A Survey of Size-Selected Subnanometer Catalysts for Fuel Cells

阻碍燃料电池技术进一步商业化的主要问题之一是电池中的贵金属含量。因此，以更低的贵金属含量创造更高的活性表面，即更小的颗粒，是一个至关重要的研究课题。最近用树枝状大分子模板合成的铂亚纳米催化剂(Pt12、Pt28和Pt60)的最新结果表明，与现有的铂/碳催化剂相比，其质量活性高出12倍。选择尺寸的铂团簇的化学合成不允许制备所有所需的团簇尺寸。另一个缺点是树枝状大分子模板不能被去除，这可能会导致催化活性降低。本文综述了从Pt1到Pt20的大小选择的亚纳米铂催化剂。用团簇科学的方法将尺寸选定的“裸”粒子从气相沉积到玻碳电极上，氧还原活性将在超高电压条件下完全通过原位测量来确定，通过旋转环盘电极的非原位测量来确定。为了寻找用于燃料电池的最活跃的氧还原催化剂，将对尺寸选定(单分散)的亚纳米铂团簇的氧还原活性的尺寸依赖关系进行全面的调查。除了简单的活性研究外，最有希望的星系团还将通过循环实验进行长期稳定性研究。利用X射线光电子能谱(XPS)、低能离子散射谱(ISS)和程序升温脱附(TPD)对电催化前后的团簇和电极表面进行研究，将从微米级和纳米级揭示催化剂降解机理的有用信息。

One of the major issues hampering further commercialization of fuel-cell technology is the precious metal content in the cells. Hence creating higher active surfaces at lower precious metal content, i.e. smaller particles, is a research topic of utmost importance. Recent results obtained on size-selected platinum subnanometer catalysts (Pt12, Pt28 and Pt60) synthesized by use of a dendrimer template indicate a 12 times higher mass activity compared to state of the art Pt/C catalysts. The chemical synthesis of size-selected platinum clusters does not allow for a preparation of all desired cluster sizes. Another drawback is that the dendrimer template cannot be removed, which may lead to decreased catalytic activity. Here a survey of size-selected subnanometer platinum catalysts from Pt1 to Pt20 is proposed. The size-selected “naked” particles will be deposited from the gas phase onto glassy carbon electrodes by the means of cluster science and the oxygen reduction activity will be determined by in-situ measurements completely under UHV conditions and ex-situ by rotating ring disk electrode measurements. A complete survey of the size-dependence of the oxygen reduction activity of size-selected (monodisperse) subnanometer platinum clusters will be carried out in order to find the most active oxygen reduction catalyst for fuel cell applications. In addition to simple activity studies the most promising clusters will be subject to long-term stability studies by cycling experiments. The investigation of the clusters and the electrode surface by a combination of X-ray photoemission spectroscopy (XPS), low energy ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD) before and after electrocatalysis will reveal useful information on catalyst degradation mechanisms on the micrometer and the nanometer scale.