476
B. D. Vasyliv et al.
the reported limit for degradation of Ni catalysts’ performance, and no additional
effect is seen applying 105 ppm. At 35 ppm the effect was found to be reversible and
to be constant with temperature from 700 to 1000 ◦ C, with or without passing anodic
current and equal for low-performance porous Ni anodes and high-performance
YSZ–Ni cermets [10]. The effect was found not to be reversible at 105 ppm [12].
Assuming that sulfur chemisorbs exclusively to the Ni surface, the data indicate
that the Ni surface is either the location of rate-limiting reactions or that it provides
a limiting species to the rate-determining reaction. It would appear that the role of
the Ni surface is fairly constant with temperature and passing of current under the
given circumstances.
Considering the impedance of a full SOFC at 1000 ◦ C, the effect of 69 ppm
sulfur is about 5% on the cell voltage, and at 800 ◦ C 10 ppm, sulfur causes about 2%
reduction of the cell voltage [11]. These observations are partially affected by the
anode usually not being the most significant limitation for well-performing SOFC.
The fuel cells with YSZ–Ni cermet anodes have been operated with up to 2000 ppm
sulfur at 950 ◦ C, maintaining output stability [10].
The aim of this work is to study the effect of hydrogen sulfide content in a
hydrogenous atmosphere on the structure, physical, and mechanical properties of
SOFC anode materials.
30.2 Materials and Methods
In order to investigate the effect of hydrogen sulfide content in a hydrogenous
atmosphere on the structure, physical, and mechanical properties of SOFC anode
materials, and based on our experience of studying such materials in atmospheres
with water vapor admixtures [13], a special experimental stand has been developed
(Fig. 30.1).
A ceramic disk or prismatic specimen (Fig. 30.1) is fixed by the holder in the
working space of a cylindrical quartz chamber, which passes through a cylindrical
furnace. The chamber allows reaching the gas pressure up to 0.5 MPa at a
temperature of 600 ◦ C. The temperature control and support are carried out thanks
to the heating system, which contains a heating unit connected to the furnace and
a thermocouple that comes in contact with the specimen. The gas supply system
contains gas cylinders (hydrogen of 99.99% purity, Ar-5 vol% H 2 , argon), a vacuum
pump for degassing, and a Kipp generator for the production of hydrogen sulfide.
A flask filled with water is provided for recycling of exhaust gas. The indicated
parts of the experimental stand are connected to the network by plastic tubes with
corresponding one- and three-way taps. A general view of the experimental stand is
given in the photo (Fig. 30.2).
We prepared a quartz chamber, providing a pressure of 0.0133 Pa with a vacuum
pump, and then ran hydrogen sulfide and additional gas in the required proportions.
Exhaust gas was disposed by passing it through a flask with water. The quartz
B. D. Vasyliv et al.
the reported limit for degradation of Ni catalysts’ performance, and no additional
effect is seen applying 105 ppm. At 35 ppm the effect was found to be reversible and
to be constant with temperature from 700 to 1000 ◦ C, with or without passing anodic
current and equal for low-performance porous Ni anodes and high-performance
YSZ–Ni cermets [10]. The effect was found not to be reversible at 105 ppm [12].
Assuming that sulfur chemisorbs exclusively to the Ni surface, the data indicate
that the Ni surface is either the location of rate-limiting reactions or that it provides
a limiting species to the rate-determining reaction. It would appear that the role of
the Ni surface is fairly constant with temperature and passing of current under the
given circumstances.
Considering the impedance of a full SOFC at 1000 ◦ C, the effect of 69 ppm
sulfur is about 5% on the cell voltage, and at 800 ◦ C 10 ppm, sulfur causes about 2%
reduction of the cell voltage [11]. These observations are partially affected by the
anode usually not being the most significant limitation for well-performing SOFC.
The fuel cells with YSZ–Ni cermet anodes have been operated with up to 2000 ppm
sulfur at 950 ◦ C, maintaining output stability [10].
The aim of this work is to study the effect of hydrogen sulfide content in a
hydrogenous atmosphere on the structure, physical, and mechanical properties of
SOFC anode materials.
30.2 Materials and Methods
In order to investigate the effect of hydrogen sulfide content in a hydrogenous
atmosphere on the structure, physical, and mechanical properties of SOFC anode
materials, and based on our experience of studying such materials in atmospheres
with water vapor admixtures [13], a special experimental stand has been developed
(Fig. 30.1).
A ceramic disk or prismatic specimen (Fig. 30.1) is fixed by the holder in the
working space of a cylindrical quartz chamber, which passes through a cylindrical
furnace. The chamber allows reaching the gas pressure up to 0.5 MPa at a
temperature of 600 ◦ C. The temperature control and support are carried out thanks
to the heating system, which contains a heating unit connected to the furnace and
a thermocouple that comes in contact with the specimen. The gas supply system
contains gas cylinders (hydrogen of 99.99% purity, Ar-5 vol% H 2 , argon), a vacuum
pump for degassing, and a Kipp generator for the production of hydrogen sulfide.
A flask filled with water is provided for recycling of exhaust gas. The indicated
parts of the experimental stand are connected to the network by plastic tubes with
corresponding one- and three-way taps. A general view of the experimental stand is
given in the photo (Fig. 30.2).
We prepared a quartz chamber, providing a pressure of 0.0133 Pa with a vacuum
pump, and then ran hydrogen sulfide and additional gas in the required proportions.
Exhaust gas was disposed by passing it through a flask with water. The quartz