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Research on the Activation of PEMFC and Design and Optimization of Anode Catalyst Layer for CO Tolerance

Author: YangChangXing
Tutor: HuMingRuo
School: Shanghai Jiaotong University
Course: Power Machinery and Engineering
Keywords: PEMFC three-step activation method anode CO-tolerance catalyst layer Pt-Ru/C electrocatalyst EIS
CLC: TM911.4
Type: Master's thesis
Year: 2012
Downloads: 61
Quote: 1
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Abstract


Proton Exchange Membrane Fuel Cell （PEMFC） is a promising power device for electrical vehicles （EV） and distributed power stations due to its advantages, such as high efficiency, no pollution, low temperature operation, quick response, etc. The ideal anode fuel for PEMFC is pure H2, but there still exist many technical problems. Reformate gas from carbonate used as anode gas can solve some of these problems and promote PEMFC’s development and application. This paper aims at designing and optimizing the anode catalyst layer of PEMFC to improve its comprehensive performances under reformate gas, the main contents are as follows.Firstly, we develop an improved activation process using a three-step method in conjunction with a cooling-after-a-stop technique for MEA. Detail information and rationale for each step is presented along with intermediate results. By carefully optimizing the operation temperature of each step of the activation procedure, the performance of a newly fabricated fuel cell can be increased and the variability decreased. In addition, we show that the cooling-after-a-stop technique can stabilize and improve fuel cell performance. The improved three-step method results in a maximal current density of 1008 mA/cm2, an increase of 14.5%, compared to the 880 mA/cm2 achieved by the one-step method.Secondly, we optimize the anode catalyst layer by electrochemical testings under （H2/air） or （H2+CO/air）,results show:（1）1.5mgPt/cm2 is the optimal loading for electrocatalyst Pt-Ru/C,loading lower than 1.5mgPt/cm2 results in low efficiency for the electrochemical reaction; loading higher than 1.5mgPt/cm2 increases the thickness of the catalyst layer so that the effect of mass transfer of fuel gas decreases, meanwhile too much loading of catalysts increase the costs.（2）20% Nafion is the optimal content within the anode catalyst layer, Nafion content lower than 20% isn’t enough for H+ transfer; Nafion content higher than 20% blocks the transfer of gases and charges.（3）PEMFC can reach 429.9mW/cm2 under 20ppmCO; PEMFC can run stably for at least 5h under 25ppmCO with its voltage higher than 0.59V（@480mA/cm2）.In the end, performances of PEMFC under reformate gas are researched, mainly on its performances under H2+CO2、H2+CO、H2+CO+CO2 and H2+CO+CO2+CH4 by changing operation parameters, such as temperature, humidity, current density. etc. Results show:（1）The effect of CO2 on PEMFC is closely related to CO2 content and the running time, high CO2 content affect the mass transfer of H2, the poisoning effect of little CO caused by RWGS reaction in short time is negligible. （2）The poisoning effect of CO on PEMFC increases with the CO content increasing especially under the high current density. Increasing the cell temperature （with fixed humidification temperatures） helps to improve its CO tolerance performance, but high cell temperature decreases the relative humidity of fuel gases so that the water content within the Nafion （ both in the membrane and catalyst layer） decrease, so the transfer of H+ is greatly hindered. The optimal operation temperatures are 60oC for humidification （both anode and cathode） and 70oC for cell.（3）PEMFC can run stably with high performances under reformate gas, it can reach 385.9mW/cm2 in 75%H2+20%CO2+5%CH4+15ppm CO.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Chemical power sources,batteries, fuel cells > Fuel cell
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