Fuel Cell Startup Bypass and Recirculation for Catalyst Protection
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Solution Overview
Problem
Fuel cells experience degradation due to residual fuel and oxidizer gases permeating through the electrolyte membrane during shutdown, leading to catalyst deterioration and reduced lifespan, especially when shutdown periods are prolonged.
Innovation Solution
A method and apparatus that utilize an oxidizer gas bypass passage and fuel exhaust gas recirculation to bypass and dilute residual gases, ensuring the fuel cell is started with controlled gas replacement, minimizing catalyst exposure to hydrogen concentration gradients and corrosion currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the fuel cell is shut down for a prolonged period, then the fuel cell stops consuming energy, but the remaining fuel gas and oxidizer gas permeate through the electrolyte membrane and degrade the electrode catalyst and catalyst support
Solution Approach 1:
The system performs preliminary action by purging residual gases from the flow passages before shutdown and introducing inert gas (nitrogen) to fill the passages during shutdown. This prevents the harmful permeation of fuel gas and oxidizer gas through the electrolyte membrane while the cell is dormant, thereby protecting the catalyst from degradation during periods when energy consumption is not occurring.
2Object-affected harmful factors
If air is supplied to the anode flow passage during shutdown to replace residual fuel gas, then fuel gas permeation is prevented, but hydrogen concentration gradients and corrosion currents may still occur during startup
Solution Approach 1:
The system performs preliminary purging of residual fuel gas from the anode flow passage before shutdown by supplying air. Additionally, during shutdown, nitrogen gas is introduced to fill the passage. This preliminary action ensures that when startup occurs, there is minimal residual fuel gas to create concentration gradients, and the nitrogen present helps maintain uniform gas distribution during the transition to operation.
Solution Approach 2:
Nitrogen gas serves as an intermediary substance during shutdown. It fills the anode flow passage and prevents direct contact between residual fuel gas and the electrolyte membrane, while also preventing air from entering and creating immediate hydrogen concentration gradients. The nitrogen acts as a buffer that maintains stable conditions during the shutdown period and facilitates smoother startup conditions.
3Object-affected harmful factors
If the oxidizer gas supply passage and oxidizer exhaust gas exhaust passage are sealed, then gas leakage is prevented, but the oxidizer gas bypass passage must be used to supply oxidizer gas to the diluter
Solution Approach 1:
The oxidizer gas supply system is segmented into multiple independent pathways: the primary oxidizer gas supply passage (sealed during startup), the oxidizer gas bypass passage (activated during startup), and the oxidizer exhaust gas exhaust passage (sealed during startup). This segmentation allows selective activation of specific passages based on operational requirements, enabling the bypass passage to supply oxidizer gas to the diluter while maintaining seals in other passages to prevent leakage.
Solution Approach 2:
The system dynamically switches between different gas supply pathways based on operational state. During startup, the oxidizer gas supply passage and exhaust passage are sealed while the bypass passage is activated. After startup completion, the system transitions to the normal operational state where the bypass passage is closed and the primary supply passage is opened. This dynamic switching manages the complexity by using control valves that automatically adjust passage configurations based on system state.
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 effectively suppresses catalyst deterioration and extends the life of the fuel cell by ensuring complete replacement of residual gases with fresh reactants, reducing hydrogen concentration gradients and preventing corrosion, thus maintaining the fuel cell's performance and longevity.
Implementation Method 1
a fuel cell that generates electric power by an electrochemical reaction between fuel gas supplied to an anode side and oxidizer gas supplied to a cathode side
Implementation Method 2
an oxidizer gas bypass passage branched from the oxidizer gas supply passage and connected to the oxidizer exhaust gas exhaust passage to bypass a fuel cell
Implementation Method 3
a fuel exhaust gas recirculation passage through which a fuel exhaust gas is recirculated to the anode side of the fuel cell
Implementation Method 4
a diluter that dilutes a fuel exhaust gas with an oxidizer gas or an oxidizer exhaust gas
Implementation Method 5
an oxidizer gas supply passage sealing device that seals the oxidizer gas supply passage
Implementation Method 6
an oxidizer exhaust gas exhaust passage sealing device that seals the oxidizer exhaust gas exhaust passage
Data Source
AI summary
In a method for starting a fuel cell system, an oxidizer gas bypass passage is operated by an oxidizer gas bypass passage controller to supply oxidizer gas to a diluter from an oxidizer gas supply device under a condition where an oxidizer gas supply passage is sealed by an oxidizer gas supply passage sealing device and an oxidizer exhaust gas exhaust passage is sealed by an oxidizer exhaust gas exhaust passage sealing device. A fuel exhaust gas recirculation passage is operated by a fuel exhaust gas recirculation passage controller to supply fuel gas to the fuel cell from a fuel gas supply device.