Titanium Alloy Separator Surface Conductivity
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Solution Overview
Problem
Current titanium and titanium alloy materials for fuel cell separators face challenges in achieving low contact resistance with carbon and maintaining durability, especially in corrosive environments with fluoride ions and under applied voltage, which limits the fuel cell's lifespan.
Innovation Solution
A titanium material or alloy with a surface structure featuring a titanium hydride layer that is converted to a titanium oxide film through heating in an oxidizing atmosphere, enhancing electrical conductivity and corrosion resistance without relying on platinum group elements or expensive plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive film is present on the titanium surface, then corrosion resistance is improved, but contact-to-carbon electrical conductivity deteriorates
Solution Approach 1:
The invention creates a non-uniform surface structure where the titanium surface contains protrusions and recesses. The protrusions maintain the passive film for corrosion resistance, while the recesses provide direct contact paths to carbon for electrical conductivity. This local differentiation resolves the contradiction between uniform corrosion protection and localized electrical contact.
Solution Approach 2:
The invention pre-forms a specific surface structure with protrusions and recesses before the fuel cell operates. This preliminary structuring ensures that even with the presence of passive film, there are predetermined contact points that maintain low contact resistance throughout the fuel cell's lifespan, avoiding the need to sacrifice durability later.
2Manufacturing precision
If the contact resistance with MEA is reduced by dispersing TiB-based precipitate, then electrical conductivity is improved, but the complexity of the production process increases
Solution Approach 1:
The invention extracts the electrical conductivity function from the bulk material composition (TiB precipitates) and relocates it to the surface morphology (protrusions and recesses). This allows the base titanium material to remain simple while achieving the desired electrical properties through surface structuring, reducing production complexity.
Solution Approach 2:
The surface protrusions and recesses act as intermediaries between the titanium base material and the carbon contact. Instead of modifying the bulk material with complex precipitates, the invention uses the surface structure as a mediator to achieve electrical conductivity while maintaining material simplicity.
3Reliability
If stainless steel is used for the separator, then durability is improved, but contact-to-carbon electrical conductivity deteriorates
Solution Approach 1:
The invention applies local quality differentiation to the titanium surface, creating protrusions that maintain the protective passive film for durability and recesses that provide direct electrical contact paths. This resolves the contradiction by having different surface regions serve different functions.
Solution Approach 2:
The invention creates a composite surface structure combining titanium with its passive film, where the titanium provides durability and the structured surface morphology provides electrical conductivity. This composite approach at the surface level allows both properties to coexist without compromising either.
4Productivity
If the fuel cell stack is compactified by using metal separators, then productivity is improved, but the risk of cracking during production increases
Solution Approach 1:
The invention uses thin film technology to create the surface protrusions and recesses on the titanium separator. This thin film structuring allows the separator to maintain flexibility and resistance to cracking during production while achieving the desired electrical conductivity and corrosion resistance properties for mass production.
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 approach results in a material with stable, low contact resistance and improved durability, effectively prolonging the fuel cell's lifetime by maintaining low contact resistance even in corrosive conditions.
Implementation Method 1
a surface structure in which TiO is distributed on an outer layer and an outermost surface is formed of a titanium oxide film
Implementation Method 2
heating treatment in an oxidizing atmosphere
Data Source
Figure 1~1(c)
Figure 2
Figure 3(a)~3
AI summary
In a titanium material or a titanium alloy material, in an oxide film formed on a surface of a titanium or a titanium alloy, the composition ratio of TiO (ITiO/(ITi + ITiO)) × 100 found from the maximum intensity of the X-ray diffraction peaks of TiO (ITiO) and the maximum intensity of the X-ray diffraction peaks of metal titanium (ITi) in X-ray diffraction measured at an incident angle to the surface of 0.3° is 0.5% or more. A titanium material or a titanium alloy material, and a fuel cell separator and a polymer electrolyte fuel cell having good contact-to-carbon electrical conductivity and good durability can be provided.