Preparation Of Solid Oxide Electrolysis Cell Components For High Temperature Steam Electrolysis

High temperature steam electrolysis (HTSE), which is the highly efficient electrolysis of steam at high temperature and utilizes the heat and electrical power supplied simultaneously by advanced nuclear reactor, provides a very promising way for the large-scale production of hydrogen in the future. The conversion efficiency of thermal energy to hydrogen in HTSE can be up to 48-59%. Solid oxide electrolysis cell (SOEC), a reverse reaction of solid oxide fuel cell (SOFC) developed vigorously worldwide in principle, is the key component of HTSE system. However, Operation in SOEC mode is fundamentally different from that in SOFC mode due to the obvious change in direction of the electrochemical reaction and various operating conditions. It is hard to get optimized performance of SOEC based on the direct reverse operation of SOFC. Therefore, SOEC puts forward new demands for materials and technology. And, it is of great importance to improve the performance of electrolyte and electrodes for the practicability of SOEC technology in the future. The main aims of this dissertation were the preparation and fabrication technique of SOEC components for the application of HTSE.1. Pre-sintering temperature of hydrogen electrode, sintering temperature of YSZ electrolyte and the thickness of electrolyte are the key factors to affect the density of the electrolyte film. When the pre-sintering temperature is over 1000℃, it is beneficial for the improvement of mechanical strength of the hydrogen electrode and in favor of the printing operation. The suitable sintering temperature of YSZ is between 1350℃and 1400℃. When the temperature is over 1450℃, the performance of SOEC will decrease quickly. And the more appropriate thickness of the electrolyte is about 10μm. The active electrode area and the electrolysis performance can be increased effectively by the microstructure modification of YSZ through the preparation of a layer porous YSZ on the surface of the dense electrolyte.2. NiO-YSZ composite powder was highly efficient synthesized via in situ urea combustion method and ammonia precipitation method, respectively. Through the comparative analysis of products, in situ urea combustion method was adopted as the preparation method in the research and the optimization of technological conditions for the synthesis was investigated. The hydrogen production performance of the single SOEC with optimized gradient hydrogen electrodes is obvious higher than that of cells with non-gradient hydrogen electrodes.3. The in-situ LSM-YSZ powder shows better reproducibility, electrolysis performance and stability than traditionally direct mixture LSM and YSZ oxygen electrode. A mechanism which involves the incorporation of SrO segregated on the surface into the LSM lattice and the generation of oxygen vacancies in the LSM electrode is proposed for the activation process with O2- oxidation on LSM electrodes.4. The electrochemical test of the single button cells assembly of the above self-prepared electrodes and electrolyte shows excellent electrolysis performance. The electrolysis voltage can be kept at 0.93-0.95 V with a hydrogen production rate up to 138 Nmlcm-2h-1 and no degradation for 50h at the current density of 0.33 Acm-2 Moreover, it is found that the increase of temperature and steam content are conducive to the electrolysis reaction. The suitable steam content is from 70% to 80%. Bi and Na elements with low melting point in the Pt collector can damage the microstructure of SOEC.In this paper, the R&D of microstructure modification technology on the surface of dense electrolyte and the novel in situ synthesis method of electrodes are beneficial for the improvement of the performance and stability of SOEC, which are the basis for the further application of HTSE technology.