I am running tubular cells Ni-YSZ | YSZ | Nd-Ni at low T (600 C). The operating condition is as below:
Fuel: H2 50 sccm/min
Air: 100 sccm/min
T: 600 C
Active cell area: 2 cm2
potentiostatic voltage = 0.7 V
I am facing a continuous degradation (current drop) at the initial 100 hours of operation. Post-morterm SEM analysis shows no sign of microstrtuctural degradation (Ni migration, agglomeration, oxidation | layers delamination, etc.) and polarization resistance is low before the test (low ohmic, activation, concentration) + the support contains enough porosity. This is what happens to all of the cells. The cells have closed caps. Cells are inside a zirconia tube. I'm afraid there is a systematic error in my long-term tests. Like the type of silver/gold paste I use for my cathode side or the position of the cell for better removal of produced water (I noticed some groups use vertical furnaces) or maybe making tubes open ended (not closed end).
I am trying to change the current collector or change the design for better removal of water inside zirconia tube holder.
I would appreciate if anyone experiencing similar problem, share their ideas with me.
Thank you all. Of course I measure the impedance. It shows no degradation before and after the test. To my knowledge, Ni(OH)2 is a volatile specimen and eventually sediments as Ni on particles with higher local polarization.
Could be a sealing issue with your testing setup. Try leak testing before and after to see if seals remain intact. Any fuel crossover from leakage leads to rapid degradation of the seals, manifolds and likely the cell itself. Also, there will be an initial reduction of your anode. There will also be sintering effects of electrodes (mainly the anode) and sealants. A rapid degradation at the start of the test is to be expected. The rate will start to level out and the data from then tends to be the most valuable.
Can you share some info, schematic of the setup you are using to seal your cell.
Its not natural for Ni to not agglomerate after 100hrs of operation.
Could be the shorting in your testing ring, as we have experienced.
Also, for more in-depth analysis you may consider X-ray CT and raman, have a look at the following:
https://www.mdpi.com/1996-1073/13/14/3552
It could be only the sealing, you must check that there are no fuel leaks between the electrodes, if there is a short circuit.
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