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Risø DTU Investigating Production of Synthetic Transportation Fuel from Renewable Electricity and CO2

SOEC cells with a proton-conducting electrolyte can operate at lower temperatures and can be used to produce different kinds of synthetic fuels. Cells with an oxide ion-conducting electrolyte require a high operating temperature which will cause the synthetic fuels to split. This type can therefore only be used to produce synthesis gas. Source: Risø. Click to enlarge.

Risø DTU, the National Laboratory for Sustainable Energy at the Technical University of Denmark - DTU, is heading an effort to transform CO2 and renewable electricity into synthetic fuels for transportation.

Making the step from electricity to chemical energy requires an electrolytic process. Through electrolysis, water is transformed into hydrogen and oxygen (and CO2 to CO and oxygen) using electricity. The Fuels Cells and Solid State Chemistry Division at DTU develops electrolytic cells for this purpose in the form of solid oxide electrolytic cells (SOEC).

An SOEC electrolytic cell is built up of ceramic materials and is, in principle, a reversed SOFC fuel cell which Risø is developing in conjunction with, among others, Topsoe Fuel Cells.

—Research Professor Mogens Mogensen from the Fuels Cells and Solid State Chemistry Division at Risø

The process in the electrolytic cells corresponds to part of nature’s own photosynthesis, which takes CO2 out of the air and transforms it into a store of chemical energy in the form of sugar.

High-temperature cells. High-temperature cells are very efficient compared with other electrolysis methods as they produce more oxygen and carbon monoxide from a given amount of electricity. This is because at high temperatures water and carbon dioxide can be split into synthesis gas (hydrogen + carbon monoxide) and oxygen using the heat, and the SOEC cell is thereby self-cooling—the heat which is inevitably produced when electricity runs through something is needed for the electrolytic process. Moreover, it is possible to utilize the heat which is often available as surplus heat from, for example, power stations and industry.

These high-temperature electrolytic cells will be good for large, central plants for manufacturing synthetic fuel from synthesis gas. The catalytic processes which follow the electrolytic process require a complete facility with a catalytic reactor coupled to an electrolytic cell plant because the synthetic hydrocarbons are not stable at such high temperatures (over 650 Degrees C). Such a facility probably needs to exceed 100 MW for it to be financially viable.

—Mogens Mogensen

Work has been conducted on the high-temperature cells for some time in SERC (Strategic Electrochemistry Research Center), where a number of enterprises and research centres are collaborating on the development of these types of electrolytic cells.

Low temperature cells for local production of synthetic fuel. For local production conditions, it is necessary to develop cells which can operate at temperatures in the 200-400 °C range. This way, small, local electrolysis plants can be established, which can be connected directly to a local wind turbine and produce synthetic fuel for the local area. The lower temperature means less heat loss and makes it easier to build small and modular electrolysis plants.

The vision is to be able to build small, modular plants, with one standing beside each wind turbine in the local area.

—Mogens Mogensen

For this to succeed, it is necessary to develop completely new materials. These will be developed within the larger Catalysis for Sustainable Energy (CASE) research initiative, which is developing catalysts to transform local renewable energy into chemical energy. CASE is headed by Professor Jens K. Nørskov from DTU Physics.

The Fuel Cells and Solid State Chemistry Division is working with two electrolyte types. One is a mesoporous ceramic material, which can absorb liquid electrolytes in their nanopores and retain them. The second type is low-temperature proton-conducting materials which uses a solid ceramic electrolyte.

Limestone from the Danish subsoil can be used to produce sustainable synthetic fuels. Source: Risø. Click to enlarge.

Limestone in the production of sustainable synthetic fuels. It is hard and costly to directly separate CO2 from the atmosphere. Professor Mogens Mogensen therefore envisages the necessary CO2 coming from other sources such as breweries and second-generation bioalcohol plants, where fermentation produces large volumes of CO2. Another local possibility is using Denmark’s most widespread raw material, limestone (calcium carbonate). Heating limestone liberates CO2, leaving quicklime (calcium oxide). Water is mixed—or ‘slaked’—with quicklime, producing slaked lime (calcium hydroxide), whereby most of the heat which was used is again released.

Slaked lime reabsorbs CO2 from the air relatively quickly. Slaked lime mixed with sand is called mortar, which has traditionally been used as a binding paste in masonry. The wet mortar between the bricks absorbs CO2 from the air and hardens through the formation of lime to a stone-hard substance that binds the bricks together.

In other words, the lime is part of a carbon cycle. The CO2 which is released when the lime is burnt is absorbed again when the slaked lime absorbs CO2 and is thereby converted back to lime. This cycle can be used to manufacture synthetic CO2-neutral fuel, Mogensen suggests.


richard schumacher

Make it so! This is precisely the path to carbon-neutral transport because it allows the world to continue using trillions of dollars' worth of existing infrastructure (distribution networks and vehicles) designed for hydrocarbon fuels.

See also


I don;t know if these people are completely mad, or just innumerate.
How on earth are you going to finance an expensive SOEC if it is dependent on the output of local wind turbines, when the wind only blows part of the time?
These bozos are only interested in extracting grants to pursue their fetishes, whatever the costs to the public.


Because they have a lot of wind to work with. Wind power provided 19.7 percent of electricity production and 24.1% of capacity in Denmark in 2007, a significantly higher proportion than in any other country - and it's still growing.

The wind resource in Denmark is actually pretty big. Onshore it has relatively modest average wind speeds in the range of 4.9–5.6 metres a second measured at 10 m height, but has very large offshore wind resources, and large areas of sea territory with a shallow water depth of 5–15 m, where siting is most feasible. These sites offer higher wind speeds, in the range of roughly 8.5–9.0 m/s at 50 m height. There have been no major problems from wind variability, although there is a temporary problem resulting from the connection of a large bloc of wind power from offshore wind farms to a single point on a weak section of the transmission network.

Denmark is connected by transmission line to other European countries and therefore it does not need to install additional peak-load plant to balance its wind power. Instead, it purchases additional power from its neighbours when necessary. With some strengthening of the grid, Denmark plans to increase wind's share even further.

While wind power accounts for almost 20% of the electricity generated in Denmark, it covers only 10–14% of the country's consumption. Power in excess of immediate demand is exported to Germany, Norway, and Sweden. The latter two have considerable hydropower resources, which can rapidly reduce their generation whenever wind farms are generating surplus power, saving water for later. In effect, this is a way for northern Europe to store wind power until it is needed. The benefit of this goes to Denmark's neighbours so they are looking at using this surplus locally of produce synthetic fuels.


Have a look;


The German company "solar fuel" developed together with the Fraunhofer Institut a process that is using surplus renewable electricity for producing synthetic gas, equivalent to natural gas for storage of excess renewable energy. The process is 60% efficient.

This synthetic gas can be used for gas driven cars and is stored in existing gas storage facilities.


Since the price of wind-energy is falling continuously and will keep falling, it will 'soon' be realy cheap. By then, it would be nice if technologies as these are mature enough to take over any fossil carbon sources and even as a source for food.

richard schumacher

It doesn't have to wind, Dave. Substitute your favorite non-fossil primary energy source.


Davemart - so what is the solution? Electric cars which will place unmanageable demands on today's grids at peak periods? Grids which are powered more by coal and nuclear than solar or wind? This does make EVs a bit of a nonesense, especially in absence of a comprehensive supporting infrastructure, except where there are token gestures by poiticians to fund a minute number charging points etc for a bit of green kudos.

The process offered could make good use of off-peak electricity. I also like the idea of introducing lime as part of the carbon cycle. And there's also less of a need to replace the current vehicle fleet prematurely which comes with its own resource and energy costs.


Using CO2 from ethanol plants makes sense. Even using CO2 from coal plants makes sense, because you use the carbon twice, it is like cutting emissions in half. We will need creative ways if we are to reduce fossil fuel usage. High temperature water splitting makes sense as well, they are on to some good ideas.



Electric cars which will place unmanageable demands on today's grids at peak periods?

What few people know is that if all cars would be replaced by EV's overnight, the total power consumption would increase by not more than 20%.

It won't happen overnight though, and energy companies have ample time to adapt and install smart chargers that they can regulate remotely to prevent grid overloads. Charging electric cars will be done at night mostly, and no extra grid capacity is necessary for that.


We don't only need synthetic organics for fuel, but for everything actually made from crude. Also for making plastic and food we could use excess green electricity.
Synthetic fatty acids or esters could easily be transformed by algae to healthy biomass and therefore to chicken, eggs, meat, milk or fish.
One windmill could produce as much animal food as tens of acres of agricultural land. If we want to preserve biodiversity, freeing the world of the need for agricultural land is the most important step.

Henry Gibson

Thanks Anne:

Stationary batteries, mentioned recently in an article on charging in Japan can well be restricted to off peak charging, but also can be used for grid support during peak hours. Most automobiles are stopped most of the time and can be charged with off peak power and also support the grid.

The French are already planning fuel production from excess electric capacity, but this should be sent to germany instead, and the coal burned there turned into gasoline instead. ..HG..

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