| The bipolar plate is one of the key materials of proton exchange membrane fuel cell (PEMFC), and its cost and performance are hindering the course of commercialization of PEMFC and the improvement of fuel cell performance directly. The performance of artificial graphite bipolar plate is excellent and it is adopted extensively. However, its manufacturing technology is relatively complicated and especially its flow channels can be only machined, so its cost is very high. The researches of various kinds of substitution on bipolar plate material have been active all the time. The modified metal bipolar plate has poor performance on corrosion-resistantce and has high costs. The conductivity of expansible graphite bipolar plate through plane is low and its flexural strength is also poor. The manufacturing of carbon composite bipolar plate is simple and it can be shaped by mould pressing effectively. It is cheap and hopeful to replace traditional engineering manufacture graphite bipolar plate. In addition, because NAFION membrane of DUPONT Company is used in PEMFC extensively, it is very essential to humidify the membrane in the course of operating the PEMFC. Humidifying through external equipment is generally adopted at present, which increase the volume of the fuel cell stack. So, it is a considerable direction to humidify the NAFION membrane through internal equipment, for example, changing the materials or structure of bipolar plate to give it humidifying function. In this way, the volume and weight of the fuel cell stack can be reduced and it is favorable to be integrated.So, in this doctoral dissertation, several kinds of novel composite bipolar plates, which were prepared using cement adhesive, for example, Sodium silicate, Aluminate cement, et al., were developed. These composite bipolar plates have hydrophilicity and contain capillary pores, which is its specialty and different from another composite bipolar plate and make it possess humidifying function during the PEMFC operating. The Physics Performance of these composite bipolar plates, for example, the electrical conductivity, the flexural strength, Pore size distribution, the water content, thermal property, resistance to acid corrosion and the H2 permeability, et al, was measured and morphology of these composite bipolar plates were investigated by scanning electron microscope (SEM). Many technique of improving the electrical conductivity and the flexural strength of composite bipolar plate were investigated including choosing uniform size conductive fillers, optimizing the mould pressing conditions, matching different size conductive fillers. In addition, resistance to acid corrosion of novel composite bipolar plates and metal ions content leaching from novel composite bipolar plates was investigated.Aluminate cement / graphite conductive composites, which will be used as the bipolar plate of proton exchange membrane fuel cell (PEMFC), were prepared by mold pressing at room temperature. The effect factors of Aluminate cement / graphite composite bipolar plate on the electrical conductivity and the flexural strength were investigated and discussed. The water content, gel capillary pore size and distribution, H2 permeability of composite bipolar plate composites were measured. The test results show that the conductivity and the flexural strength of the composite bipolar plate can meet the PEMFC requirements when the graphite content is 60wt%. The composite bipolar plate contains capillary pores and the water content of composite bipolar plate is about 7wt%, which is different from other composite bipolar plates. Therefore, it possesses self- humidifying function during the operating process of fuel cell. In addition, H2 permeability of the composite bipolar plate is little.Sodium silicate/ graphite hydrophilicly conductive composites, which will be used as the bipolar plate of proton exchange membrane fuel cell (PEMFC), were prepared by mold pressing at room temperature. The effects of graphite content, size of graphite particles, mould pressing pressure and mold pressing time on the electrical conductivity of composites were discussed. The water content of composites was investigated to different graphite content composites. The best preparation technological conditions were obtained. The results show that the conductivity of composite can reach 100S/cm and meet the requirement of conductivity of bipolar plate in PEMFC when graphite content is greater than 40wt%. The flexural strength of bipolar plate is 15MPa, Moreover, this composite bipolar plate material contains gel capillary pores and the water content can reach 9 wt%, which would be benefit to humidify proton exchange membrane while the PEMFC operates.PVDF/graphite, PVDF/Ti3SiC2, PVDF/expand graphite, PVDF/cement/graphite, PVDF/cement/Ti3SiC2 conductive composite bipolar plate were prepared by mold pressing in high temperature. The experiment results show that the conductivity of composite bipolar plate with Ti3SiC2 as conductive filler is poor. The reason may be that there is great difference between the density of PVDF and Ti3SiC2, moreover, the hydration product of cement almost wrap the Ti3SiC2. In addition, there is great influence of different blend methods (solvent method or powder method) on the conductivity of PVDF/graphite, PVDF/expand graphite.On the basis of particle grade theory, the most closely piling up theory, and calculated result of single diameter particles packing, binary particles grade and multidimensional particles grade, the technique of improving conductive composite conductivity by particles grade were acquired. The conductivity of composites containing either one kind of the same size conductive fillers or two kinds of the different size conductive fillers, which were prepared in our laboratory, were investigated. The results show that the conductivity of composites containing one kind of the same size conductive fillers increase with the increase of filler size. The conductivity of composites containing two kinds of the different size conductive fillers is the higher than that of composites containing only one kind of the big size conductive filler in the appropriate proportion of small size filler in the conductive fillers.Resistance to acid corrosion of novel Aluminate cement/graphite and Sodium silicate/graphite composite bipolar plates with self-humidifying function for proton exchange membrane fuel cell (PEMFC) was investigated in 1MH2SO4 solution at room temperature by linear sweep voltammetry measuring. Metal ions content in the corrosion solution leaching from novel composite bipolar plates was also measured by Inductively coupled plasma atomic emission spectrometry (ICP-AES). The experiment results show that the corrosion current is about 10-4.5 A/cm2 from polarization curves of novel composite bipolar plates, which shows that novel composite bipolar plates are a little acid corrosion-resistant. Al, Ca and Na ions may leach from the Aluminate cement / graphite and Sodium silicate/graphite composite bipolar plate, respectively after lMH2SO4 acid corrosion. But Al, Ca and Na ions leaching from novel composite bipolar plates are only a little percentage of the total Al, Ca and Na ions content in the composite bipolar plate after acid corrosion at 30℃. Al, Ca and Na ions content in acid corrosion solution increase a little with temperature changing from 30℃to 80℃.
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