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FuelCellEuropeHow do they work?
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A fuel cell is an electrochemical device that combines fuel and oxygen from air to produce electricity. The conversion of the fuel to energy takes place without combustion; therefore the process is highly efficient, quiet and clean When using hydrogen as fuel, the only by-products are water and heat and nearly zero GHG & toxics are emitted. A fuel cell is similar in principle to a battery but it does not run down or require recharging: as long as fuel is supplied to a fuel cell, it will continue to operate. |
Source: BallardThe catalyst
A fuel cell consists of two electrodes separated by an electrolyte. In most cases, hydrogen fuel is fed into the anode, positive charge, of the fuel cell. Oxygen enters the fuel cell at the cathode, negative charged. Encouraged by a catalyst at the boundary with the electrolyte, the electrons separate from the protons after the complete hydrogen gas molecule has traversed the porous electrode structure.The protons then pass through the electrolyte, leaving the free electrons to flow through an external circuit, creating an electric current that can be exploited - just like a battery - before returning to the cathode side, where it recombines with the proton and the oxygen to form a molecule of water.
Individual cells are "stacked" together to generate the required quantities of power. A fuel cell stack is the core of a complete fuel cell.
All fuel cells are modular. Units ranging in size from a few watts (or even mWs) to many more watts have been demonstrated and can be used as building blocks for larger systems.
The reformer
In the ideal case cells operate on hydrogen. However, a fuel cell system may include a "fuel reformer" (or "fuel processor") that can extract the hydrogen from a hydrocarbon fuel such as natural gas, ethanol/methanol, propane and even clean gasoline or diesel for use in the fuel cell. In this process the hydrogen is stripped from the fuel producing CO2, heat and water as by-products.
Ultimately, fuel cells, in combination with solar, wind and hydro power technologies, offer the promise of a totally zero-emission energy system that requires no fossil fuel and is not limited by variations in sunlight or wind flow.
Technology overview
A fuel cell consists of two electrodes separated by an electrolyte. In most cases, hydrogen fuel is fed into the anode, positive charge, of the fuel cell. Oxygen enters the fuel cell at the cathode, negative charged. Encouraged by a catalyst at the boundary with the electrolyte, the electrons separate from the protons after the complete hydrogen gas molecule has traversed the porous electrode structure.The protons then pass through the electrolyte, leaving the free electrons to flow through an external circuit, creating an electric current that can be exploited - just like a battery - before returning to the cathode side, where it recombines with the proton and the oxygen to form a molecule of water.
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Source: ECN
The stackIndividual cells are "stacked" together to generate the required quantities of power. A fuel cell stack is the core of a complete fuel cell.
All fuel cells are modular. Units ranging in size from a few watts (or even mWs) to many more watts have been demonstrated and can be used as building blocks for larger systems.
The reformer
In the ideal case cells operate on hydrogen. However, a fuel cell system may include a "fuel reformer" (or "fuel processor") that can extract the hydrogen from a hydrocarbon fuel such as natural gas, ethanol/methanol, propane and even clean gasoline or diesel for use in the fuel cell. In this process the hydrogen is stripped from the fuel producing CO2, heat and water as by-products.
Ultimately, fuel cells, in combination with solar, wind and hydro power technologies, offer the promise of a totally zero-emission energy system that requires no fossil fuel and is not limited by variations in sunlight or wind flow.
Technology overview
As mentionned above, a fuel cell generally consists of two electrodes (cathode and anode) separated by an electrolyte. The type of electrolyte is usually used to distinguish and name the different types of fuel cells.
A number of additional characteristics, such as operating temperature, efficiency and application apply to the different types of fuel cells and can vary significantly.
The table below provides you with an overview of the main types of fuel cells currently developed.
To find out more about each fuel cell types charateristics & functions, click on the names in the table.
A number of additional characteristics, such as operating temperature, efficiency and application apply to the different types of fuel cells and can vary significantly.
The table below provides you with an overview of the main types of fuel cells currently developed.
To find out more about each fuel cell types charateristics & functions, click on the names in the table.
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Electrolyte
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Hydrated Polymeric Ion Exchange Membranes
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Mobilised or Immobilised Potassium hydroxide in asbestos matrix
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Immobilised Phosphoric acid in SiC
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Immobilised Liquid Molten carbonate in LiAlO2
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Perovskites (ceramic)
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Electrodes
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Carbon
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Transition metals
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Carbon
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Nickel and Nickel Oxide
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Perovskites
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Catalyst
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Platinum
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Platinum
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Platinum
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Electrode Material
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Electrode Material
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Interconnect
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Carbon or metal
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Metal
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Graphite
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Stainless steel or Nikel
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Nikel, ceramic or steel
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Operating temperature
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40-80°C
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65-220°C
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205°C
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650°C
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60-1000°C
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Charge Carrier
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H+
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OH-
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H+
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CO3-
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O-
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External reformer for hydrocarbon fuels
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Yes
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Yes
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Yes
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No, for some fuels
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No, for some fuels and cell designs
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External shift conversion of CO to hydrogen
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Yes, plus purification to remove trace CO
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Yes, plus purification to remove trace CO and CO2
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Yes
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No
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No
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Prime cell components
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Carbon based
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Carbon based
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Graphite based
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Stainless based
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Ceramic
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Product Water Management
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Evaporative
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Evaporative
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Evaporative
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Gaseous product
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Gaseous product
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Product Heat Management
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Process gas + Liquid cooling medium
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Process gas + Electrolyte circulation
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Process gas + Liquid cooling medium or steam generation
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Internal reforming + process gas
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Internal reforming + process gas
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Source: US DoE
Last update: 12-10-2009 at 13:06
