Ceria sulfide

The sulfur tolerance of these anodes is primarily dictated by the thermodynamics of ceria sulfide and oxysulfide formation, as the sulfur concentration required for CuaS formation is significantly higher [45]. Kim et al. demonstrated that stable operation could be achieved if the sulfur level in the fuel is reduced to 100 ppmv S as thiophene in 5 mol% n-CioH22 - this is below the concentration predicted from thermodynamics for Cc202S formation. This study was followed by work of He et al. who demonstrated stable operation up to 450 ppmv H2S in H2 [46], significantly higher than the tolerance levels reported for Ni-based anodes [47]. 

It is well established that sulfur compounds even in low parts per million concentrations in fuel gas are detrimental to MCFCs. The principal sulfur compound that has an adverse effect on cell performance is H2S. A nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Chemisorption on Ni surfaces occurs, which can block active electrochemical sites. The tolerance of MCFCs to sulfur compounds is strongly dependent on temperature, pressure, gas composition, cell components, and system operation (i.e., recycle, venting, and gas cleanup). Nickel anode at anodic potentials reacts with H2S to form nickel sulfide. Moreover, oxidation of H2S in a combustion reaction, when recycling system is used, causes subsequent reaction with carbonate ions in the electrolyte [1]. Some researchers have tried to overcome this problem with additional device such as sulfur removal reactor. If the anode itself has a high tolerance to sulfur, the additional device is not required, hence, cutting the capital cost for MCFC plant. To enhance the anode performance on sulfur tolerance, ceria coating on anode is proposed. The main reason is that ceria can react with H2S [2,3] to protect Ni anode. 

Rare-earth nanomaterials find numerous applications as phosphors, catalysts, permanent magnets, fuel cell electrodes and electrolytes, hard alloys, and superconductors. Yan and coauthors focus on inorganic non-metallic rare-earth nanomaterials prepared using chemical synthesis routes, more specifically, prepared via various solution-based routes. Recent discoveries in s)mthesis and characterization of properties of rare-earth nanomaterials are systematically reviewed. The authors begin with ceria and other rare-earth oxides, and then move to oxysalts, halides, sulfides, and oxysulfides. In addition to comprehensive description of s)mthesis routes that lead to a variety of nanoforms of these interesting materials, the authors pay special attention to summarizing most important properties and their relationships to peculiar structural features of nanomaterials s)mthesized over the last 10-15 years. 

Kirk, T.J. and Winnick, J., A hydrogen sulfide solid-oxide fuel cell using ceria-based electrolytes, J. Electrochem. Soc., 140, 3494-3496 (1993). 

Ceria Cerium Sulfate Cerium Sulfide Supported-Metal Catalysts Oxygen-Storage Capacity Water-Gas Shift Steam Reforming SO2 H2S. 

C.J. Lay cock, J.Z. Staniforth, R.M. Ormerod, Biogas as a fuel for soUd oxide fuel cells and synthesis gas production effects of ceria-doping and hydrogen sulfide on the performance of nickel-based anode materials, Dalton Trans. 40 (2011) 5494-5504. 

---