Novel SOFC Repeating Unit Design for the Uniform Distribution of Temperature and Thermo-Electrochemical Reaction Zone in a Commercial Scale Stack
Authors: Lee Wooseok , Hong Jongsup 
Published: September 2023

Despite the substantial benefits provided by solid oxide fuel cell (SOFC), its low durability at high-temperature hydrocarbon-fueled operations has inhibited widespread market deployment. Thanks to the tremendous efforts of researchers, SOFC has exhibited sufficient performance to compete with other power generation technologies in the market. However, the lifespan problem due to long-term degradation remains the final obstacle for large-scale deployment. Especially when the hydrocarbon is used as fuel to take an advantage of fuel flexibility, carbon deposition can worsen the problem.
A conventional crossflow type stack has the advantage of small volume, which can increase the power and energy density, but suffereing from large nonuniformities of temperature and thermo-electrochemical reactions. However, it has nonuniform temperature and species distribution, where thermo-electrochemical reactions are concentrated at the fuel inlet region. These imbalanced distributions of temperature and species are the major limitation of conventional design since certain regions of the stack are inevitably exposed to a much harsher environment than the remaining regions. For example, nickel reoxidation may occur where fuel is depleted, interfacial separation due to high polarization may appear where electrochemical reactions are concentrated, and carbon deposition may be developed where thermochemical reactions extremely occur. These specific regions might be degraded much faster than the remaining, which can threaten the entire stability of the stack.
In this study, we present the novel SOFC stack design that can solve the instability problem of the conventional crossflow type design. First, the vertical gas manifold holes are rearranged to be placed in all perimeters, symmetrical in both diagonals [1]. Since this arrangement makes the stack consist of four symmetric parts, all thermodynamic variables and chemical reactions are distributed symmetrically, and the temperature gradient in the planar direction can be reduced. Second, the guide rib pattern and flow resistance field in the interconnect are optimized to have uniform gas distribution [2]. Finally, a new component, called a ‘cover’, is added in between the interconnect and cell to control the mass transport in a vertical direction [3]. Through the control of mass transport in the vertical direction, chemical reactions can occur in much larger regions rather than concentrated in the fuel inlet regions. To verify the advantages of the novel design, we compare it with the conventional design through the three-dimensional numerical model [4]. As shown in Figure 1, the nonuniformities of temperature, fuel concentration, and chemical reaction are improved through the design modification. Compared to the conventional design, the standard deviations of each variable in the novel design are decreased by 65.07%, 25.14%, and 20.28%, respectively. Entire design processes, various simulation results, and detailed analysis will be provided.

References

[1] J. Hong, Y.G. Bae, S.H. Lee, D.H. Kim, K.J. Yoon, J.H. Lee. (2020). A separator for a fuel cell and a fuel cell stack comprising the same. US Patent. No. 10840533.
[2] J. Hong, Y.G. Bae, S.H. Lee, D.H. Kim, K.J. Yoon, J.H. Lee. (2021). Separator for fuel cell including guide pattern and fuel cell stack including the same. US Patent. No. 11050065.
[3] J. Hong, W. Lee. (2022), Fuel cell stack including separator having gas equal distribution structure. US Patent Application. No. 18/054712.
[4] S.H. Lee, Y.G. Bae, K.J. Yoon, J.H. Lee, W. Choi, J. Hong. (2018). Key characteristics of a hydrocarbon-fueled solid oxide fuel cell examined by local thermodynamic states. Energy Conversion and Management, 174 (2018) 565-578.

Figure 1