Layered Carbon Sheet for Fuel Cell Gas Diffusion Electrode
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Solution Overview
Problem
Conventional gas diffusion electrode substrates in polymer electrolyte fuel cells face issues with flooding and delamination, particularly at low temperatures and high current densities, due to water retention and mechanical weaknesses in the carbon sheet structure.
Innovation Solution
A porous carbon sheet with specific layering and filling rate distribution, where the layer 2 has the largest filling rate and layer 3 has the second largest, ensuring proper penetration of the microporous layer and reducing delamination, is used to enhance anti-flooding characteristics and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a microporous layer is provided on a carbon sheet with highest density at one surface, then the carbon sheet has high mechanical strength, but the microporous layer does not penetrate into the carbon sheet and an interface is formed where water is easily retained causing flooding
Solution Approach 1:
The carbon sheet is designed with non-uniform density distribution where the second layer from the surface has the largest filling rate and the third layer has the second largest filling rate, creating locally optimized regions that balance mechanical strength and microporous layer penetration while preventing water retention interfaces
2Strength
If the carbon sheet has high resin density to prevent delamination, then mechanical strength is improved, but gas diffusivity decreases and water removal performance deteriorates
Solution Approach 1:
Different layers of the carbon sheet have different filling rates optimized for their specific functions: layers closer to the surface have higher filling rates for strength and delamination resistance, while deeper layers have lower filling rates to maintain gas diffusivity and water removal performance
Solution Approach 2:
The carbon sheet is divided into six layers with varying filling rates, allowing each layer to be optimized independently for either mechanical strength or mass transport properties, resolving the contradiction between delamination resistance and water removal performance
3Reliability
If the carbon sheet structure is optimized for water removal with lower density regions, then flooding is prevented, but mechanical strength decreases causing delamination in production and use
Solution Approach 1:
The carbon sheet implements spatially varying filling rates where surface-near layers (layer 2 and 3) have high filling rates for mechanical strength, while inner layers have lower filling rates for water removal, achieving both anti-flooding characteristics and delamination resistance simultaneously
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
The carbon sheet effectively suppresses internal delamination and flooding, maintaining high fuel cell performance by ensuring efficient water removal and mechanical integrity.
Implementation Method 1
when a microporous layer is provided, the microporous layer does not penetrate into the carbon sheet
Implementation Method 2
high water removal performance for discharging water generated by the electrochemical reaction to the bipolar plate
Data Source
AI summary
The purpose of the present invention is to provide a carbon sheet that is suitably employed in a gas-diffusion-electrode substrate that has excellent flooding resistance and with which it is possible to suppress internal peeling of the carbon sheet. In order to achieve the aforementioned purpose, the present invention has the following configuration. Specifically, provided is a porous carbon sheet containing carbon fibers and a binder, wherein, in a section between a surface on one side of the carbon sheet and a surface on the other side thereof, when layers obtained by dividing, under compression, the carbon sheet into six equal parts in the thickness direction are assumed to be layer 1, layer 2, layer 3, layer 4, layer 5, and layer 6, in order starting from the layer including the surface on the one side to the layer including the surface on the other side, the layer in which the packing ratio under compression is the greatest is layer 2, and the relationships of the packing ratios under compression among layer 2, layer 3, layer 4, layer 5, and layer 6 are such that layer 2 has the greatest packing ratio, and layer 3 has the second-greatest packing ratio.