Volkswagen High Temperature Fuel Cell

Press Release

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 the low temperature fuel cells (LTFC) previously known. A new high temperature mem­brane and electrodes specially adapted for this membrane will thus enable significantly more compact, cheaper and more efficient fuel cell systems for cars. The breakthrough in this type of propulsion has come a bit closer. However, the prognoses of many manufacturers for when the hydrogen fuel cell will be ready for series production and available on a grand scale have been repeatedly revised due to the imponderablities of research. This is why Volkswagen is sticking to the facts:

1999. VW Research begins the program for the development of a high temperature membrane.

2001. At the end of 2001 Volkswagen decided to carry out independ­ent development of the high temperature fuel cell – starting with basic research on the topic of membrane technology.

2003. Three years ago Volkswagen researchers achieved significant success in membrane development. But suitable electrodes were missing as the key to implementation.

2006. Today, in the Autumn of 2006, the electrode problem has for the most part been solved. The results are very promising: The high temperature fuel cells are currently being developed and tested in the Volkswagen Technology Center in Isenbüttel, specially constructed for the research of alternative drive systems and located at the gates of Volkswagen headquarters in Wolfsburg.

A peek into the future could look like this:

In about 2010. More higher performance high temperature fuel cell systems come about that are perfected step by step and will 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. Volkswagen sees no chance for the mass series pro­duction of low temperature fuel cells (LTFC) primarily being used by other car makers today due to the disadvantages related to their conceptual design.

Disadvantages of the LTFC. 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 LT fuel cell vehicle prototypes – should they be able to pass driving test cycles similar to a combustion engine – place very high re­quirements on the cooling system, making it very expensive. In addi­tion, in an LT system the supply of hydrogen gas and air must be continuously humidified, because otherwise the production of energy will break down, permanently damaging the fuel cell and bringing the electric engine being powered to a stop. This humidification also takes space, weight and money.

Advantages of the Volkswagen HTFC. The high temperature mem­brane developed by Volkswagen can in combination with newly de­signed electrodes be “driven” at temperatures of up to 160 degrees at the same output of power. A medium operating temperature of 120° C is intended for vehicle operation. And this without additional hu­midification. A distinctly simpler cooling system and water man­agement is sufficient here, significantly reducing the need for space, weight and money!

FUEL CELLS IN GENERAL /

Chemical energy turns into electrical energy. To more precisely classify the advantages of the high temperature fuel cell will require a consideration of the general workings of fuel cells. The central element of each individual fuel cell – many of which are combined into a block (stack) – is a proton exchange membrane. It is located between the anode and cathode of each fuel cell. Hydrogen flows into the fuel cell on the anode side and the cathode is supplied with air. Many of these cells in combination generate enough energy to power a vehicle. Hydrogen and oxygen react inside each cell, pro­ducing water on the cathode side. Energy is released in this process. The fuel cells thus convert the chemical energy of an oxidation proc­ess, known as “cold combustion”, directly into electrical energy. The “exhaust” produced is nothing more than clean water vapor.

Electric, not combustion engine. The fuel cell is supplied via a hydrogen tank and an external air intake. The electrical energy – the power – generated by the fuel cell is delivered via a converter and a downstream static inverter to one or more electrical engines. Conse­quently, the car runs virtually without making a sound, but definitely emission free.

FUEL CELLS IN DETAIL

General process. Hydrogen is split into electrons and protons on the anode. The positively charged protons travel through the membrane to the other electrode, the cathode. The negatively charged electrons flow through an external circuit to the cathode. This current flow powers the electrical engine of the car. On the cathode the protons react with the inflowing oxygen and the electrons to form what is called product water, which for the most part escapes from the ex­haust pipe. Approximately sixty percent of the energy employed in the form of hydrogen is converted into electricity.

Disadvantages of the LT fuel cell: In the low temperature fuel cells primarily employed up to now the protons are carried from the anode to the cathode in the membrane via a short connection of the protons with the water in the membrane. To prevent the membrane from dry­ing out the reaction gasses hydrogen and air must therefore be hu­midified. This results in two decisive disadvantages: The membrane may not, as previously outlined, heat up to above 80 degrees Celsius. The result is a very small difference in temperature between the cooling medium and surrounding air. Continuous hill climbing and trailer operation are virtually impossible. Yet in order to attain suffi­cient cooling performance LT fuel cell systems – if being used for the everyday operation of a normal car – need a cooling surface ap­proximately three times as large as for a diesel engine (!). This is without taking into consideration situations such as hill climbing and the necessarily higher cooling performance associated with it.

Cooling problem in detail. Cars with conventional combustion en­gines produce more waste heat than vehicles with fuel cell powered electrical engines. Combustion engines can release this waste heat to the environment via the engine cooling system and exhaust fumes. The fuel cell does not have this option. As a consequence of the comparatively lower operating temperature, heat is almost exclu­sively released via the cooling system, but not via the exhaust sys­tem. The result is that at the same engine output more than twice the amount of heat has to be discharged via the car radiator. And this holds true despite the efficiency advantage of the fuel cell.

LT fuel cell gasses must be continuously humidified. There is another problem: The inflowing gasses hydrogen and air dry out the electrolyte – the water molecules stored in the membrane. And this also disrupts the flow of current. This is why a special unit humidi­fies the inflowing gasses. For these reasons, apart from the actual fuel cell other complex technology must be integrated in the vehicle. The result is that the overall system is heavier.