Page 346 - Book Hosokawa Nanoparticle Technology Handbook

6.1 FUNCTIONALITY OF NANOSTRUCTURES AND THEIR CHARACTERISTIC EVALUATION FUNDAMENTALS
Electrode reaction, the conduction of electrons 3. a proper porous structure for the diffusion of
and ions and the diffusion of reaction gases are pro- fuel and reaction gases; and
gressing simultaneously, and multiple functions are 4. association of constituent particles and ther-
performed in the electrode of a fuel cell, the struc-
ture of which requires strength, heat resistance and mostable structure for strength and thermosta-
chemical stability. The relation between the bility.
functions of SOFC electrodes and porous nanos-
tructures is shown in Table 6.1.1, and an example of Without any of the functions, the high performance of
the structure of Ni-YSZ (Yttria Stabilized Zirconia) the electrode would be impossible. It is, therefore,
anode of SOFC in Fig. 6.1.2. The functions neces- essential to control the structure for a striking
sary for an are greatly dependent upon its structure, improvement in power-generation capacity.
and the electrode functions are improved by control The nanostructure of the SOFC electrode is con-
of the same. In the case of Ni-YSZ anodes, the fol- trolled by employing composite nanoparticles as raw
lowing are required for the structure: materials, which contributes to achieving a high func-
tional performance. For the control of the structure,
composite nanoparticles are utilized. Fig. 6.1.3 illus-
1. increase of the reactive interface for both Ni and trates the microscopic structure of an Ni-YSZ anode,
YSZ, due to its microscopic, homogeneous and fabricated by the screen printing and baking method,
using NiO–YSZ composite particles synthesized by
high-dispersion structure, since the electrode
spray pyrolysis (see Fig. 1.7.6, [2]) as raw materials.
reaction occurs in the interface of Ni and YSZ;
NiO–YSZ composite particles are those of the
2. networks of Ni and YSZ for the fabrication of core–shell type with NiO particles coated with micro-
good electron and ion paths; scopic YSZ particles. The structure of electrodes

Table 6.1.1
Relation between the functionality of SOFC electrodes and nanostructures.
Function Nanostructure necessary for the function
Electrode reaction characteristics Constituent particles of the electrode should be nanoscale, uniform and
highly dispersed
Electron and ion conductivity Networks of constituent particles of the electrode
Diffusion of reaction gases Proper pore size, pore size distribution and porosity
Strength, heat and chemical stability Binding force of electrode constituent particles and proper microstructure

Anode reaction: H +O 2- → H O
2
2
exhaust gas
H 2 H + H O mixture
2
2
H O rich
2
H O
2
H 2
Ni grain
Anode
H O
YSZ grain 2
H O
2

Electrolyte
O 2- O 2- O 2-

Figure 6.1.2
Morphology control of Ni-YSZ Y O stabilized ZrO cermet anode.
2
2
3
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