Design tool for estimating adsorbent hydrogen storage system characteristics for light-duty fuel cell vehicles

This work combines materials development with hydrogen storage technology advancements to address onboard hydrogen storage challenges in light-duty vehicle applications. These systems are comprised of the vehicle requirements design space, balance of plant requirements, storage system components, and materials engineering culminating in the development of an Adsorbent System Design Tool that serves as a preprocessor to the storage system and vehicle-level models created within the Hydrogen Storage Engineering Center of Excellence. Computational and experimental efforts were integrated to evaluate, design, analyze, and scale potential hydrogen storage systems and their supporting components against the Department of Energy 2020 and Ultimate Technical Targets for Hydrogen Storage Systems for Light Duty Vehicles. Ultimately, the Adsorbent System Design Tool was created to assist material developers in assessing initial design parameters that would be required to estimate the performance of the hydrogen storage system once integrated with the full fuel cell system.     

Design tool for estimating chemical hydrogen storage system characteristics for light-duty fuel cell vehicles

The U.S. Department of Energy (DOE) developed a vehicle Framework model to simulate fuel cell-based light-duty vehicle operation for various hydrogen storage systems. This transient model simulates the performance of the storage system, fuel cell, and vehicle for comparison to Technical Targets established by DOE for four drive cycles/profiles. Chemical hydrogen storage models have been developed for the Framework for both exothermic and endothermic materials. Despite the utility of such models, they require that material researchers input system design specifications that cannot be estimated easily. To address this challenge, a design tool has been developed that allows researchers to directly enter kinetic and thermodynamic chemical hydrogen storage material properties into a simple sizing module that then estimates system parameters required to run the storage system model. Additionally, the design tool can be used as a standalone executable file to estimate the storage system mass and volume outside of the Framework model. These models will be explained and exercised with the representative hydrogen storage materials exothermic ammonia borane (NH₃BH₃) and endothermic alane (AlH₃).     

An algebraic semi-empirical model for evaluating fuel crossover fluxes of a DMFC under various operating conditions

In a fuel cell of low temperature, especially a direct methanol fuel cell (DMFC), fuel crossover phenomenon plays a significant role not only in its performance evaluation and analysis, but also in the optimum control under various operating conditions. A quantitative prediction of the fuel crossover flux thus becomes essential. Generally speaking, the theoretical approaches to the issue will be dramatically complex and less practical. On the other hand, experimental schemes are time-consuming and less capable of further analysis and applications. Consequently, a semi-empirical model that incorporates dominant physical parameters and operating variables is proposed in this paper to adequately evaluate the phenomenon of fuel crossover fluxes. It is stated analytically in the form of an algebraic function, in which the fuel concentration, the current density, and the temperature of the fuel cell are considered. It is therefore more suitable for a variety of in-situ applications. In the proposed model, the methanol concentration gradient in the anode backing layer, the anode catalyst layer, and the membrane are analyzed. The transfer behavior of methanol is modeled on the basis of diffusion and electro-osmosis mechanisms. By means of the proposed model, one can obtain a better prediction and a clearer picture of the effects of operating variables and physical parameters on methanol crossover fluxes.     

An overview: Current progress on hydrogen fuel cell vehicles

The harmful consequences of pollutants emitted by conventional fuel cars have prompted vehicle manufacturers to shift towards alternative energy sources. Currently, fuel cells (FCs) are commonly regarded as highly efficient and non-polluting power sources capable of delivering far greater energy densities and energy efficiency than conventional technologies. Proton exchange membrane fuel cells (PEMFC) are viewed as promising in transportation sectors because of their ability to start at cold temperatures and minimal emissions. PEMFC is an electrochemical device that converts hydrogen and oxidants into electricity, water, and heat at various temperatures. The pros and cons of the technology are discussed in this article. Various fuel cell types and their applications in the portable, automobile, and stationary sectors are discussed. Additionally, recent issues associated with existing fuel cell technology in the automobile sector are reviewed.     

Numerical prediction on an automotive fuel cell driving system

Mathematical models were applied to predict the results of different strategies to improve automotive fuel cell driving systems. First, a fuel cell system was optimized on the base of a fuel cell stack model. Then calculations about the utilization of recovered energy from air exhaust steam were carried out. Two methods to combine the turbocharger with an electric compressor, namely in series and in parallel, were evaluated for a fuel cell system. Finally, research on the effect of removing the big power DC/DC converter, which is located between the fuel cell system and the driving motor, was conducted for a fuel cell driving system. The main results show that it is highly advantageous to connect the turbocharger with an electric compressor in series than in parallel; and that the fuel cell driving system without DC/DC converter before its motor could reach much higher performance characteristics, and even be so in lower power range while the cell voltage was designated to be lower.     

Effects of operation conditions on direct borohydride fuel cell performance

In this study, the influences of different operational conditions such as cell temperature, sodium hydroxide concentration, oxidant conditions and catalyst loading on the performance of direct borohydride fuel cell which consisted of Pd/C anode, Pt/C cathode and Na⁺ form Nafion membrane as the electrolyte were investigated. The experimental results showed that the power density increased by increasing the temperature and increasing the flow rate of oxidant. Furthermore, it was found that 20 wt.% of NaOH concentration was optimum for DBFC operation. When oxygen was used as oxidant instead of air, better performance was observed. Experiments also showed that electrochemical performance was not considerably affected by humidification levels. An enhanced power density was found by increasing the loading of anodic catalyst. In the present study, a maximum power density of 27.6 mW cm⁻² at a cell voltage of 0.85 V was achieved at 55 mA cm⁻² at 60 °C when humidified air was used.     

Design tool for estimating metal hydride storage system characteristics for light-duty hydrogen fuel cell vehicles

The U.S. Department of Energy (DOE) has developed the Framework model to simulate fuel cell-based light-duty vehicle operation for various hydrogen storage systems. This transient model simulates the performance of the storage system, fuel cell, and vehicle for comparison to DOE's Technical Targets using four drive cycles. Metal hydride hydrogen storage models have been developed for the Framework model. Despite the utility of this model, it requires that material researchers input system design specifications that cannot be easily estimated. To address this challenge, a design tool has been developed that allows researchers to directly enter physical and thermodynamic metal hydride properties into a simple sizing module that then estimates the systems parameters required to run the storage system model. This design tool can also be used as a standalone MS Excel model to estimate the storage system mass and volume outside of Framework and compare it to the DOE Technical Targets. This model will be explained and exercised with existing hydrogen storage materials.     

Research and development of on-board hydrogen-producing fuel cell vehicles

Combining with the characteristics of different types of electric vehicles, the on-board hydrogen-producing fuel cell vehicle design is adopted, which eliminates the problems about the high-pressure hydrogen storage and the hydrogenation process. The fuel cell is used as the main power source to drive the motor, and the lithium battery is used as the auxiliary power source to accelerate and recycle energy in order to meet the special requirements, like energy recovery, power and dynamic characteristics, of fuel cell vehicles. On the ADVISOR simulation platform based on MATLAB/Simulink environment, a hybrid drive model and a pure fuel cell drive model are built, and simulation and comparative analysis are performed. In the hybrid drive model, fuel cells and lithium batteries work in the highly efficient and safe operating areas respectively, and the output power of fuel cell has small fluctuations, improving energy utilization efficiency and extending the service life of the fuel cell. At the same time, the charge and discharge of the lithium battery can be effectively managed to ensure the safety of charging and prolong the service life of the lithium battery.     

Neural network model of 100 W portable PEM fuel cell and experimental verification

The inherent properties of artificial neural networks (ANNs) such as low sensitivity to noise and incomplete information make the ANN a promising candidate to model the fuel cell system. In this paper, an ANN-based model of 100 W portable direct hydrogen fed proton exchange membrane fuel cell (PEMFC) is presented. The model is built based on experimentally collected data from a portable 100 W direct hydrogen fed PEMFC in the authors’ laboratory. A multilayer feedforward ANN with back-propagation training algorithm is used to model the portable PEMFC. The ANN consists of fully connected four layers network with two hidden layers. The PEMFC ANN model is trained using extracted data from experimentally measured and calculated parameters. To validate the model, the outputs of the PEMFC ANN are compared against experimental data and results from a dynamic model of portable direct hydrogen fed PEMFC. In addition, three statistical indices to measure variations, unbiasedness (precision), and accuracy in voltage, power, and hydrogen flow are used to evaluate the PEMFC ANN model performance. The indices indicate that the maximum variations, unbiasedness, and accuracy of the voltage, power, and hydrogen flow are 1.45%, 2.04%, and 1.90%, respectively, which shows a close agreement between the outputs of the PEMFC ANN and the experimental results.     

Fuel economy evaluation of fuel cell hybrid vehicles based on equivalent fuel consumption

Fuel cell hybrid vehicles (FCHVs) have become a major topic of interest in the automotive industry owing to recent energy supply and environmental problems. Consequently, fuel economy evaluation methods of FCHVs have a popular research topic. The initial state of charge (SOC) and the final SOC of the battery have to be identical in an evaluation of the fuel economy of an FCHV. In an actual driving situation or during a forward simulation, however, the final SOC depends on the power management strategy, which is usually different from the initial SOC. To consider the effect of the difference between the initial and final SOC on fuel economy evaluation, the concept of equivalent fuel consumption, based on the optimal control, is introduced in this paper. A rule-based power management strategy is applied to an FCHV, and its fuel economy is evaluated in terms of the equivalent fuel consumption and compared to the optimal control result.     

Fuel sensor-less control of a liquid feed fuel cell system under steady load for portable applications

This study presents a novel fuel sensor-less control scheme for a liquid feed fuel cell system that does not rely on a fuel concentration sensor. The proposed approach simplifies the design and reduces the cost and complexity of a liquid feed fuel cell system, and is especially suited to portable power sources, of which the volume and weight are important. During the reaction of a fuel cell, the cell's operating characteristics, such as potential, current and power are measured to control the supply of fuel and regulate its concentration to optimize performance. Experiments were conducted to verify that the fuel sensor-less control algorithm is effective in the liquid feed fuel cell system.     

The computer-aided analysis for the driving stability of a plug-in fuel cell vehicle using a proton exchange membrane fuel cell

In order to analyze the driving stability of a plug-in fuel cell vehicle (PFCV), a computer-aided simulator for PFCVs has been developed. PFCVs have been introduced around the world to achieve early commercialization of an eco-friendly and highly efficient fuel cell vehicle. The plug-in option, which allows the battery to be recharged from the electricity grid, enables a reduction in size of the fuel cell system (FCS) and an improvement of its durability. As such, the existing limitations of the fuel cell - such as its high cost, poor durability, and the insufficient hydrogen infrastructure – can be overcome. During the design phase of PFCV development, simulation-based driving stability test is necessary to determine the sizes of the electric engine of the FCS and the battery. The developed simulator is very useful for analyzing the driving stability of the PFCV with respect to the capacities of the FCS and battery. The simulation results are in fact very close to those obtained from a real system, since the estimation accuracy of PFCV component models used in this simulator, such as the fuel cell stack, battery, electric vehicle, and the other balance of plants (BOPs), are verified by the experiments, and the simulator uses the newly-proposed power distribution control logic and the pre-confirmed real driving schedule. Using these results, we can study which one will be the best in terms of driving stability.     

Modeling operating modes,energy consumptions,and infrastructure requirements of fuel cell plug in hybrid electric vehicles using longitudinal geographical transportation data

The fuel cell plug in hybrid electric vehicle (FCPHEV) is a near-term realizable concept to commercialize hydrogen fuel cell vehicles (FCV). Relative to conventional FCVs, FCPHEVs seek to achieve fuel economy benefits through the displacement of hydrogen energy with grid-sourced electrical energy, and they may have less dependence on a sparse hydrogen fueling infrastructure. Through the simulation of almost 690,000 FCPHEV trips using geographic information system (GIS) data surveyed from a fleet of private vehicles in the Puget Sound area of Washington State, USA, this study derives the electrical and hydrogen energy consumption of various design and control variants of FCPHEVs. Results demonstrate that FCPHEVs can realize hydrogen fuel consumption reductions relative to conventional FCV technologies, and that the fuel consumption reductions increase with increased charge depleting range. In addition, this study quantifies the degree to which FCPHEVs are less dependent on hydrogen fueling infrastructure, as FCPHEVs can refuel with hydrogen at a lower rate than FCVs. Reductions in hydrogen refueling infrastructure dependence vary with control strategies and vehicle charge depleting range, but reductions in fleet-level refueling events of 93% can be realized for FCPHEVs with 40 miles (60 km) of charge depleting range. These fueling events occur on or near the network of highways at approximately 4% of the rate (refuelings per year) of that for conventional FCVs. These results demonstrate that FCPHEVs are a type of FCV that can enable an effective and concentrated hydrogen refueling network.     

Generation of high-pressure hydrogen for fuel cell electric vehicles using photovoltaic-powered water electrolysis

Increasing the utilization of electric drive systems including hybrid, battery, and fuel cell electric vehicles (FCEV) will reduce the usage of petroleum and the emission of air pollution by vehicles. The eventual production of electricity and hydrogen in a renewable fashion, such as using solar energy, can achieve the long-term vision of having no tailpipe emissions, as well as eliminating the dependence of the transportation sector on dwindling supplies of petroleum for its energy. Before FCEVs can be introduced in large numbers, a hydrogen-fueling infrastructure is needed. This report describes an early proof-of-concept for a distributed hydrogen fueling option in which renewably generated, high-pressure hydrogen is dispensed at an FCEV owner’s home. In an earlier report we described the design and initial characterization of a solar photovoltaic (PV) powered electrolyzer/storage/dispensing (ESD) system that was a proof-of-concept for a single FCEV home fueling system. In the present report we determined the efficiency and other operational characteristics of that PV-ESD system during testing over a 109-day period at the GM Proving Ground in Milford, MI, at a hydrogen output pressure of approximately 2000 psi (13.8 MPa). The high pressure was achieved without any mechanical compression via electrolysis. Over the study period the photovoltaic solar to electrical efficiency averaged 13.7%, the electrolyzer efficiency averaged 59%, and the system solar to hydrogen efficiency averaged 8.2% based on the hydrogen lower heating value. A well-documented model used to evaluate solar photovoltaic power systems was used to calculate the maximum power point values of the voltage, current, and power of our PV system in order to derive the coupling factor between the PV and ESD systems and to determine its behavior over the range of environmental conditions experienced during the study. The average coupling factor was near unity, indicating that the two systems remained coupled in an optimal fashion. Also, the system operated well over a wide range of meteorological conditions, and in particular it responded quickly to instantaneous changes in the solar irradiance (caused by clouds) with negligible effect on the overall efficiency. During the study up to 0.67 kg of high-pressure hydrogen was generated on a sunny day for fueling FCEV. Future generations of high-pressure electrolyzers, properly combined with solar PV systems, can offer a compact, efficient, and environmentally acceptable system for FCEV home fueling.     

Study of operating conditions and cell design on the performance of alkaline anion exchange membrane based direct methanol fuel cells

Direct methanol fuel cells using an alkaline anion exchange membrane (AAEM) were prepared, studied, and optimized. The effects of fuel composition and electrode materials were investigated. Membrane electrode assemblies fabricated with Tokuyama^® AAEM and commercial noble metal catalysts achieved peak power densities between 25 and 168 mW cm⁻² depending on the operating temperature, fuel composition, and electrode materials used. Good electrode wettability at the anode was found to be very important for achieving high power densities. The performance of the best AAEM cells was comparable to Nafion^®-based cells under similar conditions. Factors limiting the performance of AAEM MEAs were found to be different from those of Nafion^® MEAs. Improved electrode kinetics for methanol oxidation in alkaline electrolyte at Pt-Ru are apparent at low current densities. At high current densities, rapid CO₂ production converts the hydroxide anions, necessary for methanol oxidation, to bicarbonate and carbonate: consequently, the membrane and interfacial conductivity are drastically reduced. These phenomena necessitate the use of aqueous potassium hydroxide and wettable electrode materials for efficient hydroxide supply to the anode. However, aqueous hydroxide is not needed at the cathode. Compared to AAEM-based fuel cells, methanol fuel cells based on proton-conducting Nafion^® retain better performance at high current densities by providing the benefit of carbon dioxide rejection.     

Towards operating direct methanol fuel cells with highly concentrated fuel

A significant advantage of direct methanol fuel cells (DMFCs) is the high specific energy of the liquid fuel, making it particularly suitable for portable and mobile applications. Nevertheless, conventional DMFCs have to be operated with excessively diluted methanol solutions to limit methanol crossover and the detrimental consequences. Operation with diluted methanol solutions significantly reduces the specific energy of the power pack and thereby prevents it from competing with advanced batteries. In view of this fact, there exists a need to improve conventional DMFC system designs, including membrane electrode assemblies and the subsystems for supplying/removing reactants/products, so that both the cell performance and the specific energy can be simultaneously maximized. This article provides a comprehensive review of past efforts on the optimization of DMFC systems that operate with concentrated methanol. Based on the discussion of the key issues associated with transport of the reactants/products, the strategies to manage the supply/removal of the reactants/products in DMFC operating with highly concentrated methanol are identified. With these strategies, the possible approaches to achieving the goal of concentrated fuel operation are then proposed. Past efforts in the management of the reactants/products for implementing each of the approaches are also summarized and reviewed.     

Numerical simulation of exchange membrane fuel cells in different operating conditions

A two-dimensional, steady state model for proton exchange membrane fuel cell (PEMFC) is presented. The model is used to describe the effect operation conditions (current density, pressure and water content) on the water transport, ohmic resistance and water distribution in the membrane and performance of PEMFC. This model considers the transport of species and water along the porous media: gas diffusion layers (GDL) anode and cathode, and the membrane of PEMFC fuel cell.     

Effect of operating parameters and anode diffusion layer on the direct ethanol fuel cell performance

A parametric study was conducted on the performance of direct ethanol fuel cells. The membrane electrode assemblies employed were composed of a Nafion^® 117 membrane, a Pt/C cathode and a PtRu/C anode. The effect of cathode backpressure, cell temperature, ethanol solution flow rate, ethanol concentration, and oxygen flow rate were evaluated by measuring the cell voltage as a function of current density for each set of conditions. The effect of the anode diffusion media was also studied. It was found that the cell performance was enhanced by increasing the cell temperature and the cathode backpressure. On the contrary, the cell performance was virtually independent of oxygen and fuel solution flow rates. Performance variations were encountered only at very low flow rates. The effect of the ethanol concentration on the performance was as expected, mass transport loses observed at low concentrations and kinetic loses at high ethanol concentration due to fuel crossover. The open circuit voltage appeared to be independent of most operating parameters and was only significantly affected by the ethanol concentration. It was also established that the anode diffusion media had an important effect on the cell performance.     

Realistic simulation of fuel economy and life cycle metrics for hydrogen fuel cell vehicles

The present work contributes an engineered life cycle assessment (LCA) of hydrogen fuel cell passenger vehicles based on a real‐world driving cycle for semi‐urban driving conditions. A new customized LCA tool is developed for the comparison of conventional gasoline and hydrogen fuel cell vehicles (FCVs), which utilizes a dynamic vehicle simulation approach to calculate realistic, fundamental science based fuel economy data from actual drive cycles, vehicle specifications, road grade, engine performance, fuel cell degradation effects, and regenerative braking. The total greenhouse gas (GHG) emission and life cycle cost of the vehicles are compared for the case of hydrogen production by electrolysis in British Columbia, Canada. A 72% reduction in total GHG emission is obtained for switching from gasoline vehicles to FCVs. While fuel cell performance degradation causes 7% and 3% increases in lifetime fuel consumption and GHG emission, respectively, regenerative braking improves the fuel economy by 23% and reduces the total GHG emission by 10%. The cost assessment results indicate that the current FCV technology is approximately $2,100 more costly than the equivalent gasoline vehicle based on the total lifetime cost including purchase and fuel cost. However, prospective enhancements in fuel cell durability could potentially reduce the FCV lifetime cost below that of gasoline vehicles. Overall, the present results indicate that fuel cell vehicles are becoming both technologically and economically viable compared with incumbent vehicles, and provide a realistic option for deep reductions in emissions from transportation. Copyright © 2016 John Wiley & Sons, Ltd.     

2-D + 1-D PEM fuel cell model for fuel cell system simulations

The water management is critical for the operation of PEM fuel cells and has a strong impact on its performance and durability. The aim of this work is the simulation-based investigation of the operation of a PEM fuel cell system with the special focus on its water management.In order to analyze these dependencies correctly, a 2-D + 1-D PEM fuel cell stack model has been developed, which on the one hand has a high level of modelling details and on the other hand meets high requirements concerning its runtime, to enable acceptable simulation times for fuel cell system simulations. The fuel cell model is integrated into an AVL Cruise-M fuel cell system simulation.An analysis is presented comparing a system operation with a fuel cell in co- and counter-flow configuration with a special focus on the local and overall water management.