To address the water management problem in proton-exchange membrane fuel cells, porous graphite composites were prepared by incorporating sacrificial pore-forming agents in the blend of graphite and a phenolic resin formed into a flat plate using compression molding. Sucrose was found to be an effective porogen in the porous plate production process. The effects of relative amounts of graphite, polymer, and porogen in the composite were studied. Bipolar plate properties such as the water uptake by wicking and vacuum infusion, gas-breakthrough pressure across the water-infused pores, electrical conductivity, and flexural strength of the plates were measured and correlated with the plate composition. The plate porosity was evaluated by determining the masses of dry and water-infused plates in air and under water. The porosity, ε, showed a linear increase with an increase in the porogen concentration in the range of 0–10%. The permeabilities, K, of water through the graphite plates with different porosity values were calculated by measuring the water flux over a range of pressures. The water permeability increased with oxidation and hydrophilization of the pore surface. Dynamic water contact angle measurements were used to characterize the effect of chemical and thermal treatments on the water wettability of the plates. The gas-breakthrough pressure of the water-infused plates was found to be linearly correlated with the parameter, , proportional to the capillary pressure of the gas–water interface of surface tension, γ, and contact angle, θ. Porous plates capable of a total water uptake greater than 25 wt %, with the gas-breakthrough pressure higher than 10 psi, through-plane electrical conductivity exceeding 100 S cm–1, and flexural strength exceeding 25 MPa were obtained.

Dual-conducting polymer films were synthesized by dispersing graphene in an aqueous solution of poly(vinyl alcohol) and 1-propyl-3-methylimidazolium iodide ([C 3 mim]I) ionic liquid and thermally converting the poly(vinyl alcohol) to polyene in the presence of hydroiodic acid catalyst. The electrical and mechanical properties of the resulting free-standing films of the nanocomposite, containing different concentrations of graphene, were analyzed using electrochemical impedance spectroscopy (EIS) and dynamic mechanical analysis (DMA), respectively. Nyquist plots (imaginary vs real components of the frequency-dependent impedance) showed two characteristic arcs representing the composite's electronic and ionic conduction pathways. The conductivity values corresponding to both charge transport mechanisms increased with temperature and the graphene concentration. The enhancement in electronic conductivity is expected because of graphene's high electron mobility. Interestingly, ionic conductivity also showed a significant increase with graphene concentration, approximately triple the extent of the rise in the electronic conductivity, even though the loss and storage moduli of the films increased. (Generally, a higher modulus results in lower ionic conductivities in ionic gels.) Molecular dynamics simulations of the three-component system provided some insights into this unusual behavior. Mean square displacement data showed that the diffusion of the iodide anions was relatively isotropic. The iodide diffusion coefficient was higher in a blend with 5 vol % graphene than in blends with 3 vol % graphene or no graphene. The improvement is attributed to the interfacial effects of the graphene on the free volume of the blend. Furthermore, an exclusion of the iodide ions from the vicinity of graphene was observed in the radial distribution function analysis. The increase in the effective concentration of iodide due to this exclusion and the increase in its diffusion coefficient because of the excess free volume are the primary reasons for the observed enhancement in ionic conductivity by adding graphene.

Proton exchange membrane fuel cells (PEMFCs) are promising power-generation sources for mobile, stationary, and emergency backup power applications. Proper water management within the cell is crucial for the optimum performance and durability of PEMFCs. Excessive water leads to the flooding of the cathode compartment, while dehydration of the membranes results in increasing resistive losses. Therefore, water management is critical to the successful implementation of PEMFCs. To optimize the water balance, various designs have been proposed and tested. These approaches include the use of more complex diffusion media and microporous layers, liquid water injection, wicking of liquid water, and the use of different flow-field pathways1. The latter two approaches seek to enable self-humidification of the PEMFCs system, thereby decreasing the cost and parasitic power losses of external components such as humidifiers. In this study, a porous hydrophilic bipolar plate with different pore structures were designed and characterized. Methods and compositions to produce fuel cell bipolar plates, with a porosity tailored for the desired up-take of water produced during fuel cell operation through capillarity, while offering sufficient resistance to permeability and leakage of gaseous fuel, are reported. The plates were composites of graphite (of different shapes and sizes) and polymer and were produced by a combination of powder or paste mixing, followed by compression molding and curing. Pore formation was engineered by adding a pore-forming agent2. Additionally, the pore surface was chemically modified using several surface modification methods. A competitive plate design and fabrication technique is adopted in order to develop a low-cost, and light weight bipolar plates with improved mechanical and electrical conductivity and with exceptional hydraulic permeability and gas breakthrough pressure. The microporous bipolar plates developed in this research are promising for making water-management in PEMFCs simpler. The results of these studies will be presented and discussed. References: Wang, Y.; Diaz, D. F. R.; Chen, K. S.; Wang, Z.; Adroher, X. C., Materials, technological status, and fundamentals of PEM fuel cells–a review. Materials Today 2020, 32, 178-203. Krishnan, S.; Harrington, M.; Pitchiya, A. P.; Putnam, Z.; Orlowski, D., Material Compositions And Methods For Porous Graphite-Polymer Composite Bipolar Plates. U.S. Patent Application 16/558,857: 2020.