Porous Electrode Substrate for Fuel Cells Using Oxidized Carbon Fibers
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Solution Overview
Problem
Existing methods for manufacturing porous electrode substrates for fuel cells face challenges such as high production costs, complex processes, uneven thickness due to sintering contraction, and difficulty in entangling carbon fibers and acrylic pulp, leading to low carbonization rates and mechanical strength issues.
Innovation Solution
A method involving the dispersion of short carbon fibers, addition of water-soluble phenolic resin, entanglement treatment, and carbonization at 1000°C or higher to create a porous electrode substrate with improved strength, gas permeability, and conductivity, using a precursor sheet with controlled bulk density and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If short oxidized fibers are used and sintered at high temperatures to reduce costs, then production costs are reduced, but contraction during sintering causes uneven thickness and increased undulation
Solution Approach 1:
The patent changes the chemical composition parameter by using oxidized carbon fibers instead of conventional carbon fibers, and controls the sintering temperature parameter to achieve carbonization while minimizing contraction. This allows cost reduction through material substitution while maintaining thickness uniformity through optimized processing parameters.
Solution Approach 2:
The patent creates a composite structure by forming a sheet from short oxidized fibers and binding them through sintering to form a carbonized composite material. This composite approach enables both cost reduction and dimensional stability by utilizing the properties of oxidized fibers that undergo controlled carbonization.
2Ease of manufacture
If carbon fibers and acrylic pulp are combined to reduce costs, then production costs are reduced, but the fibers do not entangle well causing difficulty in handling
Solution Approach 1:
The patent replaces expensive carbon fibers with cheaper oxidized carbon fibers that can be processed and carbonized in situ. This substitution reduces material costs while the carbonization process transforms the oxidized fibers into a form that entangles and bonds effectively, resolving the handling issue.
Solution Approach 2:
The patent changes the physical and chemical parameters of the fiber material by using oxidized carbon fibers with specific surface properties that enhance entanglement and bonding during sintering. This parameter change enables both cost reduction and improved handling characteristics through better fiber interaction.
3Ease of manufacture
If acrylic pulp is used to reduce costs, then production costs are reduced, but the carbonization rate is low requiring much acrylic pulp to be added
Solution Approach 1:
The patent uses oxidized carbon fibers as a cost-effective substitute for acrylic pulp, eliminating the need for large quantities of carbonizing agents. The oxidized fibers themselves serve as the carbon source, reducing material requirements and production costs simultaneously.
Solution Approach 2:
The patent changes the carbonization characteristics by using oxidized carbon fibers that have pre-treated surface chemistry enabling efficient carbonization at lower temperatures and with shorter processing times. This parameter change reduces both the amount of material needed and the production cost.
4Strength
If conventional carbon fiber sheets are used to ensure mechanical strength, then sheet strength is maintained, but the manufacturing process becomes complex and costs increase
Solution Approach 1:
The patent creates a composite material system where short oxidized fibers are combined and carbonized to form a strengthened sheet structure. This composite approach achieves the mechanical strength of conventional carbon fiber sheets while simplifying the manufacturing process by eliminating complex fiber alignment and bonding steps.
Solution Approach 2:
The patent changes the manufacturing parameters by using oxidized carbon fibers that require simpler processing conditions compared to conventional carbon fibers. The oxidized state enables lower temperature processing and simpler handling, reducing manufacturing complexity while maintaining sheet strength through controlled carbonization.
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 method results in a porous electrode substrate with enhanced mechanical strength, reduced production costs, and excellent gas permeability and conductivity, suitable for use in membrane electrode assemblies and polymer electrolyte fuel cells.
Implementation Method 1
a step for carbonizing the precursor sheet at a temperature of 1000° C. or higher
Data Source
AI summary
According to the present invention, a porous electrode substrate with greater sheet strength, lower production cost, and excellent gas permeability and conductivity as well as its manufacturing method are provided. Also provided are a precursor sheet for forming such a substrate, and a membrane electrode assembly and a polymer electrolyte fuel cell containing such a substrate. The method for manufacturing such a porous electrode substrate includes the following steps [1]˜[3]: [1] a step for manufacturing a sheet material in which short carbon fibers (A) are dispersed; [2] a step for manufacturing a precursor sheet by adding a water-soluble phenolic resin and/or water-dispersible phenolic resin to the sheet material; and [3] a step for carbonizing the precursor sheet at a temperature of 1000° C. or higher. The present invention also relates to a porous electrode substrate obtained by such a manufacturing method as well as a precursor sheet to be used for manufacturing the substrate, a membrane electrode assembly and a polymer electrolyte fuel cell.