Volkswagen high temperature fuel cell
Volkswagen Research has developed a type of high temperature fuel cell (HTFC) that is one of a kind in the world. It eliminates numerous disadvantages of low temperature fuel cells (LTFC) previously known and used in virtually every type of vehicle with this propulsion system in the world. Prof. Jürgen Leohold, head of Volkswagen corporate research comments: "The high temperature fuel cell independently developed by Volkswagen in seven years of research work will make the overall system in the car lighter, more compact, stable and cheaper. And those are the decisive criteria for putting fuel cells on the path towards mass series production." Prof. Leohold continues: "We believe that the high temperature fuel cell is part of the future. In contrast, we no longer give much chance to low temperature fuel cells going into series production."
In detail, Volkswagen Research specially developed a new membrane and new electrodes for the fuel cell. Membrane, electrodes, cells – these conceal the exceptionally complex process of extracting electrical energy from chemical energy to power the electrical engine of future fuel cell cars. If you disregard this complicated process and just look a the newly developed parts "membrane" and "electrodes", compared to the low temperature fuel cell the Volkswagen system provides the following advantages:
Low temperature fuel cells are operated at a membrane temperature of approx. 80 degrees Celsius. If the temperature greatly exceeds this value fuel cell performance breaks down and irreparable damage is done to the fuel cell. This is why vehicle prototypes with LT fuel cells have an extremely sophisticated and expensive cooling system. The cooling surface alone is approximately three times as large as for diesel engines (!). In addition, in an LT system the supply of hydrogen gas and air must be continuously humidified, because otherwise the production of energy will also break down, permanently damaging the fuel cell. This humidification of the water molecules stored in the membrane also adds unwelcome additional weight, eating up both space and money.
In contrast, the high temperature membrane developed by Volkswagen can in combination with newly designed electrodes be "driven" at temperatures of up to 120 degrees Celsius with no loss in performance. And this without humidification. Novelty and background: In the HTFC protons are exchanged via phosphoric acid. This acid has good electrolytic properties similar to water, yet demonstrates a higher boiling point. This is why a significantly simpler cooling system and water management is sufficient for the HTFC. And this significantly reduces the weight and costs. The space required for the fuel cell system is also lowered by more than 30 percent.
However, one problem remained unsolved up to now: What’s referred to as product water formed, just as on the low temperature membrane. The water permeated the membrane and washed out the phosphoric acid. This in turn interrupted the flow of current. At this point all attempts up to now to make a high temperature fuel based on familiar materials useable have failed. For this reason, intensive Volkswagen basic research came to the result that in addition to a new membrane special modifications of the electrodes are necessary which are able to prevent product water from penetrating the membranes.
The solution: On a special screen printing machine like the ones used in the field of semiconductor technology the researchers at the Volkswagen Technology Center in Isenbüttel coated several cloth elements made of carbon fiber with a new type of paste. The newly created electrodes then underwent extensive testing in fuel cell stacks. The clear results: Product water can no longer penetrate the membrane and dilute the phosphoric acid. HT technology is thus ready for the next research step. A peek into the future could look like this:
More higher performance high temperature fuel cell systems come about that are perfected step by step and are expected to power the first research vehicles in 2010. In about 2020 the first Volkswagens with a fuel cell drive that is affordable and suitable for everyday use – the decisive factors – could appear.