Multi-layered Carbon Substrate for Fuel Cell Gas Diffusion
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Solution Overview
Problem
Fuel cell gas diffusion layers (GDLs) face challenges with mechanical strength, durability, and gas diffusion performance due to high pressure from metal bipolar plates, leading to intrusion into flow fields and reduced efficiency.
Innovation Solution
A multi-layered carbon substrate with unit carbon substrates oriented in the machine direction and stacked to enhance mechanical strength and gas diffusion properties, featuring a higher ratio of carbon fibers in the machine direction than the transverse direction, and a pore size gradient to improve elasticity and resistance against pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal bipolar plate is used to decrease fuel cell price and increase energy density, then stacking pressure increases, but the GDL collapses and mechanical strength deteriorates
Solution Approach 1:
The GDL is divided into multiple layers (first GDL layer, second GDL layer, third GDL layer) with different carbon fiber orientations. This segmentation allows each layer to contribute differently to mechanical strength and gas diffusion, enabling the structure to withstand high stacking pressure while maintaining performance
Solution Approach 2:
Different regions of the GDL have different carbon fiber orientations optimized for their specific functions: the first layer has fibers oriented at 0° to the flow field direction for strength, the second layer has fibers oriented at 90° for gas diffusion, and the third layer has fibers oriented at 0° again for structural support. This local optimization resolves the contradiction between strength and pressure resistance
2Volume of moving object
If GDL thickness is reduced to shrink fuel cell stack volume, then gas diffusion performance improves, but mechanical strength decreases
Solution Approach 1:
The thin GDL is segmented into three functional layers with specific thickness ratios. This allows the overall thickness to be reduced for compactness while each layer contributes to mechanical strength through optimized fiber orientation, preventing collapse despite the reduced total thickness
Solution Approach 2:
The GDL uses a composite structure combining carbon fibers with different orientations in each layer. This composite approach enables the thin structure to achieve both reduced volume and sufficient mechanical strength by leveraging the complementary properties of differently oriented fibers
3Strength
If carbon fibers are irregularly arranged in isotropic structure, then manufacturing is simplified, but carbon fibers break and compress under pressure causing intrusion into flow fields
Solution Approach 1:
Instead of uniform isotropic arrangement, the patent implements local quality control by orienting carbon fibers in specific directions (0° and 90° to flow field) in different layers. This directional arrangement provides resistance against intrusion while maintaining manufacturing feasibility through controlled fiber placement
4Productivity
If porous bipolar plate is used to distribute air and generate turbulence, then gas distribution improves, but pressure applied to GDL increases causing collapse
Solution Approach 1:
The GDL is segmented into layers with different orientations to handle the high pressure from porous bipolar plates. The first and third layers with 0° orientation provide structural support against pressure, while the middle layer with 90° orientation maintains gas diffusion pathways, resolving the contradiction between productivity and pressure resistance
Data Source
Figure 1A~1B
Figure 2a~2b
Figure 3(a)~3(d)
AI summary
Provided is a carbon substrate for a gas diffusion layer of a fuel cell, and the carbon substrate has a structure, in which a plurality of unit carbon substrates are stacked, wherein each of the unit carbon substrates is a plate type substrate having a first surface and a second surface opposite to the first surface, carbon fibers are randomly arranged on the first surface of the each unit carbon substrate, the number of the carbon fibers arranged in a machine direction of the unit carbon substrate is greater than the number of carbon fibers arranged in a transverse direction of the unit carbon substrate from the first surface to the second surface along a thickness direction of the unit carbon substrate, and accordingly, an orientation gradient, in which the orientation in the machine direction increases from the first surface to the second surface, is shown.