Fuel Cell

Stringent emission regulations combined with customer demands for improved fuel economy and performance have forced the automotive industry to consider more advanced powertrain configurations than standard port-fuel injected gasoline engines. Modern state-of-the-art powertrain systems may combine several power sources (internal combustion engines, electric motors, fuel cells, etc.) and various exhaust aftertreatment devices (catalytic converters, lean NOx traps, particulate filters, etc.) in addition to conventional engine subsystems such as turbochargers and exhaust gas recirculation. The determination of the way in which these systems need to be operated to meet driver's torque demand, performance and fuel economy expectations while satisfying federal emission regulations is a complex and a multiobjective optimal control problem. This paper reviews some of the approaches to this problem in the context of two case studies

This paper reports on the use of cellulose paper simultaneously as electrolyte, separation of electrodes, and physical support of a rechargeable battery. The deposition on both faces of a paper sheet of metal or metal oxides thin layers with different electrochemical potentials, respectively as anode and cathode, such as Cu and Al, lead to an output voltage of 0.70 V and a current density that varies between 150 nA/cm 2 and 0.5 mA/cm 2 , subject to the paper composition, thickness and the degree of OH x species adsorbed in the paper matrix. The electrical output of the paper battery is independent of the electrodes thickness but strongly depends on the atmospheric relative humidity (RH), with a current density enhancement by more than 3 orders of magnitude when RH changes from 60% to 85%. Besides flexibility, low cost, low material consumption, environmental friendly, the power output of paper batteries can be adapted to the desired voltage-current needed, by proper integration. A 3-V prototype was fabricated to control the ON/OFF state of a paper transistor.

AbstractÐThe electrochemical compression of hydrogen is well known since years. But new developments of the polymer electrolyte membrane (PEM) fuel cells make it possible to realize the electrochemical compression in a PEM-cell with high eciency. A new cell design of PEM-cells for operation with a high pressure dierence between anode side and cathode side was developed. The puri®cation of hydrogen from carbon monoxide of the reformer gas can be integrated in the hydrogen compressor cell. Operation parameters are presented. #

As climate change becomes a more widely recognized global problem, electrical propulsion of vehicles appears to be a promising solution to cut green house gases emissions. While the automotive industry makes rapid strides towards a mature electric car market, very few initiatives have arisen in the maritime sector thus far. Existing recreational electric boats are often powered either by batteries only, photovoltaic panels and batteries, or fuel cell and batteries, with range and performances dependent upon sun radiation and hydrogen storage capacity. This study contemplates an electric propulsion system for a boat, encompassing battery, photovoltaic panels and a hydrogen fuel cell, which provide incomparable range and flexibility of use. This propulsion system has been designed for a 1/8 scale model (2 m long) of the Hidrocat catamaran in order to reach required speed and to offer suitable range. The elements of the propulsion system have been characterized individually in a laboratory and a simulation model has been created based on this testing campaign. It permits simulation of various sailing schemes as well as study and prediction of energy flows and consumptions. Several trials with the catamaran scale model were conducted while monitoring the circuit components. The experimental data acquired during live testing of the scale model were compared to the output of the simulations and both were consistent which confirmed the reliability of the simulator model. The behaviour of the propulsion system encompassing two renewable sources energy was efficient and the technological choices have been validated.

The kinetics of oxygen reduction was investigated in acid solutions on Pt monolayers deposited on modified carbon-supported PdIr nanoparticles using the rotating diskelectrode technique. Iridium is introduced into the Pd substrate in order to fine-tune the Pt-Pd interactions and to improve Pd stability under operating conditions of the fuel cell. The kinetics of the oxygen reduction reaction shows enhancement with the Pt monolayer on the PdIr nanoparticle surfaces in comparison with the reaction on Pt/

Pt nanoparticles were supported on Sb2O5.SnO2 (ATO), on carbon and on physical mixtures of ATO and carbon by an alcohol-reduction process using ethylene glycol as reducing agent. The obtained materials were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their performance for ethanol oxidation was investigated at room temperature by chronoamperometry and in a direct ethanol fuel cell (DEFC) at 100 °C. Pt nanoparticles supported on a physical mixture of ATO and carbon showed a significant increase of performance for ethanol oxidation compared to Pt nanoparticles supported on ATO or on carbon.

Recent improvements in fuel cell technology along with an increasing demand for small generator units have led to renewed interest in dispersed generation units. This work demonstrates a methodology for deploying dispersed fuel cell generators throughout a power system to allow for more efficient operation. A detailed study of the system losses and sensitivities on Eastern Washington system as part

This paper describes the RT-LAB real-time simulator implementation of the Hardware-In-the-Loop simulation of a fuel cell hybrid electric vehicle system with several 10 kHz converters. The paper demonstrates the necessity to use special IGBT bridge models that implements interpolation techniques within fixed time step simulation scheme. The paper reports on the latest advances from Opal-RT to simulate this kind of system with a 10 µs sample time. HIL computational time measurement are provided as well as a model fidelity comparison made by Toyota Motor Corp. of the RT-LAB Electrical Drive Simulator versus an actual fuel cell hybrid electric vehicle. In this paper, we describe an the methodology and simulation techniques used to make the real-time simulation of a fuel-cell hybrid vehicle with DC-DC converter and several PMSM inverter drives running with 10 kHz carrier frequency. The paper is organized in the following manner. First, typical problems regarding the real-time simulation ...

One of the current challenges for application of PEM fuel cell is to find corrosion resistant, electrically conductive, light weight, cost competitive bipolar plate material. Low temperature carburization (LTC) of stainless steels is a novel, patented process by Swagelok Company. This paper addresses the corrosion resistance characteristics of LTC SS 316 for polymer electrolyte membrane fuel cell (PEMFC) bipolar plate applications. Corrosion properties of this material were studied using potentiodynamic and potentiostatic tests in simulated (1 M H 2 SO 4 + 2 ppm HF, 0.5 M H 2 SO 4 , pH: 4.0, and 5% HCl + 5% Na 2 SO 4) PEMFC conditions. LTC SS 316 showed excellent corrosion resistance in these conditions compared to SS 316. The mechanism of anodic dissolution and general corrosion of LTC SS 316 was observed to be similar to SS 316 however the extent of LTC SS 316 corrosion was less. LTC SS 316 showed corrosion currents well below 16 A cm −2 in anodic and cathodic atmospheres under potentiostatic conditions. The potentiostatic current rapidly falls to ∼4.0 and ∼1.5 A cm −2 under anodic and cathodic conditions, respectively. LTC SS 316 was observed to form a thinner oxide layer as compared to SS 316 after 24 h of potentiostatic testing. Moreover LTC SS 316 lowered the interfacial contact resistance by approximately 24% as compared to SS 316 after corrosion testing. Hence this study clearly states the performance advantage of using LTC SS 316 as bipolar plate material as compared to conventional materials.

The fuel cell oxygen starvation problem is addressed in this paper using a robust load governor. By regulating the current drawn from the fuel cell, the pointwise-in-time constraints on the oxygen excess ratio and on the oxygen mass inside the cathode are strictly enforced to protect the fuel cells from oxygen starvation. The load governor is designed using a nonlinear reference governor approach. Parameter uncertainties such as those due to imperfect controls of temperature and humidity are handled in the load governor design using a novel approach based on sensitivity functions. Simulation results are included to demonstrate the effectiveness of the proposed scheme. The results are compared with those of a linear filter which has been proposed in the prior literature to achieve similar goals.

Methanol serves as energy carrier in direct methanol fuel cells. The decomposition pathways of methanol on Pd(1 1 1) surface in both neutral and alkaline medium are studied by density functional theory. In neutral medium, the activation barriers are rather high for both C-H and O-H bonds breaking of the first decomposition step, which accounts for the low activity of palladium in neutral medium. However, in alkaline medium, the barrier of the O-H bond breaking is greatly reduced to 77 kJ/mol, as compared to 121 kJ/mol in neutral medium, with the assistance of the hydroxyl adsorbed on the surface. The first intermediate of methoxy further decomposes stepwisely to subsequent intermediates, such as formaldehyde, formyl, and carbon monoxide. Furthermore, the carbon monoxide can combine with the adsorbed hydroxyl to form the carboxyl leading to the final product, carbon dioxide. The stepwise pathways involving methoxy, formaldehyde, formyl, carbon monoxide and carbon dioxide, are supported by experimental observations.

. Ž . Ž . Serpentine SFF and interdigitated IFF flow fields were investigated with regard to their use in a direct methanol fuel cell DMFC . The DMFC equipped with SFFs showed lower methanol cross-over, higher fuel utilisation and slightly larger voltage efficiency at low current densities. IFFs enhanced mass transport and membrane humidification allowing to achieve high power densities of 450 and 290 mW cm y2 in the presence of oxygen and air feed, respectively, at 1308C. A fuel efficiency of 90% was obtained with the IFFs in the presence of 1 M methanol feed at 1308C and a current load of 500 mA cm y2 . q 2000 Elsevier Science S.A. All rights reserved.

The notion of dominant designs deals with dominance in the market and the dominant design is thought to be dominant because of market selection forces. The notion thus ignores the possible selection that takes place in pre-market R&D stages of technological trajectories. In this paper we ask the question whether pre-market selection takes place and if this can lead to

Nowadays, in many countries the increase of generating capacity takes place in small units of so-called distributed generation (DG), and among them in hybrid power (generating) systems (HPS). They use primary energy conventional sources as well as renewable energy sources (RES), and in many cases produce electricity and heat (CHP). It is very often that definition of distributed generation is connected with definition of renewable energy sources. Using of renewable energy sources is one of the crucial components of the sustainable development, giving rationale economic, ecological and social effects. Support for development of renewable energy sources utilization became very important objective within the European Union.

The direct ethanol fuel cell (DEFC) is a promising fuel cell device, which could provide power to portable and microelectronic equipment in the future. In the present investigation, the influence of a pore-former, polytetrafluoroethylene (PTFE) and catalyst loadings in the electrocatalyst of the anode on DEFC performance is studied. The decal transfer method is used to prepare the membrane electrode assembly (MEA) using PtRu/C (40:20% by wt) as the anode catalyst, and Pt/C (40% by wt) as the cathode catalyst, a pore-former, PTFE dispersion and Nafion ionomer. The pore-former used is 10% (by wt) NaHCO3 in the catalyst ink during the preparation of MEA. The voltage-current characteristics of DEFC were monitored at different loadings of the catalyst, PTFE and a pore-former in MEA. The DEFC performance improved with the use of a pore-former and higher loading of PTFE in MEA. Higher DEFC performance is obtained because PTFE, along with the network of pores in the anode side allowed easy removal of reaction species, thereby rendering the catalyst site available for ethanol oxidation. Further, the use of a pore-former and PTFE at the anode allowed higher loading of electrocatalyst resulting in an increase in the performance of DEFC. The DEFC, with 1 mg cm−2 of catalyst loading at the anode and cathode, 10% (by wt) NaHCO3 of a pore-former, 20% (by wt) PTFE loading in catalyst ink gives maximum power density of 8.5 mW cm−2 at a current density of 31.3 mA cm−2. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

The performance characteristics of fuel cells based on proton conducting BaCeO 3 solid electrolyte doubly doped with gadolinium and praseodymium are reported. The amount of praseodymium doping is systematically varied in order to optimize the fuel cell performance. Fuel cells incorporating the optimum amount of praseodymium exhibit power density levels enhanced by a factor of three, compared to those incorporating undoped BaCeO 3 . The performance of the fuel cell is essentially the same irrespective of the fuel used. However, the performance of the fuel cell is slightly better in hydrogen than in ammonia. Nevertheless, fuel cells operated in ammonia show a greater decrease in peak power density with decreasing temperature than those operated in hydrogen. This behaviour suggests that alternative anode materials need to be utilized at lower operating temperatures.

A novel sulfonated diamine monomer, 1,4-bis(4-aminophenoxy)-naphthyl-2,7-disulfonic acid (BAPNDS), was synthesized. A series of sulfonated polyimide copolymers were prepared from BAPNDS, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and nonsulfonated diamine 4,4′-diaminodiphenyl ether (ODA). Flexible, transparent, and mechanically strong membranes were obtained. The membranes displayed slightly anisotropic membrane swelling. The dimensional change in thickness direction was larger than that in planar. The novel SPI membranes showed higher conductivity, which was comparable or even higher than Nafion 117. Membranes exhibited methanol permeability from 0.24 × 10−6 to 0.80 × 10−6 cm2/s at room temperature, which was much lower than that of Nafion (2 × 10−6 cm2/s). The copolymers were thermally stable up to 340 °C. These preliminary results have proved its potential availability as proton-exchange membrane for PEMFCs or DMFCs.

Distributed power generation is the future trend due to its ability to accommodate variety of renewable/alternative energy sources, its potential to improve the energy efficiency and power system capability, and its promise for power reliability and security. Many distributed energy sources exists such solar energy, fuel cell, micro turbine, and wind energy. Distributed power generation concept has been implemented in

In this paper, an energy system comprising three energy sources, namely PV, wind and fuel cells, is proposed. Each of the three energy sources is controlled so as to deliver energy at optimum efficiency. Fuzzy logic control is employed to achieve maximum power tracking ...

A 3D numerical study was carried out to analyze flow, heat and mass transfer first in a single half-cell cathode channel of proton exchange membrane (PEM) fuel cell. From practical point of view, it is necessary to put the appropriate number of cells in a stack. Hence, the above study on a single half-cell is extended to a stack of channels. Due to stacking, the assumption of uniform flow distribution would no longer hold true. Therefore, the channel flow-maldistribution is considered. The water formed at the active surface due to the electrochemical reaction diffuses through the porous layer and eventually enters the gas flow duct. The higher gas velocities in the duct result in faster water vapour removal which leads to a lower value of water vapour into the duct and hence a lower Nusselt number.

In this study, the Taguchi method was applied to determine optimum working conditions in obtaining maximum power density of a PEMFC. Performance measure analysis was also followed by performing a variance analysis, in order to determine the optimum levels and relative magnitude of the effect of parameters. The optimum working conditions were found to be system pressure, 5 bar; flow rate ratio of H 2 and O 2 , 1/2; temperature of fuel cell, 75 • C and temperature of humidifiers, 75 • C. Under these conditions, the amount of maximum power density was predicted as 353 mW cm −2 by using experimental results obtained according to Taguchi's orthogonal array (OA) L 9 (3 4 ). Verification experiment was done for the same optimum conditions and maximum power density was observed as 379.64 mW cm −2 . According to the results of this optimization, it was seen that pressure and humidification temperature were the effective parameters. ᭧

A novel fabrication technique for micro proton exchange membrane fuel cells (PEMFCs) based on carbon-MEMS (C-MEMS) was optimized to yield higher performance cells. Polymer manufacturing is relatively easy compared to directly patterning graphite as is typically done to make fuel cell bipolar plates. In a C-MEMS approach, fuel cell bipolar plates are fabricated by first patterning polymer Cirlex ® sheets. By subsequently pyrolyzing the machined polymer sheets at high temperature in an inert atmosphere, carbon bipolar plates with intricate groove structures to distribute the reactants are obtained. Using an improved assembly technique such as polishing the carbonized plates to minimize the contact resistance between gas diffusion layers (GDL) and bipolar plates, better pyrolysis temperature control and a better end plate design, a PEMFC with a 0.64 cm 2 active surface was fabricated using the newly developed bipolar plates. At 1 atm and 25 • C a maximum power density of ∼76 mW cm −2 was obtained, and at 2 atm and 25 • C ∼85 mW cm −2 was achieved. These data are comparable with data reported in the literature for PEMFCs and are a dramatic improvement over earlier results reported for the same C-MEMS based fuel cell. Electrochemical Impedance Spectroscopy (EIS) and cyclic voltammetry were carried out to characterize steady-state and transient characteristics of the novel C-MEMS fuel cell. (Y. Wang). 1 An exchange student from Brazil working at RERL of the UC Irvine. of electrically connecting the adjacent cells while at the same time distributing the reactant gases over the anode and cathode. Carbonbased substrates such as carbon paper and cloth constitute a typical GDL. The GDLs are placed on the membrane electrode assembly (MEA) and perform several functions: gas species transport, heat transport and last but not least the electrical connection between the bipolar plates and the catalyst layers on the proton-conductive membrane. The catalyst layers comprise the C/Pt or Pt alloy catalyst itself, an ionomer, and void space. The electrochemical reactions take place at the triple-phase boundary (TPB) of the catalyst layer, the gas phase and the ionically conductive membrane. The membrane, typically made of Nafion ® , fulfills a dual role, i.e. as the gas/electron separator and for conducting protons. The Nafion ® membrane is characterized by hydrophobic, fluorinated main chains with hydrophilic sulfonic acid pendant groups, allowing for protons to weakly interact with SO 3 − groups and to travel through the hydrated regions associated with those sulfonic groups. Different from the traditional power generation in heat engines, fuel cells are electrochemical devices and their efficiency is not limited by the Carnot heat cycle. Efficiencies of more than 50% have been achieved in many commercial units operating at low currents. Fuel cell efficiency is especially high at smaller scales and in this regard, fuel cells may be ideal for powering portable/micro electrical devices and may have the potential to replace batteries whose 0378-7753/$ -see front matter

A GPS network has been installed to monitor vertical crustal movement in the Lambert Glacier region, East Antarctica. The program commenced in January 1998 with a solar-powered GPS system installed at Beaver Lake. Solar-powered observations were also made late in the Antarctic summer of 1999. In January 2000, two new solarpowered sites will be installed to expand the monitoring network. In addition, we will be installing a hydrogen fuel cell power system at Beaver Lake to enable the equipment to operate throughout the winter months when solar power is not available. In this paper we outline the equipment which has been developed in order to operate remote GPS equipment in Antarctica, provide predictions of the expected rate of rebound and comment on preliminary results from the data collected to date.

ZeTek Power recently introduced mass manufacturable and cost effective alkaline fuel cells on the market. Today's research is focused on further improvement both in terms of performance increase and cost reduction. This research is classically performed using small (4 cm 2 ) experimental electrodes in the half-cell configuration. This allows the primary electrochemical losses in an anode or cathode to be determined independently. Additional performance losses occur when one integrates large electrodes into a module of 24 cells and in a stack comprised of many modules. By comparing the performance of half-cell experiments to that of modules, these losses can be distinguished and addressed. The information thus obtained, both for the small electrodes and in up-scaling is vital if one is to identify the key areas in which improvement is possible and where to focus future research. Furthermore, the identification of the losses in a module and system allows us to predict the final performance from half-cell measurements of a new laboratory scale experimental electrode. q

An important issue in the preliminary design of Autonomous Underwater Vehicles (AUV) is the selection of the optimal dimensions for the vehicle (sizing). These dimensions are dependent on the characteristics of the mission, the operating environment and the chosen technology. This paper presents a computer-based design-tool, which integrates all major design parameters to allow an efficient and rapid trade-off analysis between various options, for example different battery types, etc. In order to carry out fast modelling, different types of battery, fuel cell and semifuel cell options to power the AUV are pre-programmed in the dimensioning module and can be selected by the designer. An integral part of the vehicle design is sustainability and this can be determined by performing a Life Cycle Assessment (LCA) on the vehicle. LCA refers to the compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product system throughout its life cycle). For this purpose the SimaPro® system is used to model a modular AUV as a function of its external dimensions and the type of power supply. When the user is satisfied with the designed vehicle, the program can calculate the hydrodynamic variables of the vehicle and load these variables into the vehicle simulation package (DSTO V-Sim).

Environmental concerns coupled with the depletion of fuel sources has led to research on ethanol, fuel cells, and even generating electricity from vibrations. Much of the research in these areas is stalling due to expensive or environmentally contaminating processes, however recent breakthroughs in materials and production has created a surge in research on waste heat energy harvesting devices. The thermoelectric generators (TEGs) used in waste heat energy harvesting are governed by the Thermoelectric, or Seebeck, effect, generating electricity from a temperature gradient. Some research to date has featured platforms such as heavy duty diesel trucks, model airplanes, and automobiles, attempting to either eliminate heavy batteries or the alternator. A motorcycle is another platform that possesses some very promising characteristics for waste heat energy harvesting, mainly because the exhaust pipes are exposed to significant amounts of air flow. A 1995 Kawasaki Ninja 250R was used for these trials. The module used in these experiments, the Melcor HT3-12-30, produced an average of 0.4694 W from an average temperature gradient of 48.73 • C. The mathematical model created from the Thermoelectric effect equation and the mean Seebeck coefficient displayed by the module produced an average error from the experimental data of 1.75%. Although the module proved insufficient to practically eliminate the alternator on a standard motorcycle, the temperature data gathered as well as the examination of a simple, yet accurate, model represent significant steps in the process of creating a TEG capable of doing so.

This paper addresses a persistent and worsening societal dilemma worldwide: the ecological unsustainability of the automobile as the primary means for providing personal mobility. The solution to this problem will require input from all segments of society, and must include technological innovation, changes in the physical infrastructure and land use, and social, cultural, and institutional changes. A fundamental rethinking of the entire system of personal mobility is necessary. Governments can play a significant role in promoting change: by stimulating technological innovation through regulations, incentives and subsidies, by investing in the infrastructure, by providing leadership, and by organizing and supporting a debate with a focus on the system as a whole: its spatial characteristics, the motives for transport, and the alternatives that are presently not developed. From the technological perspective, one of the much-discussed solutions is a hydrogen-powered automobile. We argue that the future of this approach is questionable, and propose a fundamental re-framing of the significance of hydrogen: from viewing it as a solution to the personal mobility problem to seeing it as a medium for transporting and storing energy that has been generated elsewhere (preferably by renewable resources). A new and radically different way of seeing the problem of individual mobility, and of the roles of various stakeholders in finding solutions, is also necessary. This is the essence of higher order learning. To facilitate such learning among various societal groups, we advocate a combination of multi-stakeholder visioning processes, scenario building, backcasting exercises, and small-scale socio-technical experiments. These approaches may be practiced at various levels, from local to national, with experimentation probably being best suited for a smaller scale. An ongoing process of visioning future mobility in the Boston Metropolitan area illustrates how such approaches may be used.

Some problems can appear using Distributed Generation (DG). A better solution for clean green energy production can be made through a cluster of Renewable Distributed Resources (DR)-such as PV cells, wind turbines, fuel cells and others-and its associated loads. This is known as micro-grid, an Edison´s concept with a remarkable future in Kyoto´s Protocol era. In spite of this strategic point of view, two main stages of the micro-grid can be taken into account: grid-connected and stand alone (intentioned island). In addition, the improvement of the local reliability has an enormous importance. Furthermore, it is clearly critical to be able to use the waste heat by placing the DR near the heat load. In conclusion, it will have implemented a Combined Heat Power (CHP).

A unified treatment of the mechanism of electrocatalysis of methanol oxidation on platinum and platinum-containing alloys is put forward. The effect of various alloys is shown to be interpretable within this overall model, and methods for the systematic improvement of the rate of electro-oxidation of methanol are described. Finally, some recent results for model direct methanol fuel cells are given, showing that critical performance parameters for commercial exploitation are now achievable with modem catalytic formulations and cell designs. 0 1997 Elsevier Science B.V.

This paper describes a life cycle model for performing level-playing ®eld comparisons of the emissions, costs, and energy eciency trade-os of alternative fuel vehicles (AFV) through the fuel production chain and over a vehicle lifetime. The model is an improvement over previous models because it includes the full life cycle of the fuels and vehicles, free of the distorting eects of taxes or dierential incentives. This spreadsheet model permits rapid analyses of scenarios in plots of trade-o curves or eciency frontiers, for a wide range of alternatives with current and future prices and levels of technology. The model is available on request.

Distributed power generation is the future trend due to its ability to accommodate variety of renewable/alternative energy sources, its potential to improve the energy efficiency and power system capability, and its promise for power reliability and security. Many distributed energy sources exists such solar energy, fuel cell, micro turbine, and wind energy. Distributed power generation concept has been implemented in

The mechanism of the hydrogen evolution and reduction reactions on a nickel electrode has been examined several times, mainly because of the potential application of this material in water electrolysers and fuel cells. This work presents the results of electrochemical studies of hydrogen evolution and reduction on nickel plate in 30 wt% KOH at different temperatures ranging from 28 to 77-C. Kinetic parameters were obtained by steady state polarization experiments, compleme@d by cyclic voltammetry. Nickel showed an improved performance with increaGng temperature. It has been observed that a temperature increase from 28 to 77'C results iq an almost equal Tafel slope of 80 mV dcc-*. This bchaviour could be the impact of such factors as variation of the adsorbed hydrogen coverage with potential or the entropic contribution to the free energy of activation. However, some controversy still remains. Current density values increase with increasing temperature. A current-time dependence curve shows that the current density is constant up to 200 s, then it decreases with time. However, after loo0 s, current density is again constant and remains so up to 3000s. The apparent energy of activation AH was calculated from the Arrhenius plot.

An empirical equation [E = E 0-b log i-Rim exp (ni)] was shown to fit the experimental cell potential (E) vs. current density (i) data for proton exchange membrane fuel cells (PEMFCs), at several temperatures , pressures , and oxygen compositions in the. cathode gas mixture. The exponential term compensates for the mass-transport regwns of th~ E vs. z plot; i.e., the increase in slope of the pseudolinear region and the subsequent. rapid fall-off of the cell potential with increasing current density. As has been prevwusly shown, the terms E 0 ~nd b yield the electrode kmetic parameters for oxygen reduction in the PEMFC and R represents the resistance, predommantly ohmic and, to a small extent, the chargetransfer resistance of the electro-oxidation of hydrogen. The exponential term charactenzesthe mass-transport regwn of theE vs. i plot. The parameter n has more pronounced effects than the parameter m m this regwn. A physicochemical interpretation of these parameters is needed.

This article documents that the hydrogen economy continues to attract significant attention among politicians, the media, and some academics. We believe that an explanation lies in the way that the hydrogen economy fulfills psychological and cultural needs related to a future world where energy is abundant, cheap, and pollution-free, a ''fantasy'' that manifests itself with the idea that society can continue to operate without limits imposed by population growth and the destruction of the environment. The article begins by explaining its research methodology consisting of two literature reviews, research interviews of energy experts, and the application of symbolic convergence theory, a general communications theory about the construction of rhetorical fantasies. We then identify a host of socio-technical challenges to explain why the creation of a hydrogen economy would present immense (and possibly intractable) obstacles, an argument supplemented by our research interviews. Next, we employ symbolic convergence theory to identify five prevalent fantasy themes and rhetorical visions-independence, patriotism, progress, democratization, and inevitability-in academic and public discussions in favor of the hydrogen economy. We conclude by offering implications for scholarship relating to energy policy more broadly.

A Nation based amperometric hydrogen sensor that operates at room temperature has been developed. The electrolyte used in the sensor is Nation 117, which is a proton conducting solid polymer electrolyte. Palladium catalyst was used on the sensing side and platinum supported on carbon on the air side. The sensor functions as fuel cell, H2/Pd // Nation // Pt/O2 and the short circuit current is measured. The short circuit current is found to be linear with respect to concentration of hydrogen on the sensing side. The sensor is able to detect the concentration of hydrogen in argon down to ppb level. Details of assembly of the sensor, response behavior and applications are discussed.

Fuel Cells (PEMFC) may work as a powerful tool in the development and widespread testing of alternative energy sources. In order to obtain an adequate PEMFC model, (which could be used in the analysis of fuel cell generation systems), it is necessary to define the values for a specific group of modeling parameters. The simulation results are strongly affected by the choice of such modeling parameters.

This paper presents a dynamic model of a fuel cell system for residential power generation. The models proposed include a fuel cell stack model, reformer model and DC/AC inverter model. Furthermore a fuzzy logic (FLC) controller is used to control the active power of PEM fuel cell system. The controller modifies the hydrogen flow feedback from the terminal load. Simulation results confirmed the high performance capability of the fuzzy logic controller to control power generation. K e y w o r d s: polymer-electrolyte fuel cell, dynamic model, residential power, fuzzy controller

An analytical method has been developed to differentiate the electrical and thermal resistance of the PEM fuel cell assembly in the fuel cell operating conditions. The usefulness of this method lies in the determination of the electrical resistance based on the polarization curve and the thermal resistance from the mass balance. This method also paves way for the evaluation of cogeneration from a PEMFC power plant. Based on this approach, the increase in current and resistance due to unit change in temperature at a particular current density has been evaluated. It was observed that the internal resistance of the cell is dependent on the electrode fabrication process, which also play a major role in the thermal management of the fuel cell stack.

This paper presents the results of an optimization study using a comprehensive three-dimensional, multi-phase, non-isothermal model of a PEM fuel cell that incorporates the significant physical processes and the key parameters affecting fuel cell performance. The model accounts for both the gas and liquid phase in the same computational domain and, thus, allows for the implementation of phase change inside the gas diffusion layers. The model includes the transport of gaseous species, liquid water, protons, energy and water dissolved in the ion conducting polymer. Water is assumed to be exchanged among three phases; liquid, vapor and dissolved, and equilibrium among these phases is assumed. The model features an algorithm that allows a more realistic representation of the local activation overpotentials, which leads to improved prediction of the local current density distribution. This model also takes into account convection and diffusion of different species in the channels as well as in the porous gas diffusion layer, heat transfer in the solids as well as in the gases and electrochemical reactions. The results showed that the present multi-phase model is capable of identifying important parameters for the wetting behavior of the gas diffusion layers and can be used to identify conditions that might lead to the onset of pore plugging, which has a detrimental effect on the fuel cell performance. This model is used to study the effects of several operating, design and material parameters on fuel cell performance. Detailed analyses of the fuel cell performance under various operating conditions have been conducted and examined.