Study On Fabrication And Performance Of Proton Exchange Membrane Fuel Cell Electrodes

As global energy and environmental issues become critical, fuel cell, which is high efficient without limit of carnot cycle, environmental friendly and high reliable, is considered as the most important new energy technology in the21st century. The proton exchange membrane fuel cell (PEMFC) is promising in application to aerospace, transportation, stationary power station, etc. In recent year, PEMFC has been developed vigorously, kilowatt fuel cell technology has been close to commercialization, but the high materials’cost, especially the catalyst cost is still the main issue for wide commercialization. Therefore, the PEMFC research becomes focus on reducing the cost of materials, especially the cost of catalyst, and optimization of the membrane electrode assembly (MEA) preparation technology.Based on the ultrasonic spray method, the MEA preparation process was studied, and the uniform, stable catalyst layer and micro porous carbon layer were successfully made. The ultrasonic spraying process parameters is set as:25<H<45mm,80<S<120mm/s,20<P<40psi, R=1ml/min.0.05mgcm-2anode platinum loading MEA was successfully prepared by ultrasonic spray method. When the cathode platinum loading is0.55mgcm"2, its unit geometric area performance of0.05mgcm-2anode platinum loading MEA is almost equal to that of the0.30mgcm-2anode platinum loading MEA under the same test conditions (cell temperature is50℃, hydrogen and air are not humidified,). However, the power density per anode platinum mass loading of0.05mgcm-2MEA is7.38Wmg-1. which is nearly six times higher than that of the0.30mgcm-2MEA. It clearly shows that ultrasonic spraying method can obtain MEAs with homogeneous electrode surface, and effectively improve the catalyst’s utilization. This guarantees the preparation of MEA with low platinum loading.Preliminary study results show that the surface morphology of catalyst layer, water distribution at the interface between the catalyst surface and ultra-thin Nafion film, and catalyst dispersion play important role on MEA performance. By adjusting alcohol water ratio of the catalyst slurry, different catalyst surface morphology can be obtained. Compared to the150%standard solid content catalyst slurry, the main particle size is about290nm in50%standard solid content catalyst slurry, and the slurry is stable for a long time. By further adjusting alcohol water ratio, more homogeneous catalyst layer was obtained as confirmed by SEM and better performance of the given MEA was achieved too. For example, when the cathode and anode platinum loadings are0.55mgcm-2and0.10mgcm-2respectively, and the surface morphology is similar between50%and150%standard solid content catalyst slurry MEA, the performance of the50%MEA is as high as412mWcm-2, which is1.3times higher than the150%MEA.H2depletion test is first designed and used to discuss the water effect in the MEA under real fuel cell test condition. We found that water may still accumulate at the interface between the catalyst surface and ultra-thin Nafion film even without any humidification, which is an important reason for the dramatic performance drop of the MEA under dead-end anode (DEA) mode discharging at constant current density for long time.. This study highlights the need for further research into understanding the water transport properties of the ultrathin Nafion ionomer film (<60nm) and the water diffusion behavior at the interface between the ultra-thin Nafion film and catalyst surface under real fuel cell test conditions which is the key factor to understand electrochemical process in the MEA.