Ion exchange membranes were prepared by simultaneous radiation grafting of styrene into FEP films and subsequent sulfonation. Divinylbenzene was used as crosslinker in the grafting medium. The ...distribution of polystyrene grafts across the membrane matrix was determined by microprobe measurements. It was observed that for low levels of grafting such as 13%, crosslinked membranes had a better homogeneity in graft distribution across its matrix as compared to the non-crosslinked ones. The latter showed a much higher concentration of grafts at the surface than in the middle of the film. The membrane characteristics, such as swelling and specific resistivity as a function of the degree of grafting and crosslinking were evaluated. Membranes showed a sharp decrease in the resistivity up to ∼ 25% grafting, beyond which the decrease was not significant. The higher the crosslinker content, the higher was the ionic resistivity. A relation between the degree of grafting and membrane properties, such as degree of swelling and specific resistivity as a function of the crosslinker content was established.
Proton exchange membranes for fuel cell applications were synthesized by pre-irradiation grafting of styrene/divinylbenzene mixtures into poly(fluoroethylene-
co-hexafluoropropylene) films and ...subsequent sulfonation. Grafting of pre-existing films overcomes the problem of shaping the grafted polymer into thin membranes and makes this process a potentially cheap and easy technique for the preparation of solid polymer electrolytes.
The grafted membranes were characterized by measuring their ion exchange capacity, swelling, specific resistivity and area resistance. Due to their thickness in the range 67–211 μm, some of the membranes have a considerably lower resistance than the most widely used membrane Nafion
® 117 (DuPont). The short-term and long-term performance of these membranes was investigated in
H
2
O
2
fuel cells. Thin (< 100
μm), highly crosslinked (12% divinylbenzene) membranes show the best performance in the fuel cells. Tests for periods of up to 1400 h were performed to examine membrane stability and the degradation of grafted membranes.
Efficiency is the key parameter for the application of fuel cells in automotive applications. The efficiency of a hydrogen/oxygen polymer electrolyte fuel cell system is analyzed and compared to ...hydrogen/air systems. The analysis is performed for the tank to electric power chain. Furthermore, the additional energy required for using pure oxygen as a second fuel is analyzed and included in the calculation. The results show that if hydrogen is produced from primary fossil energy carriers, such as natural gas and pure oxygen needs to be obtained by a conventional process; the fuel to electric current efficiency is comparable for hydrogen/oxygen and hydrogen/air systems. However, if hydrogen and oxygen are produced by the splitting of water, i.e., by electrolysis or by a thermochemical process, the fuel to electric current efficiency for the hydrogen/oxygen system is clearly superior.
The main factors for reducing the consumption of a vehicle are reduction of curb weight, air drag and increase in the drivetrain efficiency. Highly efficient drivetrains can be developed based on ...PEFC technology and curb weight may be limited by an innovative vehicle construction. In this paper, data on consumption and efficiency of a four‐place passenger vehicle with a curb weight of 850 kg and an H2/O2 fed PEFC/Supercap hybrid electric powertrain are presented. Hydrogen consumption in the New European Driving Cycle is 0.67 kg H2/100 km, which corresponds to a gasoline equivalent consumption of 2.5 l/100 km. When including the energy needed to supply pure oxygen, the calculated consumption increases from 0.67 to 0.69–0.79 kg H2/100 km, depending on the method of oxygen production.
Electrochemical reduction of H2O2 at pyrolytic graphite disc electrodes of radius 2.5 mm occurs at readily accessible potentials (600 mV versus the standard hydrogen electrode) in the presence of ...yeast cytochrome c peroxidase. Introduction of the enzyme into the electrolyte solution initiates large changes in the ellipsometric angles measured for the electrode-solution interface, consistent with time-dependent enzyme adsorption. This process may be correlated with changes in electrochemical activity. Over the same time course, linear-sweep voltammograms are characterized by a transition from a sigmoidal to a peak-type waveform. It is proposed that the time-dependent behaviour may be rationalized by use of a microscopic model for substrate mass transport, in which the two-electron reduction of peroxide occurs at electrocatalytic sites consisting of adsorbed enzyme molecules. A voltammetric theory based on treating the adsorbed redox enzymes as an expanding array of microelectrodes is in excellent agreement with experiment.
► Fuel cell hybrid vehicles are under consideration. ► We consider the direct electrical coupling of a fuel cell and a battery. ► The fuel cell power is actively controlled by adjusting its operating ...pressure. ► The power demand of a vehicle is fulfilled while sustaining the battery SOC. ► Without DC/DC converter, the hybrid powertrain becomes simpler and cheaper.
The concept of passive hybrid, i.e. the direct electrical coupling between a fuel cell system and a battery without using a power converter, is presented as a feasible solution for powertrain applications. As there are no DC/DC converters, the passive hybrid is a cheap and simple solution and the power losses in the electronic hardware are eliminated. In such a powertrain topology where the two devices always have the same voltage, the active power sharing between the two energy sources can not be done in the conventional way. As an alternative, control of the fuel cell power by adjusting its operating pressure is elaborated. Only pure H
2/O
2 fuel cell systems are considered in this approach. Simulation and hardware in the loop (HIL) results for the powertrain show that this hybrid power source is able to satisfy the power demand of an electric vehicle while sustaining the battery state of charge.
Fuel Cell Modeling and Simulations John Mantzaras; Nordahl Autissier; Diego Larrain ...
Chimia,
01/2004, Letnik:
58, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Fundamental and phenomenological models for cells, stacks, and complete systems of PEFC and SOFC are reviewed and their predictive power is assessed by comparing model simulations against ...experiments. Computationally efficient models suited for engineering design include the (1+1) dimensionality approach, which decouples the membrane in-plane and through-plane processes, and the volume-averaged-method (VAM) that considers only the lumped effect of pre-selected system components. The former model was shown to capture the measured lateral current density inhomogeneities in a PEFC and the latter was used for the optimization of commercial SOFC systems. State Space Modeling (SSM) was used to identify the main reaction pathways in SOFC and, in conjunction with the implementation of geometrically well-defined electrodes, has opened a new direction for the understanding of electrochemical reactions. Furthermore, SSM has advanced the understanding of the COpoisoning-induced anode impedance in PEFC. Detailed numerical models such as the Lattice Boltzmann (LB) method for transport in porous media and the full 3-D Computational Fluid Dynamics (CFD) Navier-Stokes simulations are addressed. These models contain all components of the relevant physics and they can improve the understanding of the related phenomena, a necessary condition for the development of both appropriate simplified models as well as reliable technologies. Within the LB framework, a technique for the characterization and computer-reconstruction of the porous electrode structure was developed using advanced pattern recognition algorithms. In CFD modeling, 3-D simulations were used to investigate SOFC with internal methane steam reforming and have exemplified the significance of porous and novel fractal channel distributors for the fuel and oxidant delivery, as well as for the cooling of PEFC. As importantly, the novel concept has been put forth of functionally designed, fractal-shaped fuel cells, showing promise of significant performance improvements over the conventional rectangular shaped units. Thermo-economic modeling for the optimization of PEFC is finally addressed.
PDF