Porous Carbon Sheet Structure for Gas Flow and Compression Stability
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Solution Overview
Problem
Existing carbon papers for fuel cell gas diffusion layers face challenges in achieving simultaneous high gas permeability, high conductivity, and small residual deformation after compression, leading to performance issues such as clogging and reduced conductivity over time.
Innovation Solution
A porous carbon sheet with short carbon fibers bound by a carbonized resin, featuring a controlled pore size range of 45 to 90 μm, an average fiber diameter of 5 to 20 μm, and a specific density and thickness, produced using a method involving heating and pressurizing between hot plates to optimize gas permeability, conductivity, and compression resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the amount of carbon used as a binder is decreased to lower the density of carbon paper, then gas permeability is enhanced, but the binding points between carbon fibers and carbonized resin decrease, causing resistivity to increase
Solution Approach 1:
The patent utilizes a porous polyolefin foam sheet as the base structure, which provides inherent gas permeability through its closed-cell foam architecture. This eliminates the need to reduce binder content to achieve gas permeability, as the foam structure itself provides the necessary porosity while maintaining structural integrity and electrical conductivity through the carbon fiber network.
Solution Approach 2:
The patent creates a composite structure by impregnating carbon fibers into a porous polyolefin foam sheet. This composite approach allows the foam to provide gas permeability while the carbon fiber network provides conductivity and binding, resolving the trade-off between gas permeability and resistivity by distributing these functions to different materials within the composite.
2Reliability
If graphite particles are added to increase conductivity, then electric resistivity decreases, but the mechanical strength depends on carbon fiber density, causing large residual deformation after compression
Solution Approach 1:
The patent employs a porous polyolefin foam sheet with controlled cell structure that provides both mechanical support and gas permeability. The foam's cellular structure acts as a mechanical framework that resists compression deformation while allowing the carbon fiber network to maintain electrical conductivity without relying solely on graphite particle addition.
Solution Approach 2:
The composite of carbon fibers impregnated into porous polyolefin foam creates a synergistic structure where the foam provides mechanical strength and dimensional stability, while the carbon fiber network provides electrical conductivity. This eliminates the need to add graphite particles that would increase conductivity but compromise mechanical strength.
3Strength
If carbon fiber density is increased to improve mechanical strength, then residual deformation decreases, but gas permeability is reduced
Solution Approach 1:
The patent uses a porous polyolefin foam sheet as the base material, which provides gas permeability through its inherent cellular structure. This allows the carbon fiber density to be optimized for mechanical strength without compromising gas permeability, as the foam structure maintains the necessary porosity independent of carbon fiber content.
Solution Approach 2:
The composite structure separates the functions of gas permeability (provided by the porous foam matrix) and mechanical strength (provided by the carbon fiber reinforcement). This allows both carbon fiber density and gas permeability to be optimized independently, resolving the trade-off between these two properties.
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 solution enables a carbon paper with enhanced gas permeability, conductivity, and reduced residual deformation, effectively addressing the performance limitations of previous carbon papers and maintaining consistent fuel cell performance.
Implementation Method 1
the porous carbon sheet of the invention has all of high gas permeability, high conductivity and small residual deformation
Implementation Method 2
a porous carbon sheet comprising short carbon fibers bound by a carbonized resin
Data Source
AI summary
A porous carbon sheet obtained by binding separate carbon short fibers with a carbonization product of a resin, wherein the pore mode diameter of the sheet is 45 to 90 μm and the mean fiber diameter of the carbon short fibers is 5 to 20 μm. The sheet can be produced by thermoforming a precursor fiber sheet comprising carbon short fibers of 15 to 30 g/m2 in basis weight and a thermosetting resin of 30 to 80 g/m2 in basis weight by hot plates having a certain clearance and carbonizing the thermosetting resin contained in thermoformed precursor fiber sheet.