During the Future Performance Days event, in its headquarters in Germany, the brand unveiled its electrification strategy. It was the opportunity to give some technical details on the latest prototype, the A7 Sportback h-tron quattro.
Like the engine of a conventional A7 Sportback, the fuel cell of the Audi technical concept car is mounted in the front. It comprises over 300 individual cells that together form a stack. The core of each of these individual cells is a polymer membrane. There is a platinum-based catalyst on both sides of the membrane. Hydrogen is supplied to the anode, where it is broken down into protons and electrons. The protons migrate through the membrane to the cathode, where they react with oxygen present in air to form water vapor. Meanwhile, outside the stack the electrons supply the electrical power – depending on load point, the individual cell voltage is roughly 0.6 to 0.8 volts.
The fuel cell operates in the high-voltage range. The most important auxiliaries include a coolant pump and the recirculation fan – a turbo compressor that forces air into the cells, returning unconsumed hydrogen back to the anode and thus increasing efficiency. These components have a high-voltage electric drive and are powered by the fuel cell. Because the exhaust system transports only water, it can be made of lightweight polymer.
There is a separate cooling circuit for cooling the fuel cell. The unit, which operates at a temperature of approximately 80 degrees Celsius, places higher demands on the vehicle cooling than an equivalent combustion engine, but achieves superior efficiency of as high as 60 percent – nearly double that of a typical combustion engine.
Cold starting is possible at temperatures down to -28 degrees Celsius. A heat exchanger and a thermoelectric, self-regulating auxiliary heating element maintain pleasant temperatures in the cabin.
The car sprints from 0 to 100 km/h (62.1 mph) in 7.9 seconds and reaches a top speed of 200 km/h (124.3 mph). It can cover more than 500 kilometers (310.7 mi) on a single tank, with nothing more than a few drops of water leaving the tailpipe. The A7 Sportback h‑tron quattro uses a 170 kW electric drive system with a fuel cell as the energy source. Each of the two electric motors drive the wheels of one axle. The Audi technical concept car is a true quattro and thus unique among fuel cell automobiles.