Proceedings of the 42nd International Conference on Advanced Ceramics and Composites, Volume 39, Issue 2

Jonathan Salem, Dietmar Koch, Peter Mechnich, Mihails Kusnezoff, Narottam P. Bansal, Jerry C. LaSalvia, Palani Balaya, Zhengyi Fu, Tatsuki Ohji, Jonathan Salem, Dietmar Koch, Peter Mechnich, Mihails Kusnezoff, Narottam P. Bansal, Jerry C. LaSalvia, Palani Balaya, Zhengyi Fu, Tatsuki Ohji

• Publisher: Wiley-American Ceramic Society
• Year: 2018
• Print ISBN: 9781119543268
• eBook ISBN: 9781119543312
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Proceeding of the 42nd International Conference on Advanced Ceramics and Composites, Ceramic Engineering and Science Proceedings Volume 39, Issue 2, 2018

Jonathan Salem, Dietmar Koch, Peter Mechnich, Mihails Kusnezoff, Narottam Bansal, Jerry LaSalvia, Palani Balaya, Zhengyi Fu, and Tatsuki Ohji, Editors

Valerie Wiesner and Manabu Fukushima, Volume Editors

This proceedings contains a collection of 25 papers from The American Ceramic Society's 41st International Conference on Advanced Ceramics and Composites, held in Daytona Beach, Florida, January 21-26, 2018. This issue includes papers presented in the following symposia:

• Symposium 1: Mechanical Behavior and Performance of Ceramics and Composites

• Symposium 2: Advanced Ceramic Coatings for Structural, Environmental, and Functional Applications

• Symposium 3: 15th International Symposium on Solid Oxide Fuel Cells (SOFC)

• Symposium 4: Armor Ceramics: Challenges and New Developments

• Symposium 6: Advanced Materials and Technologies for Direct Thermal Energy Conversion and Rechargeable Energy Storage

• Symposium 8: 12th International Symposium on Advanced Processing & Manufacturing

15TH INTERNATIONAL SYMPOSIUM ON SOLID OXIDE FUEL CELLS (SOFC): MATERIALS, SCIENCE, AND TECHNOLOGY

INVESTIGATION OF (La_1-X,Ca_X)(Ni_0.25Fe_0.25Cr_0.25Co_0.25)O₃ FOR SOLID OXIDE FUEL CELLS CATHODE MATERIALS

Sai Ram Gajjala, Zhezhen Fu, and Rasit Koc

Department of Mechanical Engineering and Energy Processes, Southern Illinois University Carbondale, IL, US

ABSTRACT

In the present research, stoichiometry's of La_1-xCa_x(Fe_0.25Co_0.25Ni_0.25Cr_0.25)O₃ (x=0,0.1,0.2,0.3) (LCFCNC) were synthesized and investigated in an effort to develop a new cathode material for solid oxide fuel cells. Powders were prepared by using the polymerizable precursor method proposed by Pechini ¹. X-ray diffraction and SEM characterized the structure and morphology of the powder samples. The X-ray diffraction results revealed the formation of single phase orthorhombic distorted perovskite structure in all the four samples. Prepared powders were made into pellets and could sinter at 1400°C for 2 hours in air. SEM analysis showed densification of the pellets with the addition of calcium. Electrical conductivity measurements on the sample were made using the AC resistance bridge between the temperature range of 100-900°C in air. Study of electrical conductivity showed an increasing trend in electrical conductivity with respect to increase in temperature and the amount of calcium doped on A-site from 20mol% to 30mol% and the sample with calcium 30mol% on A-site, showed a sharp increase in electrical conductivity reaching a maximum of 50 S/cm at 800°C, demonstrating that the present materials can be used as cathode material in SOFC.

INTRODUCTION

SOFC's can generate power with no moving parts and no noise operation. With low emission of sulphur, nitrogen oxides or hydro carbon pollutants they are also environment friendly². Having these advantages over conventional power generation, SOFC's are attracting a lot of attention in power generation. Higher efficiencies in SOFC are due to thermodynamics and direct conversion of chemical energy of fuel to electrical energy. Certain kinds of steam or gas turbine power plants can take advantage of the fact that SOFCs produce a high temperature heat and utilize it to build hybrid power plants with high efficiency.

The aim of the present research is to develop a new cathode material for SOFC. This can be achieved by making modifications to the existing materials and studying their properties such as electrical conductivity at elevated temperatures of 650-1000°C, their stability in oxidizing and reducing atmosphere, fabricability and thermal expansion coefficient. This study of new materials can help improve electrical conductivity, lower sintering temperatures and improve stability by changing the doping properties ³. Having the best possible combination of ‘A' and ‘B' cations, a larger number of oxygen vacancies can be introduced which would result in bulk oxygen ion transport which is a desired characteristic from a cathode in an SOFC.

Some of the key requirements for materials of an SOFC cathode are: to have catalytic activity for oxygen dissociation, sufficient ionic conductivity to conduct the reduced oxygen (0.01-0.1 S cm^-1 for the thickness 1-100μm) ³, chemical stability and mechanical stability with other materials like interconnects, electrolyte and anode ^{3, 4}. It should also have a thermal expansion coefficient like other parts in an SOFC and adequate porosity to allow gaseous oxygen stability in an oxidizing atmosphere during fabrication and operation.

While the current SOFC cathode materials possess many advantages, there are still some disadvantages. Hence, there is a need for a material which has all the characteristics of high electronic conductivity, excellent chemical stability at elevated temperatures, desirable thermal expansion characteristics and which can be easily manufactured by sintering in conditions acceptable with other cell components. This can be achieved by modifying the present alkaline earth materials and transition materials based cathodes. The study of these new materials will help in improving electrical conductivity, lowering sintering temperatures and improving stability by changing the doping properties in the newly developed materials.

Perovskite Nickelate (LaNiO_3−δ) has good electrical conductivity properties at 750-800°C (electrical conductivity of 10 S cm⁻¹ at 800°C). LaNiO_3−δ is stable in reducing condition below the temperatures of 1270 K. When LaNiO_3−δ is heated above 1270 K, it dissociates into La₂ NiO_4+δ with a K₂ NiF₄ type structure and NiO with the separation of La₄ Ni₃ O_{10- δ} and La₃ Ni₂ O_7-δ phases at intermediate stages. This dissociation in reducing conditions and phase change at elevated temperatures limits the use of LaNiO_3−δ based perovskite materials ^5-7 and the properties can be improved by doping transition earth materials with nickel ^{8, 9}.

Cobalt based perovskite materials show higher ionic and electronic conductivities (electrical conductivity of 103 S cm⁻¹ at 1000°C) than other cathode materials, but has high thermal expansion coefficients (TEC) due to the large substitution of Cobalt ^{10, 11}. Research on Ca-doped LaCoO₃ system shows when 20% Ca was added on A-site, i...

Table of contents

• COVER
• TITLEPAGE
• COPYRIGHT
• INTRODUCTION
• MECHANICAL BEHAVIOR AND PERFORMANCE OF CERAMICS AND COMPOSITES
• ADVANCED CERAMIC COATINGS FOR STRUCTURAL, ENVIRONMENTAL, AND FUNCTIONAL APPLICATIONS
• 15TH INTERNATIONAL SYMPOSIUM ON SOLID OXIDE FUEL CELLS (SOFC): MATERIALS, SCIENCE, AND TECHNOLOGY
• Armor Ceramics: Challenges and New Developments
• Advanced Materials and Technologies for Direct Thermal Energy Conversion and Rechargeable Energy Storage
• 12th International Symposium on Advanced Processing & Manufacturing Technologies for Structural & Multifunctional Materials and Systems
• Eula