmental Science ( IF 32.4 ) Pub Date : 2018-10-04 00:00:00 , DOI: 10.1039/c8ee01855c Chang Hyuck Choi 1, 2, 3, 4 , Hyung-Kyu Lim 4, 5, 6, 7, 8 , Min Wook Chung 1, 2, 3, 4 , Gajeon Chon 1, 2, 3, 4 , Nastaran Ranjbar Sahraie 9, 10, 11, 12, 13 , Abdulrahman Altin 14, 15, 16, 17 , Moulay-Tahar Sougrati 9, 10, 11, 12, 13 , Lorenzo Stievano 9, 10, 11, 12, 13 , Hyun Seok Oh 4, 18, 19, 20 , Eun Soo Park 4, 18, 19, 20 , Fang Luo 5, 17, 21, 22, 23 , Peter Strasser 5, 17, 21, 22, 23 , Goran Dražić 24, 25, 26, 27 , Karl J. J. Mayrhofer 14, 15, 16, 17, 28 , Hyungjun Kim 4, 5, 6, 7, 8 , Frédéric Jaouen 9, 10, 11, 12, 13
Affiliation
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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 FeNxCy moieties in a representative Fe–N–C catalyst are structurally stable but electrochemically unstable when exposed in an 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 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 H2O2 or reactive oxygen species (ROS) produced during the ORR are developed.
中文翻译：
酸性介质中氧气还原过程中铁基催化剂的致命弱点†
对于催化氧化还原反应，当今，铁-氮-碳（Fe-N-C）材料是替代质子交换膜燃料电池（PEMFC）阴极中铂的最佳候选材料。尽管他们在活动和对站点结构的了解方面取得了巨大进步，但仍迫切需要提高耐用性，但由于对它们在运行过程中的降解机理了解不足，因此面临挑战。在这里，我们表明，当在酸性介质中暴露于主要的氧还原反应（ORR）副产物H 2 O 2中时，代表性的Fe–N–C催化剂中的FeN x C y基团在结构上稳定，但电化学上不稳定。我们发现暴露于H 2 O 2保持铁基催化位点不变，但通过碳表面的氧化降低其转换频率（TOF），从而导致铁基位点上的O 2结合减弱。通过碳表面的电化学还原可回收其TOF，证明了拟议的失活机理。我们的结果首次揭示了在酸性介质中进行ORR时迄今未曾料到的密钥失活机制。这项研究确定在PEMFCs的ORR催化过程中，氮掺杂的碳表面是致命弱点。在酸性而非碱性电解质中观察到的这些见解表明，如果采用合理的策略将H 2 O 2的量降至最低，则耐用的Fe–N–C催化剂对于PEMFC而言是可以实现的。 或在ORR期间产生的活性氧（ROS）被开发出来。
更新日期：2018-10-04
中文翻译：
酸性介质中氧气还原过程中铁基催化剂的致命弱点†
对于催化氧化还原反应，当今，铁-氮-碳（Fe-N-C）材料是替代质子交换膜燃料电池（PEMFC）阴极中铂的最佳候选材料。尽管他们在活动和对站点结构的了解方面取得了巨大进步，但仍迫切需要提高耐用性，但由于对它们在运行过程中的降解机理了解不足，因此面临挑战。在这里，我们表明，当在酸性介质中暴露于主要的氧还原反应（ORR）副产物H 2 O 2中时，代表性的Fe–N–C催化剂中的FeN x C y基团在结构上稳定，但电化学上不稳定。我们发现暴露于H 2 O 2保持铁基催化位点不变，但通过碳表面的氧化降低其转换频率（TOF），从而导致铁基位点上的O 2结合减弱。通过碳表面的电化学还原可回收其TOF，证明了拟议的失活机理。我们的结果首次揭示了在酸性介质中进行ORR时迄今未曾料到的密钥失活机制。这项研究确定在PEMFCs的ORR催化过程中，氮掺杂的碳表面是致命弱点。在酸性而非碱性电解质中观察到的这些见解表明，如果采用合理的策略将H 2 O 2的量降至最低，则耐用的Fe–N–C催化剂对于PEMFC而言是可以实现的。 或在ORR期间产生的活性氧（ROS）被开发出来。
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