Modeling of a Direct Carbon Fuel Cell System

Direct Carbon Fuel Cells (DCFCs) have great thermodynamic advantages over other high temperature fuel cells such as MCFC and SOFC. They can have 100% fuel utilization, no Nernst loss (at the anode) and the CO2 produced at the anode is not mixed with other gases and is ready for reuse or sequestration. So far only studies have been reported on cell development. In this paper we study the performance of a CO2-producing DCFC system model. The theoretically predicted advantages that are confirmed on a bench scale are also confirmed on a system level, except for the production of pure CO2. Net system efficiencies of around 78 % were found for the developed system. An exergy analysis of the system shows where the losses in the system occur. If the cathode of the DCFC must be operated as a standard MCFC cathode the required CO2 at the cathode is the reason why a large part of the pure CO2 from the anode is recycled and mixed with the incoming air and cannot be used directly for sequestration. Bench scale studies should be performed to test the minimum amount of CO2 needed at the cathode. This might be lower than in standard MCFC operation due to the pure CO2 at the anode side that enhances diffusion towards the cathode.

Direct Oxidation of Waste Vegetable Oil in Solid Oxide Fuel Cells

Solid oxide fuel cells with ceria, ceria-Cu, and ceria-Rh anode were demonstrated to generate stable electric power with waste vegetable oil through direct oxidation of the fuel. The only pre-treatment to the fuel was a filtration to remove particulates. The performance of the fuel cell was stable over 100 hours for the waste vegetable oil without dilution. The generated power was up to 0.25 W/cm2 for ceria-Rh fuel cell. This compares favorably with previously studied hydrocarbon fuels including jet fuels and Pennsylvania crude oil.

An Improved Design of Microchannel Fuel Processors

This paper focuses on a new systematic configuration of micro-channel fuel processors, particularly designed for portable applications. An alternative integration method of the micro-channel fuel processors is attempted to overcome the serious thermal unbalance and to minimize the system volume by introducing the direct contact method of the sub-components. An integrated micro-channel methanol processor was developed by assembling unit reactors, which were fabricated by stacking and bounding micro-channel patterned stainless steel plates, including fuel vaporizer, catalytic combustor and steam reformer. Commercially available Cu/ZnO/Al2O3 catalyst (ICI Synetix 33-5) was coated inside micro-channel of the unit reactor for steam reforming. The steam reforming reaction was conducted in the temperature range of 200°C to 260°C in the basis of reformer side end-plate and the temperature was controlled by varying methanol feeding into the combustor. More than 99% of methanol was converted at 240°C of reformer side temperature. A mechanism-based numerical model aimed at enhancing physical understanding and optimizing designs has been developed for improved micro-channel fuel processors. A two-dimensional numerical model in the reformer section created to model the phenomena of species transport and reaction occurring at the catalyst surface. The mass, momentum, and species equations were employed with kinetic equations that describe the chemical reaction characteristics to solve flow-field, methanol conversion rate, and species concentration variations along the micro-channel. This mechanism-based model was validated against the experimental data from the literature and then applied to various layouts of the micro-channel fuel processors targeted for the optimal catalyst loading and fuel reforming purpose. The computer-aided models developed in this study can be greatly utilized for the design of advanced fast-paced micro-channel fuel processors research.

Overview of Field Performance by UTC Fuel Cells’ Transportation Fuel-Cell Power Plants

UTC Fuel Cells (UTCFC) over the last few years has partnered with leading automotive and bus companies and developed Polymer Electrolyte Membrane (PEM) fuel-cell power plants for various transportation applications, for instance, automotive, buses, and auxiliary power units (APUs). These units are deployed in various parts of the globe and have been gaining field experience under both real world and laboratory environments. The longest running UTC PEM fuel cell stack in a public transport bus has accumulated over 1350 operating hours and 400 start-stop cycles. The longest running APU fuel cell stack has accrued over 3000 operating hours with more than 3200 start-stop cycles. UTCFC PEM fuel-cell systems are low noise and demonstrate excellent steady state, cyclic, and transient capabilities. These near ambient pressure, PEMFC systems operate at high electrical efficiencies at both low and rated power conditions.

Innovative Flow Field Combination Design on Direct Methanol Fuel Cell Performance

The flow-field design of Direct Methanol Fuel Cells (DMFCs) is an important subject about the DMFCs performance. Flow-fields play an important role on ability to transport fuel and drive out the products (H2O, CO2). In general, most of fuel cells utilize the same structure of flow-field for both anode and cathode. The popular flow-fields used for DMFCs are parallel and grid designs. Nevertheless, the characteristics of reactants and products are entirely different in anode and cathode of DMFCs. Therefore; the influences of the flow-fields designs on the cell performance were investigated due to the same logic for catalyst used for cathode and anode differently. To get the better and more stable performance of DMFC, three flow-fields (Parallel, Grid and Serpentine) are utilized with different combination were studied in this research. As a consequence, by using parallel flow-field in anode side and serpentine flow -field in cathode, the most and highest power output was obtained.

The Nature of Flooding and Drying in Polymer Electrolyte Fuel Cells

Two different 50 cm2 fuel cells operated at high current density (1.3A/cm2–1.5A/cm2) were visualized using neutron imaging, and the liquid water content in the flow channels and diffusion media under the lands and channels was calculated and compared. At high current density with fully humidified inlet flow, a direct comparison between flooded and non-flooded conditions was achieved by increasing the fuel cell temperature over a small range, until voltage loss from flooding was alleviated. Results indicate that a surprisingly small mass of liquid water is responsible for a significant voltage loss. The deleterious effects of flooding are therefore more easily explained with a locally segregated flooded pore model, rather than a homogeneously flooded pore and blockage phenomenon. Anode dryout was similarly observed and quantified, and results indicate that an exceedingly small mass of water is responsible for significant voltage loss, which is consistent with expectations. The results presented help to form a more complete vision of the flooding loss and anode dryout phenomena in PEFCs.

Fuel Cell Research and Development in Taiwan

Fuel cells provide a clean and efficient alternative fuel technology for transportation, residential and portable power applications. From political, social, economic, energy, environmental and technological considerations, the emerging fuel cell technology is undoubtedly well worthy of long-term investment in Taiwan. In view of the success and manufacture capability of electronics and IT industries, Taiwan may play an active role in fuel cell manufacturing and is thus conducive for international strategic alliance, both in R&D and manufacturing activities. This article provides an overview of Taiwan’s technological activities and accomplishments in fuel cells, and makes recommendations for the country’s future development and commercialization of fuel cell applications.

Modeling of a Methane Fuelled Direct Carbon Fuel Cell System

Direct Carbon Fuel Cells (DCFCs) have great thermodynamic advantages over other high temperature fuel cells such as MCFC and SOFC. They can have 100% fuel utilization, no Nernst loss (at the anode) and the CO2 produced at the anode is not mixed with other gases and is ready for reuse or sequestration. So far only studies have been reported on cell development. In this paper we study in particular the integration of the production of clean and reactive carbon particles from methane as a fuel for the direct carbon fuel cell. In the thermal decomposition process heat is upgraded to chemical energy in the carbon and hydrogen produced. The hydrogen is seen as a product as well as the power and heat. Under the assumptions given the net system electric efficiency is 22.9 % (based on methane LHV) and 20.7 % (HHV). The hydrogen production efficiency is 65.5 % (based on methane LHV) and 59.1 % (HHV), which leads to a total system efficiency of 88.4 % (LHV) and 79.8 % (HHV). Although a pure CO2 stream is produced at the anode outlet, which is seen as a large advantage of DCFC systems, this advantage is unfortunately reduced due to the need for CO2 in the cathode air stream. Due to the applied assumed constraint that the cathode outlet stream should at least contain 4% CO2 for a proper functioning of the cathode, similar to MCFC cathodes a major part of the pure CO2 has to be mixed with incoming air. Further optimization of the DCFC and the system is needed to obtain a larger fraction of the output streams as pure CO2 for sequestration or reuse.

Fuel Cell System Reliability for a Pressurised Integrated-Planar SOFC

A ceramic supported SOFC for operation at 950°C is being developed by Rolls Royce Fuel Cell Systems (RRFCS). In parallel with the evolving design of the fuel cell system, it is necessary to ensure reliability not only of the electrochemical cell, but also the main structure under both manufacture and operational constraints. With a ceramic based system for use at high temperature this presents particular challenges, and to address these, RRFCS is in partnership with leading academic institutions including Imperial College London and the University of Genoa supported by the European Union. This paper will identify potential areas of concern for reliability and integrity of the fuel cell system, and will indicate the work that is being undertaken to ensure reliability, including thermomechanical stresses arising from fluid flow, electrochemical reactions and operational temperature distributions; joining of components; assessment of the stresses within ceramic structures, manufacture tolerances of dimensions and material properties.

Direct Preparation of Ce0.8Sm0.2O1.9 Powders Oxidized With H2O2 for Low Temperature SOFCs Application

A novel method was developed to prepare fine doped ceria (DCO) powders directly. Ceria doped with 20 mol. % of samarium (Ce0.8Sm0.2O1.9, SDC) was prepared by in-situ oxidization of hydroxide precipitates with H2O2 in the solutions. The resultant powder desiccated at 85°C overnight was characterized by X-ray diffraction (XRD), thermogravimetry /differential thermal analysis (TG/DTA), and transmission electron microscopy (TEM). The XRD pattern showed that the as-dried SDC powder is single phase with a cubic fluorite structure like that of pure CeO2. An anode-supported SOFC was also fabricated based on SDC and 20wt. % (62mol. %Li2CO3–38 mol. %K2CO3) composite electrolyte, LiNiO2 as cathode and NiO as anode, by cold pressing. Using hydrogen as the fuel and air as the oxidant, the I-V and I-P characteristics exhibit excellent performances and the maximum power densities are about 696, 469, 377 and 240 mWcm−2 at 650, 600, 550 and 500°C, respectively.