Nano Technology shows promise for new way of winning electricity from coal
Traditionally, coal has been used for the production of electricity by burning it in power stations to produce steam which then turns turbines and generates power. However, researchers from Brookhaven National Laboratory, Oak Ridge National Laboratory and the New Jersey Institute of Technology have published a paper which may ultimately change that. The report was published in the journal Nature Communications June 21, 2011 and concerns the use of coal gas in fuel cell technology.
Solid oxide fuel cells can generate electricity from a range of fuels including coal gas (methane). They utilise anodes fabricated from nickel and yttria-stabilised zirconia (a ceramic), but when a hydrocarbon gas is used, the anodes rapidly become deactivated due to the formation of carbon deposits; a process known as coking. Coking can deactivate a fuel cell in as little as 30 minutes, so it is a critical problem which limits the application of the technology. The researchers report a technique for overcoming this problem, based on the use of barium oxide nanoparticles.
Barium oxide is a hygroscopic material (it absorbs water) and the researchers have taken advantage of this to enable chemical reactions to take place on the surface of the anode by depositing barium oxide nanostructures on their surface. The nanoparticles promote the oxidation of the carbon deposits (to CO2) and so keep the anode surface clean, a process that is possible even at the relatively low temperature of 750 °C. The nanoparticles vary in size from 10 to 100 nm and tend to form "islands" on the surface of the anode which do not impede the migration of electrons across the surface. The formation of the barium oxide nanoparticles can be achieved as a part of the normal anode fabrication process and is therefore compatible with existing production technology.
Standard solid oxide fuel cells run at temperatures in excess of 850 °C and require the use of expensive, special materials which limit applicability of the technology. The system reported by the researchers runs substantially cooler which potentially permits cheaper materials to be used for interconnection of cells and other components. The system has been tested for a hundred hours of operation and no evidence of coking was observed at the end of the test. Whilst this is a positive result, it needs to be set in the context that the system would ultimately run in fuel cells designed for a five year operational lifetime.
The new system also appears to offer the advantage of higher energy conversion efficiency. A conventional coal-fired power station converts about a third of the chemical energy available into power; fuel cells can push this figure up to 50%. By producing hybrid turbines and fuel cell technologies, researchers believe that up to 80% conversion might be achieved. Additionally, the technology would be well-suited to carbon dioxide sequestration systems which are being considered as a mechanism to reduce release of CO2, a greenhouse gas, to the atmosphere.
Top Image Credit: © Vladimir Konjushenko