Hierarchical Nanostructures for Fuel Cells and Fuel Reforming - Hierarchical Nanostructures for Energy Devices - page 95

high-temperature fabrication above 1000 1C. 111 By aiming for SOFC opera-
ting temperatures far below 1000 1C, the fabrication temperature can be
reduced as well and, therefore, the application of nanomaterials in SOFCs is
very likely to expand in the future.
Ceria nanoparticles are one interesting example of novel nano-scale ma-
terials for SOFC electrolytes. The grain growth of these nanoparticles can be
suppressed by a second phase, such as in core-shelled ceria-carbonate par-
ticles, which can tolerate severe heat treatment without undesired particle
growth due to the carbonate shell. 164 It has been demonstrated that such
composite electrolytes consisting of two phases are able to reach impressive
ionic conductivity due to unique transport phenomena at the interface be-
tween the phases. 134 By reducing the structure size to the nano-scale, this
interfacial area is vastly increased, thus increasing the ionic conductivity.
A larger interfacial surface area and more grain boundaries in nano-
structured materials create a high density of mobile defects in the space-
charge region. 111

d n 3 r 4 n g | 4

5.3 Fuel Reforming and Fuel Treatment for Fuel Cell
Systems

5.3.1 Fuel Reforming
A very promising approach to resolve the energy situation which mankind is
currently facing is the use of fossil and renewable fuel in combination with
novel and more ecient hydrogen-based technologies such as fuel cells. 3,4
This benefits from the continued use of the existing fuel supply infra-
structure, the exceptionally high energy density per volume and mass of li-
quid fuels, and at the same time the reduction of consumed fuel due to the
tremendously high eciency of fuel cells compared to combustion engines.
These fuels include fossil hydrocarbon fuel as well as renewable fuels such as
alcoholic and hydrocarbon biofuels (e.g. methanol or biodiesel). A major
challenge that must be solved in order to achieve this goal is the energetically
and economically ecient conversion of conventional fuels to hydrogen.
The processing of butane on catalytic nanostructures, as an example of
liquid hydrocarbon fuel reforming, has been undertaken with Rh/ceria/
zirconia nanoparticles by using packed beds with catalytic nanoparticles, 9
by using an improved reactor design, 8 and by applying a novel sol-gelation
method. 7 Conventional ceramic foams coated with Rh have already been
used for the processing of different hydrocarbons. 165-168 The idea of many of
these studies is to use a small-scale fuel-to-syngas processor as part of an
entire fuel cell system. 6
Multiple studies available in the literature investigate the reforming of
hydrocarbon fuels on micro- and nano-scale catalysts, both by numerical
modeling and by experiments. For hydrocarbon reforming, steam reforming
(SR), 169-175

.

partial oxidation (POX), 7-9,166,176-183 autothermal reforming

(ATR), 169,180,181,184-186 and thermal cracking or pyrolysis 187,188 have been