Fabrication of SOECs Hydrogen Electrode Active Layer Using Liquid Phase Grown NiO/YSZ Nanocomposite Particles

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Solid oxide electrolysis cells (SOECs), which are categorized as high temperature steam electrolysis device are receiving much attention because of its higher efficiency compared to conventional electrolysis technologies. Now a days. much efforts have been devoted on a global scale to bring SOECs into the market, particularly from the perspective of green hydrogen production and utilization. Improvement of electrolysis performance as well as long term performance stability is crucial for practical implementation of SOECs.Ni/YSZ cermet is one of the most promising materials for hydrogen electrode of SOECs, thereby it has widely been investigated. However, the electrochemical reaction rate at the cermet sometime limits overall electrolysis performance. Electrochemical reaction occurs at so-called triple-phase boundaries (TPBs) consist of Ni, YSZ and pore (steam) in the electrode. The TPB density within the unit effective volume of the electrode must be increased as high as possible to improve the performance. Although the fabrication of the electrode with finer microstructure is effective way to increase TPBs, this approach seems inferior in terms of durability for high temperature operating SOECs in common sense. However, as pointed out by Hauch et al [1], compatibility of better performance due to the formation of huge amount of TPBs and excellent durability due to suppression of microstructural changes can be expected, if the electrode is composed of uniformly distributed, finer as well as size-matched Ni, YSZ and pore phases.Here, we have attempt to fabricate active layer of SOEC hydrogen electrode with such microstructure using NiO/YSZ nanocomposite particles as starting precursor, which is grown by means of a co-precipitation method. The nanocomposite particles have finer and uniform size of approximately 200 nm diameter even after the heat treatment at 1000 ºC, suggesting prevented growth by uniformly distributing NiO and YSZ phases each other. The electrode supported cells with and without hydrogen electrode active layer was fabricated. The active layer was formed between YSZ electrolyte and NiO/YSZ supporting layer by spin-coating using the nanocomposite particles, followed by co-sintering at 1350 ºC. La0.6Sr0.4Co0.2Fe0.8O3/GdxCe1-xO2- δ (LSCF/GDC) composite oxygen electrode was formed by screen-printing onto GDC barrier layer deposited on YSZ electrolyte, followed by sintering. The performance of SOEC was tested at 750℃ under 30 %H2O-H2 atmosphere with the thermo-neutral potential of 1.3 V.The SOEC with the active layer showed high current density of 1.94 A·cm-2, which is approximately 1.5 times higher than that without active layer of 1.31 A·cm-2. Better performance of the cell with active layer can be attributed to higher TPB density formed by using homogeneous nanocomposite particles. The performance degradation rate was almost the same for the cell with and without active layer. The fact suggests that the degradation may be due to component other than the active layer.AcknowledgementThis study is partly based on results obtained from a project, JPNP21022, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).