Degradation and Recovery of LSCF Reversible Solid Oxide Cell Air Electrodes by Controlled Surface Acidity

Masahiro Yasutake^a^,^b, Han Gil Seo^b, Yohei Nagatomo^c, Junko Matsuda^a^,^d^,^e, Kazunari Sasaki^a^,^c^,^d^,^e, Harry Tuller^b

^aNext-Generation Fuel Cell Research Center (NEXT-FC), Kyushu University

^bDepartment of Materials Science and Engineering, Massachusetts Institute of Technology

^cDepartment of Hydrogen Energy Systems, Faculty of Engineering, Kyushu University

^dInternational Research Center for Hydrogen Energy, Kyushu University

^ePlatform of Inter-Transdisciplinary Energy Research (Q-PIT), Kyushu University

Proceedings of 24th International Conference on Solid State Ionics (SSI24)

Devices for a Net Zero World

London, United Kingdom, 2024 July 14th - 19th

Organizers: John Kilner and Stephen Skinner

Oral, Masahiro Yasutake, presentation 329
Publication date: 10th April 2024

Reversible solid oxide cells (r-SOC) are a key technology for realizing carbon neutrality given their ability to readily switch between fuel cell (FC) and electrolysis cell (EC) modes. Cr-induced degradation of the oxygen exchange kinetics at the air electrode remains one of the main challenges to improving the long-term stability of r-SOC ¹. Our research group has previously demonstrated the degradation and recovery of fluorite structured Pr_0.1Ce_0.9O₂ solid oxide fuel cell (SOFC) cathode performance by control of its surface acidity ^2-5. Here, we extend the investigation of the applicability of acid/base engineering to (i) the more highly electrically conductive mixed ionic and electronic conducting (MIEC) and popular perovskite structured (expressed as ABO₃) La_0.6Sr_0.4(Co_0.2Fe_0.8)O₃ (LSCF), (ii) at higher operating temperatures, and (iii) in r-SOC operating mode.

The effect of acid/base engineering on LSCF was first evaluated with the aid of symmetric cells operated in air. Cr and Ca-based oxides were used as acidic and basic additives, respectively. Cr infiltration caused a 20-fold increase in the LSCF polarization resistance compared to the unifiltrated mode in the temperature range from 500 °C to 650 °C. However, subsequent Ca infiltration largely recovered the oxygen reduction reaction activity by reducing the polarization resistance to less than twice that of the unifiltrated sample, demonstrating the ability of applying acid/base engineering to LSCF-based cathodes.

However, we discovered that these degradation and recovery effects induced by acidic and basic additives become suppressed at more elevated temperatures between 800 °C and 900 °C. STEM-EDS microstructure observations show that high-temperature conditions drive the dissolution of Cr and Ca based secondary phases into the perovskite structure of LSCF leading to a time dependent loss in their efficacy. Therefore, in order to apply acid/base engineering to the high-temperature regime for LSCF, strategies to control the dissolution of the secondary phase particles are necessary.

We also report on our evaluation of the effect of acid/base engineering on the operation of r-SOC cells. As demonstrated for FC operation in a previous study ³, we were able to demonstrate the degradation in performance with Cr-infiltration and its recovery with Ca-infiltration as well for the oxygen evolution reaction in EC operation. These results suggest that acid/ base engineering can also be applied to reversible cells.

References:

[1] [1] Golkhatmi, S. Z.; Asghar, M. I.; Lund, P. D. A Review on Solid Oxide Fuel Cell Durability: Latest Progress, Mechanisms, and Study Tools. Renewable and Sustainable Energy Reviews. 2022, 161, 112339.

[2] [2] Seo, H. G.; Staerz, A.; Kim, D. S.; LeBeau, J. M.; Tuller, H. L. Tuning Surface Acidity of Mixed Conducting Electrodes: Recovery of Si-Induced Degradation of Oxygen Exchange Rate and Area Specific Resistance. Advanced Materials, 2023, 35, 2208182.

[3] [3] Seo, H. G.; Staerz, A.; Dimitrakopoulos, G.; Kim, D.; Yildiz, B.; Tuller, H. L. Degradation and Recovery of Solid Oxide Fuel Cell Performance by Control of Cathode Surface Acidity: Case Study – Impact of Cr Followed by Ca Infiltration. J. Power Sources. 2023, 558, 232589.

[4] [4] Staerz, A.; Seo, H. G.; Klotz, D.; Kim, D. S.; LeBeau, J. M.; Tuller, H. L. The Influence of Cr-Additives on the Polarization Resistance of Praseodymium-Doped Ceria Cathodes for Solid Oxide Fuel Cells. J. Electrochem. Soc. 2022, 169, 044530.

[5] [5] Seo, H. G.; Staerz, A.; Kim, D. S.; Klots, D.; Nicollet, C.; Xu, M.; LeBeau, J. M.; Tuller, H. L. Reactivation of Chromia Poisoned Oxygen Exchange Kinetics in Mixed Conducting Solid Oxide Fuel Cell Electrodes by Serial Infiltration of Lithia. Energy Environ. Sci. 2022, 15, 4038.

Acknowledgements:

This study was by the Japan Science and Technology Agency (JST) as part of Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE), Grant Number JPMJAP2307. An initial part of this study was supported by the “Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration” of the New Energy and Industrial Technology Development Organization (NEDO) (Project No. JPNP20005). H. G. Seo and H. L. Tuller received partial support from the R.P. Simmons Chair of Ceramics and Electronic Materials, Department of Materials Science and Engineering, Massachusetts Institute of Technology.

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