In the area of Fuel Cell research the catalyst of choice for the Oxygen Reduction Reaction (ORR) is Pt on a C substrate. However the main problem with this and one of the stumbling blocks in making Fuel Cells economically appealing is the high cost of this catalyst. Thus, if it were possible to obtain the required surface activity to maximise the ORR but with less Pt present then the cost of fuel cell production would decrease dramatically. To gain an overview of the overall effect of the Pt agglomerate size on the electrocatalytic activity a study was conducted using high-resolution SECM.

A library of Pt agglomerates was created on a glassy carbon substrate allowing the determination of the effect of the Pt surface area and the size of the formed nanoclusters on the ORR. Analysis was conducted using two similar techniques. The first technique involved scanning the Pt agglomerate with a microelectrode SECM tip with the application of a potential step profile and recording the current with and without an applied substrate potential. The electrochemical images from this study produced information on the catalytic performance of each of the Pt agglomerates. The second technique involved the visualisation of each Pt agglomerate using constant-distance mode SECM in combination with a second potential pulse program. In this pulse program O₂ is firstly produced at the tip then subsequently reduced in the presence and absence of an applied substrate potential providing O₂ reduction competition between tip and sample. This competition reaction is used to elucidate electrochemically the effect of the Pt agglomerate size on the amount of oxygen reduced. The results from this combination of constant-distance mode SECM and O₂ reduction competition reaction provided a detailed image of each of the Pt agglomerates with high spatial resolution combined with a detailed view of the distribution of electrochemical activity over the agglomerate's surface.

Acknowledgement: Financial support from the MWF-NRW "Nachwuchsgruppe Brennstoffzelle" is acknowledged.

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