What are the trends in low-temperature fuel cells? The latest developments and innovations were revealed by the industry leaders in a survey commissioned by H2Expo, International Conference and Trade Fair for Hydrogen and Fuel Cell Technologies, to be held at the CCH Congress Center Hamburg from 31 August to 1 September 2005. This 5th event in the annual series will be a meeting place for delegates from industry, politics and research, to discuss developments, joint ventures and orders.

The findings of the survey show a trend towards more flexible operating temperatures in low-temperature cells, progress in Direct Methanol Fuel Cells (DMFC) and more economies in use of platinum. The increase in operating temperature of PEM cells (Polymer Electrolyte Membrane) from the conventional 80°C to between 100°C and 200°C has led to the definition of new categories, with experts now talking about medium-temperature and high-temperature PEM.

The Frankfurt based company PEMEAS, which is pursuing the fuel cell research activities of Celanese and of the former Höchst AG, is working with a PBI (polybenzimidazole) system that stores phosphorus acid instead of water in the membrane. This means there is no need for membrane moistening with water. The preferred temperature range is 160°C to 180°C. From 160°C upwards, the Membrane Electrode Assembly (MEA) becomes carbon-monoxide tolerant, i.e. the noble metal catalyst is no longer deactivated by CO. Application goals of this "Celtec" method are reformate operated stationary systems, with simple gas cleaning of the reformate. The cooperation partners include Plug Power.

Hot PEM cells are currently being tested by Vaillant. The new prototype generation operating at temperatures between 160°C and 200°C has now passed its first laboratory tests. Previously, the operating temperature was 75°C. The new system was developed in partnership with Plug Power, and is claimed to be significantly more robust, to give greater electrical efficiency, and to operate with a simplified natural gas reformer. It is expected to give cost savings, on the way to a competitive product.

Higher temperatures are likewise a part of the MEA development programme of 3M Deutschland, which indicates an operating temperature of rather more than 100°C, but not as high as 180°C. They say that this permits simplification of the PEM system. The main focus in this development is durability, robustness and improved temperature stability.

Ballard in Vancouver report operating capability at really low temperatures. Following announcements by Asian automotive manufactures of the cold-start ability of their PEM cells, Ballard now also reports frost-resistant operation. A new test cell in their laboratories completed 50 repeats of cold starting at ?20°C and the following simulated drive cycle. Between starts, the 10-cell unit together with its periphery were frozen again. Tests showed no drop in performance and no damage. The goal of further development is cold start at ?30°C. A simulated long-distance test was conducted with a range of drive cycles, showing a 5% drop in performance only after completion of nearly 2200 hours. The new cell design also gave substantial cost cuts. The company indicates that platinum coating of the electrodes was reduced by 30% to about 0.7 mg/cm² without loss of performance. Though declining to give details on water management and internal operating temperature of the test cell, Ballard claims to have achieved a technical breakthrough in this area. The currently produced PEM version Mark 902 is operated at 80°C. A new technology schedule is to be announced in April 2005, moving towards commercial availability of the cells for automotive use in 2010.

In the past, Direct Methanol Fuel Cells (DMFC) have been in the media shadow of fuel cell vehicles. In terms of design, they are derived from PEM cells and are operated at temperatures between 70°C and 80°C. Now it looks like DMFC are catching up. The Jülich Research Centre has a team of 30 working on their further development – the largest DMFC team worldwide, according to a Jülich spokesman. The previous handicap of DMFC, that is undesired methanol crossover through the membrane, has not yet been eliminated, but it has been reduced. At the present state of development, some 10 to 20% of the methanol gets into the cathode unused and is burned there. Total efficiency is currently 25%, and the aim is to achieve 30%. The electrode coating of the cell with platinum and ruthenium is to be halved from 4 mg/cm² to 2 mg/cm². The first applications are said to be envisaged for notebooks in the 50 Watt range and for small industrial trucks in the 2.5 kW range.

Methanol crossover has been reduced to the single-digit percentage range at Smart Fuel Cell (SFC). They report a new film membrane, no longer conducting protons but other ions, and also halving the amount of platinum needed. A special feature indicated by SFC is the filling of tank cartridges with straight methanol instead of with a methanol/water mixture. The latter is still required for the anode, but that is generated by recycling of cathode water. The cell is reported to be suitable for air temperatures between -35°C and +40°C. That would also permit mains-independent applications traffic monitoring and telecommunications, for example in Scandinavia. The savings in platinum are likely to reduce prices in the near future.  The operating temperature is reported to be up slightly, but still less than 100°C. The short-term goals are development and cooperation projects in the 25W class for power supply for laptops. Such units are claimed to be possible with modules the size of a DVD drive.

The Celtec V membrane from PEMEAS, currently at the experimental stage, can be operated in a range from ambient up to 160°C, which is unusually hot for a DMFC. Methanol crossover is said to be considerably reduced compared with fluorine polymer membranes, and lower-priced volume production is expected in comparison with the latter.

Alkaline Fuel Cells (AFC) are known from aerospace applications and are commercially available. With operating temperatures between 60°C and 200°C they are also counted in the low-temperature class and are regarded as sophisticated in terms of their fuel requirements –high-purity hydrogen or CO2-free reformate.

A close-to-market derivative of the AFC has been developed by Medis Technologies, New York. The portable auxiliary power source Power Pack is designed for battery charging and as an alternative power supply for conventional mobile phones, digital cameras, MP3 players and electronic games. The unit weights 200g and contains alcoholic potassium hydroxide as the electrolyte and a liquid hydrogen storage system based on borohydride. The cathode operates without platinum or other noble metals, and by the time it is launched in the market it is also to have anode operation without noble metals. For private users, the Power Pack is designed as a disposable product, i.e. no refilling is possible. According to data from Medis, the cell operates at an internal temperature of about 20°C and without perceptible heat dissipation, and is capable of operating at ambient temperatures of ?20°C and also under very hot conditions. The theoretically possible upper limit is 200°C, which is the flash point of one of the two liquids contained. A refuelable version is planned for military applications, capable of withstanding even lower temperatures. Production is to start at the end of 2005 at a rate of several thousand units a month, increasing in mid 2006 to one and a half million per month, and doubling again by the end of 2006. The product seems an elegant way of getting round the problem of standardisation, which would be needed if fuel cells are to replace batteries directly.

Aerospace and maritime applications are covered in greater detail at the H2Expo 2005, 5th International Conference and Trade Fair for Hydrogen and Fuel Cell Technologies, with the scientific conference on “Fuel Cell Systems for Transportation: Maritime, Aerospace and General Transportation”. Aspects of commercial applications will be covered by the conference on “Introducing Hydrogen Energy Technology in a Global Market”. H2Expo 2005 will be held at the CCH Conference Center Hamburg from 31 August to 1 September, daily from 9am to 5pm.