Crack propagation of planar and corrugated solid oxide fuel cells during cooling process

Ghassemi

Env Prog and Sustain Energy

2020

Converting chemical energy into electricity is done by an electrochemical device known as a fuel cell. Thermal stress is caused by high operating temperature, between 700 and 1,000 C, of solid oxide fuel cell (SOFC). Thermal stress is the main cause of crack initiation and crack propagation. This phenomenon may cause gas leakage, structure instability and cease operation of the SOFC before its lifetime. The aim of this study is to present a method that predicts the initiation of cracks in an anisotropic porous planar SOFC. The coupled governing nonlinear differential equations are solved numerically as for heat transfer, fluid flow, mass transfer, mass continuity, and momentum. An in-house computer code which is based on computational fluid dynamics, computational structural mechanics and extended finite element method is utilized and developed. This code, according to Darcy and Navier-Stokes thermofluid model, determines the temperature and stress distribution. The results show that the highest thermal stress occurs at the upper corners of cathode and at the lower corners of the anode. The maximum temperature occurs at the middle of the electrolyte cathode and electrolyte anode, while the maximum pressure occurs at the middle of the upper and lower section of the anode and cathode. In addition, the thickness of the cathode electrode at the left side is increased by 1.5%. Finally, the crack initiation occurs at the left side between the upper and lower corners of the cathode.

“…Substituting Equations (20) and (21) into Equation (19) gives the displacement equations in terms of Young's modulus as follows, respectively 28 :…”

Section: Navier Equationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical study of detecting crack initiation in a planar solid oxide fuel cell

Ghassemi

Env Prog and Sustain Energy

2020

“…Hydrogen and air are supplied as fuel and oxygen for the chemical reaction in SOFC, respectively. Generally, nickel (Ni), strontium‐doped lanthanum manganite (LSM), and yttria‐stabilized zirconia (YSZ) are chosen as the materials of the anode, cathode, and electrolyte, respectively 10,11 . The oxygen enters into the cathode and hydrogen enters into the anode during SOFC operation.…”

Section: Oxidation Mechanism Of Oxide Layermentioning

confidence: 99%

Chemo‐mechanical coupling model of solid oxide fuel cell under high‐temperature oxidation

2020

Self Cite

Summary Solid oxide fuel cell (SOFC), which is a generation device that converts chemical energy into electrical energy, has been regarded as a new generation device. The diffusion mechanism of metal cations and anions during the high‐temperature oxidation process of SOFC is proposed. Based on the equilibrium expression and diffusion equation, the chemo‐mechanical coupling relationship between oxide stress and thickness growth of the oxide layer is established by considering the influences of viscoplastic effect and oxide growth effect. The present theoretical result is consistent with the previous experimental results. In addition, the stress critical points corresponding to different parameters are different in initial oxidation stage. The oxide stress varies dramatically with time in the compressive stress phase, but it changes slowly in the tensile stress phase. The compressive stress that exists in the oxide layer increases with the growth coefficient (DNiO = 1000‐15 000 m−1) of the oxide layer. The oxide stresses in oxide layer and electrolyte reduce with viscoplastic coefficient of the oxide layer from JNiO = 8.97 × 10−5 Pa−1 s−1 to JNiO = 16.97 × 10−5 Pa−1 s−1 and anode‐oxide layer thicknesses from H = 30 μm to H = 660 μm, while they increase with viscoplastic coefficient of the anode from JNi = 3.81 × 10−5 Pa−1 s−1 to JNi = 12.81 × 10−5 Pa−1 s−1 and kinetic parabolic constant from k p = 2.9 × 10−15 m2s−1 to k p = 12.9 × 10−15 m2s−1 in whole oxidation stage. The oxide thickness increases with kinetic parabolic constant in the whole oxidation stage and this changing trend accords with parabolic diffusion law. The oxide thickness increases with temperatures increasing. The results obtained from this study will provide the reference to the researches of the chemo‐mechanical coupling model and performance optimization of SOFC under high‐temperature oxidation.

“…Results showed that the cermet damaged in an area close to the anode‐electrolyte interface and that a delamination can occur along the interface between the anode functional layer (AFL) and the anode support layer (ASL). Xie et al investigated the crack propagation of planar and corrugated solid oxide fuel cells during cooling process and found that for the corrugated SOFC, the cracks propagate more slowly and the cell is less prone to interfacial delamination compared with planar SOFC.…”

Section: Introductionmentioning

confidence: 99%

Effect of interface morphology on the residual stress distribution in solid oxide fuel cell

Cao

et al. 2020

Int J Energy Res

Summary Solid oxide fuel cell directly and efficiently converts chemical energy to electrical energy. However, the necessity for high operating temperatures can result in mechanical failure. Fuel cell is a multilayer system and its stress distribution is greatly affected by the interface morphology. In this work, cosine interfaces with different amplitudes are used to approximate the fluctuation of actual interface. The effects of interface morphology on stress state, energy release rate of crack and creep behavior have been investigated. The results show that if the interface is planar, the residual normal stress component is zero on the interface, while the nonplanarity of interface can cause the normal stress Sn and shear stress St on the interface. When the amplitude is relatively small, the max values of Sn and St on the interfaces vary linearly with increasing amplitudes in both anode and cathode. Above a certain value, nonlinearity of the interface becomes important. Max tensile Sn always occurs at the peak of convex interface, but the position of max compressive Sn varies. Max shear stress is prone to occur at 1/4 of the wavelength at small amplitude and moves towards 1/2 of the wavelength when the amplitude increases. Fracture mechanics analysis shows that the surface crack possibly penetrates into the anode function layer and then is constrained by the stiff electrolyte. On the other hand, the horizontal crack likely penetrates into the electrolyte layer when the interface is not planar. Creep analysis shows that 11 800 hours of continuous operation at high temperature cannot remove stress undulation introduced by nor‐planar interface but can make max value of Sn and St decrease around 30%.