Transition Metal-Doped DLC Coating for Durable Bipolar Plates
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Solution Overview
Problem
Existing coatings for bipolar plates in fuel cells and electrolyzers fail to provide sufficient hardness, leading to dissolution of weakly bonded carbon under harsh operational conditions, resulting in increased interface contact resistance and corrosion, especially in applications requiring longer lifetimes and high voltages.
Innovation Solution
A non-hydrogenated transition metal-doped diamond-like carbon (DLC) coating with a high sp3 fraction and carbide form of transition metals, such as tungsten, is deposited using a cathodic arc discharge method, ensuring a hardness of ≥35 GPa and uniform distribution of transition metals, preventing carbon dissolution and maintaining low interface contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If existing coatings are used for bipolar plates, then the coating can be applied, but the hardness is insufficient leading to carbon dissolution under harsh conditions
Solution Approach 1:
The patent applies composite materials by combining transition metals (groups 4d, 5d, 6d) with carbon to form a DLC coating with embedded metal carbides. This composite structure provides both the hardness of carbide particles and the protective properties of the carbon matrix, resolving the contradiction between hardness and resistance to carbon dissolution.
Solution Approach 2:
The patent changes the chemical composition parameters of the DLC coating by incorporating specific transition metals and controlling the sp3 fraction to ≥60%. This parameter change transforms the coating from a standard DLC to a high-hardness, dissolution-resistant composite DLC, simultaneously improving both hardness and reliability.
2Strength
If the sp3 fraction is increased to improve hardness, then hardness improves, but the coating may become more prone to dissolution under harsh conditions
Solution Approach 1:
The high sp3 fraction DLC matrix combined with embedded transition metal carbides creates a composite structure where the carbides act as reinforcement particles that enhance both hardness and resistance to dissolution, eliminating the trade-off between these properties.
Solution Approach 2:
The patent creates local quality variations by distributing transition metal carbide particles throughout the DLC matrix. The carbide-rich regions provide localized hardness and dissolution resistance, while the sp3-rich carbon matrix provides overall structural integrity and protection.
3Strength
If transition metals are added to improve hardness, then hardness increases, but uniform distribution of metals is difficult to achieve
Solution Approach 1:
The patent controls the concentration of transition metals within 0.1-5 at.% and maintains specific deposition parameters (substrate temperature, pressure, gas flow) to ensure uniform distribution. These parameter controls prevent metal aggregation while achieving the desired hardness through carbide formation.
Solution Approach 2:
The transition metals are incorporated into the DLC coating during the deposition process itself, ensuring uniform distribution from the beginning. This preliminary incorporation prevents subsequent aggregation or segregation that would occur if metals were added after coating formation.
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 coating provides enhanced hardness, reducing friction, improving wear resistance, and maintaining low interface contact resistance and corrosion resistance under severe operational conditions, suitable for extended lifetimes in fuel cells and electrolyzers.
Implementation Method 1
The coating is deposited by a cathodic arc discharge method
Implementation Method 2
a part of the at least one transition metal is present in the form of carbide of the at least one transition metal in the non-hydrogenated DLC as a matrix
Data Source
AI summary
The present invention relates to a metallic bipolar plate comprising a metal substrate and at least one layer of a non-hydrogenated transition metal-doped diamond-like carbon (DLC) provided on the metal substrate, wherein the non-hydrogenated DLC comprises at least one transition metal selected from groups 4d, 5d and 6d of the periodic table of elements and a part of the at least one transition metal is present in the form of carbide of the at least one transition metal in the non-hydrogenated DLC as a matrix. The non-hydrogenated transition metal-doped DLC has an indentation hardness of ≥35 GPa, preferably of ≥40 GPa. The metal-doped DLC used as a coating of metallic bipolar plates in fuel cells and electrolyzers exhibits high corrosion resistance and low interface contact resistance even for longer lifetimes (>10,000 hours) and harsh operational conditions. Therefore, the present invention also pertains to such uses, and also to fuel cells, in particular proton exchange membrane fuel cells, and electrolyzers comprising such coated metallic bipolar plates. Further, the present invention provides a cathodic arc discharge deposition method for depositing a coating of non-hydrogenated DLC comprising at least one of the above-mentioned transition metals, which is preferably the non-hydrogenated transition metal-doped DLC.