Effect of electric load and dual atmosphere on the properties of an alkali containing diopside-based glass sealant for solid oxide cells

© 2019 Elsevier B.V. All rights reserved.A new alkali-containing diopside based glass-ceramic sealant for solid oxide cells was synthesized, characterized and tested. The composition was designed to match the coefficient of thermal expansion (CTE) of Crofer22APU interconnect. The sealant has a glass transition temperature of 600°C, a crystallization peak temperature of 850°C and a maximum shrinkage temperature of 700°C, thus suggesting effective densification prior to crystallization. The CTE of the glass-ceramic is 11.5 10-6 K-1, a value which is compatible with the CTE for Crofer22APU stainless steel. Crofer22APU/glass-ceramic/Crofer22APU joined samples were tested in simulated real-life operating conditions at 800°C in dual atmosphere under an applied voltage, monitoring the electrical resistivity. The effect of two different applied voltages (0.7V and 1.3V) was evaluated. A voltage of 1.3V led to a rapid decrease in the electrical resistivity during the test;such a drop was due to the formation of Cr2O3 “bridges” that connected the two Crofer22APU plates separated by the sealant. There was no decrease in the resistivity when a voltage of 0.7V was applied. Instead,resistivity value remained stable at around 105 Ω cm for the 100h test duration. The degradation mechanisms, due to both the alkali content and the applied voltage, are investigated and discussed.Peer reviewe

Modeling of complex interfaces: Gadolinium‐doped ceria in contact with yttria‐stabilized zirconia

Gadolinium‐doped ceria (GDC ) and yttria‐stabilized zirconia (YSZ ) are well‐known electrolyte materials in solid oxide fuel cells (SOFC s). Although they can be used independently, it is common to find them in combination in SOFC s, where they are used as protective layers against the formation of secondary phases or electron conduction blockers. Despite their different optimum operating temperatures, it appears that oxygen conduction is not affected by their interface. However, the intrinsic mechanisms of oxygen diffusion at these interfaces still remain unclear. One of the main difficulties when modeling the contact between different materials, or indeed different particles of the same material, is caused by the structural complexity of these systems. If we wish to evaluate the properties of the materials, we first need to obtain a model that includes the main features of the GDC /YSZ interface, such as large‐scale defects or cation interdiffusion in the contiguous phase. Since the generation of such a mixed system is complicated, we show here how the “amorphization and recrystallization” strategy can help us to obtain realistic systems. In this, the first of our papers on the structure and properties of layered GDC /YSZ materials, we discuss the structural features of the grain boundary between GDC and YSZ obtained by molecular dynamics simulations

Effects of fabrication parameters on the performance of solid oxide electrolyzer cell

1st International Symposium on Materials for Energy Storage and Conversion (ESC-IS) -- SEP 07-09, 2015 -- Middle E Tech Univ, Ankara, TURKEYWOS: 000378359400002The microstructure has a great impact on the performance of solid oxide fuel/electrolyzer cells while the cell fabrication parameters mainly determine the microstructure of the cell components. In this study, a number of five-layered cells with 16 cm(2) active area are fabricated and the effects of several cell fabrication parameters including sintering temperature and electrode composition on the hydrogen production performance are investigated. The experimental results showed that the optimum sintering temperature of the electrolyte, cathode and anode should be 1400 degrees C, 1250 degrees C and 1075 degrees C, respectively, while the solid weight ratio of both NiO-ScSZ cathode and LSM-ScSZ anode functional layer should be 1:1. The optimized cell produces 38 Sccm H-2 at an operation temperature of 800 degrees C and 1.5 V. Then, the cell size is increased to a commercial size of 81 cm(2) active area. The final cell exhibits an acceptable H-2 production of 154 Sccm H-2 at 800 degrees C and 1.5 V. The relatively lower performance of the commercial-size cell is attributed to the inadequate current distribution/collection due to the increased surface area. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Development of anodes for direct oxidation of methane fuel in solid oxide fuel cells

1st International Symposium on Materials for Energy Storage and Conversion (ESC-IS) -- SEP 07-09, 2015 -- Middle E Tech Univ, Ankara, TURKEYWOS: 000378359400038In addition to pure hydrogen, solid oxide fuel cells (SOFCs) can utilize hydrocarbons as a fuel. However, conventional Ni-based anodes exhibit an excellent catalytic activity towards the hydrocarbon cracking reaction and thus the carbon deposition occurs in the anode. The deposited carbons quickly deactivate the anode irreversibly by covering the active surface of the anode catalyst. As a result, a significant degradation in the cell performance can be seen. In this study, the anode structure is modified by the addition of copper (Cu) and ceria (CeO2) to increase the coking resistance of the cell under direct methane fuel. In this respect, the anodes are infiltrated by different amounts of Cu and CeO2 nitrates via the wet impregnation technique to investigate the effects of Cu and CeO2 loadings on the carbon tolerance of the cell. The effects of the anode porosity and composition are also considered in the study. The carbon resistance thus the service life of the cell with Cu/CeO2/Ni/YSZ anodes is found to be significantly higher than that of conventional Ni-based anodes under direct dry methane fuel. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

Mechanical and electrochemical behavior of novel electrolytes based on partially stabilized zirconia for solid oxide fuel cells

WOS: 000355711700069In this study, 3 mol% yttria stabilized zirconia (3YSZ) is investigated as a SOFC electrolyte alternative to 8 mol% yttria stabilized zirconia (8YSZ). The mechanical and electrochemical properties of both materials are compared. The mechanical tests indicate that the thickness of 3YSZ can be reduced to half without sacrificing the strength compared to 8YSZ. By reducing the thickness of 3YSZ from 150 mu m to 75 mu m, the peak power density is shown to increase by around 80%. The performance is further enhanced by around 22% by designing of novel electrode structure with regular cut-off patterns previously optimized. However, the cell with novel designed 3YSZ electrolyte exhibits 30% lower maximum power density than that of the cell with 150 pm-thick standard 8YSZ electrolyte. Nevertheless, the loss in the performance may be tolerated by decreasing the fabrication cost revealing that 3YSZ electrolyte with cut-off patterns can be employed as SOFC electrolyte alternative to 8YSZ. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved

A review on cell/stack designs for high performance solid oxide fuel cells

WOS: 000369462100085Besides the general advantages of fuel cells, including clean and quiet operation, solid oxide fuel cells (SOFCs) as being one of the high-temperature fuel cells also provide a relatively high efficiency due to enhanced reaction kinetics at high operating temperatures, The high operation temperature of SOFC also enables internal reforming of most hydrocarbons and can tolerate small quantities of impurities in the fuel. However, a high operation temperature limits the SOFC application areas to stationary applications because of a long start-up period and also is not desirable from the viewpoint of cost reduction and longterm stability especially for the cell materials. Therefore, the lowering the operation temperature of SOFCs is crucial for the cost reduction and the long term operation without degradation as well as the commercialization of the SOFC systems. The reduced operating temperature also helps to reduce the time and to save the energy required for the system start-up enabling SOFCs to have wider application areas including mobile/portable ones. Apart from the low operating temperature, the high performance along with a small volume is another requirement for SOFC to be used in mobile applications. Both can be achieved by fabricating novel SOFCs generating a high power output at low operating temperatures. Therefore, this paper reviews the current status and related research on the development of these high performance-SOFC cell/stack designs. (C) 2015 Elsevier Ltd. All rights reserved

Novel structured gadolinium doped ceria based electrolytes for intermediate temperature solid oxide fuel cells

Novel three-layered intermediate temperature solid oxide fuel cell (SOFC) electrolytes based on gadolinium doped ceria (GDC) are developed to suppress the electronic conductivity of GDC, to improve the mechanical properties of the cell and to minimize power loss due to mixed conductive nature of GDC. Three different electrolytes are fabricated by sandwiching thin YSZ. ScSZ and ScCeSZ between two relatively thick GDC layers. An electrolyte composed of pure GDC is also manufactured for comparison. NiO/GDC and LSCF/GDC electrodes are then coated on the electrolytes by a screen printing route. SEM results show that it is possible to obtain dense and crack free thin layers of YSZ, ScSZ and ScCeSZ between two GDC layers without delamination. Performance measurements indicate that interlayered thin electrolytes act as an electronic conduction barrier and improve open circuit voltages (OCVs) of GDC based cells

Anode-supported solid oxide fuel cells with ion conductor infiltration

WOS: 000295379300005Nano ion conductor infiltration to anode andcathode side of solid oxide fuel cell (SOFC) significantly improves the performance of an SOFC. The effects of processing parameters such as molar concentration, sintering temperature and holding time are investigated. The performance of fuel cell is evaluated with a test station and an impedance analyzer. The SEM investigation showed that a nano ion conductor phase forms around the main phase in the anode and the cathode. The results showed that nano infiltration enhances significantly the performance of SOFC. The power density is found to increase around two times with infiltration. It is also found that the particle size and the porosity significantly affect the performance of infiltrated SOFC cell. While smaller infiltrated grains enhance the performance lower porosity adversely affects the performance. Copyrightr (C) 2011 John Wiley & Sons, Ltd