Fe-Cr Alloy Bipolar Plates with Conductive Coatings

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Solution Overview

Problem

Metallic bipolar plates in fuel cell stacks are susceptible to corrosion, which increases membrane and contact resistance, reducing power density, and stainless steels, while corrosion-resistant, are not optimally utilized due to lack of effective electrochemically conductive and corrosion-resistant coatings.

Innovation Solution

Bipolar plates made from an Fe-Cr alloy with surface coatings of graphitic, molybdenum doped indium oxide, Cr+N, or MoSi2 layers are used, providing enhanced electrical conductivity and corrosion resistance, reducing interfacial contact resistance and improving durability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If metallic bipolar plates are used in fuel cell stacks, then electrical conductivity is improved, but corrosion resistance deteriorates leading to increased membrane and contact resistance

Engineering Contradiction:

Improveelectrical conductivityVSAvoidcorrosion resistance

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent applies composite materials by combining metallic bipolar plates (Fe-Cr alloy) with non-metallic coating layers (graphite, PTFE, or diamond-like carbon). This composite structure allows the metal substrate to provide electrical conductivity while the coating layer provides corrosion resistance, resolving the contradiction between electrical conductivity and corrosion resistance.

Inventive Principle:

Principle #40Composite materials

2Reliability

If stainless steel bipolar plates are used, then corrosion resistance is improved, but electrical conductivity deteriorates due to lack of effective coatings

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidelectrical conductivity

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent creates a composite structure where the stainless steel Fe-Cr alloy substrate provides corrosion resistance while specialized coating layers (graphite, PTFE, or diamond-like carbon) are applied to ensure electrical conductivity. This resolves the contradiction by allowing both properties to coexist in different parts of the composite structure.

Inventive Principle:

Principle #40Composite materials

3Reliability

If thick coatings are applied to bipolar plates, then corrosion resistance is improved, but contact resistance increases

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidcontact resistance

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent employs thin film coatings (graphite, PTFE, or diamond-like carbon) that are sufficiently thin to maintain good electrical contact and low contact resistance, yet thick enough to provide adequate corrosion protection. This thin film approach resolves the contradiction between corrosion resistance and contact resistance.

Inventive Principle:

Principle #30Flexible shells and thin films

4Ease of manufacture

If no coating is applied to metallic bipolar plates, then manufacturing simplicity is improved, but durability deteriorates due to corrosion

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoiddurability

Core Design Contradiction:

Ease of manufactureVSDuration of action of stationary object

Solution Approach 1:

The patent uses composite materials with Fe-Cr alloy substrate and thin coating layers that can be applied through relatively simple processes. The coating provides durability against corrosion while the overall manufacturing process remains straightforward, resolving the contradiction between manufacturing simplicity and durability.

Inventive Principle:

Principle #40Composite materials

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 use of these coatings on Fe-Cr alloy bipolar plates enhances the electrochemical stability and conductivity, reducing corrosion and contact resistance, thereby increasing the power density and longevity of fuel cell stacks.

Implementation Method 1

Respective surface portions of the bipolar plates are provided with electrically conductive, corrosion resistant layers

Methodology Applied

Scientific EffectElectron conduction: Conduction (electrical)

Implementation Method 2

molybdenum doped indium oxide layers, an electrically conductive Cr+N layer, or an electrically conductive MoSi2 layer

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

an electrically conductive Cr+N layer

Methodology Applied

Scientific EffectNitriding: Nitriding

Data Source

PatentUS7771858B2Coated steel bipolar plates

Publication Date: 2010.08.10 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

In accordance with one embodiment of the present invention, an electrochemical conversion assembly comprises a plurality of electrochemical conversion cells and a plurality of electrically conductive bipolar plates. The electrochemical conversion cells are configured to communicate with first and second reactant supplies. Adjacent ones of the electrochemical conversion cells are separated by respective ones of the plurality of bipolar plates. The bipolar plates comprise an alloy comprising Fe and Cr. Respective surface portions of the bipolar plates are provided with electrically conductive, corrosion resistant layers that are placed in contact with portions of the electrochemical conversion cells. The corrosion resistant electrically conductive layers may comprise graphitic layers characterized predominantly by sp2 hybridized carbon-carbon bonding, molybdenum doped indium oxide layers, an electrically conductive Cr+N layer, or an electrically conductive MoSi2 layer.