A Survey of Size-Selected Subnanometer Catalysts for Fuel Cells

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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.