Fabrication and Characterization of Low Cost Electrodes for Fuel Cells

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