Effect of Nafion and platinum content in a catalyst layer processed in a radiofrequency helicon plasma system

A helicon plasma sputtering system is used to deposit small amounts of platinum on microporous carbon support composed of Vulcan XC 72 carbon particles (known as gas diffusion layer GDL) to form Pt catalysed electrodes for proton exchange membrane fuel cells (PEMFC). Electrodes with low Pt loading are prepared, assembled in custom-made membrane electrode assemblies (MEAs) and tested for the hydrogen oxydation and the oxygen reduction. Initially, the Nafion loading spread on these plasma prepared electrodes is optimized by measuring the MEA performance. It is found that the optimum Nafion loading is 1 mg cm for an electrode previously covered with 0.1 mgPt cm using the helicon plasma system. For a commercial electrode prepared by ink-processes with 0.5 mgPt cm, the optimized Nafion loading is 2 mg cm. Using the respective optimized Nafion loading, the electrical performance of the custom-made MEA with one plasma prepared electrode (either anode or cathode) is compared with that of a reference MEA from Electrochem Inc. (Pt loading per electrode of 0.5 mg cm and maximum power density of 425 mW cm) without gas humidification. The custom-made MEA fitted with an anode covered with 0.005 mgPt cm leads to the same performance than that of the reference MEA at low current density (< 500 mA cm) and high gas backpressure (3 bar). This result indicates that the catalyst utilization efficiency in the plasma prepared anode is 100 times higher than that in the commercial anode (85 kW gPt vs 0.85 kW gPt). For plasma prepared cathodes with 0.1 mgPt cm, the cathodic Pt utilization efficiency is 2.7 kW gPt, which is 3 times higher than that obtained in the commercial cathode.