Sputtered cathodes for polymer electrolyte fuel cells: insights into potentials, challenges and limitations

The level of Pt loadings in polymer electrolyte fuel cells (PEFC) is still one of the main hindrances for implementation of PEFCs into the market. Therefore, new catalyst and electrode preparation methods such as sputtering are of current interest, because they allow thin film production and have many cost saving advantages for electrode preparation. This paper summarises some of the most important studies done for sputtered PEFCs, including non carbon supported electrodes. Furthermore, it will be shown that an understanding of the main morphological differences between sputtered and ink-based electrodes is crucial for a better understanding of the resulting fuel cell performance. Especially, the electrochemical surface area (ECSA) plays a key role for a further increase in PEFC performance of sputtered electrodes. The higher surface specific activities i(k,spec) of sputtered compared to ink-based electrodes will be discussed as advantage of the thin film formation. The so- called particle size effect, known in literature for several years, will be discussed as reason for the higher i(k,spec) of sputtered electrodes. Therefore, a model system on a rotating disc electrode (RDE) was studied. For sputtered PEFC cathodes Pt loadings were lowered to 100 μg(Pt)/cm(2), yet with severe performance losses compared to ink-based electrodes. Still, for Pt sputtered electrodes on a carbon support structure remarkably high current densities of 0.46 A/cm(2) at 0.6 V could be achieved.