| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 100 === This study represents a comprehensive pulse microwave assisted polyol synthesis method to deposit Pt catalyst onto the surface of multiwalled carbon nanotubes (CNTs). Three different catalysts were prepared using three different microwave pulse configuration namely CAT 3-1 (ton : toff = 3s : 1s); CAT.2-1 (ton : toff = 2s : 1s) and CAT 3-2 (ton : toff = 3s : 2s) The microstructure, morphology and Pt loading of the as-prepared catalysts were investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and thermogravimetric analysis (TGA). XRD and HR-TEM results revealed that the CAT 3-2 catalyst possessed the smallest mean particle size of 2.1 nm and most uniform distribution among all the synthesized catalysts. The electrochemical activity and stability of the Pt-CNT electrocatalysts were investigated in 1.0 M H2SO4 using cyclic voltammetry (CV). The results indicates that CAT 3-2 exhibits the highest SESA value and fairly good stability after potential cycling > 1000 cycles as compared to other two catalyst. The order of the catalysts in terms of SESA value was found to be CAT 3-2 > CAT 2-1 > CAT 3-1.
The performance of the as synthesized catalyst for hydrogen oxidation reaction (HOR) was analyzed using single cell proton exchange membrane fuel cell (PEMFC) measurements in a membrane electrode assembly (MEA) with 5 cm2 active area at two different operating temperatures (40°C and 80°C). The as synthesized catalyst constructs the anode electrode and a commercial GDE was the cathode. The maximum power density based on anode loading for all three catalysts were found to be 5.94, 6.67 and 8.60 kW g Pt-1 at 40°C and 6.39, 8.00 and 11.41 kW g Pt-1 at 80°C for CAT 3-1, CAT 2-1 and CAT 3-2, respectively. The overall performance of the catalysts was ordered as CAT 3-2 > CAT 2-1 > CAT 3-2.
Also from these investigations it was found that microwave pulse configuration have a profound effect on the performance of the Pt-CNT catalysts. As the MP factor (ton / toff) increases the bigger particle size and poor uniformity of Pt nanoparticles can be observed on the carbon support which in turn affects the catalytic activity, stability and the maximum power density of the electrocatalyst.
Based on the catalyst characterization results, CV results and single cell performance of three Pt-CNT catalyst fabricated, CAT 3-2 electrocatalyst was selected to test further its activity towards oxygen reduction reaction (ORR) in a single cell PEMFC. The MEA fabricated with 'Homemade Cathode-Commercial Anode' configuration using CAT 3-2 was investigated using single cell system. Also the 'Commercial Anode-Commercial Cathode' MEA was tested. The experimental results revealed that the maximum power density based on cathode loading for these MEAs are 4.90 and 1.60 kW g Pt-1 at 40°C, and 5.45 and 1.90 kW g Pt-1 at 80°C for CAT 3-2 and commercial MEA, respectively. i.e., The CAT 3-2 electrocatalyst performs better compared to the commercial GDE although it has a lower Pt loading then the commercial GDE. The long term durability test of CAT 3-2 MEA also show excellent durability comparable to the commercial MEA.
All the experimental results suggest that pulse microwave assisted polyol synthesis can be utilized as effective catalyst preparation method for synthesizing PEMFC electrocatalyst with improved catalytic activity and stability towards HOR and ORR.
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