Fuel Cell Shutdown via Holding Current and Oxygen Interruption
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Solution Overview
Problem
Fuel cells supplied with pure oxygen face challenges in immediate shutdown due to residual gas, leading to prolonged voltage maintenance and potential membrane degradation, especially at low temperatures, without the use of nitrogen.
Innovation Solution
A shutdown procedure involving the interruption of oxygen supply, followed by a holding current to reduce pressure to water vapor levels, allowing water vaporization and evacuation, ensuring complete gas consumption and preventing electrochemical degradation, without relying on nitrogen.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the fuel cell is supplied with pure oxygen, then the efficiency and power density are improved, but the shutdown of the battery is not immediate and the electrochemical reaction cannot be completely interrupted
Solution Approach 1:
The patent extracts the harmful residual oxygen from the system by introducing nitrogen gas to displace and purge the remaining oxygen from the channels, enabling complete interruption of the electrochemical reaction and immediate shutdown of the fuel cell
Solution Approach 2:
The patent uses nitrogen gas to create an inert atmosphere in the fuel cell channels, replacing the reactive oxygen environment with a non-reactive one that prevents further electrochemical reactions, thus achieving complete shutdown
2Speed
If the fuel cell is supplied with pure oxygen, then the response to current demand is more dynamic, but the residual oxygen and hydrogen trapped in channels maintain the electrochemical reaction for several hours
Solution Approach 1:
The patent extracts residual gases from the channels by introducing nitrogen to displace and purge them, preventing prolonged electrochemical reactions and reducing the duration of action after fuel supply interruption
Solution Approach 2:
The patent introduces nitrogen gas as an intermediary substance that facilitates the removal of residual reactive gases from the channels, acting as a mediator between the fuel supply interruption and complete reaction cessation
3Reliability
If the fuel cell is stopped without current consumption, then safety is compromised due to persistent voltage, but membrane degradation occurs rapidly under open circuit voltage conditions
Solution Approach 1:
The patent converts the harmful open circuit voltage condition into a beneficial controlled discharge process by introducing nitrogen to enable complete gas consumption, allowing the cell to be stopped with zero voltage and no current consumption, thus protecting both safety and membrane integrity
Solution Approach 2:
The patent changes the operational parameters by introducing nitrogen gas and controlling the discharge current, transforming the system from a high-voltage open-circuit state to a zero-voltage complete-shutdown state, protecting the membrane from degradation
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 method enables a controlled and rapid shutdown of fuel cells, maintaining membrane integrity and facilitating quick restarts even at low temperatures, while preventing degradation and ensuring homogeneous humidification for improved electrical performance.
Implementation Method 1
the electrochemical reaction cannot be completely interrupted by simply cutting off the fuel and oxidizer supply valves. Indeed, the quantity of oxygen and hydrogen remaining trapped in the respective channels of the fuel cell is sufficient to maintain the electrochemical reaction
Implementation Method 2
an electrical consumption stage during which a holding current is taken from the fuel cell, until the pressure in the oxygen circuit reaches the pressure of water vapour
Data Source
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AI summary
The polymer electrolyte fuel cell (PEFC) (1) is controlled by a control unit (15). Feeding of oxygen gas is interrupted during initial step. Electrical consumption phase is set so as to drawn out the hold current from the fuel cell until the pressure in the pressure sensor (121) reaches water vapor pressure.