Design, manufacturing, and characterization of high-performance lightweight bipolar plates based on carbon nanotube-exfoliated graphite nanoplatelet hybrid nanocomposites

We report a study on manufacturing and characterization of a platform material for high-performance lightweight bipolar plates for fuel cells based on nanocomposites consisting of carbon nanotubes (CNTs) and exfoliated graphite nanoplatelets (xGnPs). The experiments were designed and performed in three steps. In the preexperimental stage, xGnP-epoxy composite samples were prepared at various xGnP weight percentages to determine the maximum processable nanofiller concentration. The main part of the experiment employed the statistics-based design of experiments (DOE) methodology to identify improved processing conditions and CNT: xGnP ratio for minimized electrical resistivity. In the postexperimental stage, optimized combinations of material and processing parameters were investigated. With the aid of a reactive diluent, 20 wt.% was determined to the be maximum processable carbon nanomaterial content in the epoxy. The DOE analyses revealed that the CNT: xGnP ratio is the most dominant factor that governs the electrical properties, and its implications in relation to CNT-xGnP interactions and microstructure are elucidated. In addition, samples fabricated near the optimized condition revealed that there exists an optimal CNT: xGnP ratio at which the electrical performance can be maximized. The electrical and mechanical properties of optimal samples suggest that CNT-xGnP hybrid nanocomposites can serve as an alternative material platform for affordable, lightweight bipolar plates.open0

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Department of Mechanical Enginering (Mechanical Engineering)Sandwich composites, owing to their weight to performance ratio and structural stability, are used in many applications, including sports equipment, automotive, and aerospace. The structural stability arises from the sandwich panel structure, which consists of three layers and two thin composites (skins) of a stiff and strong material, separated by a thick core of low-density material. These sandwich structures have optimized specific flexural stiffness, as the separation of the two skins by a low-density core increases the moment of inertia, and thus, contributes to the flexural stiffness of the panel, with only a small increase in the mass of the panel. Sandwich composites are often used in structures because of these advantageshowever, they pose a high risk of damage. To prevent damage, installing sensors for structural loads is necessary. The most commonly used detection method is to insert an optical fiber into the skin part of a composite structure and measure the refraction of light passing through the optical fiber or apply a resistance that the strain gauge sensor pulls and changes. However, in these instances, problems arisefor instance, hampered mechanical properties of the skin, spatial restrictions, requirement of an additional energy source, or difficulty in ensuring continuous use. To solve this problem, a self-powered sensor and structure module are required. First, regarding the self-powered sensor, a thermoelectric, piezoelectric, or triboelectric device can be used. For structures, continuous power generation is difficult, owing to repeated bending or friction. Meanwhile, since the sandwich composite material used as a structure is applied to differentiate between the inside and the outside, a temperature gradient occurs. In this case, the thermoelectric system is advantageous because it can continuously generate power via a temperature gradient. To apply such self-sensing sandwich composites, the following research objectives are proposed: (1) develop a carbon nanotube (CNT)/polyaide6 (PA6) composite n-type thermoelectric device with a segregated network formed by glass bubbles (GBs)(2) develop a p-type thermoelectric device with drawn chopped carbon fiber (CCF)/high-density polyethylene (HDPE)(3) apply a circuit process that connects the sensor and thermoelectric sensor using the skin of the sandwich composite material(4) recycle PET-only composite sandwiches with thermal compression for extracted PET and recompressed double-depth composite skins. To develop a thermoelectric device with a composite material, the internal structure of the composite material was designed. First, a segregated network was used to compress nanomaterials and create a path for electrons to flow in an internal structural design that is advantageous for thermoelectric devices. Second, the orientation of fibers was controlled by extruding a composite material containing short fibers and adjusting the draw ratio. Thus, a structure that is advantageous for thermoelectric devices was designed. A method to visualize the change in resistance due to piezo-resistivity upon application of pressure to the sandwich is proposed, involving the placing of a sensor on the skin of the composite material. Mechanical properties of the sensor were enhanced by functionalizing the nanomaterial of the composite material to be used as a sensor, and the resistance was measured with a wire attached to the sensor and corrected by a distance-based calculation method to visualize the pressure applied to each position. Thermoelectric elements serving as a power source were arranged at the intersections to construct the core of the composite material and the circuit for driving the sensor. The circuit was composed of a DC???DC boost converter that increases the voltage, a low-power IC chip that supplies a constant power through rectification, and an analog ampere meter (??A) that evaluates the behavior of the sensor. This dissertation presents a method for manufacturing a sensing sandwich composite by creating a structure, and specifically, for mechanically mass-producing engineering polymers and carbon nanomaterials for n-type and p-type composite materials. The pressure was visualized by using a sensor that accounts for the piezo-resistance of a functionalized nanomaterial serving as the skin of a sandwich composite. It was experimentally shown that a circuit could be driven through the connection of a manufactured thermoelectric element and a sensor.clos

Effect of dynamic friction and static friction in finite element analysis of carbon fiber preform

This paper aims to improve the accuracy of the finite element analysis for the preform shape transformation according to the difference in the type of carbon fiber and friction force. The carbon fiber type (Toray T700, Zoltek), the fiber direction (0 degrees/90 degrees, +/- 45 degrees), and the frictional force were measured, which occurred between the fiber and the mold and between the fiber and the fiber. A comparative experiment was conducted through actual preform production by designating it as a variable for element analysis. The analysis was conducted according to the difference between the static friction coefficient and the dynamic friction coefficient in the molding analysis. Within the range of the Coulomb equation, the shear angle changing was compared with the actual preform shape to show similar results

Improvement of electrical conductivity in glass bubble-carbon nanotube/polyamide 6 hybrid scale composite through novel mechanical forming and segregated network morphology

The study suggests that GB-CNT/PA6 multiscale hybrid composite can be used to create a network structure with controllable electrical conductivity, making it a promising material for various practical applications. The paper introduces a new method for controlling electrical conductivity of composite materials by creating a segregated network morphology (SNM) using a glass bubble (GB)-carbon nanotube (CNT)/polyamide 6 (PA6) multiscale hybrid composite. Instead of relying solely on CNTs, the addition of GB allows for a more economical process by reducing the required CNT concentration to achieve the desired electrical conductivity. The paper also analyzes the effects of varying GB and CNT content on electrical conductivity based on percolation theory. The results demonstrate an 18.8 times increase in electrical conductivity with the SNM approach. The study proposes that this approach could be used to create composite materials with controllable electrical conductivity, making them suitable for various applications

The preparation of highly ordered TiO2 nanotube arrays by an anodization method and their applications

The tubular-shaped nanostructure of TiO2 is very interesting, and highly ordered arrays of TiO2 nanotubes (TNTs) can be easily fabricated by anodization of the Ti substrate in specific electrolytes. Here in this feature article, we review synthesis methods for various TNTs including normal, alloy, and architectural forms such as bamboos, lace, and flowers. Specific nanosize architectures such as bamboo and lace types can be regulated by alternating voltage and further anodizing. In order to extend light response of TNTs to visible solar spectra, various dopings of specific elements have been discussed. The normal and modified TNTs are suggested for applications such as dye sensitized solar cells, water splitting, photocatalytic degradation of pollutants, CO2 reduction, sensors, energy storage devices including Li ion batteries and supercapacitors, and other applications such as flexible substrate and biomaterials.close372

Growth, detachment and transfer of highly-ordered TiO2 nanotube arrays: Use in dye-sensitized solar cells

In the present work, we report a simple method of making glass-based dye-sensitized solar cells (DSSCs) with individual free-standing TiO2 nanotube arrays.N