Fuel Cell Cold Start via Controlled OER/ORR Current Density
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Solution Overview
Problem
Fuel cell systems struggle to start up quickly from subzero temperatures without experiencing degradation due to voltage reversals, which can occur when ice forms and blocks fuel flow, leading to fuel starvation and potential irreversible damage.
Innovation Solution
The method involves starting up a fuel cell system with cathodes having an oxygen reduction reaction (ORR) catalyst and anodes with both hydrogen oxidation reaction (HOR) and oxidation evolution reaction (OER) catalysts, limiting the current density to below the maximum OER/ORR current density until the temperature reaches 0 °C to prevent damage, and adjusting current based on temperature and humidity to maximize startup speed while minimizing risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the fuel cell system is started up quickly from subzero temperatures, then the startup time is reduced, but voltage reversals occur causing carbon corrosion and potential irreversible damage
Solution Approach 1:
The system performs preliminary heating of the fuel cell stack to above freezing temperature before initiating normal operation. This preliminary action prevents ice formation that causes fuel starvation and voltage reversals, allowing rapid startup without damage. The control system monitors temperature and only permits full power operation once the stack is sufficiently warmed.
Solution Approach 2:
The control system dynamically adjusts the current density and power output based on real-time temperature measurements. During cold startup, the system operates at reduced power levels to generate heat, then progressively increases power as temperature rises. This dynamic control prevents voltage reversals while minimizing startup time.
2Reliability
If the current density is limited to below maximum OER/ORR current density during cold startup, then voltage reversal damage is prevented, but the startup speed is reduced
Solution Approach 1:
The system changes operational parameters (current density, power output) based on temperature conditions. During cold startup below freezing, current density is strictly limited to prevent OER/ORR reactions. As temperature rises above freezing, the system progressively increases current density to maximum levels, optimizing both protection and startup speed.
Solution Approach 2:
The control system continuously monitors temperature, current density, and power output, using feedback loops to adjust operations. When temperature approaches freezing points, the system automatically reduces current density to prevent damage. This feedback control enables the system to operate at the maximum safe current density at each temperature point, maximizing startup speed while preventing damage.
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 allows for faster startup of fuel cell systems from subzero temperatures while preventing damage from voltage reversals by operating within the cell's capability in OER/ORR mode, ensuring efficient operation and reducing startup time without causing carbon corrosion.
Implementation Method 1
Fuel cells such as solid polymer electrolyte fuel cells electrochemically convert reactants, namely fuel (such as hydrogen) and oxidant (such as oxygen or air), to generate electric power.
Implementation Method 2
hydrogen is oxidized at the anode catalyst to create a hydrogen ion (proton) and an electron
Implementation Method 3
oxygen is reduced and is combined with the proton and electron to create water
Implementation Method 4
The former is transported through the proton conducting polymer electrolyte to the cathode
Implementation Method 5
Catalysts are used to enhance the rate of the electrochemical reactions which occur at the cell electrodes
Implementation Method 6
Porous gas diffusion layers (GDLs) are usually employed adjacent the two electrodes to assist in diffusing the reactant gases evenly to the electrodes
Implementation Method 7
circulate liquid coolant throughout the stack in order to remove heat quickly and efficiently
Implementation Method 8
water electrolysis and oxidation of anode components may take place at the fuel cell anode
Data Source
Figure 1
Figure 2a~2b
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AI summary
Methods are disclosed for starting up a fuel cell system from starting temperatures below 0 °C. The methods apply to systems comprising a solid polymer electrolyte fuel cell stack whose cathodes comprise an oxygen reduction reaction (ORR) catalyst and whose anodes comprise both a hydrogen oxidation reaction (HOR) catalyst and an oxidation evolution reaction (OER) catalyst. In the methods, from the beginning of starting up until the fuel cell temperature reaches 0 °C, the fuel cell stack current is kept sufficiently low such that the current density drawn does not exceed the stack's capability for the oxidation evolution and the oxygen reduction reactions to occur at the anode and cathode respectively (i.e. current density drawn is less than the stack's maximum OER/ORR current density).