Methanol tolerance of atomically dispersed single metal site catalysts: mechanistic understanding and high-performance direct methanol fuel cells
Methanol tolerance of atomically dispersed single metal site catalysts: mechanistic understanding and high-performance direct methanol fuel cells
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DOI：
10.1039/d0ee01968b
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发表时间：
2020-10-01
影响因子：
32.5
通讯作者：
Wu, Gang
中科院分区：
文献类型：
--
作者：
Shi, Qiurong;He, Yanghua;Wu, Gang
质子交换膜燃料电池(PEMFCs)和直接甲醇燃料电池(DMFCs)是从便携式电子设备到汽车的很有前途的电源。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催化剂的一个显著优势是它比铂具有更好的耐甲醇能力，这可以缓解甲醇的交叉效应，并为在DMFC中使用更高浓度的甲醇提供了巨大的潜力。本文通过实验和密度泛函理论(DFT)计算研究了M-N-C催化剂在甲醇酸性电解液中的ORR催化性能。与不含金属的吡啶N、CoN4和MNN(4)活性中心相比，FeN(4)中心显示出最高的耐甲醇能力。在ORR过程中，当施加电极电位时，甲醇在MN(4)位上的吸附甚至得到加强。当甲醇浓度高于2.0M时，甲醇吸附的负面影响变得明显，但甲醇吸附不会影响4E(-)ORR途径，也不会对FeN(4)中心造成化学破坏。对甲醇引起的ORR活性损失的认识指导了DMFC中有前景的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原子并没有产生可能的协同效应，而是在金属有机骨架(MOF)中充当了去除锌的“剪刀”，这对于改善催化剂的孔隙率和提供更多的缺陷来稳定第二个吸附步骤中产生的活性FeN(4)位是至关重要的。Fe/Co-N-C催化剂显著提高了ORR催化活性，在氢气-空气和甲醇-空气条件下分别提供了502和135 mW cm(-2)的峰值功率密度，表现出两种类型燃料电池的最佳性能。值得注意的是，对甲醇耐受性的基本了解，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一条途径。
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 electrolytesviaexperiments and density functional theory (DFT) calculations. FeN(4)sites demonstrated the highest methanol tolerance ability when compared to metal-free pyridinic N, CoN4, and MnN(4)active sites. The methanol adsorption on MN(4)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 FeN(4)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 FeN(4)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 H-2-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.