Research On Triple-phase Interface Of The Ordered Membrane Electrode Assembly In Proton Exchange Membrane Fuel Cell

The ordered membrane electrode assembly(MEA),as the core component of the proton exchange membrane fuel cell(PEMFC),is the key position of redox reaction of the whole PEMFC system.For PEMFC,the cost of MEA accounts for more than half of the entire PEMFC,while the cost of catalyst accounts for about 50%of the entire MEA.In the actual application of PEMFC,in addition to reducing the cost of catalyst,improving the stability of the fuel cell is also the core research of MEA.In order to obtain excellent fuel cell performance with a lower catalyst loading,Nafion array with the larger specific surface area was used to prepare MEA with the ordered catalyst layer in the cathod side.The four close-related work improved the reaction efficiency of the the triple-phase interface of the catalyst layer.The specific researches and conclusions are as follows:1.Well dispersed Nafion array prepared by freeze-drying method to effectively improve the performance of proton exchange membrane fuel cell.In PEMFC,Nafion array membrane with the larger specific surface area and excellent proton conductivity,which is not only used as a proton exchange membrane,but also used for the catalyst loading sites.However,Nafion arrays tend to gather into bundles due to the Nafion array membrane with the large surface tension,which reduces the activity sites of the catalyst loading.The ordered MEA with Nafion array is effective to increase the utilization of Pt catalyst and reduce the cost in PEMFC.In order to gain the ideal performance,the primary step is to make well dispersed Nafion array.However,the pillars in Nafion array are prone to form bundles induced by surface tension of water,resulting in a severe reduction in the specific surface area.In this work,we successfully prepared the well dispersed Nafion array by freeze-drying method,and greatly improved the performance of ordered MEA of PEMFC.Besides,the SEM characterization clearly shows that the Nafion array remains its well dispersed structure even after hot-pressing,and plays its important role in PEMFC running.Furthermore,the PEMFCs tests showed that the peak power density of the Nafion array prepared by freeze-drying is as high as 0.763 W cm-2 when Pt catalyst at the loading 61.4 μg cm-2Pt in cathode catalyst layer,which is better than the peak power density(0.640 W cm-2)of the Nafion array PEMFC prepared by natural drying,and it is also better than the peak power density of the PEMFC prepared with the commercial Nafion membrane(0.360 W cm-2).In addition,the PEMFCs stability tests showed that the PEMFC based on Nafion array prepared by freeze-drying has a longer discharge time than the PEMFCs with Nafion array prepared by natural drying and the commercial Nafion film.Therefore,the freeze-drying method to prepare the well-dispersed Nafion can improve the Pt catalyst utilization rate and enhance the stability of the PEMFC to a certain extent.2.Enhanced triple-phase interface in PEMFC constructed by the proton conductor absorption on Pt catalyst.In this work,Nafion array membrane with the larger specific surface and higher proton conductivity was applied in cathode catalyst layer(CL)to prepare the ordered MEA and the Pt catalyst was filled into the Nafion array by sputtering.However,there is barely proton conductor at the triple-phase interfaces due to the agglomeration of Pt nanoparticles by sputtering.In order to construct the proton conductor at the cathode triple-phase interface,Nafion as the proton conductor was absorbed on the Pt particles on the principle that sulfonic acid is prone to absorb on Pt surface,aiming to improving the proton transferring efficiency.In addition,the performance of PEMFC that made from Nafion absorption on Pt in cathode CL at 61.4μg cm-2 of the Pt loading,the peak power density is as high as 0.843 Wcm-2,which is much higher than that corresponding to Pt without Nafion of 0.710 Wcm-2.Besides,the durability tests showed that PEMFCs performance with Nafion absorption on Pt can work continuously for 100 hours without obvious voltage attenuation,which is more stable than that the bare Pt of 70 h.Therefore,the introduction of proton conductor at the triple-phase interface through Nafion adsorption on the surface of the catalyst Pt by the self-assembly,not only improve the utilization rate of Pt,but also enhance the stability of the PEMFC.3.Completed triple-phase interface with the electron conductor doping by the interface regulation to improve the performance in PEMFC.The application of Nafion array in the MEA not only improves the proton transfer efficiency,but also provides a huge specific surface area and abundant reactive sites for the cathode ORR.However,the ordered catalyst layer prepared by Nafion array has a certain spatial resistance to the collector layer and the existence of the array results in that the electron transfer path of the three-phase interface of the catalyst layer can only be transferred through the tip of the array,which increases the electron transfer resistance.Therefore,in this chapter,the continuous catalyst is prepared by doping the electron conductor carbon nanotubes on the cathode catalytic layer by spraying,and the electron transfer efficiency of the three-phase interface of the cathode catalytic layer is improved.Besides,the PEMFC test results showed that the PEMFC peak power density is as high as 1.2 W cm-2 with the electron conductor doping into cathode catalyst triple-phase interface when Pt loading is at 48 μg cm-2.In summary,the introduction of electron conductor carbon nanotubes in the catalyst layer increases the continuity of the catalyst,improving the electron transfer efficiency at the three-phase interface of the catalyst layer and achieving the excellent fuel cell performance at the low catalyst loading.4.Research on water management in PEMFC with the conical Nafion array.In this work,the conical array Nafion membrane was applied to fabricate the ordered MEA with good performance in water management.First,we use the Nafion array with the strong hydrophobic surface,which is conducive to the rapid detachment of water from the surface of Nafion array membrane.Thus,the conical Nafion array was used in the cathode catalyst layer,which is conducive to the timely discharge of the product water,to effectively solve the problem of flooding in the cathode catalyst layer.In addition,the cone-array Nafion was applied to the anode self-humidification in PEMFC based on the phenomenon of water transport across the membrane under the self-driving by the surface charge gradient of the cone-shaped Nafion array.Besides,we preliminarily visualized water transport across the membrane in a cone-shaped array Nafion membrane by optical microscopy imaging.In conclusion,the conical array has a great application prospect in the management of water in PEMFC because of its ordered structure and strong hydrophobicity.