Advances in catalysis for fuel cells

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Two-phase flow and oxygen transport in the perforated gas diffusion layer of proton exchange membrane fuel cell

Liquid water transport in perforated gas diffusion layers (GDLs)is numerically investigated using a three-dimensional (3D)two-phase volume of fluid (VOF)model and a stochastic reconstruction model of GDL microstructures. Different perforation depths and diameters are investigated, in comparison with the GDL without perforation. It is found that perforation can considerably reduce the liquid water level inside a GDL. The perforation diameter (D = 100 μm)and the depth (H = 100 μm)show pronounced effect. In addition, two different perforation locations, i.e. the GDL center and the liquid water break-through point, are investigated. Results show that the latter perforation location works more efficiently. Moreover, the perforation perimeter wettability is studied, and it is found that a hydrophilic region around the perforation further reduces the water saturation. Finally, the oxygen transport in the partially-saturated GDL is studied using an oxygen diffusion model. Results indicate that perforation reduces the oxygen diffusion resistance in GDLs and improves the oxygen concentration at the GDL bottom up to 101% (D = 100 μm and H = 100 μm)

Application of multiple graphene layers as catalyst support material in fuel cells

The fuel cell electrode layer is a significant part of a fuel cell. The electrode layer is composed of the catalyst and porous electrode or gas diffusion layer. Catalyst has critical importance due to the influence on the cost and durability of fuel cells. The production of novel catalyst support materials could open up new ways in order to ensure the catalytic activity by lowering the amount of catalyst loaded [1]. At this point, utilization of multiple graphene layers as catalyst support material increase thermal and electronic conductivities of the membrane electrolyte in fuel cells. Graphene is the flat monolayer of carbon atoms in sp2 hybridization and it has exceptional electronic conductivity, high chemical and mechanical stability, and high surface area [2]. In the present work, we propose an enhanced, safer and mild technique for the separation of graphene layers from graphite to be used in the production of low-cost and durable catalyst support for polymer electrolyte membrane fuel cells. All samples were characterized in details by Scanning Electron Microscopy (SEM), XRay Diffraction (XRD), Thermal Gravimetric Analyzer (TGA), Atomic Force Microscope (AFM) and Raman Spectroscopy. [1] Y. Shao, J. Liu, Y. Wang, Y. Lin, Novel catalyst support materials for PEM fuel cells: current status and future prospects, J. Mater. Chem. 19 (2009) 46–59 [2] M. I. Katsnelson, Graphene: carbon in two dimensions, Materials Today 10 (2007), 20-2

Fuel cells : state of the art

Publication CIMNEThis report pretends to explain the state of the art of fuel cells and the applications focused on aviation, such as unmanned aerial vehicles (UAV). A fuel cell is an electromechanical device that ha the ability to convent chemical energy of a reactant directly into electricity with high efficiency. When the fuel reacts with the oxidant, the electromechanical reaction takes place and some energy is released, usually low-voltage DC electrical energy and heat. The former is used to do useful work directly and the latter is wasted or can be used in cogeneration applications. In the following sections, two concepts will be described: the unit cell and the fuel cell. The unit is the basic operating device that converts chemical energy into electricity. Multiple unit cells connected together in series make up the fuel cell, giving the desired voltage in a specific application.Preprin

Composite nanostructured solid-acid fuel-cell electrodes via electrospray deposition

Stable, porous, nanostructured composite electrodes were successfully fabricated via the inexpensive and scalable method of electrospray deposition, in which a dissolved solute is deposited onto a substrate using an electric field to drive droplet migration. The desirable characteristics of high porosity and high surface area were obtained under conditions that favored complete solvent evaporation from the electrospray droplets prior to contact with the substrate. Solid acid (CsH_2PO_4) feature sizes of 100 nm were obtained from electrosprayed water–methanol solutions with 10 g L^(−1) CsH_2PO_4 and 5 g L^(−1) Pt catalyst particles suspended using polyvinylpyrrolidone (PVP). Alternative additives such as Pt on carbon and carbon-nanotubes (CNTs) were also successfully incorporated by this route, and in all cases the PVP could be removed from the electrode by oxygen plasma treatment without damage to the structure. In the absence of additives (Pt, Pt/C and CNTs), the feature sizes were larger, 300 nm, and the structure morphologically unstable, with significant coarsening evident after exposure to ambient conditions for just two days. Electrochemical impedance spectroscopy under humidified hydrogen at 240 °C indicated an interfacial impedance of ~1.5 Ω cm^2 for the Pt/CsH_2PO_4 composite electrodes with a total Pt loading of 0.3 ± 0.2 mg cm^(−2). This result corresponds to a 30-fold decrease in Pt loading relative to mechanically milled electrodes with comparable activity, but further increases in activity and Pt utilization are required if solid acid fuel cells are to attain widespread commercial adoption

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Department of Energy Engineering (Energy Engineering)Solid oxide fuel cells (SOFCs) are recognized as next generation environmentally friendly energy conversion devices due to their high energy conversion efficiency, fuel flexibility, efficient reclamation of waste heat, and low pollutant emissions. Nevertheless, the commercialization of SOFCs has been impeded by reason of some issues associated with the high operating temperatures (800-1000oC) such as undesired reactions between cell components, high cost, and material compatibility challenges. Thus, reducing the operating temperatures toward an intermediate temperature range (600-800oC) is essential to overcome the aforementioned problems. In intermediate temperature SOFCs (IT-SOFCs), however, electrocatalytic activity toward oxygen reduction reaction at the cathode is significantly decreased, which in turn causes insufficient fuel cell performance. Current researches, therefore, have been focused on enhancing the performance of cathode for effective IT-SOFC operation. In this regard, the infiltration method could be an excellent cathode fabrication method, considering its outstanding advantages toward intermediate temperature operation. First, each optimized sintering temperature of cathode and electrolyte can be applied, ensuring the favorable characteristics for IT-SOFC operation. Second, due to relatively low sintering temperature, nano structured cathodes can be formed, resulting in enlarged surface area and enhancement of electrochemical performance. Finally, long term stability is improved because the thermal expansion coefficient between cathode and electrolyte is minimized. This thesis mainly focuses on the fabrication of SOFC cathode by the infiltration method to achieve high fuel cell performance in the intermediate temperature range. Herein, my research paper studying infiltrated cathode materials for IT-SOFC is presented as follows. - A Nano-structured SOFC Composite Cathode Prepared via Infiltration of La0.5Ba0.25Sr0.25Co0.8Fe0.2O3-?? into La0.9Sr0.1Ga0.8Mg0.2O3-?? for Extended Triple Phase Boundary Areaclos

Efficient X-ray CT-based numerical computations of structural and mass transport properties of nickel foam-based GDLs for PEFCs

Nickel foams are excellent candidate materials for gas diffusion layers (GDLs) for polymer electrolyte fuel cells (PEFCs) and this is due to their superior structural and transport properties. A highly computationally-efficient framework has been developed to not only estimate the key structural and mass transport properties but also to examine the multi-dimensional uniformity and/or the isotropy of these properties. Specifically, multiple two-dimensional X-ray CT images and/or numerical models have been used to computationally determine the porosity, the tortuosity, the pore size distribution, the ligament thickness, the specific surface area, the gas permeability and the effective diffusivity of a typical nickel foam sample. The results show that, compared to the conventionally used carbon substrate, the nickel foam sample demonstrate a high degree of uniformity and isotropy and that it has superior structural and mass transport properties, thus underpinning its candidacy as a GDL material for PEFCs. All the computationally-estimated properties, which were found to be consistent with the corresponding literature data, have been presented and thoroughly discussed