Design and Fabrication of Novel Electrode-Supported SOFC Having Honeycomb Structure

We have developed a novel and highly effective electrode-supported SOFC with honeycomb structure for intermediate temperature operation. Honeycomb supported SOFC is known as one of the most compact SOFCs due to the large electrode area per unit volume, which is attractive with regard to space saving and cost reduction. In this study, we summarized the design of channel shape, size and sequence using numerical simulation and the technologies to realize the designed honeycomb SOFC fabrication. The calculation results showed that the wall thickness and the channel size of the honeycomb had to be less than 0.22 mm and more than 0.3 mm, respectively, for the sufficient net channel surface and the acceptable pressure drop. And a cathode-honeycomb supported SOFC can be the more efficient form with the lower current collection resistance, as compared with the anode-supported type. The actually fabricated honeycomb SOFC exhibited a high volumetric power density above 1 W/cm3 at 650 °C under wet H2 fuel flow.

Recent Development of Micro Ceramic Reactors for Advanced Ceramic Reactor System

Ceramic reactors, which convert materials and energy electrochemically, are expected to solve various environmental problems, and use of micro reactor design was shown to realize high performance reactor with high thermal durability operable at lower temperatures. Our research project “Advanced Ceramic Reactor” supported by NEDO targets to develop new fabrication technology for such micro reactors and modules using conventional, commercially available materials. In this study, fabrication technology of micro tubular ceramic reactors have been investigated for aiming solid oxide fuel cells (SOFCs) application, such as small distributed power generators, APU for vehicles, and portable power sources. So far, micro tubular SOFCs under 1 mm diam. using doped ceria electrolyte and Ni-ceria based cermet for tubular support has been successfully developed and evaluated. The single micro tubular SOFC showed cell performance of 0.46 W/cm2 (@0.7 V) at 550 °C with H2 fuel. Bundle design for such tubular cell was also proposed and fabricated. Discussion will cover fabrication technology of single tubular SOFC and bundle, and optimization of the cell and bundle design by considering gas pressure loss and current collecting loss.

Economic Viability of a Molten Carbonate Fuel Cell Working With Biogas

Catalonia (Spain) has a significant potential of biogas production from agricultural activities and municipal waste. In addition, there are plenty of industrial cogeneration plants, but most of them use conventional fuels such as natural gas, and conventional energy conversion devices, such as internal combustion engines. Molten carbonate fuel cells are ultra-clean and highly efficient power generator devices capable of converting biogas into electricity and heat. Located in Lleida (Catalonia), Nufri is a fruit processing company with a long tradition on biogas production and cogeneration, with an installed capacity bigger than 4.5 MW. This study analyzes the economic viability of a fuel cell operating on biogas in Spain, on a real case basis (Nufri). Different fuel cell capacities are analyzed (from 300 kW to 1200 kW). A parametric study of different fuel cell prices ($/kW installed) is performed. Additional biogas cleanup requirements are taken into account. The results are based on the Spanish legislation, which establishes a special legal framework that grants favorable, technology-dependent feed-in premiums for renewable energy and cogeneration. Results show that the payback period ranges from 5 to 8 years depending on the fuel cell capacity and installation price.

Basic Fuel Cell Electrochemical Thermodynamic Studies: Utilization and Thermodynamic Performance for Various Fuels

This study gives information of new opportunity fuels having increasing importance is all future energy scenarios. It compares the basic thermodynamic performance of fuel cells with various fuels — ammonia, methanol, hydrogen, carbon monoxide and carbon(s). For both oxygen ion conducting and proton conducting fuel cell, where applicable, its performance as a function of utilization is considered. The fuel cell itself will be considered as a reversible electrochemical reactor, generating power and mixing substances, but without further restrictions on its design. The thermodynamic state and the excess air are further parameters of variation. The consequences of the use of air and oxygen are considered as well. The principal reversible combustion of the fuel is the base of the operation of any fuel cell. The utilisation of the fuel changes the gas concentrations on the anode and cathode side depending on the ionic transport mechanism. The reversible SOFC model was used to describe the influence of the fuel utilisation, the thermodynamic state, and the operational parameters for the fuel H2 on the local Nernst voltage in previous publications. This work has been expanded to proton conducting cells and different opportunity and hydrocarbon fuels. Ammonia is quite different and at lower utilizations appears to be a superior fuel. Methanol is superior to methane over a wide utilization range. Hydrocarbons like methane have a smaller voltage decrease during utilization than hydrogen and carbon monoxide. Excess air larger than two has a small impact on voltage loss. Direct utilization of hydrocarbon fuels without reforming is a key development path toward higher efficiency.

The Dynamic Modeling of PEMFC System for Automotive Application

Water and thermal management are crucial factors in determining the performance of PEMFC for automotive application. In order to investigate the effect of cell humidity and temperature on the performance of PEMFC, a dynamic model of a PEMFC system for automotive application has been developed by using Matlab/Simulink®. The model is composed of a PEM unit cell, membrane humidifier, and thermal management system (TMS). At first, fuel and air are well hydrated by the shell and tube humidifier, then humidified fuel and air flow into the PEMFC for electrochemical reaction. PEMFC temperature was maintained at a constant level by the thermal management system. The active area of PEM model is 240 cm2. The cell was discretized into several control volumes in the through-plane to resolve energy balance and species diffusion. The membrane humidifier model is also discretized into three control volumes in the through-plane to resolve the mass conservation and energy balance. Fuel and air are hydrated by the diffusion of the water through the membrane. The thermal management system consists of radiator, fan and pump. De-ionized water cools down the temperature of PEMFC. In order to validate the model, the model was compared with a corresponding experiment. Comparison shows that simulation results are in good agreement with experiments. And the dynamic response of PEMFC with regard to the change of current was also investigated. The model is useful to elucidate the relationships between operating conditions such as air relative humidity, temperature, etc. It is expected that this dynamic modeling of PEMFC system can contribute to the design optimization of PEM fuel cell system for vehicle application.

A Numerical Investigation Into the Use of Patterned Electrodes in a Segmented-in-Series Tubular SOFC

A typical segmented-in-series tubular SOFC consists of flattened ceramic support tubes with rows of electrochemical cells fabricated on their outer surfaces and connected in series along their length. In this design, the electrical resistance of the long current flow path is minimised by using high conductivity electrodes. Therefore the resistance of the cathode, which typically has a low electrical conductivity, is reduced by fabricating an additional high conductivity current collector layer. This study is concerned with investigating the design of this additional layer using the newly developed SOHAB multi-physics computer code. Initial simulations identified the optimum thickness of a uniform current collector with respect to cell performance and component cost. However, it was found that this uniform layer causes ionic current to concentrate near the edges of the electrolyte, potentially enhancing cell degradation. Further simulations investigated whether a patterned current collector could be designed to control the current flow within the cell and reduce this detrimental effect. It was found that, for an identical thickness collector layer, a patterned design could reduce spatial variations of ionic current by a factor of over two with a negligible effect on cell performance. Therefore, patterned current collectors represent a means to control the current flow path within a segmented-in-series cell and further improve its performance.

Fabrication of Anode-Supported Micro-Tubular Solid Oxide Fuel Cell Using an Extrusion and Vacuum Infiltration Technique

A simple and mass productive extrusion technique was applied to fabricate anode-supported micro-tubular solid oxide fuel cells (SOFCs). A standard NiO/8YSZ (Nickel oxide/8 mol % yttria stabilized zirconia) cermets anode, 8 YSZ electrolyte, and LSM (Lanthanum strontium manganite) cathode were used as the materials components. SEM (secondary electron microscopy) images indicated vacuum infiltration method successfully generated the thin electrolyte layer (10∼15 μm) with a structurally effective three phase boundaries. Fabricated unit cell showed the open circuit voltage of 1.12 V without any fuel leaking problems. Electrochemical tests showed a maximum power density up to 0.30 W/cm2 at 800 °C, implying the excellent performance as micro-tubular SOFCs. This study verified that the extrusion aided by vacuum infiltration process could be a promising technique for mass production of microtubualr SOFCs.

Control Sensitivity Study for a Hybrid Fuel Cell/Gas Turbine System

The National Energy Technology Laboratory (NETL) has developed a hardware simulator to test the operating characteristics of Solid Oxide Fuel Cell/Gas Turbine (SOFC/GT) hybrid systems. The Hybrid Performance (HyPer) simulator has been described previously, and has contributed to the understanding of SOFC/GT system operation. HyPer contains not only the requisite elements of gas turbine/compressor/generator, recuperator, combustor, and associated piping, but also several air flow control valves that are proposed as system control mechanisms. It is necessary to know how operation of these valves affects the various entities such as cathode air flow, turbine speed, and various temperatures important to the safe and efficient operation of fuel cell/gas turbine hybrid systems. To determine the interactions among key variables, a series of experiments was performed in which the effect of modulating each of the key manipulated variables was recorded. This document outlines the test methods used and presents some of the data from those tests, along with analysis and interpretation of that data in the context of control system design.

Predicting Phase-Change Rate in PEFC Gas Diffusion Layer

Water and heat are produced in the cathode catalyst layer of a polymer electrolyte fuel cell (PEFC) due to the oxygen-reduction reaction. Efficient water removal from the gas diffusion layer (GDL) to the flow channel is critical to achieve high and stable PEFC performance. Water transport and removal strongly depend on local temperature because the saturation concentration of water vapor rises rapidly with temperature, particularly in the temperature range of practical interest to PEFC applications. Detailed investigations of two-phase flow in the GDL have been reported in the literature, but not on the rate of phase change – either from liquid to vapor as in the case of evaporation or from vapor to liquid as in the case of condensation. In the present work, a two-phase, non-isothermal numerical model is used to elucidate the phase-change rate inside the cathode GDL of a PEFC. Results computed from our model enable a basic understanding of the phase-change processes occurring in a PEFC.

Power Generation Properties of a Micro Tubular SOFC Bundle Under Pressurized Conditions

A micro tubular solid oxide fuel cell (SOFC) bundle was developed based on new concept. The anode-supported micro tubular SOFCs with the cell configuration, La0.6Sr0.4Co0.2Fe0.8 O3−δ (LSCF) – Ce0.9Gd0.1O2−δ (CGO) cathode / CGO electrolyte / Ni – CGO anode were fabricated and were bundled by a porous LSCF current collecting cube 1 cm on a side. The power generation test of the fabricated SOFC bundle was carried out under pressurized conditions. Using wet 30%H2 / N2 mixture gas and air, the cubic power density of the bundle at 500°C was 0.47 Wcm−3 at 0.4Acm−2, atmospheric pressure (0.1MPa). With increasing operating pressure, the performance has been improved, and the cubic power density finally reached to 0.66 Wcm−3 at 0.6MPa. Pressurization effect for the power improvement was brought about by the open circuit voltage enhancement and reduction of the polarization resistance.