Running on pollution!
Although we know we must wean ourselves off the oil-based energy model, renewable sources of energy pose storage and transportation problems. However, a possible solution has appeared on the horizon: what about turning the polluting emissions that are saturating the atmosphere into fuel? This is exactly what the ELCAT exploratory project (Electrocatalytic Gas-Phase Conversion of CO2 in Confined Catalysts), which came to an end in February 2008, has managed to do, by converting carbon dioxide into hydrocarbons.
The energy issue is ubiquitous. It seems that nobody will miss an opportunity to remind us that hydrocarbon reserves are running out and, to compound matters, that the atmosphere is becoming saturated with carbon dioxide (CO2) – with serious consequences that evident every day. In a bid to change all this, an exciting research project has set out to design and manufacture an autonomous fuel cell able to use solar energy to convert carbon dioxide into liquid fuel that can be injected directly into an engine.
The system for doing this can produce fuel for immediate use, unlike hydrogen, for example, which requires yet more time and resources to develop the necessary distribution infrastructure.
Story of a dream
But initially the gamble was far from being won. As the carbon dioxide molecule – CO2 – is highly stable, a highly energy-consuming reaction is needed to split its constituent atoms. It was this appetite for energy that finally got the better of the Japanese team from Hitachi Green Data Center that pioneered research into the process back in the 1990s.
In spite of this, scientists still wanted to make the dream reality. At the beginning of the decade, researchers from the University of Messina (IT) decided to pick up where the Japanese had left off. This time they used solar energy. Initially solar energy removed the barriers to high energy consumption, as it is free of charge and available in unlimited supply. During the course of their work the Italian scientists noticed that an electrocatalytic reaction could be produced under ambient temperature and pressure conditions. To do this they had to use nanotubes, which have only recently been produced on a large scale. The research team then called in partners with complementary expertise. This led to the launch of the European ELCAT project in 2004.
The ELCAT project is financed to the tune of approximately € 875 000 by the NEST programme (New and Emerging Science and Technology), which is part of the European Union's Sixth Framework Programme for Research and Technological Development. Dominique Bégin, a researcher at France’s National Scientific Research Centre (CNRS), heads up the French arm of the project at the laboratory for materials, surfaces and processes for catalysis at Louis Pasteur University in Strasbourg (FR), describes ELCAT’s aims: “The project began by exploring the feasibility of the process. We were not yet interested in energy output because, in the current state of progress, it is tiny.”
What the project has done, though, is to prove that conversion is possible. “It is not only a question of basic research, but also of applying research to this feasibility, all without a profit motive,” the French scientist adds.
The beauty of soft chemistry
And the process works! A fuel cell uses carbon dioxide to produce hydrocarbons under normal conditions. The first phase is to split water molecules into protons and electrons in the first compartment of the fuel cell, using solar energy and a titanium oxide catalyst. The result is energy in the form of hydrogen and electrons, which, in a second phase, needs to be converted to a form of energy that can be used with existing infrastructure (that is to say, high energy-density liquid fuels).
In this second phase, the electrons and protons on the other side of the fuel cell are used to reduce the CO2 to hydrocarbon compounds (CxHy).
This part of the reaction takes place in carbon nanotubes, which conduct electrons. The internal walls of the nanotubes are lined with platinum to induce catalysis. This technology is the key to the success of the process, using soft chemistry (a recent discipline inspired by the metabolism of living beings to circumvent the problem of energy-intensive reactions that can be triggered only under very high pressures and/or temperatures).
However, the real beauty of the process is that it uses very small nanotubes, only around 50 nanometres in diameter. This induces a capillary action that ultimately confines the materials in the nanotube: it causes the ‘pressure’ in the nanotube to rise naturally by an infinitesimal amount. This enables CO2 to be converted in an environment where neither the pressure nor the temperature parameters have been modified and which can be considered as standard: 20°C and 1 atmosphere (= 101 325 kilopascals).
Hydrocarbons and alcohols
All these reactions take place within a single system, which has actually succeeded in producing fuel. “Last year, ELCAT’s gamble finally paid off,” says Linda Perathoner, project leader at the University of Messina (IT). “We have even produced the reaction using an iron catalyst, which costs less than platinum but also gives a lower energy output.”
The researchers made a further finding: the products emerging from the system contain not only fuel, but a mixture of hydrocarbons and alcohols. This is because the reaction between water and CO2 has two possible outcomes (hydrocarbons – CxHy – and alcohols – CxOHy). The relative proportions of each compound depend on the type of material used for catalysis (platinum, iron, etc.), their quantity, as well as the diameter of the nanotubes… a wide variety of factors that still prevents scientists from fully mastering this ratio today.
However, once they have been separated, the hydrocarbons will serve as fuel and the alcohols for the synthesis of useful derivatives, as they can be converted into compounds of use to the entire chemical industry – especially the cosmetics and pharmaceutical sectors. All these prospects are opening up in the wake of the project.
To a large extent, ELCAT’s success stems from its European partnership based on an unusual division of labour. The University of Messina research team in Italy monitored the factors of CO2 conversion into hydrocarbons and alcohols using proton exchange membranes (PEM) and carbon nanotubes. The researchers from the University of Patras (GR) studied an alternative for the formation of hydrocarbons, using oxygen anion-conducting membranes and carbon nanotubes to remove the oxygen from the reaction environment, thereby reducing the CO2 and hydrogen directly to hydrocarbons. The French scientists mass-produced nanotubes with the ideal conversion characteristics. Finally, the research team from Fritz Haber Institut in Berlin, Germany (Max Planck Institut) made available its expertise in advanced materials characterisation.
Dominique Bégin explains that, “each of the partners played a specific role by contributing their skills and expertise. And a good working relationship was crucial because the project research was not all smooth sailing. For instance, there were numerous problems in producing open nanotubes, not to mention ensuring that the platinum particles actually formed a lining inside the tubes rather than on the outside, which was successfully verified by our German partners.”
The system, which includes two conversion phases, now measures only a few square centimetres. However, it is a laboratory prototype that is currently capable of producing only a few millilitres of hydrocarbon.
A host of highly concrete prospective applications have sprung up, though. “The applications would be aimed primarily at factories and power stations, the leading culprits of CO2 emissions. They would include devices fitted in places where there are discharges, such as chimney stacks,” explains Linda Perathoner. “In ten or so years from now, this application should be under development on an industrial scale. Other ideas are emerging, too, such as building devices into car exhaust pipes, or else capturing the carbon dioxide present in the atmosphere. But once again, these are only very long-term prospects,” she adds.
Linda Perathoner mentions another, highly surprising application: “The system could be used to power a Mars observation satellite. The atmosphere of Mars, which is very rich in CO2, would make an ELCAT prototype perfect for the programme’s requirements. The satellite, orbiting around the red planet, would first use up its existing reserves of earth-based fuel, before producing its own fuel to prolong the satellite’s operating time for the return journey to Earth.”
Top priority for energy output
In the shorter term, the first thing that the ELCAT team intends to prolong is concept development. “The system prototype and the alcohol and hydrocarbon samples that it has produced are enough to convince the public and private sectors to invest in improving the process,” explains Linda Perathoner, “in particular by focusing on the energy output side.”
The project coordinators have already received offers of private sector finance to improve energy output. ELCAT is also on the list of participants in Richard Branson’s heavily publicised competition, Virgin Earth Challenge. Finally, the ELCAT team will seek new funding under the Seventh Framework Programme, just as soon as a call for projects is held in the relevant research field. The development of these technologies should open up encouraging prospects in the hope that they will be able to provide solutions to environmental and energy problems.
Delphine d’Hoop, Marie-Françoise Lefevre