TY  - THES
AU  - Unachukwu, Ifeanyichukwu Daniel
TI  - Fuel electrode degradation study for solid oxide electrolysis
PB  - RWTH Aachen
VL  - Dissertation
M1  - FZJ-2026-00392
SP  - 123
PY  - 2025
N1  - Dissertation, RWTH Aachen, 2025
AB  - The conversion of electrical energy into a chemical energy carrier in the form of hydrogen, carbon monoxide and synthesis gas can be achieved with high efficiency by using the solid oxide electrolysis technology. However, long term degradation issues, especially of the fuel electrode remain a challenge that must be resolved. This thesis therefore investigates the electrochemical performance and degradation behaviour of three different fuel electrodes: gadolinium doped ceria (GDC), Nickel-GDC and Nickel with yttria-stabilized zirconia (Ni-YSZ) under three different electrolysis modes: steam, CO2 and co electrolysis. The fuel electrode material was fabricated on an 8YSZ electrolyte support while the air electrode is made of lanthanum strontium cobalt ferrite (LSCF) with a GDC barrier layer sandwich between the electrolyte and the LSCF. Thus, the cell configuration is represented as Fuel electrode//8YSZ//GDC//LSCF. Their performance and electrochemical processes were investigated by direct and alternating current measurements in the different electrolysis modes in the 750-900 °C temperature range. Distribution of relaxation times (DRT) analysis and non-linear least square method were employed to resolve frequency-dependent electrode processes. The analysis reveals that the GDC fuel electrode is dominated by low-frequency surface exchange processes originating from the double phase boundary sites (DPB), while the Ni-GDC electrodes are dominated by sub-surface mid-frequency processes. For the Ni-YSZ, the underlying processes are dominated by mid/high-frequency processes, mostly from the triple-phase boundary sites (TPB). With regard to the performance, the Ni-GDC single cells exhibited the highest current density across the three electrolysis modes while the GDC and Ni-YSZ showed similar current density in the different electrolysis modes. In the degradation analysis, Ni-YSZ exhibited the highest degradation rate in steam electrolysis followed by Ni-GDC while the GDC showed the least degradation. On the other hand, during CO2 electrolysis, the GDC electrodes showed the highest degradation rate, while Ni-YSZ exhibited a degradation rate slightly higher than those of Ni-GDC. The post-test analysis reveals that GDC particle coarsening and loss of GDC percolation was the major contributor to the degradation rates in the GDC and Ni-GDC single cells. Furthermore, GDC migration and covering of the Ni particles were also seen to contribute to the degradation rates in the Ni-GDC cells. For the Ni-containing cermet of Ni-YSZ and Ni-GDC, Ni migration and agglomeration remain significant contributors to the degradation rate. The degradation processes were observed to be facilitated by an increase in steam partial content.
KW  - Hochschulschrift (Other)
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2025-06190
UR  - https://juser.fz-juelich.de/record/1050640
ER  -