Chromium Nitride Coating Adhesion for Fuel Cell Bipolar Plates
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Solution Overview
Problem
Existing bipolar plates for fuel cells, particularly those made of stainless steel, face challenges in achieving low contact resistance and good adhesion of the coating layer, which affects their electrical conductivity and durability during manufacturing processes like stamping.
Innovation Solution
A manufacturing process involving a stainless steel substrate coated with a chromium nitride layer using physical vapor deposition, where the coating layer's surface and interface zones have specific atomic compositions and structures to ensure low oxygen content, enhancing adhesion and conductivity, and the coating is directly applied without intermediate layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a chromium nitride coating layer is applied on a stainless steel substrate using conventional PVD methods, then the coating layer provides corrosion resistance and electrical conductivity, but the contact resistance exceeds 100 mΩ.cm² and adhesion is insufficient during stamping operations
Solution Approach 1:
The patent applies local quality by creating distinct zones within the coating layer with different compositions: a first zone at the substrate interface enriched in chromium and nitrogen for strong adhesion, and a second zone at the surface optimized for low contact resistance. This spatial differentiation of properties resolves the contradiction between adhesion and electrical performance.
Solution Approach 2:
The patent implements preliminary action by controlling the deposition sequence and composition gradients during the PVD process before the stamping operation occurs. The coating is pre-engineered with an adhesion-optimized interface zone that prevents detachment during subsequent manufacturing operations.
2Ease of manufacture
If the coating layer is made thinner to reduce manufacturing cost and improve flexibility, then the electrical conductivity and corrosion resistance are improved, but the adhesion and durability during stamping deteriorate
Solution Approach 1:
The patent resolves this contradiction by making the coating layer thin overall (50-200 nm) for cost and flexibility, while creating a localized first zone at the substrate interface with enhanced chromium and nitrogen concentration that provides exceptional adhesion strength, preventing detachment during stamping despite the reduced overall thickness.
Solution Approach 2:
The patent uses composite material principles by creating a multi-zoned coating structure with different compositional characteristics within the same layer. The first zone has higher Cr and N content for adhesion, while the second zone has optimized composition for electrical properties, achieving both thin-film benefits and durability.
3Reliability
If intermediate layers are added between the stainless steel substrate and chromium nitride coating to improve adhesion, then the coating durability is enhanced, but the manufacturing complexity and contact resistance increase
Solution Approach 1:
The patent applies segmentation by dividing the coating layer into two distinct zones with different compositions rather than using separate intermediate layers. The first zone serves the adhesion function that intermediate layers would provide, while the second zone maintains low contact resistance, eliminating the need for additional manufacturing steps.
Solution Approach 2:
The patent merges the adhesion function (typically provided by intermediate layers) and the electrical conductivity function into a single multi-zoned coating layer. The first zone provides adhesion to the substrate while the second zone provides low contact resistance, combining multiple functions in one integrated structure.
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 process results in bipolar plates with contact resistances below 10 mΩ.cm², improved adhesion, and sustained electrical performance, reducing the risk of coating detachment during manufacturing and operation.
Implementation Method 1
a coating layer 5;5' based on chromium nitride, the coating layer 5;5' optionally comprising oxygen, said coating layer 5;5' being obtained by physical vapor deposition (PVD)
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
The invention relates to a method for manufacturing a metal strip or sheet, which includes: providing a substrate (3) made of stainless steel; and depositing a layer of chromium nitride onto the substrate (3) by physical vapour deposition (PVD) in a deposition facility (14) including a deposition chamber (20) and a chromium target (22) arranged in the deposition chamber (20). The deposition chamber (20) includes a deposition area (30) that has a length strictly shorter than the length of the deposition chamber (20) and at least one first forbidden area (32). During the deposition, the chromium nitride is deposited onto the substrate (3) only in the deposition area (30) and no chromium nitride is deposited onto the substrate (3) in the forbidden area (32).