Vehicles with on-board fuel cells could help to make mobility more sustainable. In an electrochemical process, the fuel cell converts hydrogen and oxygen into electrical energy that drives the motors. In this process, the hydrogen and oxygen are turned into water – no harmful gases leave the exhaust. However, hydrogen filling stations are a very rare species; in Germany today just about three dozens of them are offering their services. The supply chain is rather complex and ineffective: Typically the hydrogen is transported in large, heavy gas cylinders. A 100 kilogram gas cylinder contains just about one kilogram of hydrogen – not a very reasonable mass ratio. As an alternative, tank trucks could transport larger amounts of liquid hydrogen. However, the containers for liquid hydrogen have to be cooled down to an extremely low temperature of -250°C (23.5 Kelvin or -415°F). The efforts to achieve these low temperatures make the whole thing uneconomical.
The EU Nemesis2+ project, fathoms out alternatives. One possibility would be converting diesel fuel to hydrogen. “Thus, the existing infrastructure could be utilised; diesel is ubiquitously available”, explains project manager Stefan Martin. “Of course, the converter station needs to be placed near the filling station to make it worthwhile.”
For the project, the scientists had build a compact prototype converter from Dutch project partner HyGear. The unit fits into a standard transport container and turns 20 litres of diesel fuel into about 4.4 kilograms of hydrogen. This is about the amount required to fill the hydrogen tank of a typical fuel cell vehicle like the Mercedes-Benz B-class.
But does it make sense first to convert crude oil to diesel and then the diesel to hydrogen? Yes, says Martin. Diesel has an energy density seven times higher than hydrogen. Thus, transporting the diesel is much more cost and energy efficient than transporting the hydrogen gas cylinders. The conversion process currently has an efficiency of about 70 percent which