Design And Optimization Of Proton Exchange Membrane Fuel Cell Short Stack

Proton exchange membrane fuel cell（PEMFC）is a clean energy technology that can directly convert chemical energy into electrical energy.With the advantages of low operating temperature,high energy conversion efficiency,fast start-up and high energy density,it has received extensive attention from countries all over the world.However,the high cost of construction has also become the main factor restricting the development of PEMFC.In this thesis,the short stack of proton exchange membrane fuel cell is constructed and assembled,and the operating conditions are optimized to achieve the best output performance.The use of plastic to replace the traditional bipolar plate materials and the preparation of membrane electrode assembly with gradient catalyst layer can reduce the cost and improve the output performance obviously.The main research results are as follows:（1）Design and build 2-5 segments of PEMFC short stacks with graphite as the bipolar plate material,and the effective area of each single cell is 4 cm².By changing the test conditions such as intake pressure,intake flow,test temperature,cathode relative humidity,anode relative humidity to optimize the output performance and make it reach the optimal value.Among them,the highest output performance of the 4 segments of PEMFC short stack can reach 19.2 W,and the highest output performance of the 5 segments of PEMFC short stack can reach 25.78 W.In addition,PTFE bipolar plates were used instead of graphite bipolar plates to build a three-section proton exchange membrane fuel cell short stack.In addition,poly tetra fluoroethylene（PTFE）bipolar plates were used instead of graphite bipolar plates to build a 3 segments of PEMFC short stack.Firstly,the PTFE bipolar plates only retain the function of supporting and transmitting gas,and add cheap copper（Cu）conductive tape covered the top of the flow channel to play the role of conduction and current collection.The maximum output power of the first method can reach 11.92 W.Secondly,putting the conductive tape on the upper edge of the flow field on both sides of the bipolar plate and extending the gas diffusion layer so that the gas diffusion layer can be connected with the conductive tape,and they can complete the conductive effect together.The highest power can reach 7 W.The above two solutions can give a new perspective to reduce the cost of PEMFC short stacks using cheap plastic material bipolar plates and conductive tape.（2）After selecting the most suitable commercial gas diffusion layer and mass ratio of ionic polymer to carbon（I/C）of catalyst ink,a membrane electrode assembly with two-layer gradient cathode catalyst layer is prepared using commercial platinum loaded on carbon（Pt/C）with a Pt loading of 60.0%and 37.7%.The optimal ratio is obtained by testing the difference in the amount of catalyst used in the two layers.When the catalyst loading of the two layers are same,the highest output performance can reach 1.19W/cm².On this basis,commercial Pt/C with a platinum loading of 20.0%was introduced to prepare a three-layer gradient cathode catalyst layer membrane electrode assembly which can further reduce the amount of precious metal while maintain or improve the PEMFC performance.The peak power of three layer gradient membrane electrode assemblies with the loading of 0.3 mg _Pt/cm²,0.15 mg _Pt/cm² and 0.125mg _Pt/cm² can reach 1.45 W/cm²,1.31 W/cm² and 1.32 W/cm².All the peak power densities of above three gradient membrane electrode assemblies are higher than those of single-layer membrane electrode assemblies with same loading prepared by traditional methods whose peak power are 1.25 W/cm²,1.20 W/cm² and 1.22 W/cm².Since the amount of Pt used in the cathode catalyst can be reduced and the performance can be well improved,the production cost of the fuel cell stack can be reduced efficiently.