- Tiguan prototype lets people experience the year 2020 today
- Tiguan is the first fuel cell powered SUV by Volkswagen
- 125 mile range without a trace of noxious emissions
Volkswagen is introducing a highly relevant SUV with a fuel cell drive system in Los Angeles: the Tiguan. Compared to earlier prototypes, further performance gains were realized in the fuel cell drive, and its efficiency has been optimized. The fuel cell system, with its total output power of 80 kW, was integrated in the engine compartment of the Tiguan. That is where the electric motor operates too. It develops a maximum power of 100 kW. The top speed of the Tiguan HyMotion is 87 mph (140 km/h); the 1,870 kilogram prototype accelerates from 0 to 100 km/h in about 14 seconds.
The energy storage medium is a lithium-ion battery with a charge capacity of 6.8 Ampere-hours (Ah). It has a power output of 22 kW. The battery is charged via recovered braking energy (regeneration) or the fuel cell. The battery system is installed in the car’s cargo area; specifically, it is located under the dual cargo floor that is available on the production Tiguan. The new 700-bar hydrogen tank that was developed is integrated in the space under the rear bench seat and the cargo area. It can hold 3.2 kilograms of hydrogen (H) – and that is enough for about 125 emissions-free driving miles (about 200 kilometers). The fuel cell outputs the generated electrical energy – the power – to the electric motor via a converter and a downstream inverter. This means that the Tiguan can be driven silently and emissions-free.
Basic operation of fuel cells
The key element of each individual fuel cell – numerous cells are combined to form a block (stack) – is a proton-conducting membrane. It is located between the anode and the cathode of each fuel cell. Hydrogen flows into the cell on the anode side, and air on the cathode side. Many of these cells operating together as a network generate sufficient energy to drive a vehicle. In each cell, hydrogen and oxygen react and combine to form water on the cathode side. That is how the fuel cell converts the chemical energy of an oxidation process, a so-called “cold” combustion process, directly into electrical energy. The “exhaust” is nothing more than clean water vapor.
High temperature fuel cell follows low temperature system
In the future, however, all of this will operate even more compactly, economically and efficiently. Because Volkswagen Research has developed a unique high-temperature fuel cell (HTFC), whose design is unique worldwide. It eliminates the numerous disadvantages of previously known low-temperature fuel cells (LTFC) used in nearly all types of vehicle in the world that utilize this drive system.
Membrane and electrodes re-invented
Specifically, a key focus of Volkswagen Research efforts has been on developing a new membrane and electrodes for the fuel cells. Membranes, electrodes, cells – underlying these terms is an exceptionally complicated process for obtaining electrical energy from chemical energy, as outlined above, and to use it to drive the electric motor of the fuel cell car. If one overlooks the complexity of this process for a moment and focuses exclusively on the newly developed membrane and electrode components, the Volkswagen system offers these advantages compared to the low temperature fuel cell:
Comparison of low and high temperature fuel cells
The low-temperature fuel cell is operated at a membrane temperature of about 80 degrees Celsius. If the temperature rises significantly above this value, fuel cell performance collapses, and the cell experiences irreparable damage. Therefore, prototypes with LT fuel cells have an extremely complicated and expensive cooling system. The radiator surface alone is about three times as large as that for diesel engines (!). In addition, in a LT system the supply of hydrogen and air gases must be constantly humidified; otherwise energy production breaks down and the fuel cell is permanently damaged. This humidification causes water molecules to be embedded in the membrane, which also introduces undesirable added weight, and the process wastes space and money. The high-temperature membrane developed by Volkswagen, together with a new electrode design, on the other hand, can be continually “driven” – without power loss – at temperatures of 120 degrees Celsius. And indeed without humidification.
New approach: In the HTFC, proton conduction occurs via phosphoric acid. This acid has electrolytic properties that are as good as those of water, but it exhibits a higher boiling point. Therefore, the HTFC can operate with a considerably less complicated cooling system and water management. And that reduces weight and costs significantly. Moreover, the space requirement of the fuel cell system is reduced by over 30 percent.
Product water is undesirable
However, there was still an unresolved problem here: As in the case of the low temperature membrane, product water was formed. The water permeated the membrane and leached out the phosphoric acid. This in turn interrupted the flow of electric current. At this point, all attempts to make a high temperature fuel cell based on materials known to be suitable for vehicles had failed. The conclusion of intensive basic research by Volkswagen was that besides a new membrane, it was also necessary to make special modifications to the electrodes to prevent product water from penetrating the membranes.
Finding a solution by screen printing
The solution: On a special screen printing machine, like the ones used in the semiconductor industry, researchers coated carbon fleece elements with a new type of paste. The redesigned electrodes then underwent extensive testing in fuel cell stacks. The clear result: The product water could not penetrate the membrane to dilute the phosphoric acid. This meant that HT technology could be used for the next phase of research. A preview of the future might look like this:
Increasingly more powerful high-temperature fuel cell systems are created, which are perfected step-by-step and are actually used to drive initial research vehicles in the year 2010. By 2020 the first Volkswagen might appear with a fuel cell drive – and this is crucial – that would offer everyday utility and be affordable.
All data and equipment contained in this press release apply to models offered in the USA. They may differ in other countries. All information is subject to change or correction.
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