Study On The Material Transport Properties Of Platinum-based Nanoporous Metal Electrodes In The Catalytic Layer Of Proton Exchange Membrane Fuel Cells

With the current energy shortage and environmental pollution problems becoming more and more serious,the development of new sustainable and environmentally friendly energy conversion devices has become a current research hotspot.Fuel cell（FC）is an electrochemical device that can use hydrogen as fuel.It has broad development prospects because it does not produce substances that pollute the air during the process of converting chemical energy into electrical energy.After years of exploration,one strategy to achieve the goal of reducing the cost of proton exchange membrane fuel cells is to reduce the platinum（Pt）load from high to lower without sacrificing power density.Certain results have been achieved.Even so,the traditional commercial Pt/C catalyst still does not meet our requirements for catalyst loading,performance and stability.Therefore,we need to design and develop electrodes with high power density,high stability,and low Pt load to meet our requirements.The nanoporous metal film catalyst has the characteristics of high specific surface area,bi-continuous structure,high porosity,high electronic conductivity,ultra-thin thickness,self-supporting,etc.,making it attract attention in the development of fuel cell technology.Compared with traditional commercial Pt/C catalysts,due to the unique structure of the nanoporous metal film catalyst,the problem of corrosion of the carbon support is overcome,and the structural collapse caused by the corrosion of the support is further improved,which affects the oxygen and water transmission in the fuel cell.In this thesis,by designing and adjusting the structure of platinum-based nanoporous metal electrodes used in fuel cells,it meets the requirements of reducing platinum loading without losing fuel cell performance,achieving higher oxygen transmission in the fuel cell and improving water management issues.The specific research content is as follows:（1）The active role of ultra-thin catalyst layer based on platinum-modified nanoporous gold（NPG-Pt）in improving fuel cell performance and oxygen transmission was studied.The results show that the construction of the ultra-thin NPG-Pt catalytic layer can significantly improve the performance of the ultra-low Pt proton exchange membrane fuel cell.In addition,this structure is more conducive to the drainage of water from micron-sized pores.For fuel cells,liquid water flows smoothly through the cathode,which greatly reduces the resistance of oxygen in the catalyst layer of the ultra-low platinum proton exchange membrane fuel cell.Facts have proved that the NPG-Pt ultra-thin catalytic layer facilitates the entry of oxygen and the discharge of water,and improves the oxygen transport capacity of the catalytic layer.Compared with commercial Pt/C catalysts,it has a smaller oxygen transmission resistance.Furthermore,we prepared an ultra-thin NPG-Pt catalytic layer with a hierarchical pore structure.Under the ultra-low Pt loading of the fuel cell cathode（about 50.0μg）,the oxygen transmission resistance of the NPG-Pt ultra-thin catalytic layer with this hierarchical pore structure is 4.7 s/cm,and the power density of the fuel cell reaches 105 m W cm^-2.The platinum-modified nanoporous gold（NPG-Pt）ultra-thin catalytic layer with a hierarchical pore structure is used for ultra-low Pt proton exchange membrane fuel cells with nanoporous metal electrodes with high oxygen transport capabilities.（2）Study the improved water management when the ultra-thin nano-porous metal film catalyst is used in the catalytic layer of the proton exchange membrane fuel cell.A comparative analysis of the fuel cell performance with the presence of gaseous water and liquid water in the fuel cell when the platinum-modified nanoporous metal film catalyst is used as the fuel cell catalytic layer.The NPG-Pt catalyst was heat treated at different temperatures to explore its electrochemical performance and battery performance.We found that when using NPG-Pt as the fuel cell cathode catalyst layer,the platinum loading is 39.3μg cm^-2,the fuel cell power density at80°C is 693 m W cm^-2,and the fuel cell power density at 105℃reaches 910 m W cm^-2,which is an improvement of 23%compared with fuel cell performance at 80°C.The fuel cell power density at 80°C is 731 m W cm^-2,while the platinum loading of the commercial Pt/C catalyst is 45.0μg cm^-2,and the fuel cell power density at 105°C is only 801 m W cm^-2.These results show that after we appropriately increase the operating temperature of the fuel cell,when NPG-Pt is used as the fuel cell catalyst layer,it can significantly improve the mass transfer polarization loss caused by the water flooding of the cathode catalyst layer due to the hydrophilic characteristics of the membrane surface.At higher temperatures,the water in the fuel cell mainly exists in gaseous form,which facilitates the transfer of substances in the fuel cell,further improves the fuel cell water management problem,and improves the performance of the fuel cell.