The Belchatow power plant, Europe's largest lignite power plant, in Poland. A team of Dutch researchers have a way – in the laboratory, at least – to wring power from everyday emissions of such plants. Image: Flickr/Bilfinger SE
LONDON – Power-generating stations worldwide release 12 billion tons of carbon dioxide every year as they burn coal, oil or natural gas; home and commercial heating plants release another 11 billion tons. A team of Dutch scientists has a use for it.
Power plants could, they argue, pump the carbon dioxide through water or other liquids and produce a flow of electrons – and therefore more electricity.
This would be enough, they argue, to create 1,750 terawatt hours of extra electricity annually – about 400 times the output of the Hoover Dam in the Nevada – and all without adding an extra gasp of carbon dioxide into the atmosphere. The exhaust from one cycle of electricity production could be used immediately to deliver another flow of power to the grid.
They make the claim in the journal Environmental Science and Technology Letters, published by the American Chemical Society. The claim rests on a 200-year-old technique pioneered by Sir Humphry Davy and Michael Faraday: electrolysis.
Behind the reasoning is a simple proposition, namely that every chemical event involves some exchange of energy. In a solution, this movement of energy involves electrons, and ions that migrate to cation or anion electrodes. In a mix of two different solutions, the final mixture has an energy content lower than the sum of the two original solutions. But since energy cannot be created or destroyed, therefore there must be some energy available for exploitation.
Bert Hamelers of Wetsus, a Netherlands-based collaboration between companies and research institutes exploring water technology, and colleagues from Wageningen University report that they used porous electrodes and flushed carbon dioxide into water. They got a flow of current as the gas reacted with water to make carbonic acid, which in the electrolyte became positive hydrogen ions and negative ions of the bicarbonate HCO3. As the pH of the solution rose, the bicarbonate became a simple carbonate; the higher the CO2 pressure, the greater the increase of ions in the solution.
In their experiment, they found that as they flushed their aqueous electrolyte with air, and alternately with CO2, between their porous electrodes, a supply of electricity began to build up. Since the air that comes from the chimneys of fossil fuel-burning power stations contains up to 20 percent of CO2, even the emissions represent a potential for more power.
They found they could get even more power if instead of a water solution they used an electrolyte of monoethanolamine. In experiments, this delivered an energy density of 4.5 mW a square meter.
The irony is that this electrical energy is already potentially available at the top of the power station chimney, because on release one "solution" of greenhouse gas – in the stack's emissions – mixes with a different-strength solution – in the ambient air – all the time.
Nobody of course has a way of harvesting this power directly, but an old-fashioned experiment with electrodes in a laboratory shows that huge quantities of potential power are being lost every day, in unexpected ways.
It would require huge investment – and a great deal of engineering ingenuity – to turn greenhouse emissions into yet more electricity, but such research is a reminder that scientists everywhere are looking for clever new ways to power the planet.
Dan Li, a materials engineer at Monash University in Australia, reports in the journal Science that he and his team have developed a graphene-based super-capacitor that is compact, and can be recharged quickly, but can last as long as a conventional lead-acid battery.