| Proton Exchange Membrane Fuel Cell (PEMFC) is a device that directly converts the chemical energy of fuel and oxidant into electrical energy. It is recognized as the most promising power generation technology in the 21st century because of its 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. Its quality directly affects the output power and lifetime of the cell stack, and its cost accounts for about 40 percent of the total cost of a cell stack, thus, directly determines the commercialization pace of the PEMFC.To solve the existing problem of high cost of the bipolar plates for PEMFC, a number of explorations and attempts have been carried out in the development of high-performance, low-cost PEMFC bipolar plate materials and processes in this paper, taking natural flake graphite and modified phenolic resin as the main raw materials. And the application performances of the graphite/polymer composite bipolar plate under PEMFC operating conditions were studied.In this study, electric conductivity and flexural strength were chosen as the major quality indicators of the bipolar plate. The influences of phenolic resin to epoxy resin ratio, resin content, graphite type, graphite size, carbon black content, solvent ratio, composite preparation ways and mixing time, molding pressure, dwell time and curing temperature on the structure and properties of the graphite/polymer composite bipolar plate were researched. The results showed that the mechanical properties of the bipolar plates significantly improved by adding suitable epoxy resin to the phenolic resin system. Using ultrasonic dispersion technology allows composite materials in the mixture mixed more uniformly, which have greatly increased the performance of the composite bipolar plate. The optimum technics for preparing graphite/polymer composite bipolar plates are:epoxy resin 10wt% in the binder; resin content 15wt%; take -200 mesh natural flake graphite as the main conductive aggregate;carbon black content 4wt%;solvent ratio 1.0;ultrasonic dispersion 1 h; molding pressure 160～200 MPa; dwell time 1～3 min and curing temperature 175℃. The study has prospects of forming the graphite/polymer composite bipolar plate in one-step, sharply reducing the production process, shortening the production cycle and reducing the production costs, thus, have a promising future. The graphite/polymer composite bipolar plates prepared under the optimum conditions have a density over 1.85 g·cm-3, a conductivity over 120 S·cm-1, a flexural strength over 38 MPa, and can meet the standards of the United States Department of Energy (DOE). The simulation experiments showed that the composite bipolar plates have a stable performance in the PEMFC operating environment, except that the property of gas permeability needs further improvement. Single cell test showed that PEMFC assembled with graphite/phenolic composite bipolar plates has a open-circuit voltage of 0.9 V, and can reach a maximum power density of 0.66 W·cm·2 at the current density of 1.56 A·cm-2. Compared with the single cell assembled with non-porous graphite bipolar plates, the cell voltage and power density is lower in large current density conditions because of its lower electric conductivity. |
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