Environmental Engineering Reference
In-Depth Information
Fig. 4.8
Example of current-voltage characteristics in a PEFC. (Figure reproduced from data in
Antoni et al. 2009. Characterization of single cell PEFC performances using US/Japan/EU pro-
cedures and hardwares. Fuel Cell Seminar and Exposition, Nov. 16-19, 2009, Palm Springs, CA,
USA)
catalytic activity. A purification process is thus necessary for a hydrogen station,
and for a stationary fuel cell system that uses town gas as the fuel.
• Water management. The electrolyte membrane requires high humidity to have
enough proton conductivity. However, too much humidity causes condensation
of water which blocks the gas channels. A system for precise humidity control is
required.
• Durability. Several sources of degradation have been pointed out for PEFC. Dis-
solution of the Pt catalyst and damage to the electrolyte membrane can cause
severe problems. Operating conditions have been optimized for stationary and
mobile systems to avoid severe degradation.
• Cost. The use of Pt catalyst contributes to the high cost of PEFC. The limited
platinum resources will also become a significant problem if fuel cell vehicles
are widely commercialized. Reduction in the amount of Pt is still a major focus
of research and development for PEFC.
4.5
Mechanism and Features of SOFC
In contrast to the PEFC, a SOFC operates at temperatures higher than 600 °C.
The electrolyte of the SOFC is a ceramic membrane that conducts oxide ion, O
2 −
.
Figure
4.9
shows a schematic view of the crystal structure of a typical electrolyte
material, yttria stabilized zirconia, YSZ, which is zirconium oxide in its high tem-
perature phase (cubic fluorite phase) stabilized by replacing a part of Zr
4+
ions with
