Silicon Oxide Carbon Bilayer Coatings for Fuel Cell Bipolar Plates
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Solution Overview
Problem
Bipolar plates in fuel cells face challenges with high contact resistance and corrosion, particularly due to the passive oxide film on metallic surfaces, which requires expensive coatings and leads to metal dissolution, affecting the efficiency and durability of the fuel cells.
Innovation Solution
A silicon oxide-coated carbon bilayer is applied to the metal plates, reducing contact resistance to less than 40 mohm-cm2 and improving corrosion resistance by creating a hydrophilic surface with a contact angle less than 30 degrees, enhancing water management and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallic bipolar plates are used, then mechanical strength is improved, but contact resistance increases due to passive oxide film formation
Solution Approach 1:
The patent applies a composite coating structure consisting of a bottom layer (e.g., titanium nitride or other adhesion-promoting layer) and a top carbon layer. This composite structure combines the benefits of metal substrate strength with the electrical conductivity of carbon, resolving the contradiction between mechanical strength and contact resistance. The bottom layer ensures strong adhesion to the metal substrate while the carbon top layer provides low contact resistance.
Solution Approach 2:
The patent modifies the surface properties of the bipolar plate by applying coatings that change the electrical and chemical parameters of the surface. The carbon coating specifically changes the surface conductivity parameter, reducing contact resistance from typical metallic values to carbon-like low resistance values while maintaining the underlying metal's mechanical properties.
2Reliability
If expensive electrically conductive coatings are applied, then contact resistance is reduced, but manufacturing cost increases
Solution Approach 1:
The patent applies coating only to specific areas where electrical contact is needed, such as the flow channel surfaces and contact areas with gas diffusion layers. This localized coating approach reduces the amount of expensive coating material required while still achieving the desired low contact resistance performance at critical interfaces.
Solution Approach 2:
The patent uses carbon-based coatings which, while providing excellent electrical conductivity, are generally more cost-effective than noble metal coatings like gold. The coating process parameters are optimized to achieve adequate thickness and performance without excessive material usage, balancing cost and performance.
3Reliability
If titanium nitride coatings are applied, then corrosion resistance is improved, but water affinity decreases with contact angle close to 60°
Solution Approach 1:
The patent creates a composite coating system where the bottom layer (e.g., titanium nitride) provides corrosion resistance and the top carbon layer provides hydrophilic properties for effective water management. This composite structure allows each layer to perform its specialized function, achieving both corrosion protection and proper water transport.
Solution Approach 2:
The patent differentiates the surface properties of different regions of the bipolar plate. The flow channel surfaces are coated with hydrophilic carbon to promote water removal, while other areas may have different coating compositions optimized for their specific functions. This local differentiation of surface properties enables effective water management throughout the cell.
4Strength
If metal bipolar plates are used, then mechanical strength is improved, but corrosion occurs leading to metal dissolution
Solution Approach 1:
The patent extracts the corrosive metal surface from the system by applying a protective carbon-based coating that acts as a barrier between the metal substrate and the corrosive fuel cell environment. This coating prevents direct contact between the metal and corrosive species, eliminating the source of metal dissolution while preserving the mechanical strength of the metal substrate.
Solution Approach 2:
The patent employs a composite structure with an inner corrosion-resistant layer (such as titanium nitride or other protective coating) and an outer carbon layer. This composite provides dual protection: the inner layer prevents corrosion of the metal substrate, while the outer carbon layer provides electrical conductivity and chemical stability in the fuel cell environment.
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 silicon oxide-coated carbon bilayer effectively reduces contact resistance and corrosion, improving the efficiency and durability of fuel cells by maintaining stable performance over time and reducing operational costs.
Implementation Method 1
improving corrosion resistance by creating a hydrophilic surface with a contact angle less than 30 degrees
Implementation Method 2
A carbon layer is disposed over at least a portion of the metal plate while a silicon oxide layer is disposed over at least a portion of the carbon layer
Data Source
AI summary
A flow field plate for fuel cell applications includes a metal with a carbon layer disposed over at least a portion of the metal plate. The carbon layer is overcoated with a silicon oxide layer to form a silicon oxide/carbon bilayer. The silicon oxide/carbon bilayer may be activated to increase hydrophilicity. The flow field plate is included in a fuel cell with a minimal increase in contact resistance. Methods for forming the flow field plates are also provided.