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

Abstract

In this study three identically constructed ten-layer stacks with electrolyte supported cells were tested in exothermic steam and co-electrolysis mode at elevated pressures of 1.4 and 8 bar. Investigations during constant-current operation at a current density of-0.5 A cm-2 and a reactant conversion of 70% over 1,000-2,000 h were carried out. The inlet gas composition for steam electrolysis was 90/10 (H 2 O/H 2) and 63.7/31.3/3.3/1.7 (H 2 O/CO 2 /H 2 /CO) for co-electrolysis operation. All stacks showed highly similar resistances at the beginning of the tests indicating a high level of accuracy and repeatability during manufacturing. The stack operated in steam electrolysis mode at 1.4 bar showed comparably low degradation of 8 mV kh-1 cell-1 , whereas the stack operated at 8 bar showed an approximately four times higher degradation. The third stack was operated in co-electrolysis mode at 1.4 and 8 bar and showed noticeably higher degradation rates than during steam electrolysis mode. The predominant increase of the ohmic resistance during operation was identified to be mainly responsible for the observed degradation of all three stacks, whereas the increase of the polarization resistances played a subordinate role. Within the post-test analysis, noticeably high nickel depletion was observed for the stack operated at the highest pressure in steam electrolysis mode. Furthermore, partial delamination of electrodes was observed. The degradation is discussed with relation to phenomena and experimental parameters during operation.

Ni migration in solid oxide cell electrodes: Review and revised hypothesis

“…Studies following this work showed that it was gas stream sulfur-based impurities in quantities of 15-20 ppb in the CO 2 feed for the CO 2 electrolysis that initiated the severe degradation. Also silica is often observed, and for example Riedel et al [45] used ultrapure water with a Si concentration of 4 to 7 µg L −1 for steam raising for an SOEC stack test over 1000 h and found an average of ca. 2.3 wt.% Si across the fuel electrode thickness at the inlet and spots with up to 5.5 wt.% Si close to the electrodeelectrolyte interface.…”

Solid oxide electrolysis cells – current material development and industrial application

“…66,78 In addition to its physical characteristics, 8YSZ is still the material of choice due to its cost advantages over scandiastabilized zirconia (ScSZ) and gadolinium-doped ceria (GDC). Fuel electrode-supported cells with an 8YSZ electrolyte have proven their long-term stability in various tests conducted at Forschungszentrum Jülich, 25,37,79,80 Topsoe, 81,82 EPFL, 38 CEA, [83][84][85] DTU, 86 DLR, 87,88 and EIFER. 89 3.1.3.…”

CHEMampere: Technologies for sustainable chemical production with renewable electricity and CO2, N2, O2, and H2O

“…An overview of the functionality of the different cell types in the different conditions can be found here. [41,[49][50][51] High-temperature electrolysis is very attractive in terms of efficiency, for H 2 and CO production, compared to low-temperature technologies. This is even more favourable if a heat source is available to reduce the heat demand of the electrolysis process.…”

“…An overview of the functionality of the different cell types in the different conditions can be found here. [ 41,49–51 ]…”