Graphitic, porous carbons for catalysts with increased stability in the proton exchange membrane fuel cell

质子交换膜燃料电池(PEMFC)被认为对可持续能源的成功利用非常重要，因为它能够将可持续产生的氢气转化为电能。该技术面临的挑战主要是提高电催化剂的活性和稳定性。这一关键部件通常由以碳材料为基础的催化剂载体组成，活性金属(例如铂)分散在其上。在过去的几年里，通过优化活性成分的结构，例如以PtNi等金属合金的形式，可以显著提高这些催化剂的活性。催化剂的稳定性主要受碳载体的限制。使用非碳载体材料可以缓解碳载体固有的一些缺点，例如抗氧化性低。然而，这些材料还会带来其他缺点，比如导电性差。最近，人们报道了用多孔空心石墨球作为电催化剂载体时的一种非凡的稳定性。稳定的原因是内部孔隙率、大小类似于分散的铂颗粒的介孔以及碳材料的石墨化结构的组合。与通常使用的含有外部孔洞的炭黑不同，这些新型支撑体似乎将活性金属‘捕获’在孔洞内。这表明碳载体的稳定性可以提高到令人满意的水平。在这项建议中，所描述的发现将被应用于开发用于稳定的PEMFC催化剂的具有内孔的新型介孔、石墨化碳载体。发展的基础是碳化物的反应提取得到的碳化物衍生碳(CDC)，而孔结构和石墨化程度等关键参数可以通过碳化物前体和提取温度的选择来调整。得到的碳非常纯净，材料性能可以获得重复性很高的材料。初步工作表明，在1200°C以上的提取温度下可以获得介孔和石墨炭，这将在项目中用于改变CDC基碳载体的石墨化程度和孔径大小。此外，还应开发一种在这些载体上沉积铂的方法，从而使金属在孔隙系统中均匀分散。随后，铂团簇将被烧结到气孔的大小，以允许“捕获”。所得到的催化剂将通过半电池测量来测试其对氧还原反应的活性和稳定性。进一步的见解将通过用IL-TEM对原始的和使用过的电催化剂进行表征来获得。在外部合作中，优化后的材料将在单堆燃料电池实验中进行研究，以确保其在实际条件下的长期稳定性。

The proton exchange membrane fuel cell (PEMFC) is believed to be of great importance for a successful usage of sustainable energy, because it enables the conversion of sustainably produced hydrogen into electricity. Challenges for this technology are mainly increasing activity and stability of the electrocatalyst. This key component usually consists of a catalyst support based on carbon materials on which the active metal (e.g. platinum) is dispersed. In the last years the activity of these catalysts could be considerably increased by optimizing the structure of the active component, for instance in the form of metal alloys like PtNi. The stability of the catalyst is mainly limited by the carbon support. Employing non-carbon support materials can mitigate some of the disadvantages carbon supports inherit, e.g. the low stability against oxidation. Yet these materials give rise to other drawbacks like a poor electrical conductivity. Recently an extraordinary stability was reported when employing porous hollow graphitic spheres as electrocatalyst support. Reason for the stability is seen in the combination of inner porosity, mesopores with size similar to the dispersed platinum particles and the graphitic structure of the carbon material. In contrast to the typically used carbon black containing outer porosity these novel supports seem to 'trap' the active metal inside the pores. This shows that the stability of carbon supports can be increased to a satisfying level. In this proposal the described findings shall be applied to develop new mesoporous, graphitic carbon supports with inner porosity for stable PEMFC catalysts. The development will base on Carbide Derived Carbons (CDC) that are obtained by the reactive extraction of carbides, while crucial parameters like pore structure and degree of graphitization can be adjusted by the choice of carbide precursor and extraction temperature. The resulting carbon is very pure and the material properties can be obtained with a high reproducibility. Preliminary work showed that mesoporous and graphitic carbons are obtained at extraction temperatures above 1200 °C, which shall be employed within the project to vary the degree of graphitization and pore sizes of CDC based carbon supports. Furthermore a method for the deposition of platinum on these supports shall be developed, which result in homogeneous dispersion of the metal within the pore system. After Subsequently, the platinum clusters will be sintered to the size of the pores to allow for 'trapping'. The resulting catalysts will be tested regarding their activity and stability for the Oxygen Reduction Reaction with half-cell measurements. Further insights will be obtained by characterization of the pristine and used electrocatalysts with IL-TEM. In external cooperation optimized materials resulting will be studied in single stack fuel cell experiments for their long-term stability under realistic conditions.