Hansen, Karin Vels1; Jacobsen, Torben3; Thydén, Karl Tor Sune1; Wu, Yuehua1; Mogensen, Mogens Bjerg1
1 Department of Energy Conversion and Storage, Technical University of Denmark2 Imaging and Structural Analysis, Department of Energy Conversion and Storage, Technical University of Denmark3 Department of Chemistry, Technical University of Denmark4 Fundamental Electrochemistry, Department of Energy Conversion and Storage, Technical University of Denmark
In situ surface reductions of NiO-YSZ-Al2O3 composites into Ni-YSZ-Al2O3 cermets were carried out at 312–525 °C in a controlled atmosphere high-temperature scanning probe microscope (CAHT-SPM) in dry and humidified 9 % H2 in N2. The reduction of NiO was followed by contact mode scanning of topography and conductance. A reproducible sequence of events was observed which included a conductance decrease upon hydrogen introduction and a reappearance of conductance after some time. It was found that this incubation time from introduction of hydrogen and until conducting Ni appeared was temperature dependent and followed the Arrhenius equation. For samples reduced in dry hydrogen, the Arrhenius plot showed two regions with different activation energies. Scanning electron microscopy confirmed a difference in microstructure between these temperature regimes. A strong retarding effect of steam (H2O) on the nucleation time of Ni particles was observed.
Journal of Solid State Electrochemistry, 2014, Vol 18, Issue 7, p. 1869-1878
High-temperature scanning probe microscopy; Surface conductance; In situ NiO reduction; Incubation period