Abstract:
Fuel cell is an emerging, cleanest, environmental friendly and pollution free
technology, which converts chemical energy of fuel into electricity, heat and power
without combustion. Fuel cells are categorized according to their electrolytic
materials and working temperature. Solid oxide fuel cell (SOFC) is the most
dominant and prominent among the fuel cell family. In other words, fuel cell is one
of the most competitive candidates that could provide possibly accomplishments.
Conventionally, Ni-YSZ cermet anode is used in SOFC, which works in the
temperature range of 800-1000oC. Although this anode possesses a high
electrochemical activity, high performance as well as electronic conductivity yet it
requires a high working temperature to achieve the optimal results. Its high working
temperature is the present draw back which becomes a major barrier to its
commercialization. If this cell has to be commercialized then there is need to find
suitable electrode materials that can operate successfully at low operating
temperature. Keeping this in mind, many new electrode materials have been
introduced in the present work, which have been classified into two groups; one is
containing Ni partially while the other is completely Ni free.
New electrode materials were prepared by introducing nano technique using
either dry or wet chemical method with an added advantage of low manufacturing
temperature. In order to fabricate a complete fuel cell, the compatible electrolyte
materials were also prepared by co-precipitation method. These materials exhibited
an excellent performance at comparatively low temperature (400-600 oC).
For SOFC electrode and electrolyte purpose, CuNiZnGdCe (CNZGC),
Al0.1NixZn0.9-x (ANZ), Cu0.2Mn0.2Zn0.6 (CMZ), Ba0.05Cu0.25FexZn0.7-x (BCFZ)
Ba0.15Fe0.10Ti0.15Zn0.60 (BFTZ), Ba0.4Sr0.6Co 0.3Mn0.7 (BSCM), La0.1Sr0.9Co0.2Zn0.8
(LSCZ), Na2CO3-K2CO3- Ca0.2Ce0.8 (NK-CDC) and Gd0.1Ce0.9-Y2O3 (Y-GDC)
materials were successfully synthesized by solid state reaction method or wet
chemical and co-precipitation method. These electrodes and electrolyte materials
were characterized by XRD, SEM, TEM, electrochemical and electrical techniques.
It has been found that the BCFZ-5 having a composition of Ba0.05Cu0.25Fe0.10Zn0.60
shows an electrical conductivity equal to 25.84 at hydrogen atmosphere. It also
exhibited the maximum power density of 741.87mW/cm2 and 933.41mW/cm2 for
symmetrical and asymmetrical fuel cell testing schemes. On the basis of these
results, BCFZ-5 material is considered a promising electrode/anode candidate for
low temperature solid oxide fuel cell.
Different approaches have been implemented to reduce the present cost of
electrode and electrolyte materials for solid oxide fuel cell. For example;
I.
II.
Use of cheap raw material
Lowering of sintering temperature
III. Reduction of sintering time
IV. Lowering of operating/working temperature
It has been noted that the substitution of zinc compound Zn(NO3)2.6H2O in place of
nickel oxide (NiO) has reduced the cost by a factor of ≈25 in addition to the lowering
of manufacturing and operating temperature, which also reduces the cost indirectly by
saving energy and time. Moreover, the cost has been further reduced by a factor of 35
and
18
when
samarium
nitrate
Sm(NO3)3.6H2O
and
gadolinium
nitrate
Gd(NO3)3.6H2O are respectively replaced by calcium nitrate Ca(NO3)2.4H2O.
The lowering of working temperature from 1000 to 550oC is a major
achievement that would not only reduce the running cost yet it may help in
commercialization of solid oxide fuel cell.
In a nut shell the electrodes and electrolytes proposed in the present work
have successfully lowered the manufacturing as well as working temperature and
hence the operational cost along with a significant reduction in the manufacturing
cost of solid oxide fuel cell (SOFC).
Key words:
Solid Oxide Fuel Cell (SOFC), Zn Based Electrodes, Nano-composites
Electrodes, Energy Conversion Device, Ceria Carbonated Fuel Cell, Advanced Fuel
Cell, Efficient Device, BCFZ anode, NKCDC electrolyte, Novel Cathode