Cluster catalysis is of large interest in current research.[1] Due to the strong influence of cluster size on morphology and electronic structure a wide range of catalytic activity and selectivity can be achieved.[2] This can be utilised to minimise the amount of total catalytic material needed and to gain a better understanding of fundamental aspects of catalysis.

To investigate the effect of small Pt-clusters in terms of the hydrogen evolution reaction (HER) clusters are deposited mass-selected employing a quadrupole mass filter by magnetron sputtering. Complex ion optics allow to manipulate the particle beam and to apply the cluster ions on a surface of choice. [3] To achieve a homogeneous cluster coverage the beam profile can be checked in-situ utilising an array of 3x3 measurements fields. Cluster coverages are recorded by monitoring the ion current upon deposition time. Titanium dioxide was used as supporting material since it is a model system for passivation layers which are currently employed on solar cells for solar to hydrogen devices. [4] In addition, the cluster deposition process was controlled by transmission electron microscopy.

First promising results in electrochemistry measurements were achieved using a mass distribution of soft landed Pt-clusters with a size of a couple of tens. The number of platinum clusters was chosen in a way that they should form a thin porous layer. To estimate the layer thickness after deposition photoelectron spectroscopy is employed. Also, this was done to analyse sintering after the electrochemical measurements. The transport of the samples was realized under controlled conditions using a mobile vacuum chamber. The electrochemistry measurements took place under ambient conditions utilising a commercial ZAHNER cell. In 0.1M H₂SO₄ at -0.6V vs RHE a current density of 41.6 mA cm^-2 could be observed. The total mass of the supported platinum within the area of interest (0.502 cm²) was 1.4±0.4 µg resulting in a electric current of 30±8 A mg^-1 platinum. This huge current per mass indicates that a high fraction of the deposited atoms is catalytically active. This is due to the high ratio of surface to bulk atoms in small clusters. Whereas the stability in H₂SO₄ is better than anticipated, only a 3mV drop at 2.5mA over 600s occurs. In 0.1M KOH a loss of 33mV within the same period can be received. After several hours of measurements, some kind of degradation from the surface can be observed. This can be validated in the XPS spectra in an intensity loss of the Pt_4f core line compared to the Ti_2p core line and also in the overall activity for the HER.