Papers by Keyword: Ni Oxidation

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Authors: Jian Xin Zhu, Bo Yu
Abstract: High temperature steam electrolysis (HTSE) through solid oxide electrolysis cells (SOEC), a promising high-efficiency and zero-emission way to large-scale hydrogen production, has been received increasingly international interest. The hydrogen production efficiency of HTSE is more than 50%. In this paper, the electrochemical performance and microstructure change of single button cells operating in both fuel cell (SOFC) and electrolysis modes (SOEC) were studied at 850°C. Also, the degradation mechanisms of hydrogen electrodes were investigated. The results showed that OCV decreased from 0.944 V to 0.819 V when the steam content increased from 20% to 80%. The voltage began to increase rapidly at relatively higher current density for lower steam content because of steam starvation; however, steam starvation did not occur at higher steam content. The ASR data decreased from 1.68 to 0.645Ωcm2 with the increase of steam contents, while steam content had little effect on ASR data in SOFC mode. The polarization loss of the single cell was higher in electrolysis mode than that in fuel cell mode. The microstructure of the hydrogen electrode changed obviously after electrolysis process. Furthermore, the performance degraded at high steam partial pressure due to the oxidation of Ni grains at the interface of hydrogen electrode.
Authors: Cheol Jin Kim, In Sup Ahn, Kwon Koo Cho, Sung Gap Lee, Jun Ki Chung
Abstract: LiNiO2 thin films for the application of cathode of the rechargeable battery were fabricated by Li ion diffusion on the surface oxidized NiO layer. Bi-axially textured Ni-tapes with 50 ~ 80 μm thickness were fabricated using cold rolling and annealing of Ni-rod prepared by cold isostatic pressing of Ni powder. Surface oxidation of Ni-tapes were conducted using tube furnace or line-focused infrared heater at 700 °C for 150 sec in flowing oxygen atmosphere, resulted in NiO layer with thickness of 400 and 800 μm, respectively. After Li was deposited on the NiO layer by thermal evaporation, LiNiO2 was formed by Li diffusion through the NiO layer during subsequent heat treatment using IR heater with various heat treatment conditions. IR-heating resulted in the smoother surface and finer grain size of NiO and LiNiO2 layer compared to the tube-furnace heating. The average grain size of LiNiO2 layer was 0.5~1 μm, which is much smaller than that of sol-gel processed LiNiO2. The reacted LiNiO2 region showed homogeneous composition throughout the thickness and did not show any noticeable defects frequently found in the solid state reacted LiNiO2, but crack and delamination between the reacted LiNiO2 and Ni occurred as the reaction time increased above 4hrs.
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