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

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.

Degradation of Ni-YSZ Electrodes in Solid Oxide Cells: Impact of Polarization and Initial Microstructure on the Ni Evolution

“…This statement must explain a large part of the higher experimental degradation rates measured for the Cell B compared to Cell A. Moreover, it is worth reminding that the destabilization of the oxygen electrode material accelerated under electrolysis current must also contribute to the overall cell degradation [14,21].…”

“…This latter phenomenon represents a significant contribution to the global cell degradation [19]. Indeed, it has been shown that the Ni-YSZ cermet is subjected under operation to a Ni agglomeration resulting in a phase coarsening and a migration changing the Ni distribution in the electrode [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32].…”

“…In terms of operating conditions, Ni migration has been observed after aging in SOEC operation [21,22,31,37,38] or SOFC mode [29,39]. However, some experimental results suggest that the severity of the phenomenon could be aggravated under electrolysis conditions because of the high cathodic overpotential [21,22]. In addition, it has been reported that the high steam partial pressures could accelerate the process [40].…”

Investigation of the Long‐term Stability of Solid Oxide Electrolysis Stacks under Pressurized Conditions in Exothermic Steam and Co‐electrolysis Mode

“…However, the reported degradation data are mostly hard to compare since cell concepts, materials and experimental conditions such as reactant flows, gas composition, conversion, voltage or current density strongly differ from one study to the other. Experimental investigations on the long-term stability of SOEC stacks are less available but highly required to identify and promote potential developments on cell, stack or system level [5,[16][17][18][19][20][21][22][23].…”

Optimization of the Perturbation Amplitude for EIS Measurements Using a Total Harmonic Distortion Based Method

“…On the other hand, EIS deals with materials in which ionic conductivity dominates over electronic conductivity [2]. To date, this technique has been applied in a wide range of applications, such as supercapacitors [3][4][5], corrosion [6][7][8][9][10][11], solar cells [12][13][14], electrolysers [15][16][17][18], electrochemical sensors [19][20][21], batteries [22][23][24][25], and fuel cells [26][27][28][29], amongst others. Today, it is considered as one of the fundamental electrochemical techniques [30].…”