Chromium deposition and poisoning of La(0.8)Sr(0.2)MnO3 oxygen electrodes of solid oxide electrolysis cells.

Kongfa Chen,Junji Hyodo,San Ping Jiang,Tatsumi Ishihara,Aaron Dodd,Na Ai,Li Jian

doi:10.1039/c5fd00010f

Abstract

The effect of the presence of an Fe-Cr alloy metallic interconnect on the performance and stability of La(0.8)Sr(0.2)MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe-Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn(2+). This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions.

Highlights

PaperSolid oxide electrolysis cells or solid oxide electrolyzers (SOECs or SOEs) operating at high temperatures of 700–1000 C are highly efficient to store the electrical energy generated by renewable sources such as solar and wind power into chemical energy of fuels such as hydrogen, syngas and methane
The results indicate that the deposits with distinct crystal facets formed on the yttria-stabilized zirconia (YSZ) electrolyte surface between the contact rings and on the lanthanum strontium manganite (LSM) electrode inner surface are most likely the SrCrO4 phase and the small particles formed on the YSZ electrolyte surface within the contact rings and on LSM inner surface are a combination of Cr2O3 and Cr2O5
Cr deposition occurs in the LSM electrode bulk and in particular on the YSZ electrolyte surface and on LSM electrode inner surface close to the electrode/electrolyte interface

Summary

Introduction

PaperSolid oxide electrolysis cells or solid oxide electrolyzers (SOECs or SOEs) operating at high temperatures of 700–1000 C are highly efficient to store the electrical energy generated by renewable sources such as solar and wind power into chemical energy of fuels such as hydrogen, syngas and methane. SOECs are reversible solid oxide fuel cells (SOFCs), and state-of-the-art SOFC materials such as nickel-based cermets, yttria-stabilized zirconia (YSZ) electrolyte and lanthanum strontium manganite (LSM) perovskites can be directly applied as electrode and electrolyte materials in SOECs. A major issue for the development of SOECs is the signi cant performance degradation during long-term operation,[1,2] and the decay of oxygen electrodes has been regarded as the major cause, at high currents.[3,4] The degradation of oxygen electrodes has been extensively studied and several degradation/ failure modes of the oxygen electrodes have been proposed. For the (La,Sr) (Co,Fe)O3 (LSCF) oxygen electrodes a er the electrolysis test for 9000 h, the perovskite structure is partly demixed, accompanied by microstructure change and formation of Co3O4; and a dense SrZrO3 layer is observed at the Gd-doped ceria (GDC) interlayer/YSZ electrolyte interface.[14,15] Separation of GDC interlayer from the YSZ electrolyte has been reported.[16,17]

Results

Discussion

Conclusion