A Comparison Between Life Cycle Assessment of an MCFC System, An LFG-MCFC System, and Traditional Energy Conversion Systems

The present work aims at evaluating the environmental impact caused by fuel cell systems in the production of electric energy. The very low pollutant emission levels in fuel cells makes them an attractive alternative in ultra clean energy conversion systems. Actually, to truly understand the environmental impact related to fuel cells, it is necessary to study their “cradle-to-grave” life, from the construction phase, during the conversion of primary fuel into hydrogen, to its disposal. The tool used in this analysis is the Life Cycle Assessment approach; in particular the environmental impact of a fuel cell system has been simulated through the software SimaPro 5.0. Thanks to this approach, once the critical process regarding the production of energy by fuel cell system, (i.e. the production of hydrogen by natural gas steam reforming), has been determined, an analysis of the use of landfill gas as a renewable source to produce hydrogen was done. Finally, the production of electric energy by fuel cell systems was compared to that by some conventional energy conversion systems. A second comparison was done between the Molten Carbonate Fuel Cell (MCFC) fuelled by landfill gas and natural gas.

Design Concepts for Directed Exit Flow in Micro Fuel Cells

Miniature and micro fuel cells continue to advance as promising alternatives for efficient and portable electric power. This paper presents a study of experimental modifications to the exit flow configuration of microchannels used in small proton-exchange-membrane fuel cells. New concepts for exit geometry are presented, which promote effective water removal and provide reactant back-pressure in an efficient and self-contained manner. Cell assembly is designed such that reactants must necessarily flow laterally through the gas diffusion electrodes near the exit, rather than simply pass over the free backside surfaces of these electrodes. Multiple prototypes were produced using microfabrication techniques with channel sizes of 100 and 200 microns, and performance was tested using a hydrogen-air test station with programmable electronic load. One of the new concepts in particular showed a marked improvement from 28 mW/cm2 peak power density under baseline conditions to 37 mW/cm2 for the modified design under similar operating conditions. The design offers an opportunity for higher performance in miniature fuel cells with low gas consumption and no additional cost.

The Analysis of the Operating Characteristics in a 600W Air Cooling Portable PEMFC

To maintain proper operating conditions is important to get optimal output power of a polymer electrolyte membrane fuel cell (PEMFC) stack. The air cooled fuel cell stack is widely used in sub kW PEMFC systems. The higher the power density of a stack, however, the more difficult it is to get well balanced operating conditions for the system such as the relative humidity, the temperature of stack, the rate of usage of reactant and so on. A 600W air cooled PEMFC stack was experimentally investigated to evaluate the design performance and to get optimal operating conditions for the portable application. The relationship between the operating conditions and the performance was analyzed. The results can be used as design criteria for portable PEMFC under various conditions.

Dynamics of Solid Oxide Fuel Cell Operation

The dynamics of solid oxide fuel cell operation (SOFC) have been considered previously, but mainly through the use of one-dimensional codes applied to co-flow fuel cell systems. In this paper a cross-flow geometry is considered. The details of the model are provided, and the model is compared with some initial experimental data. For parameters typical of SOFC operation, a variety of transient cases are investigated, including representative load increase and decrease and system shutdown. Of particular note are results showing cases having reverse current over significant portions of the cell, starting from the moment of load perturbation up to the point where equilibrated conditions again provide positive current. Consideration is given as to when such reverse current conditions might most significantly impact the reliability of the cell.

Numerical Model of a Single Phase, Regenerative Fuel Cell

A code for numerical simulating the fluid flow and electrochemistry of a single phase regenerative fuel cell is presented. Due to the potentially tiny geometries and complex multi-physical interactions, modeling presents a chance to obtain detailed quantitative data and much needed understanding about physics within the reactor. The Regenesys XL200 fuel cell has the industrial application of large scale energy storage and is the focus of this work. A two dimensional, binary reduction reaction system has been created to represent the XL200 and test the code. Commercially available CFD software Fluent was used to calculate the flow field and subroutines were used to create the dynamic calculation of electrochemistry at the reaction surface. The effect of changing the total applied potential across the domain on the potential and species concentration distribution within the domain was investigated. Results show that the code is producing qualitatively feasible results that represent the tight multi-physical coupling. The code is currently not validated against physical experimental results and this will be the focus of future work.

Role of Defects on Mechanical Response of Nafion® Membranes for Fuel Cell Applications

Nafion® manufactured by Dupont is a widely used membrane material for polymer electrolyte membrane (PEM) fuel cell. Such membranes are made thin and also have to be hydrated during operation to increase proton conductivity of the cell. Since the membranes are made thin, and do not posses high mechanical properties, they are prone to any handling induced damage. In this paper, we have made an initial attempt to demonstrate the capability of thermal wave imaging nondestructive evaluation (NDE) technique in detecting various types of damage entities such as scratches, folding, and pin pricks in the membrane material. In addition, the effect of hydration and handling induced damage on the tensile behavior of Nafion® membrane is studied. It is observed that the damaged and as-received hydrated samples exhibit lower modulus and yield strength than the corresponding dry counterparts.

Development of Methanol Reformer for the Portable PEFC Power System by ITRI

In order to apply the PEFC power generation system in near future, ITRI is cooperating with Taiwanese local electrical company to develop a compact methanol reformer. This methanol reformer can simultaneously catalyze autothermal and steam reforming reactions, depending on the application. Except the catalyst for methanol steam reforming and low temperature water gas shift reactions, ITRI has developed several catalysts for autothermal reforming, high temperature water-gas shift, and CO preferential oxidation reactions. We have integrated these catalysts to assemble a methanol reformer prototype. The characteristics of this methanol reformer operated at steady state are the maximum flow rate of hydrogen being 39 L/min (corresponding to 2.4 kWe), H2 concentration being 45∼65%, CO concentration less than 50 ppm, and the cold startup time less than 35 minutes. In addition, we have been developing a catalyst for methanation reaction. We hope to shorten the start-up time to less than 20 minutes and the volume of the reformer being reduced in half by integrating a good methanation catalyst into my next generation methanol reformer.

Direct Alcohol Fuel Cell for Automotive Applications and Vehicle Modeling

This paper describes the study made by COPPE/UFRJ which goal is the development of fuel cells systems for automotive applications. The study is divided in two parts. The first is the development of a PEM direct fuel cell. In addition a method for experimentally determine the possibility of using a fuel in a fuel cell is developed. The components of catalysts are also tested such as Tin and Ruthenium in a Platinum coated electrode. The second part is the control system for a fuel cell powered vehicle. The vehicle power is modeled from its actions and losses. A power of 80kW seems to be a great choice if made of 50kW from the fuel cell system and 30kW from an accumulator such as a pack of batteries or a super capacitor.

A Novel Approach to Designing Highly Efficient and Commercially Viable Biofuel Cells

A biofuel cell is an electrochemical device in which the energy stored in a fuel, such as ethanol, is converted to electrical energy by the means of the catalytic activity of enzymes. Biofuel cells have traditionally suffered from low power densities and short lifetimes due to the fragility of the enzyme catalyst. Utilizing a novel quaternary ammonium salt treated Nafion membrane for enzyme immobilization in a biofuel cell results in increases in power densities and enzyme lifetimes to commercially viable levels. Additionally, this method provides sufficient protection to develop a membrane electrode assembly style (MEA) biofuel cell, an important step for commercialization. Previously, it has not been possible to create a MEA-style biofuel cell due to the denaturing of the enzyme that would occur at the high temperatures experienced during the heat pressing step of fabrication. Quaternary ammonium salt treated Nafion membranes provide sufficient protection for the enzyme to retain activity after exposure to temperatures of 140°C. Thus, a MEA-style biofuel cell can be created. Preliminary results yield biofuel cell MEAs with power densities ranging from 0.15 to 1.49 mW/cm2 and open circuit potentials of 0.360 to 0.599 V.

Modeling the System and Component Performance Interactions of a SOFC Based APU for Changes in Application Load: Transient Response and Control Strategy

Solid-Oxide-Fuel-Cell (SOFC) stacks respond in seconds to changes in load while the balance of plant subsystem (BOPS) responds in times several orders of magnitude higher. This dichotomy diminishes the reliability and performance of SOFC electrodes with changes in load. In the same manner current and voltage ripples which result from particular power electronic subsystem (PES) topologies and operation produce a negative effect on the SOFC stack subsystem (SS) performance. The difference in transient response among the sub-systems must be approached in a way which makes operation of the entire system not only feasible but ensures that efficiency and power density, fuel utilization, fuel conversion, and system response are optimal at all load conditions. Thus, a need exists for the development of transient component- and system-level models of SOFC based auxiliary power units (APUs), i.e. coupled BOPS, SS, and PES, and the development of methodologies for optimizing subsystem responses and for investigating system-interaction issues. In fact the transient process occurring in a SOFC based APU should be systematically treated during the entire creative process of synthesis, design, and operational control, leading in its most general sense to a dynamic optimization problem. This entails finding an optimal system/component synthesis/design, taking into account on- and off-design operation, which in turn entails finding an optimal control strategy and control profile for each sub-system/component and control variable. Such an optimization minimizes an appropriate objective function while satisfying all system constraints. A preliminary set of chemical, thermal, electrochemical, electrical, and mechanical models based on first principles and validated with experimental data have been developed and implemented using a number of different platforms. These models have been integrated in order to be able to perform component, subsystem, and system analyses as well as develop optimal syntheses/designs and control strategies for transportation and stationary SOFC based APUs. Some pertinent results of these efforts are presented here.