Nanopower for fuel cells
The fuel cell research at Aalto University entered the nano era as four research teams at the same campus put their heads together.
The teams focus on the optimisation of fuel cell components and the understanding of fuel cell phenomena. The team at the Department of Chemistry, led by Docent Tanja Kallio, is studying direct methanol fuel cells containing carbon electrodes that are separated by a fixed polymer electrolyte membrane. The methanol fed on the anode is oxidized. In other words, the methanol gives away electrons that are carried to the cathode on the outer circuit. Siellä ne ottaa vastaan pelkistyvä happikaasu.
“Commercial solutions are still a long way off because the maximum power density of the cells is still only 50 milliwatts per square centimetre,” says Tanja Kallio.
The oxidation of methanol requires a precious metal catalyst, which is attached on the surface of the carbon anode. Kallio’s team is testing anodes made of carbon nanofibres and carbon nanotubes that will help to achieve a higher surface to volume ratio than traditional anodes made of amorphous carbon powder.
“A larger reaction surface speeds up oxidation, which in turn means that there is less need for an expensive precious metal catalyst. Carbon nanomaterials are also more durable than amorphous carbon, which makes the cell longer-lasting,” explains Kallio.
If the anode reaction proceeds effectively, molecules larger than methanol can be used as fuels. These include bioethanol and glycerol, a byproduct of the biodiesel production process.
Incomplete oxidation results in compounds such as aldehydes, which the cell does not need for proper functioning. Complete oxidation only produces carbon dioxide and water. At the same time, less fuel means more energy.
Cooperation has power
The carbon nanofibres and carbon nanotubes are manufactured by a team led by Professor Esko Kauppinen. Both are made of graphene layers. In the tubes, the layers are rolled up around a hollow centre whereas in the fibres, the layers are on top of each other. The fibres and tubes are functionalised using such substances as carboxylic acid groups after which platinum ruthenium nanoparticles are attached on them as catalyst. A research team led by Professor Outi Krause attaches catalysts on functionalised carbon nanomaterials using the atomic layer deposition (ALD) method, while the team led by Professor Sami Franssila manufactures micro fuel cells.
“We have an excellent chain made of material manufacturers and people testing the materials. It's great to cooperate with people from your own campus,” says Tanja Kallio, expressing her thanks to all those involved. Funding provided as part of Aalto University’s MIDE research programme brought the teams together. The Multidisciplinary Institute of Digitalisation and Energy (MIDE) has resulted in the forming of cooperation consortia at the Otaniemi campus the aim of which is to achieve synergy benefits in project planning and implementation and in the use of the project results.
The author is a Doctor of Science in Chemical Engineering and works as a researcher at Aalto University.
maija.pohjakallio [at] aalto [dot] fi
Turning energy directly into electricity
Fuel cells convert chemical energy directly into electricity. Unlike internal combustion engines, fuel cells do not convert heat into mechanical energy, which means higher efficiency.
Basically, fuel cells function in the same way as batteries. However, whereas fuel cells are continuously supplied with fuel from external sources, disposable batteries have the necessary fuel inside them.
Fuel cells can be used in a wide range of applications, such as mobile phones and other portable electrical equipment, cars and technology supplying buildings with electricity and heat.
High development and manufacturing costs and the absence of fuel distribution networks have slowed down the introduction of fuel cells. However, there is a great deal of optimism concerning the commercial breakthrough of fuel cells. A number of large companies, such as Toshiba, IBM, GM, Toyota, Opel and Honda have invested heavily in fuel cell research. Daimler aims to bring a Mercedes-Benz car using hydrogen fuel cells on the market in 2014.