Due to an increase in demand for sustainable energy sources, solid oxide fuel cells (SOFCs) have received more attention owing to their huge potential for power production in portal transport applications. Almost all solid oxide fuel cells are arranged either in parallel or series in order to facilitate voltage output. An interconnect is needed to connect the cells. It connects the cathode of one cell to the anode of the other, yet physically separates the cells.
An interconnect should be non-porous with 100% relative density to avoid the mixing of fuel and oxygen. Above all, it must be stable in oxidizing and reducing environments, have high electrical conductivity, chemical stability and sintering attributes. It can be metallic or ceramic. One desirable material for a ceramic interconnect in solid oxide fuel cell is the doped Lanthanum Chromite based perovskite material.
The cathode material should as well meet stringent requirements. Therefore, the shortcomings in perovskite oxide materials adopted for cathode and interconnect fabrication can be overcome through the synthesis of new materials by adding or modifying the transition metals in the current materials to enhance chemical stability, low sintering temperature, electronic and ionic conductivity, and thermal expansion coefficient.
Researchers led by Professor Rasit Koc at Southern Illinois University developed cathode and interconnect material for solid oxide fuel cells. Their main aim was to develop and evaluate cathode and interconnect materials for SOFC which will meet the exacting requirements of SOFC manufacturers. These requirements are fabricability (sinterability) at temperatures 1400oC and below at lower cost, high electronic conductivity, chemical stability in reducing and oxidizing conditions and coefficient of thermal expansion match with other cell components. Dr. Zhezhen Fu of University of Maryland says “The developed sinterable materials with very high electrical conductivity are critical in the commercialization of low temperature solid oxide fuel cells (LT-SOFCs)”. The research work on La(Cr,Co,Fe,Ni)O3 is now published in Ceramics International.
The authors prepared the powders through the Pechini approach. They mixed metal nitrates and lanthanum carbonate as starting materials in stoichiometric proportions. The resulting mixture was then mixed with ethylene glycol and citric acid forming a polymer that broke to form powder precursor. The precursors were calcined, ball milled, and pressed to form circular pellets. The microstructure developed completely in the course of the sintering process. The sintered samples were polished and thermally etched for microstructure analysis.
samples were prepared for electrical conductivity measurement. Each sample was subjected to resistance measurements. The pellets were then heated in a furnace and resistance measured as a function of temperature in the range of solid oxide fuel cell operation.
Through the Pechini polymer complexing approach, the authors were able to synthesize five compounds into a single phase of LaCo0.7Cr0.1Fe0.1Ni0.1O3 (LCo7CFN), LaNi0.7Cr0.1Co0.1Fe0.1O3 (LNi7CCF), and LaCr0.25Co0.25Fe0.25Ni0.25O3 (LCCFN), LaFe0.7Cr0.1Co0.1Ni0.1O3 (LFe7CCN), were sintered to a relative density of 98%, 82%, 94%, and 91% respectively at about 1400 °C for two hours in air. Transit liquid phases formed under the sintering conditions and contributed to the high relative densities. LaCr0.25Co0.25Fe0.25Ni0.25O3 (LCCFN), posted the highest electrical conductivity.
Among the lanthanum perovskite oxides, LaCo0.7Cr0.1Fe0.1Ni0.1O3 (LCo7CFN) and LaCr0.25Co0.25Fe0.25Ni0.25O3 (LCCFN) appeared to comprise building blocks for interconnect fabrication owing to their high relative densities (94-98 %) and excellent electrical conductivity (>50 S/cm). LaNi0.7Cr0.1Co0.1Fe0.1O3 (LNi7CCF) with high electrical conductivity and relative density of approximately 82% was selected to be a suitable candidate for the porous cathode. Currently, these materials are being doped with Ca on the La site to further enhance their properties.
Abhigna Kolisetty, Zhezhen Fu, and Rasit Koc. Development of La(Cr,Co,Fe,Ni)O3 system perovskites as interconnect and cathode materials for solid oxide fuel cells. Ceramics International, volume 43 (2017), pages 7647–7652.
Department of Mechanical Engineering and Energy Processes, Southern Illinois University, 1230 Lincoln Drive, Carbondale, IL 62901, United States.Go To Ceramics International