The Study Of Preparing Proton Exchange Membrane Fuel Cell Electrodes With Extremely Low Pt Loads By The Ultrasonic-spray Technique

In today’s society, energy and environment problems become the focus of attention. Mining and utilization of traditional fossil energy polluted the environment and caused energy crisis, even causing the outbreak of war between the nations. Energy is the power and source of the sustainable society, the exploitation of clean and renewable energy technology is a priority. There are certain advantages of proton exchange membrane fuel cell(PEMFC) in the field of new energy: high energy conversion rate without limitation of carnot cycle; produced into water which is clean; low working temperature; long working time; high stability and so on. The cell is promising in application to aerospace, military equipment, automobile, power station, etc. So PEMFC becomes the hot spot of various countries’ scholars. At present, the high preparation cost is the main obstacle which limits its commercialization, we can synthesize new types of catalysts and optimize the preparation technology of membrane electrode assembly(MEA), which is aimed to reduce catalyst Pt loading in order to lower the MEA production cost.We mainly studied how to optimize the MEA preparation. Ultrasonic spraying technology, can secondly disperse the slurry in the preparation of membrane electrode gas diffusion layer and catalyst layer, which ensures the uniformity of thin layers and particle dispersion under the best spraying process parameters. On this basis, we get the optimum carbon loads of the membrane electrode gas diffusion layer and the most suitable catalyst composition proportion. The optimum carbon loads are 1.5 and 2.0 times standard carbon loads, under which the catalyst slurry can adhere to the electrode effectively and mass transfer in the reaction process can proceed smoothly. Catalysts are highly dispersed using 30% standard solid content catalyst slurry. The catalyst layer structure is good to increase the active zone area and improve the utilization rate of Pt.We prepared successfully the MEA with extremely low Pt loads under the mature process. When the anode and cathode Pt loadings are 0.05 and 0.15 mgcm-2, the highest power density is up to 464 mWcm-2 and the power density per platinum mass is up to 3.09 Wmg-1(the Tcell is 50℃ and two polar gases are not humidified), which is 3.6 times higher than that of the 0.55 mgcm-2 MEA. What’s more, the MEA perform well under the simulated automotive work environment. Its power density and power density per plantinum mass can be up to 788 m Wcm-2 and 3.94 Wmg-1. Besides, it also has a wide range of humidity adaptability. Above all, the MEA with extremely low Pt loading has great application prospect and commercial value.N2 permeation experiment is first designed to explain how the N2 and water effect the cell performance. By the experimental results, when the cell is working under dead-end anode mode, water distribution in MEA is the main reason which leads to the decrease of the reversible cell voltage. If we explore Nafion ultrathin film properties and the diffusion and transfer mechanism of water in it from the microscopic view, we will deepen the understanding of the electrochemical process in MEA.