Fuel Cell Anode Shutdown Dosing to Prevent Re-Oxidation
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Solution Overview
Problem
During an operation stop, nickel in fuel cell anodes can undergo re-oxidation, leading to volumetric expansion and stress on the fuel cell structure, potentially causing delamination or cracking of the electrolyte due to oxygen diffusion from the cathode layer.
Innovation Solution
A fuel cell system with a controller that adjusts the dosing rate of a methanol-water mixture based on temperature to prevent re-oxidation, using a higher proportion of methanol at elevated temperatures to inhibit nickel re-oxidation, and a carrier gas to deliver the mixture to the fuel cell stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel cell system stops operation, then the system can be shut down or idle, but the nickel anode undergoes re-oxidation causing structural damage
Solution Approach 1:
The system applies preliminary protective action by introducing a reducing gas atmosphere (hydrogen or carbon monoxide) into the anode chamber before and during operation stop. This counteracts the oxidizing environment that would otherwise form during shutdown, preventing nickel re-oxidation and maintaining anode structural integrity without requiring continuous fuel consumption.
Solution Approach 2:
The system creates a protective reducing atmosphere environment in the anode chamber using inert or reducing gases (hydrogen, carbon monoxide, or nitrogen). This inert/reducing environment isolates the nickel anode from oxygen exposure during operation stop, preventing re-oxidation reactions while allowing the system to be shut down or idle safely.
2Reliability
If methanol is dosed at high proportion, then re-oxidation prevention is improved, but the complexity of dosing control increases
Solution Approach 1:
The dosing system dynamically adjusts the proportion of methanol versus water or carrier gas based on real-time temperature readings from the fuel cell stack. During high-temperature operation stops (>300°C), the system increases methanol proportion to enhance reducing atmosphere effectiveness. During lower temperature stops, it reduces methanol proportion, simplifying control and reducing complexity while maintaining adequate protection.
Solution Approach 2:
The system changes the compositional parameter of the dosed gas mixture based on temperature conditions. By adjusting the methanol-to-water or methanol-to-carrier-gas ratio according to temperature thresholds, the system optimizes re-oxidation prevention effectiveness while avoiding the need for overly complex control mechanisms, as the adjustment logic is temperature-driven and straightforward.
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 prevents re-oxidation of the anode by maintaining a reducing atmosphere, reducing the risk of nickel tetracarbonyl formation and minimizing stress on the fuel cell structure, thereby protecting the fuel cell from damage during temperature changes.
Implementation Method 1
The reformer may be configured to reform methanol-water mix supplied thereto to generate hydrogen (H2) and carbon monoxide (CO) to prevent re-oxidation of the anode of the fuel cell stack
Implementation Method 2
The catalytic converter may be configured to oxidize at least a portion of the gas stream
Implementation Method 3
the nickel in the anode of the fuel cells may undergo a re-oxidation, by the oxygen in the air diffused from the cathode layer or introduced into the anode chamber
Data Source
AI summary
A fuel cell system includes a hotbox configured to house a fuel cell stack, the fuel cell stack including a temperature sensor configured to detect temperature inside the fuel cell stack. The system includes a first tank including a first valve and configured to store methanol. The system includes a second tank including a second valve and configured to store water. The system includes a controller communicatively coupled to receive signals from the temperature sensor and control each of the first valve and the second valve. The controller is configured to set a dosing rate of methanol, based on a temperature of the fuel cells stack, to a predefined dosing rate and initiate operating at least one of the first valve and the second valve to deliver a mixture of methanol and water at the predefined dosing rate to prevent re-oxidation of an anode of the fuel cell stack.