Small Fuel Cells 2007

Direct Methanol Fuel Cells: Components, MEAs, Fuel

The afternoon session of day one was chaired by Dr. Hyuk Chang of Samsung Advanced Institute of Technology (SAIT), Samsung, Korea.

Emory S. De Castro of E-TEK Division, PEMEAS Fuel Cell Technologies, described “Advancement in DMFC Electrode/MEA Structure and Diagnostic Methods.” E-TEK continues to study MEA component integration to optimize performance. On the cathode side, one compromise involved water ejection vs. catalyst utilization. On the anode side the trade-off is between methanol accessibility and cross-over. Both PtRu anode and Pt cathode catalysts must be finely dispersed with large surface areas, while the anode’s PtRu must be well alloyed. Diagnostic methods have been developed to examine issues of: cathode flooding, the capability to manage water accumulation, and the extent of methanol penetration into the anode porous structure and cross-over. Commercial production of MEAs is now moving towards a second generation of high performance products.

Philip Cox of PolyFuel Inc. spoke on “Role of Membrane in Determining DMFC System Performance.” The integration of the membrane with the other components is a central focus at PolyFuel. Hydrocarbon membranes are being engineered to optimize the power density, fuel efficiency and fuel cell operating conditions over a range of system architectures. Membrane production is focusing on hydrocarbon polymer chemistry, roll-to-roll membrane production, catalysis application methods, quality and pilot production standards, and process control.

Shigeaki Satoh of Kurita Water Industries Ltd., Japan, described “Development of the “Solid-State Methanol Fuel for Direct Methanol Fuel Cells (DMFC).” He described the development of a novel “solid-state methanol” fuel based on a clathrate compound technology, which traps and contains methanol as a “guest” compound in a host compound. This gives major improvements in the areas of safety and portability of methanol. A liquid-free DMFC for a portable battery charger is under development based on this technology. In addition, this technology is being extended to the storage of hydrogen fuel.

Ceramic Technologies Across Different Fuel Systems

Michael Stelter of Fraunhofer IKTS delivered a talk titled “Multilayered Ceramic Micro Fuel Cell Systems and Components”. He described how multi-layer ceramics can be used to improve micro fuel cell systems. Fraunhofer IKTS, combines multi layer ceramics and thick film technology for miniaturized PEM or DMFC stacks, and also to form complete micro systems. A low sintering temperature material can be used to form small reactors or even micro stacks. The goal is to seamlessly integrate the active fluidic elements and to extend the temperature range of small SOFC components and systems. The result represents a complete 3-D integration of electronics, fluidics and electrochemistry.

Yoshihiro Kawamura of Core Technologies R&D Division, CASIO Computer Co. Ltd., Japan, presented a paper titled “A Micro Fuel Processor with Microreactor for a Small Fuel Cell System.” Over the past several years CASIO has been working on a micro fuel processor with a methanol reformer for “on-demand production” of hydrogen for a small PEMFC system. A special thermal insulation structure allows a fast heat-up time of six seconds. Adequate H2 production is achieved with low CO concentration. The next step is to develop reliable, durable operation with various portable devices.

Paul J.A. Kenis of the Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign spoke on “Ceramic Microreactors for Reforming of Hydrocarbons.” He opened with some brief comments about another of his efforts to produce membraneless fuel cells using lamina flow in micro-fluidic structures. This main presentation described the structure, integration, and characterization of Ru on silicon carbide monoliths inside alumina microreactors. These reactors reform hydrocarbons such as propane at high fuel conversion and high hydrogen selectivity at temperatures above 800°C. The temperature is selected to avoid coking/deactivation of the catalyst supports. Over 99% ammonia conversion has been obtained at T>700°C, giving 54sccm H2. Results from propane at T>950°C show 18sccm H2 at 99.9% conversion. Future directions include integration of WGS and PROX reactors.

Poster Presentations

At the end of day one, a dedicated poster discussion time was included. During the meeting, 16 posters with published abstracts were displayed including Biofuel Cells, Nick Akers of Akermin Inc.; Fluor-free Membranes, O. Ballabio of Pirelli Labs, Italy; Separated Semi-Permeable Membranes, Robert Bening of Kraton Polymers; Carbon Supported Platinum Catalyst, Young-Hun Cho of Seoul National University in Korea; Micro Fuel Cell Stickers, Anders Lundblad of The Royal Institute of Technology in Stockholm, Swede Direct Borohydride Fuel Cells, George H. Miley of the University of Illinois; and Miniaturized SOFC, Ji-Won Son of KIST of Korea.

Hydride and Borohydride Technologies

The first morning session in day two was chaired by Professor George H. Miley of the University of Illinois at Urbana-Champaign. He noted that this was the first time in the conference series that a full session was devoted to this topic.

Richard M. Mohring of Millennium Cell Inc. discussed “Chemical Hydride Technology for Portable PEM FC Applications.” Millennium Cell is developing chemical hydride-based hydrogen storage technology to power PEM fuel cells for diverse applications within the military, medical, industrial, and consumer markets. These power sources combine a sodium borohydride-based “Hydrogen on Demand®” technology with PEM fuel cells. Examples include the Protonex P2 solider power system which uses three 24-hour fuel cartridges to replace a 13 battery pack, thus reducing both weight and cost. Jadoo 100W cartridges for IFS24 radio and XRT can reduce weight by 50-60% compared to standard units. A supply system combined with a Gecko passive PEM cell in a small video camera was demonstrated at the conference.

Fumiharu Iwasaki of the R&D Division, Micro & Nano Technology Center, Seiko Instruments Inc., talked about their “High Power Passive Type PEFC Using Chemical Hydride.” He was describing a small-scale fuel cell system where the H2 fuel is generated from chemical hydrides without power consumption. The goal is a unit with a higher power output than for the previously demonstrated passive models. A five-stack, 10W system with size 200x65x53 mm provides 20Whr at 11.1 volts. A 50W system under development has demonstrated 100Whr.

Philippe Capron of DTNM/LCH, Atomic Energy Commission (CEA) of France, described “CEA Development of a DBFC (Direct Borohydride Fuel Cell).” CEA is developing the technology for novel portable fuel cells, namely Direct Borohydride Fuel Cells, which operate at room temperature. An alkaline anion-exchange membrane and composite electrodes in which non-noble metals may be used (e.g., Ag, Ni) are employed. The high theoretical electromotive potential (1.64V compared to 1.23V for PEMFC), and high theoretical yield (0.91 compared to 0.83 for PEMFC) are important advantages of the DBFC. Use of borohydride-based liquid fuel achieves a high specific energy which is very competitive with batteries for small power devices. To date, power densities of 200mW/cm2 and 140m/cm2 have been achieved with 2M and 5M NaBH4 solution, respectively, during 500 hours of operation. Catalysts to suppress H2 production at the anode have been successfully developed. Work on further improvements by reducing membrane permeation is under way.

DMFC/Catalysts

Olaf Conrad of CMR Fuel Cells (UK) Ltd., presented “Compact Mixed-Reactant DMFCs: Enabling Stack Power Densities of Greater than 500W/l.” A unique mixed-reactant flow-through fuel cell stack architecture was demonstrated earlier. Now the technology has been improved to enable power densities of several hundred W/l. Materials development, MEA architecture and stack engineering were discussed. The continued development of selective catalysts like RuSex/C and RhxSy/C are key to competitive power. A three-cell bipolar stack (10cm2/ MEA) providing 0.75W (80°C) and giving an active stack power density of ~500W/l was described. Extensive CFD modeling was used to design the unique “hole-type” MEAs.

Xiaoming Ren of Acta S.p.A., described the company’s effort to achieve “Breakthroughs and Challenges in Platinum-free Portable Power.” Increasing attention is being paid to platinum-free catalysts in alkaline anionic membrane fuel cells for portable power applications. Acta offers a range of HYPERMEC™ platinum-free catalysts to address this need. Tests were reported for a variety of fuel cells, including an ethanol fueled unit giving 28mW/cm2 (room T) over 800 hours of static operation. Performance at 80°C increased to 145 mW/cm2. A direct sodium borohydride/air cell achieves ~150mW/cm2 (Room T) with 5% NaBH4 solution. Methanol, ethylene and glycerol cells were also noted. Ultimate goals include 1000hr durability, Pt-free catalysts, cheap membranes and reduced (or no) external electrolyte.

Russell Marvin of MTI Micro Fuel Cells, gave a paper titled “Progress in Developing DMFC Technology to Beat Current Battery Performance.” Progress in advancing DMFCs vs. batteries is largely focused on increasing run-time. This revolves on optimization of fuel cell size, fuel tank size, packing efficiency, and fuel economy. He showed graphs of how critical trade-offs among these factors can beat the battery on run-time. Fuel economy seems to be a strong driving factor for longer run-times. Cell voltage, crossover, DC-DC converter efficiency, and parasitics lose also need to be optimized. Power vs. voltage trade-offs along with DC-DC converter challenges and topologies were discussed.

SOFCs

The afternoon session was opened by Jerry Hallmark of Motorola. He noted that the high temperature achieved in SOFCs offers advantages for select applications where thermal and heat management is possible.

Jerry L. Martin of Mesoscopic Devices LLC gave the first paper titled “Portable Solid Oxide Fuel Cell Systems.” Mesoscopic Devices has demonstrated several compact, portable solid oxide fuel cell generators that build on advances in lightweight, efficient balance of plant equipment and high power density stacks. SOFC generators of 75 and 250 Watts are being commercialized. Versions of these systems have been demonstrated operating on either kerosene or propane. The 250W net (280W gross) unit gives 28-30% efficiencies and 28V DC. Applications include remote sensing, leisure vehicles and boats, and portable power tools.

Mark L. Richardson of SOFCell and a consultant for Alberta Research Council (ARC) in Canada described “Tubular Micro-SOFC for Remote Power Applications.” ARC is developing a Tubular Micro Solid Oxide Fuel Cell (¼SOFC). It offers two main potential advantages: substantial increase in the electrolyte surface area per unit volume of a stack and quick start up. Since fuel cell power is directly proportional to the electrolyte surface area, a reduction of the ¼SOFC tube diameter from 22mm to 2mm increases the electrolyte surface area in a stack at least eight times. Due to its thin wall, a ¼SOFC has extremely high thermal shock resistance and low thermal mass. The characteristics are fundamental to obtaining rapid start up and turn off times in these systems.

Aaron Crumm of Adaptive Materials Inc. presented “Commercialization of Portable Solid Oxide Fuel Cell Systems.” Adaptive Materials has developed micro-tubular fell cell systems for military applications in the 20 to 50W power range. Advantages of this include the use of commercially available light hydrocarbons (ultimately going to JP8) as a fuel source. These systems operate at energy densities >1000 Whr/kg (20W), with the potential to achieve 1500Whr/kg over a ten-day mission. This exceeds current battery performance and also provides a significant weight reduction. Initial field tests identified some problems which have now been overcome to offer good durability, high system efficiency, operation in extreme environments, load following, no (or low) thermal or acoustic signatures, and sulfur tolerance.

Advances in Fuel and System Design

Erhard Ogris and Sebastian Schebesta, Alvatec Production and Sales GmbH, described an approach to “Elegant Hydrogen Generation Based on Reactive Metal Alloys.” A major challenge for hydrogen-based fuel cells is the safe storage of fuel or, alternately, on-the-spot production. Alvatec is studying ways to generate pure hydrogen by a reaction of metal alloys such as Li3AL2, CaAL19 and Mg2AL3. Generators providing from 0.6 to 100sccm are being developed for use with fuel cells from 0.1 to 100W. One example uses the generator in combination with the 50-180mW Fraunhofer PEM Micro fuel cells. These generators produce a high steady hydrogen flow rate plus easy handling, good safety and low cost.

Anders Lundblad of myFC AB in Sweden described an “Easy-to-Replace Passive Type Fuel Cell Sticker.” The flexible “sticker” fuel cell design is adhesively attached to a support with hydrogen feed. Despite a very simple design, the “sticker” fuel cell can provide power density levels of ~300 mW/cm2. “Stickers” are suitable for mass production (i.e., inexpensive) and easy to replace. Tests indicate 600mW/cm3, less than ~€1 per W. The first application target is a mobile phone charger, followed by a phone add-on, then full integration into the phone.

The closing talk by Erik Kjeang of the Institute for Integrated Energy Systems, University of Victoria, (IESVic) described a “High-Performance Microfluidic Vanadium Fuel Cell.” This design incorporates a high-surface area porous carbon electrode. A peak power density of 70mW/cm2 has been obtained at room temperature, significantly higher than previously reported for microfluidic fuel cells. In addition, low-flow rate operation demonstrates excellent fuel use. To optimize the design, various options such as use of graphite rods vs. carbon paper for diffusion layers have been examined. The microfluidic vanadium design is aimed at cost-effective and rapid fabrication. IESVic plans next to extend this to biofuel.