Higher temperatures for low temperature fuel cells
Polymer electrolyte membrane fuel cells are generally considered to be the most viable approach for mobile applications.
However, these membranes require humid operating conditions, which limit the working temperature to less than 100 °C,
while higher temperatures would lead to a lower sensibility towards the catalyst-toxic carbon monoxide.
New proton exchange membrane (PEM) fuel cells might operate at temperatures of 200 °C instead of 80 °C in the future.
This would be made possible by introducing a "new" 20-year-old membrane rediscovered by Celanese AG for fuel cell production.
In cooperation with Honda and Plug Power (USA) the company formerly known as Hoechst is developing the so-called
polybenzimidazol (PBI) polymere membrane which could become part of a new fuel cell.
Increased operating temperature enables hydrogen efficiency of several thousand ppm carbon monoxide.
Until now only high-purity hydrogen with a purity of less than 50 ppm CO can be used. At low temperatures the "catalytic
converter toxin" carbon monoxide reacts with platinum in the fuel cell, which often leads to destruction of the cell.
At 200°C this might no longer happen. If the new membrane does in fact tolerate higher carbon monoxide quantities,
particularly onboard methanol or fossil fuel reformers in mobile applications would benefit from this.
Costly cleaning units could be reduced, while using the additional energy for heating purposes.
A second possibility:
New research shows that solid acids such as CsHSO4 and Rb3H(SeO4)2 offer the advantage of anhydrous proton transport and
high-temperature stability up to 250 °C. This is the result of a study by Sossina M. Haile, which was published in the
April edition of scientific magazine "nature".
A cell composed of a CsHSO4 electrolyte membrane (about 1,5mm thick) may operate at 150 to 160°C and reach 1,11 V open
circuit voltage and current densities of 44mAcm-2 at short circuit. The higher open circuit voltage compared to
polymer-electrolyte fuel cells may lead to better overall system efficiencies.
Further advantages include greater tolerance of the catalysts to carbon monoxide due to the raised temperature, and a
reduction in control hardware. These results would constitute a leap in fuel cell technology research, provided they can be
reproduced in other scenarios.
Source: H2Report, S. Geitmann, Jan. & Jul. 2001
