Studies Of The Microstructure Of Membrane Electrode Assembly For Direct Methanol Fuel Cells

Direct methanol fuel cells (Direct Methanol Fuel Cell, DMFC) is viewed as a promisingpower source for protable devices due to its simplicity in structure, convenience in fuelstorage/refilling, environmentally friendly, and higher energy density (theoretical energydensity4800Wh.L-1) of the system, The structure of membrane electrode assembly (MEA) isessential for the performance and stability of direct methanol fuel cell (DMFC). In thisdissertation, the relationship between the structure and the performance of MEA was studied,aiming at reducing the polarization losses in the MEA. The main research results are asfollows:1. Three novel gas diffusion layers (GDLs) are fabricated by introducing CeO2nanoparticles into the different region of micro-porous layer (MPL). In oder to research themechanism of mass transfer of oxygen, performances of the cells with the novel cathodeGDLs and that with conventional GDL are examined by direct methanol fuel cells (DMFCs)single cell performance tests. The tests results show that the introduction of cerium oxide canimprove the oxygen transport in the cathode GDL under low stoichiometric ratio (<4) feedingrate, and the improvement is more significant under higher temperature. Under the air feedingrate of2stoichiometric ratio at80oC, the DMFCs with the novel cathode GDLs aresignificantly increased the cell voltage compared to that with conventional GDL, while theimprovement of the mass transfer of oxygen by CeO2introducing in the microporous layerclose to the catalytic layer side and close to the side of the flow channel. The GDL modifiedwith CeO2in MPL inner increases the cell voltage by49%(@150mA/cm), and improves thesingle cell’s peak power density by64%. Secondly, the GDL modified with CeO2in MPLouter increases the cell voltage by49%and improves the single cell’s peak power density by46%.2. Methanol mass transfer coefficient is based investigate the influences of the variousfactors on the mass transfer coefficient, including the preparation for the anode catalyst layer,the content of catalyst and kinds of carbon and carbon loading of the microporous layer. Theresults show that the load within the range investigated (7.0~14.0mg cm-2), under the airfeeding rate of3stoichiometric ratio at80oC, when the methanol feed is1.0mol L-1, theDMFCs with PtRu black catalyst layer containing an amount of9.2mg cm-2has optimalperformance, the single cell’s peak power density by126mW cm-2, it has the best gas andliquid transfer properties; At the same catalyst loading conditions (PtRu black,14.0mg cm-2), compared with single anode catalyst layer, the single cell assembled with the double anodecatalyst layer has the maximum peak power density of up to136mW cm-2. The double anodecatalyst layer has higher mass transfer coefficient of methanol, and is beneficial totransmission of methanol on the interface catalyst layer/distribution layer; Six differentanode gas diffusion layers (GDLs) are fabricated by adopting VulcanXC-72R and BlackPearls2000, and modifing content of two carbon in microporous layer, compared permeableand ventilate of the anode diffusion layer microstructure, then, the effects of gas and liquidmass transfer of the anode diffusion layer microstructure are detected by concentration of CO2means on DMFC single cell performance. Experimental results show that, compared to theXC-72R, AB carbon has low porosity and high total porosity, which improved porosity andpermeability of anode GDLs, within the range investigated (0.5~1.5mg cm-2), the anodeGDL with AB (1.0mgcm-2) has the best gas and liquid transfer properties, DMFC isassembled with optimal battery performance, which has low methanol permeation, dischargesthe most CO2at per unit time and has maximum mass transfer coefficient of methanol.