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April 21, 2005

Current trends in High Temperature Fuel Cells

Source: Fuel Cell Today

Current trends in high-temperature fuel cells are the subject of a survey conducted on behalf of H2Expo. This year’s International Conference and Trade Fair on Hydrogen and Fuel Cell Technologies will be held at the CCH-Congress Centre Hamburg (CCH) on 31 August and 1 September. It is the fifth meeting in the series, bringing together representatives from industry, politics and research to exchange views on the latest developments, joint ventures and orders.
Applications for fuel cells
High-temperature fuel cells are used in small power stations, for home power and as auxiliary power units (APUs) in vehicles. Due to their high operating temperature and their long heating-up time, they are not suitable for portable applications. The high-temperature fuel cells include those with a ceramic electrolyte, mostly zircon oxide, known as SOFC (Solid Oxide Fuel Cells), reaching an operating temperature of 900°C, and those with molten carbonate electrolyte, known as MCFC (Molten Carbonate Fuel Cells). Both types are suitable for internal reforming of natural gas.

Home energy supply and auxiliary power units
More companies are moving into SOFC development, particularly in the 1-30 kW range. Research is well advanced, for example at Sulzer Hexis in Winterthur. They are developing a product called “Galileo 1000N” for power plants for single-family houses, with an output of 1 kW electric and 2.5 kW thermal, now close to series production; they report efficiency of more than 30%. Though reformer operation was successful with biogas, heating oil and propane gas, they are now concentrating on natural gas. The major challenge, according to one developer there, is the service life of the fuel cell. The aim is to achieve a service life of 5-7 years for the stack, which is operated between 850 and 950°C. For another application area, the Jülich Research Centre has developed a natural gas SOFC with an output of nearly 12 kW electric power, which has been tested in continuous operation for almost a year. Originally the stack had a temperature window of 900°C to 1000°C. The operating temperature has now been reduced to between 650°C and 750°C in order to permit use of lighter, lower cost materials. A further temperature reduction is desirable, but there are physical limits where the ceramic material loses its conductivity. A diesel reformer for SOFCs has also been developed at the Jülich facility. This combination could be used as an auxiliary power unit (APU) for diesels for application in trucks. Further development is needed for a kerosene powered APU for aircraft. Whereas modern diesel fuel contains less than 10 ppm sulphur, kerosene may contain 100 to 300 ppm sulphur. The reformer therefore needs a desulphurization system, which is currently being developed in Jülich. There are also reports indicating that Airbus wishes to use fuel cell systems with kerosene in its aircraft, and is currently working hard on this subject with system manufacturers. APU applications for buildings and for large vehicles are a subject of the work of EBZ GmbH in Dresden. The company uses stacks supplied by subcontractors, and has completed a demonstrator with 1.5 kW electric output. Operation with liquid gas has been tested, and reformers are currently being developed for diesel and kerosene operation. EBZ is aiming at an output range of 3-50 kW.

Fuel cell power stations
Siemens is regarded as the leader in SOFC power stations. A system with 100 kW electric output will be delivered to Turin in the near future, and in 2005 or 2006 one of these systems is to be delivered to Hanover and one to Alaska. Stack output is to be increased to 125 kW by then. After five or ten further units, the intention is to manufacture a small series in three or four years’ time. The stack operates at 950°C with an overall electric efficiency of 46% and is claimed to achieve a service life of at least 40,000 hours. The rule for electrolyte conductivity is “as hot as possible”. The high temperature is no problem for the fully ceramic, metal-free design of the stack. But temperature reduction is being researched in parallel.

Worldwide development efforts
Further SOFC developments in Europe are known to be in progress at the Hamburg University of Applied Sciences, the DLR Institute of Engineering Thermodynamics in Stuttgart (aiming at 650- 800°C), the Haldor Topsoe company in Denmark (aiming at less than 800°C and more than 200 kW), Elcogen in Estonia (targeting 1-100 kW, mid-range temperature) and ALPPS in Austria (diesel APUs in the output range 1-50 kW). Most of the other stack developers are based in the USA: Acumentrics (1-10 kW), Analytic Power (small cells), Ascent (aiming at 20 W-30 kW), CellTech (aiming at 1-5 kW, Ceramatec (aiming at 550°C, 1-25 kW), Delphi (APUs), FuelCell Energy (aiming at 650°C, 1-5 kW) and SOFCo-EFS (1-5 kW). Some of the American developers have funding from the government initiative SECA (Solid State Energy Conversion Alliance), which specifically supports the 3-10 kW sizes. In Canada, Fuel Cell Technologies (5 kW) is developing ceramic cells, and in Australia Ceramic Fuel Cells (0.5-200 kW) is active in this area. There are also a large number of universities and academic institutes worldwide. For small SOFCs there is a trend towards the medium temperature ranges, i.e. well below 900°C. One of their advantages is the shorter heating up time.

Use of different fuels
An operating temperature of 650°C is already ideal for molten carbonate cells. The molten salt material becomes liquid at 490°C and internal reforming of hydrocarbons starts from about 550°C. This reforming is necessary particularly for bi-fuel and multi-fuel systems, which permit changing between different fuels, such as natural bas and biogas. The American MCFC manufacturer FuelCell Energy (FCE), claims to have solved the problem of electrode corrosion, which occurs due to impurities in the fuel. They are also working on further cost reduction. FCE’s German partner, that is MTU CFC Solutions in Munich, has been using the American stacks as the basis for small power stations here, which are undergoing trials at various locations under the name Hot Module. MTU CFC Solutions aim to build the complete power station themselves before long. They expect to present their own MCFC development in late 2005 or early 2006. Installation of the next three Hot Modules is planned in the HafenCity area of Hamburg, and in Krefeld and Aalen. There are also plans for shipboard applications, as a particularly quiet way of generating power. The world of MCFC experts is an elite international community. Projects are known to be in progress at Ansaldo Fuel Cells in Italy (100 kW, aiming for 500 kW by 2006), Chubu Electric Power in Japan (300 kW) and GenCell in the USA (40 kW), and research projects at about ten universities and academic institutes.

Fuel cells at H2Expo
The subject of aerospace and maritime applications will be covered at H2Expo 2005, 5th International Conference and Trade Fair on Hydrogen and Fuel Cell Technologies in the framework of the scientific conference on “Fuel Cell Systems for Transportation: Maritime, Aerospace and General Transportation”. Aspects of marketing will be covered by the conference on “Introducing Hydrogen Energy Technologies in a Global Market”. H2Expo 2005 will be held at the CCH-Congress Center Hamburg on 31 August and 1 September, from 9am to 5pm on both days.