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Various approaches for the smart curing processes in the fabrication of large hybrid composite blades have been employed to determine whether smart curing, which has multiple heating and cooling processes during the total curing time, is applicable to the adhesive process between carbon fiber-reinforced plastic (CFRP) and glass fiber-reinforced plastic (GFRP). Therefore, investigating the adhesive strength and residual thermal stress between CFRP and GFRP is very important. In an experimental approach, the adhesive strengths of CFRP/GFRP single-lap joint specimens were compared according to surface treatment techniques and curing conditions. The proper roughness of the CFRP surface and the application of smart curing are very effective for the manufacture of CFRP spar cap wind turbines. The simulation results from the analytical approach demonstrated that when the final curing temperature was reduced by the smart curing process, the residual thermal stress and thermal shear stress in the blade were also reduced, resulting in an increased adhesive strength in the adhesive layers between the CFRP spar caps and GFRP skin. It was determined that large hybrid wind blades with CFRP spar caps could be efficiently manufactured using a smart curing process.

The successful reconstruction of the skin equivalents that closely resemble normal human skin tissue greatly relies on maintaining the structural integrity throughout the air-liquid culture. Therefore, this study presents a novel strategy to prepare 3D Agarose-Well which enhances structural integrity of reconstructed skin equivalents. Hydrogel forming of agarose with agarose-g-C18, which synthesized a hydrophobically modified agarose, generated the 3D Agarose-Wells that possess various hydrophilic/hydrophobic balances. As a result, the agarose-fibrils in the well, assembled with penetrated collagen in dermis layer were proved to enhance the structural integrity and further regulate the mechanical strength from 6.8 kPa to 20.9 kPa. Overall, this new strategy to prepare the skin equivalents in the 3D Agarose-Well would be actively used in tissue engineering, drug delivery, and cosmetics, etc.

Although there are various pre-existing technologies for engineering vasculatures, multiscale modeling of the architecture of human vasculature at a capillary scale remains a challenge. In this study, a novel technology is developed for the production of a functional, multiscale microvasculature comprising of endothelialized channels and tissue-specific capillary networks. Perfusable, endothelialized channels are bioprinted, after which angiogenic sprouts are grown into user-designed capillary networks. The induction of branched and liver-lobule-like capillary networks confirm that the technology can produce various types of tissue-specific multiscale microvasculatures. Further, the channels and capillaries are deemed to be functional when evaluated in vitro. An ex vivo assay demonstrates that the microvasculature can induce neovessel ingrowth, integrate with host vessels, and facilitate blood flow. Remarkably, blood flows through the implanted capillary network without any change in its morphology. Finally, the technology is applied to produce a vascularized liver tissue; it significantly improves its hepatic function. It is believed that this new technology will create new possibilities in the development of highly vascularized and functional tissues/organs on a clinically relevant scale.

To use implantable biomedical devices such as electrocardiograms and neurostimulators in the human body, it is necessary to package them with biocompatible materials that protect the internal electronic circuits from the body’s internal electrolytes and moisture without causing foreign body reactions. Herein, we describe a hydrogel surface-modified polyurethane copolymer film with concurrent water permeation resistance and biocompatibility properties for application to an implantable biomedical device. To achieve this, hydrophobic polyurethane copolymers comprising hydrogenated poly(ethylene-co-butylene) (HPEB) and aliphatic poly(carbonate) (PC) were synthesized and their hydrophobicity degree and mechanical properties were adjusted by controlling the copolymer composition ratio. When 10 wt% PC was introduced, the polyurethane copolymer exhibited hydrophobicity and water permeation resistance similar to those of HPEB, however, with improved mechanical properties. Subsequently, a hydrophilic poly(vinyl pyrrolidone) (PVP) hydrogel layer was formed on the surface of the polyurethane copolymer film by Fenton reaction using an initiator and crosslinking agent and the effect of the initiator and crosslinking agent immobilization time, PVP concentration and crosslinking agent concentration on the hydrogel properties were investigated. Finally, MTT assay showed that the hydrogel surface-modified polyurethane copolymer film displays excellent biocompatibility.

Tilting pad journal bearings have been employed for turbine , compressor, pump, and generator applications owing to their high loading capacity, excellent stability, and service durability at high operation speed compared to conventional journal bearings. For high-speed and high-performance applications, tilting pad journal bearings should reduce the rotor vibration. Therefore, the bearings are designed to have excellent damping characteristics. In this study, composite tilting pad journal bearings consisting of carbon fiber/epoxy composites and a backup metal are fabricated to increase the dynamic performance and durability. A modal analysis is performed to investigate dynamic stability of the composite tilting pad. Moreover, the damping coefficient of fluid film, oil film pressure, and orbit of rotor are calculated with respect to the liner materials under a hydrodynamic lubrication state. To verify the analysis results, hydrodynamic lubrication tests of composite and white metal tilting pad journal bearings are conducted using an industrial test bench. As a result, the composite tilting pad journal bearing has effectively reduced the rotor vibration and increased the stability and durability of the bearing system compared to the white metal tilting pad journal bearing.

Proton exchange membrane fuel cells (PEMFCs) are one of the most popular alternative power sources for next-generation automobile applications. A bipolar plate is a multifunctional component that performs various roles in the PEMFC stack. Recently, thin ( In this study, the ECR between bipolar plates without bulk resistance were measured to present a standard contact resistance value. The ECR of various types of carbon-based materials for bipolar plate was investigated with respect to hardness and resistivity. A mechanical abrasion method using sandpaper was applied to the surface of CFRPs to remove the resin-rich area and control the surface topology. As a result, the ECR between bipolar plates was quantified with respect to the surface hardness, resistivity and roughness, and optimum surface treatment conditions were obtained to minimize the ECR.

The cellular components of Akkermansia muciniphila are considered potential biotherapeutics for the improvement of obesity, diabetes, and metabolic diseases. However, the molecular-based mechanism of A. muciniphila for treatment of obesity, which can provide important evidence for human research, has rarely been explored. Here, we applied integrative multiomics approaches to investigate the underlying molecular mechanism involved in obesity treatment by A. muciniphila. First, the treatment with a cell lysate of A. muciniphila reduced lipid accumulation in 3T3-L1 cells and downregulated the mRNA expression of proteins involved in adipogenesis and lipogenesis. Our proteomic results revealed that A. muciniphila decreased the expression of proteins involved in fat cell differentiation, fatty acid metabolism, and energy metabolism in adipocytes. Moreover, A. muciniphila significantly reduced the level of metabolites related to glycolysis, the TCA cycle, and ATP in adipocytes. Interestingly, serine protease inhibitor A3 (SERPINA3) homologs were overexpressed in the 3T3-L1 cells treated with A. muciniphila. Small interfering RNA (siRNA) transfection demonstrated that A. muciniphila upregulates SERPINA3G expression and inhibits lipogenesis in adipocytes. Taken together, our multiomics-based approaches enabled to uncover the molecular mechanism of A. muciniphila for treatment of obesity and provide potent anti-lipogenic agents.

The carbon/epoxy composite bipolar plate is a promising substitute for the conventional graphite bipolar plate for the vanadium redox flow battery due to its high mechanical property and productivity. The carbon/epoxy composite bipolar plate, a multifunctional structure, requires expanded graphite coating or additional surface treatments to decrease the interfacial contact resistance. However, expanded graphite coating has low durability under vanadium redox flow battery operating condition and surface treatments are costly to implement. In this work, excess resin-absorbing method is developed with polyester fabric to uniformly remove the resin-rich layer and expose carbon fibers on the surface of the carbon/epoxy composite bipolar plate. This method not only decreases the interfacial contact resistance by exposing carbon fibers but also forms a unique ditch pattern which is desirable to fix carbon felt electrode in place. Durability against acidic environment, mechanical property, and gas permeability of the composite bipolar plate manufactured by excess resin-absorbing method is investigated.

Carbon fiber reinforced polymer composites are ideal substitutes for the brittle graphite bipolar plate in lightweight proton exchange membrane fuel cells (PEMFCs) because of their high specific strength and stiffness. Among the various types of carbon composite bipolar plates, non-woven carbon felt based composites have recently attracted attention because they require much lower curing pressures than unidirectional carbon fiber or carbon fabric composites. In this work, a carbon felt composite bipolar plate is developed for a high-temperature PEMFC (HT-PEMFC) using randomly oriented non-woven carbon felt and a cyanate ester-modified epoxy. The cathode and anode are integrated into a single bipolar plate to reduce the thickness and weight of the HT-PEMFC stack. The developed composite bipolar plate exhibits superior electrical properties because of the bare carbon fibers exposed on the surface by the soft layer method. In addition, the bipolar plates are dimensionally stable under high-temperature and high-pressure conditions. Finally, a cell test is performed on a 3-cell HT-PEMFC stack to investigate the cell performance.

Carbon fiber reinforced polymer composites are ideal substitutes for brittle graphite for electrically conductive bipolar plates because of their high mechanical property and productivity. Early composite bipolar plates suffered from high electrical contact resistance due to the resin-rich area formed on the surface. To decrease the electrical contact resistance, the “soft layer method” was developed, which exposed bare carbon fibers on the composite surface. This method significantly improved the electrical as well as mechanical properties of composite bipolar plates. The remaining problem for wider commercialization of composite bipolar plates is their high fabrication pressure. In this work, a non-woven carbon felt composite bipolar plate was developed to obtain improved electrical properties with low fabrication pressure. The soft layer method was also used to expose bare carbon fibers. Compared to conventional high fiber volume fraction composite bipolar plates, the developed bipolar plate exhibited superior electrical properties.

Although aluminum structures are generally used for robot structures due to their high specific strength, aluminum feet for fast running biped robots are vulnerable to fatigue failure due to the low fatigue limit and low vibration damping of aluminum structures under repeated impact loadings on the feet. On the other hand, carbon/epoxy composites not only have a much higher specific fatigue limit but also have a higher material damping than that of aluminum. In this study, a carbon/epoxy composite foot structure of a biped robot was developed. The composite foot structure was designed for optimum performances such as weight saving, natural frequency, damping, and compliance for vibration isolation. Then its performances were analytically and experimentally obtained and compared with those of an aluminum foot structure. Finally, an optimum configuration of the composite foot structure was suggested for the reliable dynamic performance of the biped robot.

In this work, composite journal bearings were fabricated using a carbon-fiber/phenol composite and carbon-fiber/epoxy composite to solve the seizure problem of a metallic journal bearing under the oil cut situation. Friction coefficients of two composite materials were measured through the wear test under the same conditions as the oil cut situation, and the material properties were measured at the elevated temperature of the oil cut situation. Next, the stress distribution of the composite journal bearings was investigated by using finite element analysis (FEA) with respect to the friction coefficients between the rotor and bearing, and the Tsai-Wu failure index was calculated to investigate the possibility of failure. To verify the failure analysis results, the oil cut tests for the composite journal bearings were conducted using the industrial test bench. The oil cut test results indicate that the carbon fiber/epoxy composite journal bearing is more durable than the carbon fiber/phenol composite journal bearing.

The vanadium redox flow battery (VRFB) is a promising energy storage system (ESS) which can decrease the risk of power outage by storing electricity energy at non-peak time, and using at peak time. Among various ESSs, the VRFB is one of the safest and most flexible systems due to its unlimited capacity, non-explosiveness, and infinite lifetime. Since the compaction pressure on the carbon felt electrode (CFE) inside the stack of VRFB is relatively small, the electrical contact resistance between the CFE and bipolar plate (BP) largely affects the cell efficiency. In this study, a carbon fiber/polyethylene (PE) composite BP-CFE assembly has been developed to decrease the contact resistance between the BP and CFE by embedding the CFE into the PE matrix of the carbon fiber composite BP through local thermoplastic welding process to decrease the electrical contact resistance. To evaluate the performances of the BP-CFE assembly, the areal specific resistance (ASR) and gas permeability were measured. Also the acid aging tests were performed to measure the stack reliability. Finally, the performances of the BP-CFE assembly were measured and compared with those of the conventional bipolar plate during the charge/discharge cycles of a VRFB stack.

Since the energy demand increases continuously and there are difficulties of increase of energy supply doe to environmental pollution, there has been strong demand for an energy source such as fuel cells as well as an energy storage system (ESS). Although fuel cells and ESSs have been considered as future energy conveniences, they have not been widely employed because their structures such as bipolar plates (BP), endplate (EP) or flow frames (FF) are made of either brittle graphite, weak polymers or ceramic coated stainless steel to meet the requirements of high electrical conductivity under strong acid environment such as the target values of Department of Energy (DOE) of USA. To circumvent the weak characteristics and difficulty of manufacturing of these structures, the carbon composite BP and the hybrid composite EP composed of carbon and glass composites for the proton exchange membrane fuel cell (PEMFC) and vanadium redox flow battery (VRFB) and the glass composite flow frame (FF) for the VRFB have been developed. The design methods for these composite structures with the appropriate processing techniques are explained in detail. The performances and endurance tests for these structures have been evaluated and compared to the targets of DOE.

The carbon/epoxy composite bipolar plate is an ideal substitute for the brittle graphite bipolar plate for proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs) because of its high mechanical properties and easy manufacturing. However, due to the resin-rich area that forms on its surface, the carbon/epoxy composite bipolar plate requires an expanded graphite coating to decrease the areal specific resistance (ASR). The expanded graphite coating not only increases the manufacturing costs but also has very low mechanical properties. In this work, an innovative manufacturing method that exposes carbon fibers on the surface of the carbon/epoxy composite bipolar plate was developed. Soft release films were inserted between the mold and the composite to prevent the formation of a resin-rich area and to expose carbon fibers on the surface of the bipolar plate. The developed method considerably decreased the ASR of the carbon composite bipolar plate without an expanded graphite coating, which satisfied the target established by the Department of Energy (DOE) of United States. The effects of the soft layer on the mechanical and electrical properties of the carbon composite bipolar plate were investigated.

Composite bipolar plates for vanadium redox flow batteries (VRFBs) and fuel cells are coated with expanded graphite to decrease the interfacial contact resistance of the carbon composite. The bipolar plates of vanadium redox flow batteries are exposed to electro-chemical corrosion, which might degrade the graphite coating layer. From two types of graphite foil, i.e., pyrolytic graphite and expanded flake-type graphite, the former has higher durability because its graphene sheets are crystallized in a planar direction with a highly oriented structure, which has a stronger van der Waals bonding. In this study, the characteristics of the pyrolytic graphite and expanded flake-type graphite are investigated with respect to the porosity of graphite. The durability of the graphite coating of the carbon/epoxy composite bipolar plate during the electrochemical reaction in vanadium electrolytes, based on highly concentrated sulfuric acid, is investigated. The areal specific resistances (ASRs) of the bipolar plates coated with pyrolytic graphite are measured, from which the ASR is expressed in terms of modulus of the graphite based on the Hertzian contact model. A single cell test is performed to evaluate the performance of the developed bipolar plate.

The bipolar plate is a major component determining the cost, volume and performance of a PEMFC (Polymer Electrolyte Membrane Fuel Cell) stack. Carbon composite/epoxy has been considered to be a potential material for bipolar plates due to its good mechanical properties, electrical conductivity and corrosion resistance. However, the long curing time of the epoxy matrix under high pressure remains an obstacle for mass production. In this study, a continuous process using hot rolling for the mass production of carbon/phenol composite bipolar plates has been developed. To accelerate the curing reaction of the phenolic resin, a p -toluene sulfonic acid catalyst was used. The temperature, time and steps for continuous hot rolling process were optimized with cure monitoring using a dielectrometry method. The areal specific resistance (ASR) and mechanical properties of the carbon/phenol composite bipolar plate were measured with respect to the manufacturing process. The surface of the composite bipolar plates was coated with graphite to reduce the ASR. It was found that the composite bipolar plate produced by the optimized hot rolling process satisfied the Department of Energy (DOE) targets.

The primary components of proton exchange membrane fuel cell (PEMFC) systems are bipolar plates, end plates, membrane electrode assemblies (MEAs), gas diffusion layers (GDLs), and gaskets. The PEMFC composed of many components induces sealing problem of the stack, which affects the fuel efficiency, reliability, and maintenance costs of the system. Conventional PEMFCs are sealed with numerous elastomeric gaskets to seal the stack, which increases the manufacturing and assembly costs. To reduce the assembly time and to increase the sealing reliability without the use of gaskets, a gasket-integrated carbon/silicone elastomer composite bipolar plate is developed. Silicone elastomer is employed rather than conventional glassy thermoset or thermoplastic polymers for the matrix of the composite bipolar plate, where the silicone elastomer works as gaskets due to its resilience. The mechanical and electrical properties of the developed carbon/silicone elastomer composite are investigated at both room temperature and operating temperature of high-temperature PEMFCs (HT-PEMFCs). The sealability of the gasket integrated composite bipolar plate is tested.

Composite sandwich structures are widely employed in various applications, due to their high specific stiffness and specific bending strength compared to solid panels. Lately, for that reason, the advanced composite sandwich structures are employed in satellite structures: materials should be as light as possible with the highest attainable performance. This study is majorly focused on inserts employed to the composite sandwich satellite structures. A new hybrid insert design was developed in precedent study to reduce the mass of the sandwich structure since the mass of the satellite structure is related to high launching cost (1). In this study, the thermal characteristics and behavior of the precedently developed hybrid insert with carbon composite reinforcing web and the conventional partial insert were numerically investigated.

The high temperature proton exchange membrane fuel cell (HT-PEMFC) operating from 120 °C to 220 °C is able to overcome many technical issues related to the low-temperature PEMFC (LT-PEMFC), such as their complex water/thermal management to prevent flooding/drying out of the membrane and their low tolerance to carbon monoxide. In a PEMFC stack, the bipolar plates are a major component, contributing 50% of the total cost and 80% of the total weight. In this study, a composite bipolar plate was developed using resole type phenolic and continuous carbon fiber to improve the high-temperature performance (∼220 °C) for use in HT-PEMFC applications. To improve the mechanical and electrical properties, the nano-size carbon black was mixed with phenolic resin. A pre-cure process using hot rolling was developed to achieve partial wetting of the carbon fiber felt on the carbon/phenol composite bipolar plate surface. The randomly oriented carbon fiber felt was co-cure bonded with the pre-cure process to modify the surface of the composite bipolar plates by exposing the bare carbon fibers on the outer surface, which reduced the ASR (areal specific resistance). The developed composite bipolar plate satisfied the DOE technical targets.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity. In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties. In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

The hydrogels are widely used in various applications, and their successful uses depend on controlling the mechanical properties. In this study, we present an advanced strategy to develop hydrogel actuator designed to stimulate live cell clusters by self-folding. The hydrogel actuator consisting of two layers with different expansion ratios were fabricated to have various curvatures in self-folding. The expansion ratio of the hydrogel tuned with the molecular weight and concentration of gel-forming polymers, and temperature-sensitive molecules in a controlled manner. As a result, the hydrogel actuator could stimulate live cell clusters by compression and tension repeatedly, in response to temperature. The cell clusters were compressed in the 0.7-fold decreases of the radius of curvature with 1.0 mm in room temperature, as compared to that of 1.4 mm in 37 &deg, C. Interestingly, the vascular endothelial growth factor (VEGF) and insulin-like growth factor-binding protein-2 (IGFBP-2) in MCF-7 tumor cells exposed by mechanical stimulation was expressed more than in those without stimulation. Overall, this new strategy to prepare the active and soft hydrogel actuator would be actively used in tissue engineering, drug delivery, and micro-scale actuators.

The proton exchange membrane fuel cell (PEMFC) is composed of bipolar plates, end plates, membrane electrode assemblies (MEAs) and gas diffusion layers (GDLs), from which the bipolar plate is a major component to determine the cost, volume and performance of the PEMFC stack. In this study, the bipolar plate has been developed using carbon fabric/phenolic composite because phenolic resin has much faster cure reaction than epoxy resin, which enables the carbon/phenolic resin based bipolar plate to be mass-produced. The p-toluene sulfonic acid catalyst is used to accelerate the curing reaction of carbon fabric/phenolic, and the electrical conductivity and tensile strength of the composites are measured with respect to catalyst content because these two characteristics of composite determine the performance of composite bipolar plate. The experimental results show that the curing time of the carbon fabric/phenolic decreased much as the amount of catalyst is increased. However both the tensile strength and interfacial contact resistance of the composite also decrease as the amount of catalyst is increased because the excess catalyst works as impurities in the composite. Therefore, an optimum content of the catalyst is investigated considering the electrical conductivity with little compromise of mechanical properties.

Proton exchange membrane (PEM) fuel cell systems are environmentally friendly power sources that have many potential applications. Although carbon fiber composite bipolar plates have high strength and stiffness with good corrosion resistance in an acid environment, they exhibit only a marginal electrical conductivity, which compromises the efficiency of PEM fuel cells. In this work, electrically conductive particles (graphite powder and carbon black) are sprayed onto carbon–epoxy composite prepregs of a bipolar plate to decrease the electrical resistivity of the bipolar plate. The electrical resistance and mechanical properties are measured using conventional test methods. In addition, a unit cell performance assessment is conducted with the developed carbon composite bipolar plates and compared with that of the conventional bipolar plate.

A carbon fiber composite gasketless bipolar plate for proton exchange membrane (PEM) fuel cells was developed using the groove of a trapezoidal shape, which develops large contact stresses due to a wedge mechanism. The surface of the composite groove was modified to increase gas tightness without using rubber gaskets. Graphite, polyimide (PI) and polyethylene terephthalate (PET) film were co-cure bonded on the surface of the bipolar plate during the compression molding process to change its surface hardness, which could affect the gas tightness. Additionally, plasma surface treatment and mechanical abrasion were used to modify the surface morphologies. Corrosion and gas tightness tests on the surface modified bipolar plates were performed to verify the reliability of the gasketless sealing method.

The bipolar plates have several functions in Proton Exchange Membrane Fuel Cell (PEMFC); separating flow channels between gases, connecting electrical paths between cells in series and providing structural supports for the stack. Although the carbon fiber epoxy composite bipolar plates recently developed, have high specific stiffness and strength, they have relatively high electrical resistance compared to graphite bipolar plates due to their high surface electrical contact resistance, which requires additional surface treatment such as graphite layer coating. In this research, a new manufacturing method for the carbon fabric/graphite hybrid bipolar plate which consists of two carbon fiber fabrics and an expanded graphite foil liner between them, has been developed in order to increase the productivity of PEMFC and reduce its manufacturing cost by exposing bare carbon fabrics to decrease the surface electrical contact resistance of bipolar plate. Phenolic resin was chosen rather than epoxy resin for the matrix material to decrease both material cost and manufacturing time, and the optimum areal density of phenolic resin was determined experimentally. Also the corrosion resistance, electrical contact resistance and mechanical properties of the hybrid bipolar plates were measured.

Polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell (PEMFC) is composed of bipolar plates, end plates, membrane electrode assemblies (MEAs) and gas diffusion layers (GDLs). Among the constituents of PEMFCs, the bipolar plates are major components, which make up a large portion of the stack volume and cost. In this study, the bipolar plate has been fabricated using carbon fabric/phenolic composite for mass production because the phenolic resin cures much faster than epoxy resin. Because the phenolic resin becomes brittle after being fully cured, it is mixed with carbon black to increase the ductility. The surface of the carbon fabric/phenolic composite bipolar plates has been treated with flame to reduce the interfacial contact resistance. The experimental results show that the contact resistance of the carbon fabric/phenolic composites bipolar plate decreases as the flame-treatment temperature and time increase due to the degree of carbonization of the phenolic resin, while the flexural strength decreases because the carbonization of phenolic resin increases its brittleness. Therefore, the optimum flame surface treatment temperature and processing time for the carbon fabric/phenolic composite bipolar plates are investigated to optimize the electrical conductivities and mechanical properties.

The bipolar plates of proton exchange membrane (PEM) fuel cell systems serve many functions, such as electrically connecting cells in series, separating gases in adjacent cells and providing structural support for the stack and flow channels of water and gases. Although carbon fiber composite bipolar plates have high strength and stiffness as well as corrosion resistance in acidic environments, they do not yield a sufficiently high electrical conductance, which compromises the efficiency of PEM fuel cells. To increase the electrical conductance of the bipolar plate, a composite hybrid bipolar plate with bypass-connected gas diffusion layers (GDLs) has been developed. The graphite foil coating method, which was developed in preceded study, is applied to decrease the contact resistance between the bipolar plates and the GDLs. Moreover, to minimize the contact resistance between the hybrid bipolar plates and gas diffusion layers by allowing continuous electron conduction though the unit cell, a bypass connection is made between the bipolar plates and the GDLs. The experimental results show that the developed hybrid bipolar plate has a 98% lower electrical resistance than the conventional composite bipolar plates.

Conventional bipolar plates for proton exchange membrane (PEM) fuel cells use extra rubber gaskets to seal the stack, which require an additional curing process at high temperature and increase the manufacturing and assembling time. To reduce the assembling time of fuel cell stacks and achieve gas sealability without using extra gaskets or curing cycles, innovative gasketless carbon composite bipolar plates were developed. To ease the assembling of the cell stacks, special grooves on the edge of the composite bipolar plate are provided for mechanical joining and the behavior of the bipolar plates under the stack compaction pressure conditions was investigated by FE analysis. The mechanical properties of the grooves were measured by the compressive strength test and compared with the FE analysis results. The sealability of the gasketless bipolar plate with grooves was tested to verify the integrity of the design.

In this study, in order to increase the electrical conductivity, a carbon composite-metal hybrid bipolar plate has been developed using pre-forming method followed by a plasma surface treatment. A pre-formed metal foil between the carbon fiber/polymer composite plates promotes the metal foil to follow the shape of the channels of the bipolar plates without tearing and permits a continuous flow of electrons. The pre-formed metal foil also reduces the residual stress between the composite and metal foils, which helps prevent delamination between the composite and metal foils. The composite surface has been treated with plasma to increase the contact area between the carbon fiber and the gas diffusion layer (GDL). The composite-metal hybrid bipolar plates have only 1.4% of the total electrical resistance of that of the conventional composite bipolar plates. Unit cell test results have proved that the developed composite-metal hybrid bipolar plates with reduced total electrical resistance increase the cell performance.

A Polymer Electrolyte Membrane Fuel Cell or Proton Exchange Membrane (PEM) fuel cell stack is composed of a Gas Diffusion Layer (GDL), an Membrane Electrode Assembly (MEA), and bipolar plates. The electrical resistance of the bipolar plates for a PEM fuel cell should be very low, so that the electricity generated in the fuel cell is conducted through the bipolar plates with minimum electrical loss. In this study, a plasma etching treatment was developed to decrease the contact resistance between a GDL and continuous-carbon/epoxy composite bipolar plate. The treatment removes the resin-rich layer of the composite surface, which is the source of the majority of the electrical resistance of the bipolar plate. The optimum plasma treatment condition was determined by calculating the resin etching depth, taking into consideration the carbon fiber dimensions of the GDL and the continuous-carbon/epoxy composite bipolar plate. Scanning Electron Microscopy (SEM) analysis was performed on the surface of the composite bipolar plate for each variation of plasma surface treatment. In addition, the tensile strength and the electrical resistance (in the through-thickness direction) of the composite bipolar plate were measured for the different plasma surface treatment conditions.

Polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell (PEMFC) is composed of bipolar plates, end plates, membrane electrode assemblies (MEAs) and gas diffusion layers (GDLs). Among the constituents of PEMFCs, the bipolar plate is a key component that collects and conducts the current from cell to cell. The electrical resistance of the bipolar plate, which consists of the bulk material resistance and interfacial contact resistance between the GDLs and the bipolar plates, should be reduced to improve the performance of the fuel cell. In the present study, a bipolar plate made of plain weave carbon fiber epoxy composite is developed to increase the manufacturing productivity of the fuel cell and to decrease the bulk electric resistance. A graphite coating method is performed on the bipolar plate to reduce the interfacial contact resistance between the GDLs and the bipolar plates and to limit the transport of gases through the bipolar plates. The experimental results show that the bulk resistance of the plain weave carbon composite bipolar plate is about 50% less than that of a carbon composite bipolar plate made of unidirectional carbon fiber epoxy composites with the same thickness. Moreover, a 2 μm graphite coating on the bipolar plate effectively prevent gas transport through the bipolar plate.

A PEMFC (polymer electrolyte membrane fuel cell or proton exchange membrane fuel cell) stack is composed of GDLs (gas diffusion layers), MEAs (membrane electrode assemblies), and bipolar plates. One of the important functions of bipolar plates is to collect and conduct the current from cell to cell, which requires low electrical bulk and interfacial resistances. For a carbon fiber epoxy composite bipolar plate, the interfacial resistance is usually much larger than the bulk resistance due to the resin-rich layer on the composite surface. In this study, a thin graphite layer is coated on the carbon/epoxy composite bipolar plate to decrease the interfacial contact resistance between the bipolar plate and the GDL. The total electrical resistance in the through-thickness direction of the bipolar plate is measured with respect to the thickness of the graphite coating layer, and the ratio of the bulk resistance to the interfacial contact resistance is estimated using the measured data. From the experiment, it is found that the graphite coating on the carbon/epoxy composite bipolar plate has 10% and 4% of the total electrical and interfacial contact resistances of the conventional carbon/epoxy composite bipolar plate, respectively, when the graphite coating thickness is 50 μm.

Composite sandwich structures which are widely employed in satellite structures require many inserts for assembly. In this study, a new lightweight insert for sandwich structures was developed by reinforcing the web of insert with high strength carbon composite to increase the loading capability with reduced mass. Finite element analysis was performed to numerically predict the load capability of the new insert as well as to investigate the effects of the new insert on the structural reliability. The load capability and the failure modes of the composite sandwich structures assembled with the inserts were measured by the pull-out and shear tests and compared with the calculated results.

An aluminum/composite hybrid bipolar plate with a bypass aluminum channel has been developed. The mechanical abrading technique and electromagnetic-carbon technique are employed for surface modification of aluminum and composite, respectively. The optimum processes of surface modification techniques for aluminum and composite are investigated to promote intimate contact between aluminum and carbon fibers of composite for low electrical resistance. After the surfaces of the aluminum and carbon fiber prepregs are treated with the surface modification techniques, they are co-cured with the single-type of bipolar plate to lower the electrical contact resistance. In this study, it has been found that the hybrid bipolar plate has only 3% of the electrical resistance of the conventional composite bipolar plates.

In this study, a novel gas sensor based on evanescent field coupling between single mode side polished fiber and solvatochromic dye dispersed polymer waveguide was demonstrated. We fabricated a side polished optical fiber device as a volatile organic compounds gas detector. Solvatochromic dye was coated on the top of the side polished optical fiber to take advantage of evanescent field coupling. The solvatochromism can be defined as the phenomenon whereby a compound changes color, either by a change in the absorption or emission spectra of molecule, when reacted in different VOCs. The device reacted to polarity gases like a hexane, butane, xylene etc. The resonance wavelength was shifted by the xylene concentration which range was 0.1 ppm ~ 100 ppm. Also, the response with the concentration was lineer and the detection limit was 0.1 ppb.

and were added in the concentration of 1 - 3 wt.% to improve long-term stability for the thick film gas sensor. Short-term sensor resistances up to 90 h were measured to investigate the stabilization time of initial resistance in air. Long-term resistance drifts in air and in gas to 5000 ppm methane for the sensors annealed at for 1 h and continuously heated at an operating temperature of were also measured up to 90 days at an interval of 1 day. The long-term drifts in methane sensitivity for the three metal oxide-doped sensors are closely related to methane sensitivity level, catalytic activity, and long-term drift in sensor resistance in air. Those stabilities are mainly discussed in terms of oxidation state and catalytic activity.

A micro sensor array with the highly sensitive porous tin oxide thin films employing the noble metal catalysts of Pt and Au on a new micro-hotplate, dangled in air by Pt bonding wires, has been designed and fabricated. The micro hot plate was made of N/O/N Si diaphragm with area of 1.9×2.1 mm2. The power consumption was reduced by decreasing the thickness of substrate. The sensor array was applied to recognizing the explosive gases within the range of threshold limit values (TLVs), employing principal component analysis. The result showed that the micro sensor array was qualified for classifying obviously the kinds and quantities of the explosive gases.

Thermal properties of a sensor array ( 3 mm ×5 mm in diaphragm dimension) with 12 sensing elements were optimized with a view to realizing the discrete operating temperature of each sensing element of the sensor array. This sensor array with single heater on a glass diaphragm over front-etched silicon bulk realizes a new concept of a sensor array: an array of sensor elements operated at different temperatures can yield more information than single element measurement. Thermal properties including temperature distribution over the sensing elements and cross sectional temperature profile of glass substrate were simulated by commercial finite element method (FEM) package. The proposed micro-sensor array could provide well-integrated array structure because it has only single heater at the center of the diaphragm and used two kinds of metal oxide layers with various operating temperatures.

In this paper, impedance variations of SnO 2 -based gas sensor array are measured in gases. Back propagation algorithm of pattern recognition [1,2] is used to distinguish a species and concentration of gases with analog signals of impedance variation from sensor array. When the impedance variation presents as the quantities of rising and falling time to 100 kHz pulse input signal of a prepared circuit in gases, the sensor array system distinguishes gas species and concentration with back propagation algorithm which deals with rising time and falling time from sensor array. SnO 2 -based sensing materials on a sensor array are SnO 2 –Pt, SnO 2 –La 2 O 3 , SnO 2 –Au/Pd, and SnO 2 –Pd–V 2 O 5 using thick film process techniques. The proposed sensor array for pattern recognition with impedance variation is proper to enhance stability, selectivity, and reproducibility to gases.