Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

1.
 
Introduction 
Continuously increasing population and industrial growth has increased the consumption and 
demand of energy. The total world’s energy consumption showed a steep increment within the 
last 40 years [1]. Fossil fuels are expected to remain the main energy sources in the forthcoming 
decades. However, their combustion is widely recognized as critical, since it contributes strongly 
to global air pollution and global warming [2]. Clean, efficient and environmental-friendly 
energy source are therefore desired to be investigated by engineers and scientists.
In response to the critical need for a cleaner and efficient energy technology, fuel cells are 
considered as one of the most effective solutions to energy and environment problems that we 
face today [3]. A fuel cell is an energy conversion device that converts the chemical energy of a 
fuel gas directly to electrical energy [4, 5]. In this respect solid oxide fuel cells (SOFCs) have 
recently emerged to be a promising technology due to their reliable performance and optional 
wide applications in full-scale industrial and large-scale electricity-generating stations. Small 
SOFC based systems might be even used in mobile applications [3]. A SOFCs system utilizes a 
solid ceramic as electrolyte and operates at rather high temperatures (600-1000°C). They make it 
possible to supply clean energy with high electrical efficiencies of 45-50% and, hence, obvious 
significant environmental benefits [6, 7].
Figure 1-1: Operating principle of a SOFC [8]. 

---

Introduction 
2 
The operating principle is illustrated in 
Figure
1-1
. Fuel flows on the anode side of the SOFC, 
and air on cathode side. The oxygen from the air is ionized, which allows it to permeate the 
electrolyte membrane. Although in principle a SOFC has a very simple structures, it is still a 
challenges with respect to structural design and mechanical stability. After long periods of SOFC 
layer development the main focus concentrates nowadays on planar and tubular designs (
Figure 
1-2
) [9]. Each of these designs has its specific benefits and drawbacks. Tubular design 
demonstrated good mechanical strength and sealing convenience, while the planar design offers 
a higher power density and lower manufacturing costs and therefore attracts increasing interests 
of industry [10-12].
Figure 1-2: a) Tubular design and b) planar SOFC design [9]. 
The planar-designed SOFCs can be distinguished into the electrolyte-supported and the 
electrode-supported concept. The former generally uses a rather thick electrolyte (100-200 µm) 
as mechanical supporting part of the cell. Due to the relatively high ohmic resistance of the thick 
electrolyte, the typical operating temperatures of this concept are 850-1000°C [9]. Since 
electrolyte resistance is the most significant obstacle to reducing the operation temperature, a 
thinner electrolyte is preferred. Then the function of mechanical stabilization is shifted to one of 
the electrodes. In this approach, the anode is mostly favored due to its good electrical 
conductivity, hence, the ohmic resistance does not depend on its thickness [13]. The main 
component of anode-supported SOFC is a multilayered cell consisting of thin electrolyte and 
electrode layers supported by a thick porous anode substrate. 

---

Introduction 
3 
Since the single cell can only generate a limited amount of electricity, metallic interconnectors 
are normally used to connect single cells into a series [14]. A nickel mesh is typically inserted as 
the anode current collector [15]. To prevent the gases from mixing and to provide electrical 
insulation as well as bonding, a gas-tight sealing is essential along the edges of cell layers and 
interconnect layers as well as between individual cells [16]. 
Figure