Solid Oxide Fuel Cell Air Electrode Dual Porosity Structure
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Solution Overview
Problem
Solid oxide fuel cells (SOFCs) face a challenge in simultaneously enhancing gas diffusivity and bonding strength between electrodes and current-collecting members, as high porosity is beneficial for gas diffusion but detrimental to bonding strength, and vice versa.
Innovation Solution
The SOFC design incorporates a dual porosity structure where the bonding portions with a current-collecting member have a lower porosity to enhance bonding strength, while the remaining portions have a higher porosity to facilitate gas diffusion, allowing for efficient gas passage and increased reaction area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the porosity of the electrode material is increased to enhance gas diffusivity, then the output of the SOFC is improved, but the bonding strength between the electrode and the current-collecting member deteriorates
Solution Approach 1:
The electrode is designed with non-uniform porosity distribution: the gas introduction region has high porosity (30-60%) to enhance gas diffusion and reaction, while the bonding region has low porosity (10-30%) to ensure strong bonding with the current-collecting member. This local differentiation resolves the contradiction between gas diffusivity and bonding strength.
2Reliability
If the porosity of the electrode material is decreased to enhance bonding strength, then the reliability of the SOFC is improved, but the gas diffusivity in the electrode deteriorates
Solution Approach 1:
The electrode structure differentiates porosity by region: the bonding region maintains low porosity (10-30%) for reliable current collection and structural integrity, while the gas introduction region maintains high porosity (30-60%) for efficient gas diffusion and electrochemical reactions, thus achieving both reliability and productivity.
3Ease of manufacture
If the porosity of the electrode is made uniform, then the manufacturing process is simplified, but it becomes impossible to simultaneously achieve high gas diffusivity and high bonding strength
Solution Approach 1:
The electrode employs spatially varying porosity with distinct zones: a high-porosity region for gas diffusion and a low-porosity region for bonding. This can be achieved through controlled fabrication processes such as selective sintering or additive manufacturing, balancing manufacturing feasibility with performance requirements.
Solution Approach 2:
The electrode is segmented into functionally distinct regions with different porosity characteristics. The gas introduction region and bonding region are spatially separated and optimized independently, allowing each zone to perform its specific function optimally without compromising the other.
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 dual porosity structure simultaneously improves gas diffusivity and bonding strength, leading to increased output and reliability of the SOFC by reducing reaction resistance and enhancing the bonding area between electrodes and current-collecting members.
Implementation Method 1
the gas is supplied to a reaction field in the electrode through many pores present in the electrode. From the viewpoint of enhancing diffusivity of the gas in the electrode
Implementation Method 2
a solid electrolyte film bonded to the fuel electrode; and an air electrode that reacts a gas containing oxygen, and that is bonded to the solid electrolyte film so as to sandwich the solid electrolyte film between the fuel electrode and the air electrode
Implementation Method 3
a fuel electrode that is in contact with a fuel gas to react the fuel gas
Implementation Method 4
an air electrode that reacts a gas containing oxygen
Data Source
Figure 1
Figure 2
AI summary
In a solid oxide fuel cell (SOFC) having a fuel electrode, a solid electrolyte film, and an air electrode, which are stacked, a conductive current-collecting mesh is bonded to a surface (upper surface), opposite to a bonding surface (lower surface) with the solid electrolyte film, of the sheet-like air electrode. Plural "bonding portions" that are bonded to the current-collecting mesh and plural "non-bonding portions" that are not bonded to the current-collecting mesh are present on the upper surface of the air electrode. In the air electrode, regions (regions indicated by fine dots in the figure, dense portion) having a porosity smaller than a porosity of the other region (region indicated as white in the figure, porous portion) are respectively formed on the position in the middle of the thickness of the air electrode from each "bonding portion". The average of the porosity of the dense portion is 20% or more and less than 35%, while the average of the porosity of the porous portion is 35% or more and less than 55%. This structure can provide an SOFC that can simultaneously attain the enhancement in the gas diffusivity in the electrode and the enhancement in the bonding strength of the bonding portion between the electrode and the current-collecting member.