1. Study on Double Perovskite as a Solid Oxide Regenerative Fuel Cell Cathode
Material
YoungJin Kwon† and Joongmyeon Bae (Dept. of Mechanical Engineering, KAIST)
†Presenting author,
Abstract
It has been increasing interest in hydrogen(H2) as an alternative energy carrier. Because the H2 has high energy density, pure emission and it is easy to be transported by using a pipeline. But H2 doesn’t exist on the earth as a fuel. For this reason, it must be generated. There are several ways of producing H2 such as by photocatalytic water splitting, gasification of biomass, solar thermochemical water splitting and water electrolysis driven by solar cell or wind turbine. Among these technologies, Solid oxide regenerative fuel cell(SORFC) is a practical and efficient method for the industrial field. High operating temperature improves the electrode kinetics and reduce the SORFC electrolyte resistance, leading to lower losses in cell performance. Due to similarity to Solid oxide fuel cell(SOFC), advances have been made in the development of SORFC based on cell assemblies with structure nickel-yttria stabilized zirconia(Ni-YSZ) fuel electrode / YSZ electrolyte / lanthanum strontium manganite-YSZ(LSM-YSZ) air electrode. The previous study show that the performance discrepancies of the cell in operation between the electrolytic and galvanic modes could be varied, depending on the electrode materials. Moreover, the Ni-YSZ most widely used fuel electrode has several problems even though its great catalytic performance. One of them is degradation of the fuel electrode because of Ni particle’s redox reaction and agglomeration. Therefore it is necessary to develop an alternative fuel electrode material. Double perovskite electrode material is one of the promising candidate for the fuel electrode of the SORFC because of its high catalytic performance and stability at SOFC mode. In this study, We studied on the Double perovskite Pr0.5Br0.5MnO3-δ(PBMO) as a fuel electrode material of SORFC. PBMO was infiltrated into the scaffold structure of the electrolyte, La0.8Sr0.2Ga0.85 Mg0.15O3-δ (LSGM) and synthesized at the low temperature because second phase generated when it annealed at high temperature. The Half cell test was conducted to investigate the electrochemical performance of the electrode material at the steam rich atmosphere
Introduction
▪ High temperature water electrolysis for Hydrogen production
- Decrease electric energy demand for water electrolysis
- Efficiency improvement of Hydrogen production with heat source (Ex. : Nuclear power plant, Solar thermal power plant)
▪ Solid Oxide Electrolysis Cell
- Operating Temp. : 600 ~ 1,000 ℃ - Composition : Anode / Electrolyte / Cathode (Ceramic materials)
- Reaction mechanism :
▪ Objective
- Critical problem of Ni widely used cathode material when it exposed to H2O : Redox and agglomeration
- Application of Oxide catalysts as cathode material.
: Highly stable but low catalytic performance
- Performance improvement by using double perovskite catalysts and infiltration methode (Catalytic performance : Electric conductivity, Activation energy)
Experiment
▪ Infiltration methode
- Porous scaffold electrolyte structure fabrication over 1,000℃ - Catalysts infiltration with solution at scaffold structure - Catalysts synthesis lower 1,000 ℃
→ Avoid 2nd phase generation with electrolyte and catalyst.
→ Catalytic performance improvement due to increasement of Three Phase Boundary (TPB) ▪ Electric conductivity measurement
- 4-probe way
→ Measurement at reduction atmosphere(H2 5%).
→ Equation : V/I = R = ρL/S(S=w x h) - Comparison of PBMO and conventional perovskite catalysts
▪ Experimental set up
- Half cell fabrication & test with EIS analizer
→ Electrolyte supported symmetric porous electrode with infiltration → Half cell test with impedance analysis according to catalysts loading
Electrolyte
Anode
Cathode
Schematic diagram of Infiltration methode
CO2, H2O
CO, H2 O2
O2-
electron
SOEC mode
Cathode
Anode
Electrolyte
(Oxygen electrode)
(Hydrogen electrode)
Cathode
Anode
4-probe electric conductivity test bench
Conceptual diagram of redox mechanism(ref)
Results
▪ Micro structure analysis
- Confirmation of LSGM porous scaffold structure
▪ Chemical compatibility measurement
- Well distributed PBMO in LSGM scaffold structure
- X-RD analysis with PBMO and LSGM (electrolyte material)
- PBMO synthesis temp. : 950 ℃ → 2nd phase generation over 1,000℃
▪ EIS analysis
- Arrhenius plot comparison : Ni-YSZ and PBMO
(Eaover PBMO 9.7wt% ≤ EaNi-YSZ)
- 18 ~ 19 wt% loading PBMO show high perfomance
- Comparison with conventioanl cathode material : La0.75Sr0.25Cr0.5Mn0.5 (LSCM), La0.8Sr0.2Cr0.95Ru0.05 (LSCR), La0.4Sr0.6Ti0.4Mn0.6 (LSTM)
- Over 20 wt% loading Impedance increase
- PBMO electric conductivity : 83 S/cm
SEM image before infiltration
SEM image after infiltration (15.2wt%)
Scaffold structure of electrode
Electrolyte
PBMO
LSGM scaffold
2nd Phase
Arrhenius plot of Ni-YSZ and infiltrated PBMO
EIS analysis of PBMO loading mount
Chemical compatibility of LSGM and PBMO
Electric conductivity of PBMO , LSCM, LSTM and LSCR
Conclusion
▪ Performance improvement according to loading amount
- Activation Energy : 0.45 eV(Ni-YSZ : 1.16 eV)
▪ PBMO & LSGM chemical compatibility at catalysts synthesis temp.
- Optimum amount of loading : 18 ~ 19 wt%
- Possibility of PBMO synthesis at LSGM scaffold structure by using infiltration methode
▪ Limitation & Future Work
▪ PBMO electric conductivity : 83 S/cm > σConventional perovskite catalysts
- Full cell measurement
Acknowledgement
This work was supported by the Global Frontier R&D Program on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Education, Science and Technology, Korea and by the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Knowledge Economy, Republic of Korea.
The authors also thank to the funding from he Korea CCS R&D Center(KCRC) grant(No 2014M1A8A ) funded by the Korea government(Ministry of Science, ICT & Future Planning) and KEPCO & Korea Western Power Co.
New Energy Conversion System Lab., Dept. of Mechanical Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon , Republic of Korea