Motor Corp. says it has made substantial improvements in several key fuel cell components — the stack, methanol reformer, air compressor and metal hydride storage tank.
At an environmental symposium held shortly before the Tokyo Motor Show in October, the automaker claims to have tripled the fuel cell stack's output to 70 kilowatts by improving electrode efficiency.
When it first exhibited the fuel cell-powered FCEV in 1996, stack output was 25 kilowatts.
Specifically, the automaker reduced both volume and weight by integrating the cooling water and hydrogen and oxygen humidification loops into a single circuit, a structure already employed by Ballard Power Systems.
says the reduced stack's volume is 65 liters and it weighs 165 lbs. (75 kg). Toyota research executive Hiroyuki Watanabe claims the new stack meets specifications set for 2004 by the U.S. Energy Department's PNGV (Partnership for a New Generation of Vehicles) program for size and performance.
Meanwhile, Toyota engineers raised efficiency of the methanol reformer to 83%, while shortening transient response to under 10 seconds.
Residual carbon monoxide also was reduced to less than five parts per million (ppm).
These results were achieved primarily by reducing the size of the reformer, specifically by integrating the fuel evaporation, reforming reaction and carbon monoxide reduction components into a single unit.
An industry analyst explains that the trend “is to thermally integrate everything so that residual heat from one process or section can be used in another process or section where heat is not produced. For instance, the gas cleanup phase produces considerable heat, which in turn can be used to vaporize the fuel.”
Also contributing to improved reforming efficiency is the adoption of a new catalyst, which both lowers the reaction temperature in the reformer and shortens startup time. Toyota claims to have reduced startup time to under three minutes. When up and running, the 40L unit supplies 750L of hydrogen per minute, according to the company. The reformer weighs 44 lbs. (20 kg).
The fuel cell's air compressor also was upgraded. Toyota claims to have raised efficiency above 60% by switching to a “silent scroll” compressor, which the company claims eliminates the need for lubricating oil for the scrolls.
Finally, the automaker says it improved storage properties and raised capacity of the 60L metal hydride tank by modifying the internal heat exchanger shape and integrating the previous three units into one.
Packed with 220 lbs. (100 kg) of the alloy, the tank stores 4.8 lbs. (2.2 kg) of hydrogen.
In research laboratories, the company has achieved 3% hydrogen storage by weight with a titanium-series hydride. When the original FCEV was displayed, it achieved only 1.2%.