Multilayer Coating for Corrosion Resistant Metal Bipolar Plate
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Solution Overview
Problem
Metal bipolar plates, such as stainless steel, face issues with elution of elements during fuel cell operation, leading to contamination and performance degradation due to the formation of insulating passive layers and pinholes in coatings, which are costly and prone to scratching.
Innovation Solution
A multi-layer coating comprising alternating oxide-forming layers of titanium or titanium alloys and elution-resistant layers of noble metals or tantalum is applied to the metal substrate, effectively blocking pinholes and providing redundant protection against elution and corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer coating is used to protect metal bipolar plates, then the coating can provide basic corrosion resistance, but it is prone to scratching and pinholes which lead to elution and contamination
Solution Approach 1:
The coating is divided into multiple alternating layers of oxide-forming material (e.g., titanium) and elution-resistant material (e.g., noble metals). This segmentation creates a multi-layer structure where each layer performs a specific function: oxide-forming layers provide corrosion resistance through passive oxide layers, while elution-resistant layers block pinholes and prevent metal elution. The segmented structure addresses the limitations of single-layer coatings by distributing protective functions across multiple layers.
Solution Approach 2:
The invention uses composite material structure combining different types of materials with complementary properties. The oxide-forming layers (titanium, doped titanium, or titanium alloys) form protective oxide barriers, while the elution-resistant layers (noble metals or tantalum) provide pinhole blocking and prevent metal ion release. This composite approach creates a synergistic effect where the combination of materials provides superior protection compared to individual materials alone.
2Reliability
If thicker coating layers are used to block pinholes and prevent elution, then corrosion resistance improves, but material costs and processing complexity increase
Solution Approach 1:
Instead of using a single thick coating layer, the protective function is segmented into multiple thin alternating layers. Each layer is relatively thin, but the cumulative effect of multiple layers provides comprehensive protection against pinholes and elution. This segmentation reduces the total material required while maintaining or improving protective performance, and simplifies processing compared to applying one very thick layer.
Solution Approach 2:
The invention changes the parameters of the coating structure by using multiple thin layers instead of fewer thick layers. The alternating composition of oxide-forming and elution-resistant materials creates a structure where pinholes in one layer are blocked by subsequent layers. This parameter change (from thick single-layer to thin multi-layer) reduces material costs while maintaining protection effectiveness.
3Ease of manufacture
If noble metal layers are made thinner to reduce cost, then material costs decrease, but the coating becomes more susceptible to pinholes and corrosion
Solution Approach 1:
The noble metal elution-resistant layers are segmented into multiple thin alternating layers separated by oxide-forming layers. Each thin noble metal layer is protected by adjacent oxide-forming layers that provide corrosion resistance and block pinholes. This segmentation allows the use of thinner, less expensive noble metal layers while maintaining overall coating reliability through the combined protection of multiple layers with different functions.
Solution Approach 2:
The composite structure combines thin noble metal layers with oxide-forming layers to create a synergistic protective system. The oxide-forming layers (titanium-based) provide corrosion resistance and pinhole blocking, allowing the noble metal layers to be thinner and less expensive. The composite material approach distributes the protective functions, so that reducing noble metal thickness does not compromise overall reliability because the oxide layers compensate for the reduced noble metal protection.
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 multi-layer coating significantly reduces elution and corrosion, enhances the strength and toughness of the bipolar plates, and decreases material and processing costs by using thinner, more cost-effective layers while maintaining electrical conductivity.
Implementation Method 1
the formation of insulating passive layers
Implementation Method 2
a first oxide-forming layer contacting the metal substrate
Implementation Method 3
effectively blocking pinholes and providing redundant protection against elution and corrosion
Implementation Method 4
elution-resistant layers of noble metals or tantalum
Data Source
AI summary
The present disclosure includes a fuel cell bipolar plate including a coating and methods for forming the coating. The bipolar plate may include a steel substrate and a coating contacting the steel substrate. The coating may include a plurality of alternating oxide-forming layers and elution resistant layers. The oxide-forming layers may include pure titanium, doped titanium, or a titanium alloy (e.g. doped/alloyed with niobium, zirconium, vanadium, silver, tantalum, yttrium, scandium, or nitrogen) and the elution resistant layers may include a noble metal or tantalum (e.g., gold, iridium, ruthenium, or tantalum). There may be 2-20 layers each of the oxide-forming layers and the elution resistant layers. The coating may prevent elution of iron ions from the steel substrate, for example, by forming oxide plugs in defects or pinholes in the oxide forming and/or elution resistant layers. The coating may also reduce the total usage of precious metals, such as gold.