Connecticut Global Fuel Cell Center

Catalysis will play a very important role in successful commercialization of fuel cells. The two important areas are processing of hydrocarbon fuels to produce hydrogen and reactions of hydrogen and oxygen at the anode and cathode to generate power. Both of these steps require efficient catalysts. The team's efforts center on developing novel catalysts for both fuel processing and electrocatalysis applications. Investigations are being carried out on catalyst development, characterization and testing for partial-oxidation reforming of hydrocarbon fuels (methanol and gasoline), with the primary objective of minimizing the amount of carbon monoxide (CO) produced during the reaction. The ultimate goal is to produce a CO-free hydrogen stream, since traces of carbon monoxide in this mixture poison the fuel cell's platinum catalyst and degrade fuel cell performance. Another active research area is the development of novel electrode materials that require significantly less platinum than today's commercial electrodes.

Ionomers for PEMs

Proton exchange membrane (PEM) fuel cells incorporate a polymer electrolyte membrane, a crucial component that serves both as the electrolyte and a separator to prevent direct physical mixing of the hydrogen and the oxygen. The polymer electrolyte material contains ionizable groups, usually a metal sulfonate or sulfonic acid. The anionic charge is fixed onto the polymer, and the mobile cations are electrostatically associated with the fixed charges on the polymer. The charge carriers, i.e., protons, migrate through the membrane by "hopping" sequentially from one fixed charge to another.

Dr. Weiss' research centers on developing new ionomers and blends to serve as high-temperature PEMs. He has over 25 years experience in the synthesis, characterization and application of ionomers, which are polymers that contain modest amounts of bonded acid or neutralized acid groups. Microphase separation of the ionic groups provides a pathway for ion-transport when the membrane is swollen with a polar solvent such as water. His fuel cell research is conducted in collaboration with Dr. Montgomery Shaw and funded by the National Science Foundation and Connecticut Innovations Inc. The research encompasses the synthesis of sulfonate ionomers based on poly(aryl ether ketones), which exhibit high-temperature stability to >300°C and exceptional mechanical properties, and the study of complexes of ionomers with non-ionic polymers containing complementary functional groups, e.g., proton acceptors. Drs. Weiss and Shaw envision that interpolymer complexation will provide an interconnected morphology in which a pathway conducive to ion-transport develops by segregation of the functional groups to an interfacial region that percolates through the membrane. That strategy represents an entirely new approach for achieving ion-transport in a membrane and may reduce or eliminate the need to hydrate a PEM to achieve conductivity.

PEM Fuel Cell Research

Interest currently focuses on proton exchange membrane fuel cells that use a solid ionomer as the electrolyte. The relatively low operating temperature of this electrolyte makes it more suitable for use in a vehicle rather than cells using other higher temperature electrolytes. Advancements are needed in the components of this cell to make it commercially viable, including a better proton exchange membrane and improved porous electrodes. The membrane needs a modification of its properties to increase the migration rate of desirable species such as protons. The electrodes involve the transfer of mass, heat, and electrical charge and must be improved and optimized. Improved catalysts are also needed to increase the reaction rates in these electrodes. Our research activities involve both experimental studies and theoretical modeling of the processes to provide interpretation of the data and ultimate optimization of performance.

Portable Direct Methanol Fuel Cell System

Demand for light weight portable fuel cells is increasing at a rapid rate. Based on this growing demand, the Connecticut Global Fuel Cell Center is leading a multidisciplinary research and development (R & D) team effort that involves 14 engineering faculty members and 1 chemistry faculty member. This program includes research and development activities encompassing the proton exchange membrane, the bipolar plates, power conditioning circuitry, system thermal management, vibration and shock suppression, system control scheme and computer aided modeling. The R & D efforts will be interwoven with product development activities culminating in the production of one portable 150 watt direct methanol fuel cell system.

Solid Oxide Fuel Cell Research Group

Our research is primarily involved in the high temperature (greater than 600oC) electrical and mechanical properties of solid state ionic and electronically conducting materials. Applications for such materials include, but are not limited to, solid oxide fuel cells (SOFC), oxygen separation membranes and oxygen pumps and sensors. To date the work has concentrated on the properties of new and existing SOFC materials.

Solid Oxide Fuel Cell

A SOFC is a high temperature all solid state electrochemical reactor that converts the energy of a fuel directly into electricity, without the requirement of intermediate steps.

Most SOFC's run at between 850-1000oC, however in the next generation of SOFC systems, emphasis is being placed on lowering the temperature of operation to 600 - 800oC, as this will greatly reduce sealing problems, allow the use of cheaper materials (such as the interconnect, and the BOP) and allow for internal reformation reaction temperatures to be optimized.

Figure 1 shows an exploded view of a SOFC system with the ceramic components described.

The main emphasis of the SOFC research group is:

Explore the high temperature mechanical/structural relationships of new and existing SOFC materials. This is primarily for electrolyte and electrode supported structures (such as anode supports) and also examines how these components behave under "real" operating conditions. Computer modeling of the structures in different SOFC configurations is also performed to understand the best configuration for a particular application.

Study of new electrolyte systems based on the perovskite structure; this is from the viewpoint of its electrical, mechanical and behavioral/stability within a SOFC operating environment.

Optimization of the fabrication of SOFC systems using extrusion and tape casting methods to produce single cells and small stacks in different configurations (eg micro-tubular and planar).

Running small stacks and single cells under different operating conditions and different fuels; studying the cells' long-term behavior.

In-situ internal reforming reactions, particularly for liquid fuels such as diesel, and gaseous fuels such as natural gas.

Mechanical and structural modeling of SOFC stacks.

Fabrication of intermediate temperature SOFC stacks using new and existing electrolyte/electrode configurations.

Integration of SOFC stacks into real-life environmental conditions (long term studies under real loads, for example)

Solid Oxide Fuel Cell Sealing

UConn participated in the SECA Core Technology Program in developing a layered integrated composite seal for Solid Oxide Fuel Cells. Sealing is a critical issue in the development of reliable SOFC stacks, particularly the planar-type. Sealing has direct impact on the efficiency and longevity of SOFC stacks. SOFC seal material is subjected to a large set of stringent requirements that include mechanical (e.g. CTE match) and chemical compatibility with other cell stack components, high temperature stability, and adequate electrical resistivity, etc. The UConn seal development team(together with Inframat Corp. and Physical Accoustics Corp.) developed a layered composite seal that consisted of thin layers of metals, porous ceramics, and hermetic fillers (e.g. glass). Part of the seal can be deposited on the interconnect plate using plasma spray method. Instead of relying on a single sealant material, our composite seal is engineered so that each layer helps satisfying a subset of the structural and functional requirements. The layers in the composite seal are arranged to allow a gradual transition of thermal-mechanical properties and to minimize adverse chemical interactions of the constituent materials at high temperature. The phase one work has demonstrated subscale seals with superior thermal cycling resistance and chemical stability.

Durability of Membranes/MEAs in PEM Fuel Cells

Polymer electrolyte membrane (PEM) fuel cell, which relies on an ionomer-based membrane electrolyte to enable the transport of protons and the separation of electrochemical redox reactions, is currently widely pursued for transportation applications. High cost and poor durability remain to be significant barriers for commercial market penetration of PEM technology. PEM performance degradation is an extremely complicated process that involves the numerous mechanisms across several disciplines. Mechanical failure of membranes in the form of pinholes and fractures/tears is commonly observed in PEM stacks. Rapid performance loss due to gas cross-over and sometimes catastrophic failure shortly follow the mechanical breach of membranes. Improving the mechanical endurance of the electrolyte membrane is critical for extending the life of PEM stacks. An approach based on experiments and numerical modeling is being developed to help understand and elucidate the mechanical failure modes and mechanisms. Experiments have revealed that membrane strength can degrade rapidly under certain PEM operation conditions. The molecular nature of such degradation process is also being investigated. Membrane failure occurs when its "strength" drops below the mechanical stress/strain induced by RH cycling. A mechanistic approach is being developed to predict the remaining strength and stack life by tracking the evolution of these two variables.

Researchers at the Connecticut Global Fuel Cell Center have been busy tackling the challenges of harvesting hydrogen from the myriad sources that comprise a diversified energy portfolio. Fossil fuels, including natural gas, diesels and gasified coal, provide multiple sources of hydrogen within the constraints of our existing energy infrastructure. Green fuels, including methane biogas, ethanol and butanol fermentation products, and bio-diesels derived from vegetable oils, provide renewable hydrogen sources that are produced locally and comprise a carbon-neutral (i.e. zero greenhouse emissions) energy cycle. In all of these cases, fuel reforming is critical to the successful creation of a hydrogen-based energy infrastructure and economy.

Research combines faculty expertise in (i) catalysis and surface science, (ii) kinetics and reaction engineering, (iii) materials science, and (iv) environmental engineering to develop efficient reforming systems. Objectives include (i) minimize catalyst and overall reformer costs, (ii) maximize reforming thermal and fuel efficiencies, (iii) ensure long-term stability of reforming technology, and (iv) minimize environmental impact of reforming waste, by-products. Current specific research projects at the CGFCC include (i) conversion of bio-diesel and/or vegetable oils to hydrogen, (ii) conversion of ethanol-water mixtures to hydrogen, and (iii) direct utilization of methane bio-gas to electricity.

Hydrogen Purification

A primary challenge to the creation of a hydrogen infrastructure is the purification of hydrogen fuels prior to use by fuel cells. Impurities ranging from carbon monoxide to sulfur may degrade performance of fuel cell systems over time; thus the removal of these impurities prolongs the lifetime of fuel cells. Faculty at the CGFCC represent diverse experience with porous and non-porous membranes constructed from polymeric, metallic, ceramic and cermet materials, for the purpose of purifying hydrogen produced from fuel reforming. Objectives include (i) identifying key mechanisms of hydrogen purification in novel cermet materials as well as investigating electrochemical purification techniques using PEM systems, (ii) maximizing hydrogen purification rates, while (iii) minimizing materials and operations costs.