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Abstract A major obstacle to the development of commercially successful electric vehicles (EV) or hybrid electric vehicles (HEV) is the lack of a suitably sized battery. Lithium ion batteries are viewed as the solution if only they could be “scaled-up safely”, i.e. if thermal management problems could be overcome so the batteries could be designed and manufactured in much larger sizes than the commercially available near-2-Ah cells. Here, we review a novel thermal management system using phase-change material (PCM). A prototype of this PCM-based system is presently being manufactured. A PCM-based system has never been tested before with lithium-ion (Li-ion) batteries and battery packs, although its mode of operation is exceptionally well suited for the cell chemistry of the most common commercially available Li-ion batteries. The thermal management system described here is intended specifically for EV/HEV applications. It has a high potential for providing effective thermal management without introducing moving components. Thereby, the performance of EV/HEV batteries may be improved without complicating the system design and incurring major additional cost, as is the case with “active” cooling systems requiring air or liquid circulation.

Abstract When a lithium ion polymer battery (LiPB) is being cycled, one major cause for degradations is the irreversible side reactions between ions and solvent of electrolyte taking place at the surface of anode particles. SEM analysis of cycled battery cells has revealed that the deposits from the side reactions are dispersed not only on particles, but also between the composite anode and the separator. Thus, the solid electrolyte interface (SEI) becomes thicker and extra deposit layers are formed between composite anode and separator. Also, XPS analysis showed that the deposits are composed of Li 2 CO 3 , which is ionic conductive and electronic nonconductive. Based on the mechanisms and findings, we identified four degradation parameters, including volume fraction of accessible active anode, SEI resistance, resistance of deposit layer and diffusion coefficient of electrolyte, to describe capacity and power fade caused by the side reactions. These degradation parameters have been incorporated into an electrochemical thermal model that has been previously developed. The terminal voltage and capacity of the integrated model are compared with experimental data obtained for up to 300 cycles. Finally, the resistance of the deposit layer calculated by the model is validated against the thickness of the deposit layer measured by SEM.

Abstract Flexible thermoelectric power generators fabricated by evaporating thin films on flexible fiber substrates are demonstrated to be feasible candidates for waste heat recovery. An open circuit voltage of 19.6 μV K per thermocouple junction is measured for Ni–Ag thin films, and a maximum power of 2 nW for 7 couples at ΔT = 6.6 K is measured. Heat transfer analysis is used to project performance for several other material systems, with a predicted power output of 1 μW per couple for Bi2Te3/Sb2Te3-based fiber coatings with a hot junction temperature of 100 °C. Considering the performance of woven thermoelectric cloths or fiber composites, relevant properties and dimensions of individual thermoelectric fibers are optimized.

Abstract The total energy storage system cost is determined by means of a robust performance-based cost model for multiple flow battery chemistries. Systems aspects such as shunt current losses, pumping losses and various flow patterns through electrodes are accounted for. The system cost minimizing objective function determines stack design by optimizing the state of charge operating range, along with current density and current-normalized flow. The model cost estimates are validated using 2-kW stack performance data for the same size electrodes and operating conditions. Using our validated tool, it has been demonstrated that an optimized all-vanadium system has an estimated system cost of -1 for 4-h application. With an anticipated decrease in component costs facilitated by economies of scale from larger production volumes, coupled with performance improvements enabled by technology development, the system cost is expected to decrease to 160 kWh -1 for a 4-h application, and to $100 kWh -1 for a 10-h application. This tool has been shared with the redox flow battery community to enable cost estimation using their stack data and guide future direction.

SOFC composite electrodes of yttria-stabilized zirconia (YSZ) and either LaNi(0.6)GFe(0.4)O(3) (LNF) or La0.91Sr0.09Ni0.6Fe0.4O3 (LSNF) were prepared by infiltration to a loading of 40 wt% of the perovskite into Porous YSZ using aqueous solutions of the nitrate salts. XRD measurements indicated that the perovskite structures were formed following calcination at 850 degrees C, at which temperature the LNF and LSNF form small particles that coat the YSZ pores. Heating to 1100 degrees C causes the particles to form a dense film over the YSZ but caused no solid-state reaction. Calcination of an LNF-YSZ composite to 1200 degrees C led to an expansion of the LNF lattice, suggesting introduction of Zr(IV) into the perovskite; further heating to 1300 degrees C caused the formation of La2Zr2O7. For 850 degrees C calcination, the electrode performance of both LNF-YSZ and LSNF-YSZ composites was similar to that reported for composites of YSZ and La0.8Sr0.2FeO3 (LSF), with a current-independent impedance of approximately 0.1 Omega cm(2) at 700 degrees C in air. For 1100 degrees C calcination, both LNF-YSZ and LSNF-YSZ composites exhibited impedances that decreased strongly under both anodic and cathodic polarization. The implications of these results for preparing electrodes based on LNF and LSNF are discussed.

Abstract Proper water management plays an essential role in the performance and durability of Polymer Electrolyte Fuel Cells (PEFCs), but it is challenged by the variety of water transport phenomena that take place in these devices. Previous experimental work has shown the existence of fluctuations between low and high current density levels in PEFCs operated with wet hydrogen and dry air feed. The alternation between both performance states is accompanied by strong changes in the high frequency resistance, suggesting a cyclic hydration and dehydration of the membrane. This peculiar scenario is examined here considering liquid water distributions from neutron imaging and predictions from a 3D two-phase non-isothermal model. The results show that the hydration-dehydration cycles are triggered by the periodic condensation and shedding of liquid water at the anode inlet. The input of liquid water humidifies the anode channel and offsets the membrane dry-out induced by the dry air stream, thus leading to the high-performance state. When liquid water is flushed out of the anode channel, the dehydration process takes over, and the cell comes back to the low-performance state. The predicted amplitude of the current oscillations grows with decreasing hydrogen and increasing air flow rates, in agreement with previous experimental data.

Abstract A novel dot matrix and sloping baffle flow field plate for proton exchange membrane fuel cell (PEMFC) cathode is designed. The plate consists of dispersive and arrayed blocks with sloping angles as shoulders. Features of the plate include a large fluid domain, and air guidance in two directions is achieved by sloping sides of the block. The cell output performance, internal transport process and liquid water removal process of the PEMFC with the matrix flow field are numerically investigated by three-dimensional two-phase full cell model and volume of fluid (VOF) model. The simulation results show that compared with the parallel and serpentine flow field, the matrix flow field can achieve high cell output performance by both improving oxygen supply to gas diffusion layer (GDL) and uniform distribution. Comparing five matrix flow fields with different block sizes and numbers shows that adequate contact area between the plate and GDL for current conductor is critical. For liquid water removal process in the matrix flow field, liquid water is hardly blocked by arrayed blocks and can leave GDL quickly. In summary, the matrix flow field fits high current density demand of PEMFC well, and some new perspectives on flow field design are presented.

Widespread implementation of polymer electrolyte membrane fuel cell (PEMFC) powerplants for stationary and vehicular applications will be dependent in the near future on using readily available hydrocarbon fuels as the source of the hydrogen fuel. Methane and propane are ideal fuels for stationary applications, while methanol, gasoline, and diesel fuel are better suited for vehicular applications. Various means of fuel processing are possible to produce a gaseous fuel containing H2, CO2 and CO. CO is a known electrocatalyst poison and must be reduced to low (10's) ppm levels and CO2 is said to cause additional polarization effects. Even with no CO in the feed gas a H2/CO2/H2O gas mixture will form some CO. Therefore, as a first step of developing a PEMFC that can operate for thousands of hours using a reformed fuel, we used an anode gas feed of 80% H2 and 20% CO2 to simulate the reforming of CH4. To investigate the effect of reformate on cell performance and endurance, a single cell with an active area of 58 cm2 was assembled with a membrane electrode assembly (MEA) furnished by Texas A&M University using IGT's internally manifolded heat exchange (IMHEX™) design configuration. The MEA consisted of a Nafion 112 membrane with anode and cathode Pt catalyst loadings of 0.26 and 1.46 mg/cm2, respectively. The cell was set to operate on a synthetic reformate–air at 60°C and 1 atm and demonstrated over 5000 h of endurance with a decay rate of less than 1%/1000 h of operation. The cell also underwent four successful thermal cycles with no appreciable loss in performance. The stable performance is attributed to a combination of the IGT IMHEX plate design with its inherent uniform gas flow distribution across the entire active area and MEA quality. The effects of temperature, gas composition, fuel utilization (stoics) and thermal cycle on cell performance are described.

Abstract International Fuel Cells Corporation is conducting a US Environmental Protection Agency (EPA) sponsored program to demonstrate energy recovery from landfill gas using a commercial phosphoric acid fuel cell power plant. The US EPA is interested in fuel cells for this application because it is the cleanest energy conversion technology available. This paper discusses the results of Phase I, a conceptual design, cost, and evaluation study. The conceptual design of the fuel cell energy recovery concept is described and its economic and environmental feasibility is projected. Phase II will include construction and testing of a landfill gas pretreatment system which will render landfill gas suitable for use in the fuel cell. Phase III will be a demonstration of the energy recovery concept.