Fuel Cell Stack Shutdown Oxygen Diffusion Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for switching off fuel cell systems do not effectively prevent oxygen diffusion into cathode chambers during shutdown, leading to carbon corrosion and oxide formation, which reduces the system's protection duration and service life.
Innovation Solution
A method involving maintaining cathode chambers under excess pressure with an oxygen-depleted gas mixture, expanding this gas mixture through the cathode supply and exhaust paths, and separating the cathode chambers from the environment to prevent oxygen ingress, using existing adjusting means like valves or flaps to maintain pressure and extend the inert gas atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel cell stack is shut down without maintaining oxygen exclusion, then the shutdown process is simple and quick, but oxygen penetrates into the anode chambers causing carbon corrosion and oxide formation that reduces service life
Solution Approach 1:
The patent applies preliminary action by maintaining an oxygen-depleted atmosphere in the cathode chambers during the shutdown period before restart. The cathode chambers are kept under excess pressure with oxygen-depleted gas mixture from the moment shutdown is initiated, ensuring that when the system restarts, no atmospheric oxygen has penetrated into the anode chambers to cause carbon corrosion or oxide formation on catalytic materials.
Solution Approach 2:
The patent creates an inert atmosphere by filling the cathode chambers with an oxygen-depleted gas mixture (primarily nitrogen and water vapor from diffusion processes) during shutdown. This inert environment prevents oxygen from reaching the anode chambers and reacting with the catalytic materials, thereby protecting the fuel cell stack during the idle state between shutdown and restart.
2Reliability
If hydrogen is used to flush and react with oxygen in cathode chambers during shutdown, then oxygen is chemically bound and removed, but hydrogen consumption increases and the reaction proceeds slowly in a diffusion-controlled manner
Solution Approach 1:
The patent extracts oxygen from the cathode chambers by maintaining excess pressure with oxygen-depleted gas mixture, which prevents oxygen diffusion into the anode chambers. Instead of using hydrogen to chemically react with and bind oxygen (which would consume hydrogen), the system simply excludes oxygen through pressure differential, thereby removing the need for hydrogen consumption for oxygen removal.
Solution Approach 2:
The system uses its own existing resources - the oxygen-depleted gas mixture already present in the cathode chambers from normal operation - to maintain protection during shutdown. The gas mixture naturally contains nitrogen and water vapor from diffusion processes, and by maintaining excess pressure with this existing mixture, the system protects itself without requiring additional hydrogen supply or external flushing operations.
3Ease of operation
If atmospheric oxygen is allowed to penetrate into anode chambers during shutdown, then the shutdown procedure is simpler, but upon restart the air-air start causes carbon corrosion and oxide formation on catalytic materials
Solution Approach 1:
The patent applies preliminary anti-action by preemptively maintaining oxygen exclusion in the cathode chambers during shutdown, preventing oxygen from penetrating into the anode chambers before the harmful effects can occur. By keeping the cathode chambers under excess pressure with oxygen-depleted gas mixture throughout the shutdown period, the system prevents the condition that would lead to carbon corrosion and oxide formation upon restart.
Solution Approach 2:
The system performs preliminary protection by establishing and maintaining the oxygen-depleted atmosphere in cathode chambers before any potential oxygen ingress could occur. The excess pressure condition is maintained from the moment shutdown is initiated, ensuring that when restart occurs, the protective atmosphere is already in place and atmospheric oxygen cannot penetrate into the anode chambers to cause harmful effects.
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
This approach extends the protection period of the fuel cell stack against air-air start damage, minimizing oxygen diffusion and thus prolonging the system's service life by maintaining an oxygen-free environment within the fuel cell stack.
Implementation Method 1
the oxygen-depleted cathode operating gas present in the cathode chambers is expanded via the cathode supply path and/or the cathode exhaust path
Implementation Method 2
a penetration of atmospheric oxygen into the anode chambers of the fuel cell stack takes place that, when the system is restarted, can lead to a significant alteration of the fuel cells
Data Source
AI summary
The invention relates to a method for switching off a fuel cell system (100) havinga fuel cell stack (10), that has anode chambers (13) and cathode chambers (12), anda cathode supply (20) having a cathode supply path (21) for supplying an oxygenated cathode operating gas into the cathode chambers (12), a compressor (23) arranged in the cathode supply path (21) and a cathode exhaust path (22) for discharging a cathode exhaust gas from the cathode chambers (12).The method comprises the steps of:(a) Maintenance of the cathode chambers (12) under excess pressure while preventing a flow of cathode operating gas through the cathode chambers (12) while keeping the cathode operating gas that is present in the cathode chambers (12) oxygen-depleted;(b) Expansion of the oxygen-depleted cathode operating gas present in the cathode chambers (12) via the cathode supply path (31) [sic] and/or the cathode exhaust path (22), and(c) Separation of the cathode chambers (12) from the environment.