Fuel Cell Cathode Corrosion Mitigation via Re-circulation and Shorting
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Solution Overview
Problem
Fuel cell systems experience significant cathode carbon corrosion due to pressure differentials and air/hydrogen fronts during shut-down and start-up, leading to reduced catalyst support and performance, despite existing mitigation techniques like air purge and cathode re-circulation, which can be improved.
Innovation Solution
Combining cathode re-circulation and stack short-circuiting techniques at system shut-down and start-up, utilizing a compressor for air flow, a hydrogen source, switches for power management, a cross-over valve, and a controller to selectively control the re-circulation and short-circuiting processes, minimizing air/hydrogen front residence time and potential drops across the membrane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If air purge is used to remove hydrogen from anode at shut-down, then hydrogen removal is improved, but cathode carbon corrosion increases due to air/hydrogen front
Solution Approach 1:
The system performs preliminary action by initiating cathode re-circulation before the air/hydrogen front reaches the cathode, and by pre-positioning the anode crossover valve to control when air enters the anode. This timing prevents the corrosive front from forming or minimizes its exposure time to the cathode carbon layer.
Solution Approach 2:
The patent introduces an intermediary mechanism - the anode crossover valve - that controls the timing and location where air enters the anode side. This valve acts as a mediator between the air supply and the membrane, allowing hydrogen removal while delaying air exposure until the hydrogen has sufficiently cleared, thus protecting the cathode from corrosion.
2Object-affected harmful factors
If cathode re-circulation is used to reduce oxygen, then cathode corrosion is reduced, but system complexity increases
Solution Approach 1:
The cathode re-circulation system performs multiple functions: it removes oxygen from the cathode to prevent corrosion, it manages water condensation during shut-down, and it prepares the system for rapid restart. By combining these functions into a single re-circulation loop controlled by existing valves, the patent avoids adding excessive complexity while achieving multiple protective goals.
Solution Approach 2:
The cathode re-circulation system uses the system's own resources - recirculating existing cathode exhaust gas back through the cathode - rather than introducing external substances or complex additional systems. This self-service approach reduces corrosion using materials already present in the system.
3Object-affected harmful factors
If high purge rates are used to decrease front residence time, then corrosion is reduced, but energy consumption increases
Solution Approach 1:
The system performs preliminary hydrogen removal from the anode using low-power ventilation or residual flow before activating high-power compressor purge. This preliminary action removes the bulk of hydrogen without requiring maximum compressor power, reducing overall energy consumption while still achieving corrosion protection.
Solution Approach 2:
The patent uses periodic or staged purging rather than continuous high-rate purging. The anode crossover valve is opened in controlled stages, allowing hydrogen removal in phases. This periodic action reduces the average power requirement compared to sustained high-rate purging, while still achieving the goal of minimizing front residence time.
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
Effectively reduces cathode carbon corrosion by managing gas flows and potentials, ensuring minimal corrosion and optimal performance during fuel cell operation by controlling gas flows and potentials across the membrane.
Implementation Method 1
This hydrogen gas is able to diffuse through or cross over the membrane and react with the oxygen in the cathode side
Implementation Method 2
The air purge also creates an air/hydrogen front that causes the cathode carbon corrosion, as discussed above. Thus, it is desirable to reduce the air/hydrogen front residence time to be as short as possible, where the front residence time is defined as the anode flow channel volume divided by the air purge flow rate. Higher purge rates will decrease the front residence time for a fixed anode flow channel volume.
Implementation Method 3
it is known to pump a mixture of air and a small amount of hydrogen through the cathode side of the stack at system shut-down so that the hydrogen and oxygen combine in the cathode side to reduce the amount of oxygen, and thus the potential that causes the carbon corrosion
Implementation Method 4
a third switch connects power from the stack to a shorting resistor
Data Source
AI summary
A fuel cell system that employs a process for minimizing corrosion in the cathode side of a fuel cell stack in the system by combining cathode re-circulation and stack short-circuiting at system shut-down and start-up.