PEM Fuel Cell Controlled Shutdown Procedure
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Solution Overview
Problem
Proton exchange membrane fuel cells (PEMFCs) experience significant performance degradation due to repeated start-stop cycles and varying operating conditions, particularly in automotive applications, leading to reduced durability and lifespan.
Innovation Solution
A method for minimizing degradation by implementing a controlled shut-down and start-up procedure that involves gradually reducing anode and cathode gas supply, monitoring output voltage and gas pressures, shunting cells to prevent high voltage buildup, and filling/flushing with inert gas to reduce reactant consumption and mitigate degradation mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the fuel cell operates in a wide range of conditions including frequent start-stop cycles, then the adaptability to automotive applications is improved, but the durability and lifespan are drastically reduced
Solution Approach 1:
The patent applies preliminary action by performing a controlled shut-down procedure before the fuel cell is fully stopped. This involves gradually reducing reactant supply, maintaining voltage within a safe range, and controlling the electrochemical reactions to prevent harmful conditions during the transition from operation to shutdown, thereby protecting the fuel cell from degradation caused by frequent start-stop cycles
Solution Approach 2:
The patent implements beforehand cushioning by introducing a controlled shut-down phase that acts as a buffer between full operation and complete shutdown. During this phase, the fuel cell operates at reduced power with controlled reactant supply, preventing abrupt voltage changes and harmful electrochemical conditions, thus cushioning the system against stress that would otherwise reduce durability
2Quantity of substance
If the fuel cell is shut down frequently to allow battery charging, then the battery charge level is maintained, but the start-stop cycles contribute to performance degradation
Solution Approach 1:
The patent applies preliminary action by implementing a controlled shut-down procedure that prepares the fuel cell for shutdown in advance. This involves gradually reducing reactant supply while maintaining voltage within a safe range, preventing harmful high-voltage conditions that occur during abrupt shutdowns, thereby reducing degradation even when frequent shutdowns are necessary for battery charging
3Loss of time
If the supply of anode gas and cathode gas is abruptly interrupted during shut-down, then the shut-down time is reduced, but high cell voltage builds up causing degradation
Solution Approach 1:
The patent applies preliminary action by gradually reducing reactant supply before complete shutdown. This controlled reduction allows the electrochemical reactions to wind down naturally, preventing abrupt voltage spikes that would occur with immediate shutdown, while still achieving a relatively quick transition to the shutdown state
Solution Approach 2:
The patent implements feedback by continuously monitoring cell voltage during the shut-down process and adjusting reactant supply accordingly. When voltage approaches the upper limit of the safe range, the reactant supply is further reduced, creating a closed-loop control system that prevents voltage buildup while optimizing shut-down 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
The method effectively reduces the impact of start-stop cycles on fuel cell performance, conserves reactants, and extends the lifespan of PEMFCs by maintaining reactant pressures below ambient levels and using inert gases to counteract degradation mechanisms.
Implementation Method 1
Electrochemical fuel cells of the above-mentioned type convert reactants, typically a stream of hydrogen and a stream of oxygen, into electric power and water
Implementation Method 2
The protons migrate through the solid polymer electrolyte towards the cathode
Implementation Method 3
the hydrogen moves through the porous electrode layer and is oxidized by the catalyst to produce protons and electrons
Implementation Method 4
The electrons travel from the anode to the cathode through an external circuit, producing an electrical current
Data Source
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AI summary
The present invention provides a method of operating a PEM fuel cell comprising an anode feed circuit and a cathode feed circuit for feeding of an anode side (14) with a reactant gas and for feeding a cathode side (16) with a cathode gas. Said method adapted for shutting down and for starting of an electricity generating operation of the fuel system, in the shut-down mode comprises the steps of : decreasing the supply of reactant gas and cathode gas in response of a shut-down signal, monitoring an output voltage of at least one cell of a fuel cell stack (12), monitoring the reactant gas pressure and the cathode gas pressure, electrically shunting of the at least one fuel cell in response of the output voltage reaching a predefined voltage level, at least reducing the pressure of the anode side (14) to a predefined pressure level by means of at least one pump (16, 18), and filling and/or flushing of at least the anode side (14) with an inert gas.