Refuelling with hydrogen

Bridging technology for sustainable hydrogen mobility

“One promising application is the production of hydrogen from diesel and biodiesel directly on site at conventional filling stations, which would make it much more convenient to fill up fuel cell vehicles, as well as further support the breakthrough of this technology," says project manager Stefan Martin, from the DLR Institute of Engineering Thermodynamics in Stuttgart. Fuel cell vehicles could pave the way for more sustainable mobility in the future: through an electrochemical process, the fuel cell converts hydrogen and oxygen into water and electricity. The resulting current produced is then turned into kinetic energy by an electric motor. Currently, there are less than forty hydrogen filling stations in Germany – one of the reasons why fuel cell vehicles are still struggling to enter the market. "The technology developed during the NEMESIS 2+ project could act as a bridge for creating the necessary hydrogen infrastructure, which would enable fuel cell vehicles to be filled up across the country," concludes Martin.

Rather than delivering hydrogen in lorries within compressed gas cylinders, the process being investigated by DLR scientists uses the existing infrastructure for storing and transporting diesel and biodiesel. The only added ingredient is a compact facility for producing the hydrogen. Compared to pressurised hydrogen, liquid fuels, such as diesel, are characterised by their higher volumetric energy density, which makes them easier to transport and store. The prototype that has been built by the Dutch project partner, HyGear, produces 4.4 kilograms of hydrogen from 20 litres of biodiesel in one hour – this roughly corresponds to the fuel tank of a B-Class F-cell vehicle.

Challenges: stable process and high purity

Until now, the primary form of hydrogen production on an industrial scale has been by natural gas steam reforming. During this process, the hydrocarbons in the gas are converted at high temperature into a hydrogen-rich mixture of gases. The hydrogen is then separated out during an additional process step. "Using steam reforming to produce hydrogen from diesel and biodiesel is much more laborious. The reason for this is the deactivation of the employed catalysts by deposition of carbon and sulphur impurities on their surface, which causes a reduction in the amount of hydrogen produced," Martin explains. With the help of laboratory experiments and simulations, DLR researchers have re-examined the entire process systematically, and have been able to identify the optimal operating conditions. "This knowledge now allows us to produce high-quality hydrogen with a purity of 99.999 percent, and for the first time, we are able to produce hydrogen from diesel and biodiesel through a process that is stable over a long period," Martin continues. The efficiency of the process, from start to finish, amounts to approximately 70 percent. A techno-economic evaluation, which was also carried out during the EU project, determined maximal production costs of 5.80 euro per kilogram of hydrogen. This figure is already close to the economic efficiency of the prototype.

About the NEMESIS 2+ project