Fuel Cell Stack Solid Electrolyte Layer Thermal Stress Management
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Solution Overview
Problem
In a fuel cell stack, the center fuel cells experience uneven thermal expansion due to differences in thermal conductivity between the fuel cells and current collecting members, leading to potential damage to the solid electrolyte layer during startup.
Innovation Solution
The fuel cell stack incorporates a zirconia-based solid electrolyte layer with varying concentrations of tetragonal and cubic crystal zirconia, as determined by Raman spectrum analysis, to manage thermal stress across the stack, with higher concentrations in center fuel cells and lower in end fuel cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the fuel cell stack uses uniform heating during startup, then the current collecting members heat up rapidly due to high thermal conductivity, but the center fuel cell experiences uneven thermal expansion and stress damage due to lower thermal conductivity
Solution Approach 1:
The patent applies local quality by varying the crystal phase composition of zirconia in the solid electrolyte layer according to position. Center fuel cells contain tetragonal crystal zirconia (3-10 wt%) to increase thermal conductivity and reduce thermal stress, while end fuel cells contain only cubic crystal zirconia. This localized material property adjustment addresses the thermal conductivity imbalance caused by uniform heating.
Solution Approach 2:
The patent changes the chemical composition parameter of the solid electrolyte layer by controlling the content of tetragonal crystal zirconia. Center fuel cells have 3-10 wt% tetragonal zirconia while end fuel cells have 0 wt%, creating a gradient structure that modifies thermal conductivity and thermal expansion characteristics to match the heating pattern during startup.
2Stability of the object's composition
If the solid electrolyte layer uses cubic crystal zirconia for high stability, then the structural stability is improved, but the thermal conductivity is insufficient to handle rapid temperature changes during startup
Solution Approach 1:
The patent creates a composite material structure by combining cubic crystal zirconia (providing structural stability) with tetragonal crystal zirconia (providing enhanced thermal conductivity). The solid electrolyte layer contains 90-97 wt% cubic zirconia and 3-10 wt% tetragonal zirconia in center fuel cells, creating a composite that achieves both stability and thermal management.
Solution Approach 2:
The patent applies local quality by selectively adding tetragonal crystal zirconia only to center fuel cells where thermal conductivity is most needed. The end fuel cells maintain pure cubic zirconia composition, creating a spatially varying material property that optimizes performance for each position's thermal environment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration inhibits damage to the solid electrolyte layer by strengthening the framework structure, reducing thermal stress and maintaining electric conductivity, thereby enhancing the durability and performance of the fuel cell stack.
Implementation Method 1
there is a difference in the degree of thermal expansion of a fuel cell and a current collecting member that is connected thereto
Implementation Method 2
since the thermal conductivity of a current collecting member is high when compared to the fuel cell
Data Source
AI summary
A fuel cell stack includes seven current collecting members and six fuel cells that are alternate stacked with reference to the stacking direction. Each of the six fuel cells includes an anode, a cathode and a solid electrolyte layer that is disposed between the anode and the cathode and contains a zirconia-based material as a main component. The six fuel cells include a first fuel cell disposed in the center with reference to the stacking direction, and a second fuel cell disposed in one end with reference to the stacking direction. An intensity ratio of tetragonal crystal zirconia to cubic crystal zirconia in a Raman spectrum of the solid electrolyte layer of the first fuel cell is greater than an intensity ratio of tetragonal crystal zirconia to cubic crystal zirconia in a Raman spectrum of the solid electrolyte layer of the second fuel cell.