A Detailed Post Mortem Analysis of Solid Oxide Electrolyzer Cells after Long-Term Stack Operation

Carolin E. Frey,Ludger Blum,Doris Sebold,Norbert H. Menzler,Qingping Fang

doi:10.1149/2.0961805jes

Carolin E. Frey, Ludger Blum + Show 3 more

Open Access

https://doi.org/10.1149/2.0961805jes

Copy DOI

Abstract

A long-term test with a two-layer solid oxide electrolyzer stack was carried out for more than 20 000 hours. The stack was mainly operated in a furnace environment in electrolysis mode, with 50% humidification of H2 at 800°C, a current density of −0.5 Acm−2 and steam conversion rate of 50%. After ∼18 000 hours of operation in electrolysis mode, the voltage and area specific resistance degradation rates were ∼0.6%/kh and 8.2%/kh, respectively. A detailed post mortem analysis of cells including ICP-OES and microstructural analysis was conducted. Two main degradation phenomena were observed in the cells: In the fuel electrode, the depletion and agglomeration of nickel were visible. At the air electrode, demixing of the air electrode and diffusion of strontium took place. This was observed in the formation of strontium zirconate at the interface between the electrolyte and the GDC barrier layer as well as in the formation of strontium oxide and strontium chromate on top of the cells. Strontium oxide was even found in pores on top of the electrolyte.

Highlights

Solid oxide electrolysis cells (SOECs) offer the possibility to convert surplus electricity generated by regenerative sources like wind and solar power directly into hydrogen by water splitting
Electrochemical results The electrochemical characterization was described by Fang et al [13]
The demixing of the air electrode leads to the segregation of strontium, which is visible in the formation of strontium zirconate at the interface between electrolyte and the GDC barrier layer as well as in the formation of strontium oxide and strontium chromate on top of the cells

Summary

Introduction

Solid oxide electrolysis cells (SOECs) offer the possibility to convert surplus electricity generated by regenerative sources like wind and solar power directly into hydrogen by water splitting. Post-test analysis of this stack revealed silicon impurities at the fuel electrode interface to the electrolyte and sulfur inclusion along cracks of the oxygen electrode. After 1000 h and 2000 h, Cr substitution in (La,Sr)CoO3 lowered the electrical conductivity of the so-called bond coat, which we would refer to as the chromium retention layer and contact layer, and partial oxygen electrode delamination could be seen [11]. Based on these studies, there is a need for further post-test analysis of long-term electrolysis stacks to investigate degradation phenomena and increase the lifetime of SOEC stacks under different working conditions. Experimental The detailed experimental setup of the two-layer F10-design counter-flow stack (internal number: F1002-165) is described in Fang et al [12] The following table gives a brief overview of the anodesupported cells (ASCs in SOFC mode) and stack components used

Electrolyte Fuel electrode

Results and discussion

Air inlet

Fuel in Expected values substrate

Conclusion