Entering the Hot Phase

The automotive future lies with fuel-cell technology – or so we are repeatedly told. That is why Volkswagen is researching the actual potential of fuel cells as part of its Fuel and Powertrain Strategy. The combination of hydrogen-driven fuel cells and electric drive is often reported in the media to be a promising alternative to present-day combustion engines. Today’s petrol and diesel engines still run predominantly on petroleum-based fuels. But the black liquid that keeps the global economy oiled has some distinct disadvantages: petroleum combustion accelerates climate change, it is becoming successively more expensive because it is increasingly costly to mine and existing reserves are finite.

In its final stage, Volkswagen AG’s Fuel and Powertrain Strategy culminates in electric-drive mobility and is thus focused on renewable forms of automobile energy.

The electric motor is driven by a battery and/or a fuel cell. In light of their specific properties, such systems are viewed as having a supplementary function rather than competing with other forms of drivetrain. The following combinations and applications are conceivable:

• Battery-driven vehicles – urban mobility for short-distance commuters (~100km)
• A combination of battery and fuel cells – as range extenders for extended urban mobility, i.e. for mid-range distances (~250 km)
• Fuel-cell vehicles – for long-distance mobility (~500km)

The key benefit of electric-drive concepts lies in the fact that they produce no local emissions and use renewable forms of energy. Our focus here is on the activities surrounding fuel cells.

Development of fuel-cell automobiles at Volkswagen

Volkswagen began carrying out research into fuel cells in 1997 as part of its so-called Capri project, which included work on a VW Golf estate with 20 kilowatt (kW) of fuel-cell power.
By 2001, a Bora HyPower, developed in co-operation with the Swiss Paul Scherrer Institute and equipped with a 40-kW fuel cell, even crossed the Simplon Pass (at an altitude of over 2,000 metres) as part of a test-drive campaign. The Touran HyMotion was then fitted with an 80-kW electric motor driven by a combination of fuel cells and an electric battery. The latest test vehicles are two Tiguan HyMotions feature 100-kW-class fuel-cell stacks.

What all our trial vehicles have had in common to date is that they were fitted with low-temperature fuel cells. There are, however, a number of drawbacks in principle to such so-called low-temperature polymer electrolyte fuel cells (PEFC). While they are much more efficient than conventional combustion engines, the waste heat they generate is not split into exhaust gas flow and coolant, but needs to be wholly channelled off via the cooling system. As a consequence, much larger cooling surfaces are needed than those required for combustion engines. As the temperature rises, the catalytic converter (generally made of platinum) becomes more and more active. Operation at a relatively low temperature of around 80 degrees centigrade presents an obstacle to eventually cutting back on the use of this expensive precious metal. The relatively low operating temperature also has the disadvantage that contamination contained in the gases (e.g. carbon monoxide (CO), sulphur dioxide (SO2) or hydrogen sulphide (H2S) and other so-called catalyst contaminators) is likely to collect in the catalyst converter, reducing its efficiency. Thus, low operating temperatures make it difficult to achieve reliable long-term stability.

One way to solve these problems is to increase the operating temperature of the fuel cell.

Cutting-edge high-temperature fuel cell offers clear advantages
It is before this background that Volkswagen researchers have spent the past eight years developing a fuel cell, at the heart of which is a new kind of membrane that operates at a high temperature and enables a smaller, more efficient and lower-priced overall system. We use phosphoric acid as the electrolyte in this high-temperature PEM fuel cell to raise the temperature ceiling, so that the operating temperature can rise to as much as 160 degrees centigrade. This fuel-cell type does not require gas humidification, meaning less space is required and less cost is involved than for the conventional low-temperature PEM FC system. Initial vehicle prototypes which use this high-temperature technology could be built from around 2010.

These high-temperature fuel cells developed by Volkswagen were awarded the special prize as a “Sensible Innovation” by Germany’s biggest consumer magazine, Guter Rat. “I am happy to accept this award on behalf of my research team,” said Prof Jürgen Leohold, the head of Volkswagen Group Research. “We have done basic research and the extremely promising results of our work have shaped the course of things to come in the field of fuel-cell technology.”

Fuel-cell cars not due to reach series maturity before 2025
Both fuel-cell and battery technology offer potential for the creation of an efficient concept for sustainable automobile drive. What is important, however, is that the electricity or hydrogen used is generated from renewable sources of energy such as solar energy, wind or water.

The use of hydrogen as a provider of energy in the transport sector presents a number of challenges, solutions to which can not be expected to be found anytime soon. These challenges are

• to develop affordable fuel-cell or hydrogen storage technology suitable for everyday use
• to enable the inexpensive generation of hydrogen from renewable sources of energy
• to establish a widespread hydrogen infrastructure.

In our estimation, it will take up to 20 years to actually solve these challenges. 

More information on the topic of fuel cells and electric drivetrains at Volkswagen is available in our brochure entitled “Making Zero Emissions Possible”, retrievable here as a PDF file.