Microscope Analysis for the Study of the Ageing Processes of Solid Oxide Fuel Cells Fueled by Blends of Hydrogen and Natural Gas.

Transcription

1 Microscope Analysis for the Study of the Ageing Processes of Solid Oxide Fuel Cells Fueled by Blends of Hydrogen and Natural Gas. Renate Hiesgen, Jürgen Kraut, Jürgen Haiber, Gerhard Buchinger*, Thomas Raab *, Dieter Meissner* University of Applied Sciences Esslingen Department of Basic Sciences Kanalstr. 33 D Esslingen,Germany *University of Applied Sciences, Wels, Austria

2 Outline 1. Scanning Electron Microscopy 2. Atomic Force Microscopy

3 Preparation for Analysis Embedding the cell into acrylic glas without the inner current grid Drilling holes through the upper surface to allow the electron beam to inpinge the inner electrode surface

4 Cross Section Electrodes Electrolyte

5 SEM Images cell with inner current grid view into the tube through one of the holes drilled

6 Electronic Contact Layer Silver contact layer

7 Cross Section Interface Electrode- Electrolyte

8 Cell Fueled with Hydrogen Inner contact with connecting grid

9 Cell Fueled with Hydrogen Cathode with interface to the electrolyte Zoom into the interface region

10 Cell Fueled with Hydrogen Anode surface topography no contamination visible

11 Cell Fueled with Methane Typical Working Cycle heating in N 2 from 200 C to 800 C (to prevent oxidation of the contacts) at 800 C reduction of the anode in 50 ml/min H 2 for 30 min, heating to 850 C, recording an I/V-curve, P= 198 mw/cm 2 at 0.7 V, after operation for 5 hours at 0.7 V under constant conditions change of the gas to 50 ml/min methane, operation for 20 hours under methane, after an initial degradation the power reached the same values as in H 2 for 5 hours followed by strong degradation to 80 mw/cm 2, after cooling down the cell, carbon layers were visible even with the naked eye.

12 Cell Fueled with Methane Cross section topography Ni/YSZ-Anode (50 vol% Ni) Material contrast: Bright = high atomic number

13 Cell Fueled with Methane Cross section Silver contact layer Cathode Electrolyte Ni/YSZ-Anode (approx. 50 vol% Ni)

14 Cell fueled with Methane Anode with Carbon contamination and Ni-particles

15 Cell Fueled with Methane Anode with Carbon contamination and Ni-particles

16 Cell Fueled with Methane Anode surface topography Carbon fibrils after use Material contrast: bright = high atomic number Ni-particles at the end of fibrils

17 Cell Fueled with Methane La-crystals in silver layer on the cathode electrode surface Higher resolution image of the crystals

18 Cell Fueled with Methane Cathode-electrolyte topography Material contrast cathode - electrolyte

19 Cell Fueled with Methane Current grid with carbon layer topography Material contrast carbon layer on Ni

20 AFM Analysis, area = 25 µm 2 Anode with carbon layer Topography Height = 2,5 µm Stiffness of the surface dark = soft material Adhesion forces with the surface bright = high adhesion forces Rough surface Soft material at the edges with high adhesion: Carbon contamination

21 AFM Analysis, area = 25 µm 2 Anode with carbon layer Topography Height = 0,6 µm Stiffness of the surface dark = soft material Adhesion forces with the surface bright = high adhesion forces Rough surface Soft material at the edges with high adhesion: Carbon contamination

22 Cell Fueled with CH 4 /H 2 /H 2 O Working conditions heating to 850 C, 20 hours under pure H 2 with 66,6 % humidity, 15 h with 27 % methane in H 2 and 66,6 % H 2 O in the gas.

23 Cell Fueled with CH 4 /H 2 /H 2 O Anode no Carbon contamination some agglomeration visible Zr enriched region Ni enriched region

24 Cell Fueled with CH 4 /H 2 /H 2 O Anode delamination of anode and electrolyte

25 Cell Fueled with CH 4 /H 2 /H 2 O Cathode/Electrolyte cross section two layers with different density

26 Cell Fueled with CH 4 /H 2 /H 2 O Cathode Cathode Outer surface (right) Electrolyte (left) Electrolyte with silver crystals

27 Cell Fueled with CH 4 /H 2 /H 2 O Working temperature: 900 C Flow Conditions: 50 ml/min H 2 or CH 4 / H 2 blends with 66,6 % moisture The tested methane concentrations have been 0, 25 Vol%, 50 Vol% and 75 Vol%

28 Anode Structure after Experiment with 66.6 % Moisture at 900 C open structure delamination

29 Summary: Main Results Carbon is formed on surfaces preferably at edges and pores, Carbon formation leads to fiber formation lifting nickel catalyst particles from the surface, Silver contact layers may lead to lanthanum segregation from the cathode layer.

30 Thank You!