| Proton Exchange Membrane Fuel Cell (PEMFC) is a device that directly converts the chemical energy of the fuel and oxidant into electrical energy. It is recognized as the most promising power generation technology in the21st century because of it’s high efficiency, low emission, simple structure, et al. Bipolar plate is a critical component of the PEMFC, which distributes fuel and oxidant to the membrane electrode and provides electronic connection between single cells. It’s quality directly affects the output power and life time of the cell stack, and it’s cost accounts for about40percent of the total cost of a cell stack, while the high cost of FC is a key obstacle to its wide application.Therefore, searching materials and manufacturing methods for high performance and low cost bipolar plate has been very important. With the above background, new materials and manufacturing methods for bipolar plates are explored in this study.The composite bipolar plates have been preparated firstly using of synthetic graphite and phenolic resin in this article. The preparation technology of synthetic graphite/phenolic resin composites was studied preliminarily. The influences of the raw material configuration, molding technology and heat treatment process on the performance of bipolar plates were investigated, and the forming molding technology of the composite bipolar plates was established. Research results show that the electrical property and mechanical property of bipolar plates preparated using synthetic graphite as conductive fillers are both low, and it can not meet the actual application requirements. On this basis, the author screened graphite raw materials and the mix method, and the natural graphite/phenolic resin composites was preparated using natural graphite as conductive aggregates and using ultrasound decentralized methods. The preparation technology of the composite bipolar plates forming process and heat treatment process was studied detaily. Research results indicate that the performances of bipolar plates preparated using the natural graphite were improved compared to those preparated using the synthetic graphite, and the conductivity and flexural strength are increased to3times respectively. Using ultrasound dispersion technology, composites components are mixed more uniform, and the comprehensive performance of composite bipolar plates are greatly improved. The flexural strength of composite bipolar plates increases and the conductivity decreases with increase of resin content.and the addition of carbon black and curing temperature have the optimal value. The influences of molding pressure and time on the performance of bipolar plates is the same. With the increase of molding pressure and the extension of holding time, conductivity and flexural strength of bipolar plates are increasing, and the suitable forming pressure is about200MPa, the holding time is1minute.For the natural graphite/phenolic resin composite bipolar plates have low mechanical performance, carbon fiber and coupling agent were used to reinforce composites strength. The influences of carbon fiber content, different carbon fiber processing methods, coupling agent species, coupling agent content and coupling agent added methods on the electrical conductivity and mechanical properties of composite were investigated respectively. Research results show that the conductivity of composite bipolar plates is decreased with the incease of carbon fiber content, the flexural strength is increased firstly and then decreased. Carbon fiber being liquid handling at the same temperature, the conductivity and flexural strength of bipolar plates increase with processing time increases, and at the same handing time, electrical conductivity and flexural strength of bipolar plates increase as the processing temperature increase. Adding Coupling agent, mechanical property of bipolar plates is effectively improved. Using different types coupling agent and a different adding way, the coupling agent content has the optimal value.On the basis of the study on the natural graphite/phenolic resin composite bipolar plates, the binder resin has been improved, and we used phenolic resin modified by epoxy resin as binder. The influences of resin ratio, resin content, graphite granularity, carbon black content, solvents ratio, molding pressure, molding time, curing temperature and other factors on the structure and properties of natural graphite/modified phenolic resin composite bipolar plates have been investigated. The results indicate that the mechanical properties of the bipolar plates significantly improved by adding suitable epoxy resin to the phenolic resin system. The optimum dosage of binder decrease. At optimal composite materials preparation technology, bipolar plate molding technology and heat treatment technology, the preparated bipolar plates have the density greater than1.85g/cm3, conductivity greater than120S/cm, flexural strength greater than40MPa, which have been able to meet the standards of U.S. Department of energy (DOE).The expanded graphite/phenolic resin composite bipolar plates have been preparated taking the advantage of expanded graphite and using it as a conductive aggregates, phenolic resin as binder. Results show that with the increase of expanded graphite content, conductivity of bipolar plates increases, while flexural strength decreases.the addition methods of carbon black has a great influence on bipolar plates performance.As an important component of the fuel cell, in addition to the basic performance, bipolar plate needs to meet the operational performance. Therefor, the operational performances of bipolar plates such as wettability, absorbent, thermal stability, thermal expansion, corrosiveness, gas impermeability and single-cell performance also have been investigated. Results show that the composite bipolar plates which were developed in this paper were hydrophilic. those contact angle is between81°-86°, there almost has no infulence of water absorption on the conductivity and strength of bipolar plates. In the range of fuel cell working temperature (80-100℃), thermal stability of bipolar plates is very good. Thermal expansion rate is also very low, the order of magnitude is10-6K-1. In PEMFC working temperature range, bipolar plates almost dosen’t becom deformation due to thermal expansion. In simulation cell working environment immersion corrosion, weightlessness is0.1-0.6%. In electrochemical corrosion, the corrosion current densitys are less than5pμA/cm2. In this research corrosion resistance of three bipolar plate is good, which can meet the need of bipolar plates. Simulation experiments of single cell show that the composite bipolar plates have a more stable performance in PEMFC run environment. For the PEMFC assembled with graphite/phenolic composite bipolar plates, the open-circuit voltage is about0.9V, and the maximum power density can reach to0.66W·cm-2at the current density of1.56A·cm-2... |
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