Performance of La0.8Sr0.2Co0.8Ni0.2O3-δ-Based Oxygen Electrode for Solid Oxide Electrolysis Cells

Solid oxide electrolysis cell (SOEC), considered as the reverse reaction of solid oxide fuel cell (SOFC), is expected as a highly efficient way to produce hydrogen environmentally friendly. The reduction of operating temperature and enhancement of the durability are now vital requirements for industrial commercialization of SOEC. The cost of the system can be reduced by reducing the operating temperature from the traditional 1000^◦C to 600-800^◦C. La_0.8Sr_0.2Co_0.8Ni_0.2O_3-δoxides (LSCN) were selected as innovative mixed electronic and ionic conductivity (MIEC) oxygen electrode materials because of their high electrical conductivity and electrocatalytic activity with low thermal expansion coefficient (TEC)[1]. The biggest degradation issue for SOEC is the delamination of the oxygen electrode from electrolyte [2].

In the present work, we fabricated two kinds of LSCN-based oxygen electrodes to improve the structural stability. The solution impregnated La_0.8Sr_0.2Co_0.8Ni_0.2 + Gd doped CeO₂(LSCN+GDC) oxygen electrode and LSCN-GDC composite oxygen electrode based on Ni-YSZ hydrogen electrode-support button cells are fabricated to assess their performance and the stability. For LSCN-GDC composite oxygen electrode, on the one hand, GDC was added for its high oxygen ion mobility at intermediate temperature and mechanically and chemically compatible with LSCN. On the other hand, the graded LSCN and GDC powder can form a porous continuous structure to improve the mechanical stability. GDC layer was used for making a barrier between LSCN-GDC composite oxygen electrode and YSZ electrolyte to avoid interfacial reaction [3]. For the impregnated LSCN+GDC oxygen electrode, distributing the LSCN nanoparticles on the porous GDC scaffold can transfer the reaction sites from the electrode/electrolyte interface to the LSCN nanoparticles/GDC grains interface in the bulk of the electrode.

Before and after electrolysis mode at constant operating conditions, current-voltage (I-V) tests and Electrochemical Impedance Spectroscopy (EIS) were measured and compared to trace any increase in ohmic and polarization resistance of the cells. Besides, the stability of the button cell was studied in galvanostatic SOEC operation.  Results show that the impregnated LSCN+GDC composite oxygen electrode exhibited lower ohmic resistance for the high conductivity provided by continuous LSCN nanoparticles and comparable polarization resistance at 800^◦C before the electrolysis, and more durable during the SOEC operation. Post-experimental analyses were conducted using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to characterize the changes of microstructure and phase after operations, especially the interface condition of the oxygen electrode and electrolyte, to investigate and compare the degradation mechanisms.

[1] X. Xu, F.Z. Wang, Y.H. Liu, J. Pu, B. Chi and J. Li. J. Power Sources, 196, 9365(2011).

[2] M.A. Laguna-Bercero. J. Power Sources, 203, 4(2012).

[3] J. Chen, F.L. Liang, L. Liu, S.P. Jiang and J. Li. J. Hydrogen Energy, 34, 6845(2009).