Hierarchical Nanostructures for Fuel Cells and Fuel Reforming - Hierarchical Nanostructures for Energy Devices - page 93

d n 3 r 4 n g | 4

Figure 5.2 Solid oxide fuel cell (SOFC) working principle.

gas flow. As a product of this oxidation reaction, electrons are created, which
travel through an external circuit to the cathode, where they are required for
the oxygen dissociation reaction. The water vapor generated during the
oxidation reaction diffuses through the porous anode into the gas stream
and is removed from the fuel cell. Besides the generated electric power, a
significant amount of heat is produced due to ionic and electronic resistance
of the materials and reaction polarization. Since SOFCs are operated at high
temperature, the exergy content of this heat generation is high, enabling
ecient combined heat and power (CHP) generation, in contrast to low-
temperature fuel cells.

.

5.2.4.2 Electrolyte Materials in Solid Oxide Fuel Cells
The goal of increased fuel cell performance and eciency can be achieved by
improving the catalytic activity of the electrodes and the ionic conductivity of
the electrolyte. Taking advantage of the fast development of better micro-
and nanofabrication methods and functional materials of the past decades,
satisfactory cell performance can be achieved at lower temperature,
sometimes referred to as an intermediate to high temperature range
(600-1000 1C). 135 Further reduction of the SOFC temperature to intermediate
temperatures (500-600 1C) or lower is required for successful commercial-
ization of realistic SOFC applications thanks to reduced operational and
installation cost and increased system reliability. 136-141 The faster start-up
and shutdown for intermediate-temperature SOFCs extends the range of