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Methanol tolerance of atomically dispersed single metal site catalysts: mechanistic understanding and high-performance direct methanol fuel cells
Energy & Environmental Science ( IF 32.5 ) Pub Date : 2020-08-17 , DOI: 10.1039/d0ee01968b
Qiurong Shi 1, 2, 3, 4, 5 , Yanghua He 1, 2, 3, 4, 5 , Xiaowan Bai 5, 6, 7, 8 , Maoyu Wang 5, 9, 10, 11 , David A. Cullen 5, 12, 13, 13, 14 , Macros Lucero 5, 9, 10, 11 , Xunhua Zhao 5, 6, 7, 8 , Karren L. More 5, 12, 13, 13, 14 , Hua Zhou 5, 15, 16, 17 , Zhenxing Feng 5, 9, 10, 11 , Yuanyue Liu 5, 6, 7, 8 , Gang Wu 1, 2, 3, 4, 5
Affiliation  

Proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are promising power sources from portable electronic devices to vehicles. The high-cost issue of these low-temperature fuel cells can be primarily addressed by using platinum-group metal (PGM)-free oxygen reduction reaction (ORR) catalysts, in particular atomically dispersed metal–nitrogen–carbon (M–N–C, M = Fe, Co, Mn). Furthermore, a significant advantage of M–N–C catalysts is their superior methanol tolerance over Pt, which can mitigate the methanol cross-over effect and offer great potential of using a higher concentration of methanol in DMFCs. Here, we investigated the ORR catalytic properties of M–N–C catalysts in methanol-containing acidic electrolytes via experiments and density functional theory (DFT) calculations. FeN4 sites demonstrated the highest methanol tolerance ability when compared to metal-free pyridinic N, CoN4, and MnN4 active sites. The methanol adsorption on MN4 sites is even strengthened when electrode potentials are applied during the ORR. The negative influence of methanol adsorption becomes significant for methanol concentrations higher than 2.0 M. However, the methanol adsorption does not affect the 4e ORR pathway or chemically destroy the FeN4 sites. The understanding of the methanol-induced ORR activity loss guides the design of promising M–N–C cathode catalyst in DMFCs. Accordingly, we developed a dual-metal site Fe/Co–N–C catalyst through a combined chemical-doping and adsorption strategy. Instead of generating a possible synergistic effect, the introduced Co atoms in the first doping step act as “scissors” for Zn removal in metal–organic frameworks (MOFs), which is crucial for modifying the porosity of the catalyst and providing more defects for stabilizing the active FeN4 sites generated in the second adsorption step. The Fe/Co–N–C catalyst significantly improved the ORR catalytic activity and delivered remarkably enhanced peak power densities (i.e., 502 and 135 mW cm−2) under H2–air and methanol–air conditions, respectively, representing the best performance for both types of fuel cells. Notably, the fundamental understanding of methanol tolerance, along with the encouraging DMFC performance, will open an avenue for the potential application of atomically dispersed M–N–C catalysts in other direct alcohol or ammonia fuel cells.

中文翻译:

原子分散的单金属中心催化剂的甲醇耐受性:机理的理解和高性能直接甲醇燃料电池

质子交换膜燃料电池(PEMFC)和直接甲醇燃料电池(DMFC)是从便携式电子设备到车辆的有前途的电源。这些低温燃料电池的高成本问题主要可以通过使用无铂族金属(PGM)的氧还原反应(ORR)催化剂来解决,特别是原子分散的金属-氮-碳(M-N-C ,M = Fe,Co,Mn。此外,M–N–C催化剂的显着优势是其对甲醇的耐受性优于铂,可减轻甲醇的交叉效应,并具有在DMFC中使用较高浓度甲醇的巨大潜力。在这里,我们通过实验和密度泛函理论(DFT)计算研究了M–N–C催化剂在含甲醇的酸性电解质中的ORR催化性能。分与不含金属的吡啶鎓N,CoN 4和MnN 4活性位点相比,有4个位点显示出最高的甲醇耐受能力。当在ORR期间施加电极电势时,甚至会增强MN 4位上的甲醇吸附。当甲醇浓度高于2.0 M时,甲醇吸附的负面影响变得很明显。但是,甲醇吸附不会影响4e - ORR途径或化学破坏FeN 4网站。对甲醇引起的ORR活性损失的理解指导了DMFC中有希望的M–N–C阴极催化剂的设计。因此,我们通过化学掺杂和吸附相结合的策略开发了一种双金属位Fe / Co–N–C催化剂。在第一个掺杂步骤中引入的Co原子没有产生可能的协同效应,而是充当了去除金属-有机骨架(MOFs)中Zn的“剪刀”,这对于改变催化剂的孔隙率和提供更多的稳定缺陷至关重要。第二吸附步骤中产生的FeN 4活性位点。Fe / Co–N–C催化剂在H 2下显着提高了ORR催化活性,并显着提高了峰值功率密度(502和135 mW cm -2空气和甲醇空气条件分别代表了两种燃料电池的最佳性能。值得注意的是,对甲醇耐受性的基本理解以及令人鼓舞的DMFC性能,将为原子分散的M–N–C催化剂在其他直接酒精或氨燃料电池中的潜在应用开辟道路。
更新日期:2020-10-14
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