Bio-inspired design, fabrication and testing of bipolar plates for PEM fuel cells

The flow field of a bipolar plate distributes reactants for polymer electrolyte membrane (PEM) fuel cells and removes the produced water from the fuel cells. It greatly influences the performance of fuel cells, especially the concentration losses. Two approaches were developed to improve flow field designs in this dissertation. One is inspired by the biological circulatory structures and called bio-inspired designs, which have great potential to transport reactant efficiently and hence improve fuel cell performance. Another way is using a network-based optimization model to optimize the conventional flow field configurations, i.e., pin-type, parallel and serpentine designs, to improve flow distributions within the channels. A three-dimensional, two-phase numerical model was developed to investigate the mass, velocity and pressure distributions within the different flow fields and also the final fuel cell performance. Selective Laser Sintering, which provides a cost- and time-efficient way to build parts with complicated geometries, was used to fabricate graphite composite bipolar plates with these developed designs. Different graphite materials, including natural graphite, synthetic graphite, carbon black, and carbon fiber, were investigated in order to achieve higher electrical conductivity and flexural strength of the fabricated bipolar plates. Experimental testing of the PEM fuel cells with these fabricated bipolar plates was carried out to verify the numerical model and compare the performance for different flow field designs. Both the numerical and experimental results demonstrated that the bio-inspired designs and the optimized designs could substantially improve the fuel cell performance compared to the traditional designs --Abstract, page iv

Experimental Study of Polymer Electrolyte Membrane Fuel Cells using a Graphite Composite Bipolar Plate Fabricated by Selective Laser Sintering

Selective Laser Sintering (SLS) can be used to fabricate graphite composite bipolar plates with complex flow fields for Polymer Electrolyte Membrane (PEM) fuel cells. The additive manufacturing process can significantly reduce the time and cost associated with the research and development of bipolar plates as compared to other fabrication methods such as compression molding. In this study, bipolar plates with three different designs, i.e., parallel in series, interdigitated, and bio-inspired, were fabricated using the SLS process. The performance of these SLS-fabricated bipolar plates was studied experimentally within a fuel cell assembly under various operating conditions. The effect of temperature, relative humidity, and pressure on fuel cell performance was investigated. In the tests conducted for this study, the best fuel cell performance was achieved with a temperature of 75 ⁰C, relative humidity of 100%, and back pressure of 2 atm

Bio-Inspired Design of Bipolar Plate Flow Fields for Polymer Electrolyte Membrane Fuel Cells

The flow field of a bipolar plate distributes hydrogen and oxygen for polymer electrolyte membrane (PEM) fuel cells and removes the produced water from the fuel cells. It greatly influences the performance of fuel cells, especially regarding reduction of mass transport loss. Flow fields with good gas distribution and water removal capabilities reduce the mass transport loss, thus allowing higher power density. Inspired by natural structures such as veins in tree leaves and blood vessels in lungs, which efficiently feed nutrition from one central source to large areas and are capable of removing undesirable by-products, a mathematic model has been developed to optimize the flow field with minimal pressure drop, lowest energy dissipation, and uniform gas distribution. The model can be used to perform optimal flow field designs, leading to better fuel cell performance for different sizes and shapes of bipolar plates. Finite element modeling (FEM) based simulations and in-situ experiments were conducted to verify some of the flow field designs obtained using the developed mathematic model

Comparison of Compression Molding and Selective Laser Sintering Processes in the Development of Composite Bipolar Plates for Proton Exchange Membrane Fuel Cells

Bipolar plates are key components of Proton Exchange Membrane (PEM) fuel cells. They carry current away from the cell and withstand the clamping force of the stack assembly. Therefore, PEM fuel cell bipolar plates must have high electrical conductivity and adequate mechanical strength, in addition to being light weight and low cost in terms of both applicable materials and production methods. In order to attain these goals, we have manufactured graphite-carbon- polymer composite plates using Compression Molding (CM), which is suitable for mass production, and Selective Laser Sintering (SLS), which is suitable for making prototypes. In this paper, the electrical conductivity and flexural strength of the bipolar plates fabricated using the CM process versus constitutive materials are experimentally studied. The properties of bipolar plates fabricated using the CM process are compared with those of plates fabricated using the SLS process. Natural graphite (NG), synthetic graphite (SG), carbon black (CB), and carbon fiber (CF) are used as the constitutive materials for both processes, with epoxy resin employed as the binder matrix. By varying the volume fraction of each constituent, the distribution of the electrical conductivity and flexural strength of parts made using the CM and SLS processes are obtained, and the similarities and differences of the effects of the various constituents between these two processes are compared

Photothermally Induced Alkyl Radicals and Pyroptosis Synergistically Inhibit Breast Tumor Growth

Photothermal therapy (PTT) is an emerging local tumor ablation technique with clinical translation potential. After the NIR-II laser irradiates the tumor, the photothermal agent Hu-Kaiwen ink (Ink) converts light energy into hyperthermia and maintains the temperature at 42-45°C, thus achieving a low-temperature photothermal therapy. Alkyl radicals can kill tumor cells by overcoming the hypoxic microenvironment of the tumor. The photothermal reaction can induce the conversion of alkyl radicals from 2,2′-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH) and thus have a synergistic tumor inhibition effect. the DNA methyltransferase inhibitor decitabine (DCT) can induce pyroptosis and cause inflammation and immune response to achieve systemic immunity. In this way, a synergistic combination of photothermal, alkyl radicals and pyroptosis could be used to kill breast tumor cells. Sodium alginate (ALG) was used as a carrier to form a hydrogel structure, which can improve the stability and duration of action of the mixed drugs. The significant tumor growth inhibitory effect of composite hydrogels has been demonstrated in both in vitro and ex vivo studies

Complete temporal mode analysis in pulse-pumped fiber-optical parametric amplifier for continuous variable entanglement generation

Mode matching plays an important role in measuring the continuous variable entanglement. For the signal and idler twin beams generated by a pulse pumped fiber optical parametric amplifier (FOPA), the spatial mode matching is automatically achieved in single mode fiber, but the temporal mode property is complicated because it is highly sensitive to the dispersion and the gain of the FOPA. We study the temporal mode structure and derive the input-output relation for each temporal mode of signal and idler beams after decomposing the joint spectral function of twin beams with the singular-value decomposition method. We analyze the measurement of the quadrature-amplitude entanglement, and find mode matching between the multi-mode twin beams and the local oscillators of homodyne detection systems is crucial to achieve a high degree of entanglement. The results show that the noise contributed by the temporal modes nonorthogonal to local oscillator may be much larger than the vacuum noise, so the mode mis-match can not be accounted for by merely introducing an effective loss. Our study will be useful for developing a source of high quality continuous variable entanglement by using the FOPA