Serdar Erkan

EFFECT OF GAS DIFFUSION LAYER CHARACTERISTICS AND ADDITION OF PORE-FORMING AGENTS ON THE PERFORMANCE OF POLYMER ELECTROLYTE MEMBRANE FUEL CELLS

The performance of five layer membrane electrode assemblies having different characteristics of gas diffusion layers was determined at 70°C cell temperature and ambient pressure. The maximum power density at 0.6 V was 0.36 W/cm2 for the membrane electrode assembly prepared with the gas diffusion layer having minimum thickness (SGL BC 30 type). On the other hand, the maximum power density at 0.5 V was 0.44 W/cm2 for the membrane electrode assembly prepared with SGL BC 34 type gas diffusion layer. It was found that resistance of a membrane electrode assembly is strongly dependent on gas diffusion layer thickness. Moreover, membrane electrode assemblies prepared with carbon paper gas diffusion layers resulted in higher performance than the assembly prepared with carbon cloth gas diffusion layer. Addition of pore-forming agents, which were ammonium carbonate, ammonium bicarbonate, ammonium sulfonate, and ammonium oxalate, to the catalyst ink lowered the performance.

Ultrasonic Spray Coating Technique for High-Performance PEM Fuel Cell Electrode Manufacturing

The fabrication technique of membrane electrode assembly (MEA) significantly affects the performance and durability of proton exchange membrane (PEM) fuel cell. In the present study, ultrasonic spray coating technique has been used for manufacturing different sizes of gas diffusion electrodes up to 400 cm2. The catalyst ink was composed of 70 wt% catalyst and 30 wt% Nafion in a solution of 1:7 water to 2-propanol. The platinum loading of the electrode has been adjusted to 0.4 mg Pt/cm2. Commercial Pt/C catalysts have been used having different platinum content. Catalyst ink has been sprayed onto the gas diffusion layer using an ultrasonic spray coating instrument operating at 48 kHz. Coating process was fully computer controlled, and it was programmed according to the coating area, spray flow rate, and multiple layer coating. The performance of electrodes has been tested in a single PEM fuel cell. The power densities reached with the new method were 0.53, 0.74, 0.77, and 0.88 W/cm2 for 20, 40, 50, 70 % Pt/C catalyst by keeping the platinum loading constant, respectively. The power density increased 2.5 times compared to “spraying of catalyst ink with air pressure atomizing spray gun”. Uniform thin film has been achieved with ultrasonic coating method. Multiple layer formation retained the porosity of the electrode, impeded flooding on the electrode surface during the coating process, and enhanced transport of reactant during the fuel cell operation. Therefore, high-performance, reproducible, and large area electrodes could be manufactured by ultrasonic spray coating technique.