Reversible Solid Oxide Cells: Durability of Co-Impregnated Fuel Electrodes
Authors: Matsubara Kyoko , Ikegawa Kazutaka , Tachikawa Yuya , Matsuda Junko , Sasaki Kazunari 
Published: December 2024

1.Introduction

The use of renewable energy is essential to realize a decarbonized society, but solar power generation, for example, is affected by weather conditions. Reversible Solid Oxide Cells (r-SOC)1,2 have been attracting attention because they can perform both power generation (SOFC) and electrolysis (SOEC) in a single cell and can adjust the supply and demand of electricity. The conventional cermet fuel electrodes used in r-SOCs, such as Ni-YSZ, have technical issues such as Ni particle agglomeration and Ni sublimation under high partial pressure of water vapor3,4. Therefore, our research group has developed an alternative fuel electrode with highly dispersed catalytic Ni particles and GDC on the surface of conductive backbone (La-Sr-Ti oxide (LST) and Gd-doped ceria (GDC)), denoted here as Ni-GDC co-impregnated fuel electrode. This is fabricated by highly dispersing catalytic Ni particles and GDCs on the surface of LST and GDC to achieve higher durability5. Here in this study, we apply various Ni-GDC co-impregnated fuel electrodes with different Ni and GDC loadings and evaluate their initial electrochemical performance and long-term durability especially in SOEC mode.

2.Experimental

Four types of Ni-GDC co-impregnated fuel electrodes, LST-GDC-only fuel electrodes as the backbone, Ni-YSZ and Ni-GDC cermet fuel electrodes as cermet-based fuel electrodes for comparison were used in this study. The Ni-GDC co-impregnated fuel electrode consists of LST and GDC porous composite electrode framework, which was co-impregnated with Ni and GDC as catalysts. Details of the cell with the Ni-GDC co-impregnated fuel electrode are compiled in Fig. 1(a). Each cell was fabricated using LSCF/GDC for the air electrode and YSZ for the supporting electrolyte plate. The structure of the Ni-GDC co-impregnation cell is shown in Fig. 1(b). Initial performance tests and SOEC 1000-hour durability tests were conducted at an operating temperature of 800°C and 50%-humidified hydrogen.

3.Results and discussion

Figure 1(c) shows the results of SOEC 1000-hour durability tests for the Ni-YSZ cermet fuel electrode, the Ni-GDC cermet fuel electrode, and the Ni-GDC co-impregnated fuel electrode. The Ni-GDC co-impregnated fuel electrode exhibited less degradation than the cermet fuel electrode. Since the backbone of the co-impregnated fuel electrode, LST-GDC consists of stable oxides, it is considered to be more durable than the conventional cermet fuel electrodes which have Ni-based backbone structure. The Ni-GDC co-impregnated fuel electrode is also considered to suppress Ni aggregation by highly-dispersing Ni and GDC catalysts on its stable framework.
FIB-SEM micrographs of the Ni-GDC co-impregnation fuel electrode before and after the SOEC 1000-hour durability test is shown in Fig. 1(d). Growth of the co-impregnated Ni particles was observed, but the Ni particles were small relative to the entire fuel electrode and the amount of Ni loaded was low, leading to a longer overall durability of the fuel electrode due to such a co-impregnated microstructure.

Acknowledgements

A part of this research was supported by JST's Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE) (Grant No. JPMJAP2307). An initial part of this study was supported by NEDO (JPNP20005). We thank all the parties concerned.

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Figure 1