NiO/YSZ/Pt 전해셀의 고온 수증기 전해에 의한 수소제조 특성

유지행,이시우,한인섭,우상국,홍기석,김영운,서두원 한국수소및신에너지학회 2006 한국수소 및 신에너지학회논문집 Vol.17 No.1

High temperature electrolysis is a promising technology to produce massively hydrogen using renewable and nuclear energy. Solid oxide fuel cell materials are candidates as the components of steam electrolysers. However, the polarization characteristics of the typical electrode materials during the electrolysis have not been intensively investigated. In this study, NiO electrode was deposited on YSZ electrolyte by spin coat process and firing at 1300 ℃. Pt electrode was applied on the other side of the electrolyte to compare the polarization characteristics with those by NiO during electrolysis. The H2 evolution rate was also monitored by measuring the electromotive force of Lambda probe and calculated by thermodynamic consideration. At low current density, Pt showed lower cathodic polarization and thus higher current efficiency than Ni, but the oxidation of Ni into NiO caused the increase of anodic resistance with increasing current density. High overpotential induced high power consumption to produce hydrogen by electrolysis.

압출공정에 의해 제조된 Ni-YSZ 원통형 음극지지체의 특성

유지행,이시우,우상국,김영운,박건우,서두원 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.12

The microstructure of Ni-YSZ cermets was controlled with fine and coarse starting powders (NiO and YSZ) to obtain a optimumstrong and conductive tubular anode support for SOFCs. Three types of cermets with different microstructures, i.e., coarse Ni-fineYSZ, fine Ni-coarse YSZ, and fine Ni-fine YSZ, were fabricated to investigate their electrical and mechanical properties. The cermetsfrom fine NiO powder showed high electrical conductivity due to the enhanced percolation of Ni particles. The cermet by fine Ni andcoarse YSZ showed excellent electrical conductivity (>1000 S/cm) despite its high porosity (~40%) but it showed poor mechanicalstrength due to the lack of percolation by YSZ particles and due to large pores. Thus fine NiO and YSZ powders were used to makestrong and conductive Ni-YSZ support tube by extrusion. The microstructure of the anode tube was modified by the amount ofpolymeric additives and carbon black, a pore former. Ni-YSZ tube (porosity ~34%) with the finer microstructure showed betterwiththe length from 20 to 40cm were successfully fabricated with the optimized composition of materials and polymeric additives.

고온 수증기 전해기술을 이용한 수소제조

유지행,우상국,김선동,서두원,한인섭,홍기석 한국에너지학회 2010 한국에너지공학회 학술발표회 Vol.2010 No.10

Spin-coating 공정에 의해 제조된 음극 지지형 고체산화물 연료전지

유지행,이희락,우상국,Yu, Ji-Haeng,Lee, Hee-Lak,Woo, Sang-Kuk 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.12

NiO-YSZ anode-supported single cell was prepared by spin-coating YSZ and LSM slurries as electrolyte and cathode, respectively. Dense YSZ electrolyte film was successfully prepared on the porous NiO-YSZ anode substrate by tuning pre-sintering temperature of NiO-YSZ and co-firing temperature. The thickness of YSZ film was controlled by the solid content of slurry and coating cycles. The experimental conditions affecting on the thickness of YSZ film was discussed. Single cells with the active electrode area ${\sim}0.8\;cm^2$ were prepared by spin-coating the cathode layers of LSM-YSZ mixture and LSM consequently as well. The effects of the pre-sintering temperature and thus the microstructure of NiO-YSZ substrate on the current-voltage characteristics of co-fired cell were investigated.

Preparation and Electrochemical Performance of Electrode Supported La_0.75Sr_0.25Ga_0.8Mg_0.16Fe_0.04O_(3-δ) Solid Oxide Fuel Cells

유지행,박상운,우상국 한국세라믹학회 2011 한국세라믹학회지 Vol.48 No.5

In this paper, investigations of thick film La_0.75Sr_0.25Ga_0.8Mg_0.16Fe_0.04O_(3-δ) (LSGMF) cells fabricated via spin coating on either NiOYSZ anode or La_0.7Sr_0.3Ga_0.6Fe_0.4O_3 (LSGF) cathode substrates are presented. A La-doped CeO_2 (LDC) layer is inserted between NiO-YSZ and LSGMF in order to prevent reactions from occurring during co-firing. For the LSGF cathode-supported cell, no interlayer was required because the components of the cathode are the same as those of LSGMF with the exception of Mg. An LSGMF electrolyte slurry was deposited homogeneously on the porous supports via spin coating. The current-voltage characteristics of the anode and cathode supported LSGMF cells at temperatures between 700℃ and 850℃ are described. The LSGF cathode supported cell demonstrates a theoretical OCV and a power density of ~420mWcm^2 at 800℃, whereas the NiO-YSZ anode supported cell with the LDC interlayer demonstrates a maximum power density of ~350mW cm^2 at 800℃, which decreased more rapidly than the cathode supported cell despite the presence of the LDC interlayer. Potential causes of the degradation at temperatures over 700℃ are also discussed.

LSC/GDC (50 : 50 vol%) 활성층이 LSCF/GDC (20 : 80 vol%) 복합 분리막의 산소투과 거동에 미치는 영향

차다솜,유충열,주종훈,유지행,한문희,조철희 한국막학회 2014 멤브레인 Vol.24 No.5

본 연구에서는 LSCF/GDC (20 : 80 vol%) 복합 분리막 표면에 LSC/GDC (50 : 50 vol%) 활성층을 코팅한 후 활성층의 열처리 온도, 두께, 침투법을 이용한 STF 도입이 산소투과 특성에 미치는 영향을 고찰하였다. 활성층 도입은 복합 분리막의 산소 투과 유속을 급격히 증진시켰으며 이는 활성층 성분인 LSC/GDC (50 : 50 vol%)가 전자 전도성 및 표면 산소 분해 반응을 증진시켰기 때문이었다. 활성층의 열처리 온도가 900˚C에서 1000˚C로 증가한 경우, 산소 투과 유속은 증가하였고 이는 분리막과 활성층 사이 그리고 활성층의 결정입간 접촉이 증진하여 산소이온과 전자 흐름을 증진시켰기 때문으로 설명되었다. 코팅층의 두께가 약 10μm에서 약 20μm로 증가한 경우, 산소 투과 유속은 오히려 감소하였는데 이는 코팅층의 두께가 증가할수록 기공을 통한 공기 중의 산소 유입이 어려워지기 때문으로 설명되었다. 또한, 코팅층에 침투법을 이용하여 STF를 도입한 경우가 STF를 도입하지 않은 경우 보다 높은 산소 투과 유속을 보였는데 이는 도입된 STF가 산소 분해하는 표면 반응 속도를 촉진시키기 때문이다. 본 연구로부터 LSC/GDC (50 : 50 vol%) 활성층 코팅 및 특성 제어는 LSCF/GDC (20 : 80 vol%) 복합 분리막의 산소투과 증진에 매우 중요함을 확인하였다. In the present study, disc-type LSCF/GDC (20 : 80 vol%) dual-phase membranes having porous LSC/GDC (50 : 50 vol%) active layers were prepared and effect of active layers on oxygen ion transport behavior was investigated. Introduction of active layers improved drastically oxygen flux due to enhanced electron conductivity and oxygen surface exchange activity. As firing temperature of active layer increased from 900˚C to 1000˚C, oxygen flux increased due to improved contact between membrane and active layer or between grains of active layer. The enhanced contact would improve oxygen ion and electron transports from active layer to membrane. Also, as thickness of active layer increased from 10 to 20μm, oxygen flux decreased since thick active layer rather prevented oxygen molecules diffusing through the pores. And, STF infiltration improved oxygen flux due to enhanced oxygen reduction reaction rate. The experimental data announces that coating and property control of active layer is an effective method to improve oxygen flux of dual-phase oxygen transport membrane.

프로톤 전도성 SrCe_0.95Gd_0.05O_3-α-Ce_0.9Gd_0.1O_2-β 복합체 멤브레인의 수소투과 특성

김환수,유지행,신민재 한국수소및신에너지학회 2011 한국수소 및 신에너지학회논문집 Vol.22 No.2

Proton conductors have attracted considerable attention for solid oxide fuel cell (SOFC), hydrogen pump,gas sensor, and membrane separators. Doped SrCeO_3 exhibits appreciable proton conductivity in hydrogencontaining atmosphere at high temperature. However commercial realization has been hampered due to the reactivity of SrCeO_3 with CO_2. The chemical stability and proton conductivity are dependent on dopant type. The purpose of this work is to investigate chemical stability of SrCe_0.95Gd_0.05O_3-α-Ce_0.9Gd_0.1O_2-β composites in CO_2 and H_2 gases. Thermogravimetric analysis (TGA) was performed in gaseous CO_2 and electrical conductivity of the composites were also measured between 500 and 900℃ in air and H_2 atmosphere. SrCe_0.95Gd_0.05O_3-α-Ce_0.9Gd_0.1O_2-β composite membranes showed good chemical stability of in CO_2 atmosphere and high conductivity at hydrogen condition. The hydrogen permeation of SrCe_0.95Gd_0.05O_3-α-Ce_0.9Gd_0.1O_2-βcomposite membranes was investigated as a function of volumetric content of SrCe_0.95Gd_0.05O_3-α. The SrCe_0.95Gd_0.05O_3-α-Ce_0.9Gd_0.1O_2-β(6:4) membrane with a thickness of 1.0 mm showed the highest hydrogen permeability with the flux reaching of 0.12 ml/min・cm^2 at 800℃ in 100%H_2/N_2 as feed gas.

Dual Phase 전도성 CO₂ 분리막: 메커니즘, 미세구조 및 전기전도도

이시우,유지행,우상국,Lee, Shi-Woo,Yu, Ji-Haeng,Woo, Sang-Kuk 한국세라믹학회 2007 한국세라믹학회지 Vol.44 No.8

Novel conductive $CO_2$ membranes composed of dual phases, molten carbonates and electronic conducting ceramics, were investigated. As the microstructure control of electronic conducting ceramic supports is extremely important to keep the molten carbonates stable in the membranes by a capillary force applied by the pore structure of the supports, we have scrutinized the microstructure of the electronic conducting supports utilizing microscopic images and gas permeability measurement. From the evaluation of the electrical conductivities of the molten carbonates and the electronic conducting ceramic supports, we found that the ionic conductivity of the molten carbonates could determine $CO_2$ flux through the dual phase membranes if the surface exchange rate were relatively high enough.

EB-PVD법에 의해 제조된 YSZ 전해질의 전기적 특성

신태호,유지행,이시우,한인섭,우상국,현상훈,Shin, Tae-Ho,Yu, Ji-Haeng,Lee, Shiwoo,Han, In-Sub,Woo, Sang-Kuk,Hyun, Sang-Hoon 한국세라믹학회 2005 한국세라믹학회지 Vol.42 No.2

나노 코팅 기술로써 빠른 증착 속도와 미세구조 제어가 용이하여 항공기 엔진 부품 열차폐 코팅으로 널리 이용되는 Electron Beam Physical Vapor Deposition (EB-PVD)세라믹 코팅 기술을 연료전지 전해질 제조에 적용하였다. EB-PVD 법을 이용하여 NiO-YSZ 기판에 YSZ 전해질을 약 10$\mu$m의 두께로 짧은 시간에 코팅하였으며 증착온도에 따라 나노 구조의 표면을 가진 YSZ 막을 얻을 수 있었다. 연료전지 전해질로서의 특성을 평가하기 위하여, 같은 조건의 코팅으로 $Al_{2}O_3$기판에 전해질을 동일한 조건으로 코팅하여 전해질의 전기적 특성을 평가하였다. 또한 양극물질로서 $LaSrCoO_3$ 분말을 일반적인 스크린 프린팅 기법으로 코팅하여 EB-PVD의 코팅을 이용한 고체산화물 연료전지 제조 가능성에 대하여 논의하였다 Electron Beam Physical Vapor Deposition (EB-PVD) is a typical technology for thermal barrier coating with Yttria Stabilized Zirconia (YSZ) on aero gas turbine engine. In this study EB-PVD method was used to fabricate dense YSZ film on NiO-YSZ as a electrolyte of Solid Oxide Fuel Cell (SOFC). Dense YSZ films of -10 $\mu$m thickness showed nano surface structure depending on deposition temperature. Electrical conductivities of YSZ film and electric power density of the single cell were evaluated after screen- printing $LaSrCoO_3$ as a cathode.

고상반응에 의하여 제조된 Li2ZrO3의 이산화탄소 흡수 및 소결 특성

이시우,유지행,우상국 한국세라믹학회 2006 한국세라믹학회지 Vol.43 No.5

We synthesized lithium zirconate using solid-state reaction and analyzed thermal properties (TG/DTA) of starting materials and the synthesized one. When Li2ZrO3 powder was exposed to CO2 environment at 500℃, 93% of the theoretical absorption weight was gained within 280 min with fairly high sorption rate. Almost all the absorbed CO2 was generated by heating the sample to 800℃. We also investigated densification behavior of Li2ZrO3 under CO2 environment. By sintering Li2ZrO3 at 760℃ using 2-step process, we obtained dense product, composed mainly of Li2ZrO3 and ZrO2, with relative density of 92%.