Transcript Fuel cell Description

Introduction to Fuel Cells
Hocking College
Nelsonville Ohio
July 24, 2007
Fuel Cells Generally Contain
Anode
Anode Catalyst
Cathode
Cathode Catalyst
Gas Diffusion Layer
Electrolyte
A load to complete the circuit
Continuous feed of fuel
Continuous feed of air or oxygen
Types of Fuel Cells
Fuel Cells are generally named by the
electrolyte in the cell.
An exception to this is the methanol fuel
cell, which is called the Direct Methanol
Fuel Cell (DMFC).
Types of fuel cells
PEM (polymer electrolyte membrane fuel
cell)
DMFC (polymer electrolyte membrane fuel
cell)
SOFC (solid oxide fuel cell)
MCFC (molten carbonate fuel cell)
AFC (alkaline fuel cell)
PAFC (phosphoric acid fuel cell)
A Fuel Cell Converts Chemical
Energy to Electrical Energy
Load
Gas Diffusion Layer
Gas Diffusion Layer
e-
H+
Fuel
Air or Oxygen
Hydrogen
Anode
Cathode
Electrolyte
Catalyst
Catalyst
The Electrical Energy is in the form
of DC voltage
The voltage is usually between 0.5 and 1.0
volts DC (direct current).
Several fuel cells are connected together
in series to obtain higher voltages 25—100
volts.
These fuel cells connected in series are
called stacks.
The fuel cell stacks still give DC voltage.
An Inverter is used to change the
DC voltage to AC voltage
(alternating current).
Direct Current (DC) has a voltage that is
always in one direction.
DC voltage is the kind of voltage that
comes from a battery.
Alternating Current (AC) has a voltage that
varies from positive to negative 60
times/second (50 times/second in Europe).
Normal household current is AC.
Fuel Cell
Type
Electrolyte
Anode Gas
Cathode Gas
Temperature
Efficiency
Proton Exchange Membrane
(PEM)
solid polymer membrane
hydrogen
pure or atmospheric oxygen
75°C
(180°F)
35–60%
Alkaline
(AFC)
potassium hydroxide
hydrogen
pure
oxygen
below
80°C
50–70%
Direct Methanol
(DMFC)
solid polymer membrane
methanol solution in water
atmospheric
oxygen
75°C
(180°F)
35–40%
Phosphoric Acid
(PAFC)
Phosphoric Acid
hydrogen
atmospheric
oxygen
210°C
(400°F)
35–50%
Molten Carbonate
(MCFC)
AlkaliCarbonates
hydrogen,
methane
atmospheric
oxygen
650°C
(1200°F)
40–55%
Solid Oxide
(SOFC)
Ceramic Oxide
hydrogen,
methane
atmospheric
oxygen
800–1000°C
(1500–1800°F)
45–60%
Each type of fuel cell is particularly
suited to certain applications:
PEM: most versatile, used for portable power,
transportation, and stationary power
DMFC: used for portable power
SOFC: primarily used for stationary power, in
development for transportation (e.g. semi trucks)
MCFC: power plants
AFC: power and water production for space
vehicles (e.g. Apollo and Space Shuttle
spacecrafts), in development for more general
use
PAFC: stationary power, power plants
Each type of fuel cell has particular
advantages and disadvantages
PEM & DMFC: solid construction, low temperature, sensitive to
impurities, can only be used with hydrogen or methanol.
SOFC: can be used with many fuels, doesn’t require precious metal
catalysts, solid, rugged, very high temperature, expensive materials.
MCFC: can be used with many fuels, efficient, doesn’t require
precious metal catalysts, high temperature, very corrosive
electrolyte.
AFC: most efficient medium for oxygen reaction - high performance,
doesn’t require precious metal catalysts, sensitive to carbon dioxide,
caustic medium.
PAFC (phosphoric acid fuel cell): same electrochemical reactions as
PEM, but not as sensitive to impurities in the fuel, very corrosive.
Advantages
PEM & DMFC: solid construction, low
temperature
SOFC: can be used with many fuels,
doesn’t require precious metal catalysts,
solid, rugged, very high temperature (high
enough for power generation)
Advantages
MCFC: can be used with many fuels, efficient,
doesn’t require precious metal catalysts, high
temperature (high enough for power generation)
AFC: most efficient medium for oxygen reaction
- high performance, doesn’t require precious
metal catalysts
PAFC (phosphoric acid fuel cell): same
electrochemical reactions as PEM, but not as
sensitive to impurities in the fuel
Disadvantages
PEM & DMFC: low temperature (low grade
energy), must have pure hydrogen.
SOFC: very high temperature, expensive
materials.
MCFC: liquid, high temperature , very corrosive
electrolyte
AFC: liquid, sensitive to carbon dioxide, caustic
medium, low temperature (low grade heat)
PAFC: liquid, very corrosive, low temperature,
(low grade heat)
Typical fuel cells run on
hydrogen and oxygen
Methane, methanol, and other
hydrogen containing compounds can
be reformed to make hydrogen.
Air is usually used instead of pure
oxygen.
PEM Fuel Cell
Cathode Backing
Anode Backing
Anode Flowfield
Cathode Flowfield
(hydrogen)
PEM
(oxygen)
Pt Catalyst
Pt Catalyst
Source: Thampan, PEM Fuel Cell as a Membrane Reactor
PEM or DMFC Fuel Cell
Components
CCM (Catalyst Coated Membrane): Proton-conducting
membrane plus 2 electrodes
GDL (Gas Diffusion Layer): Carbon cloth or paper with
carbon particle filler and Teflon
Anode and Cathode plate: Graphite, carbon composite
or metal with machined or stamped ‘flow field’
Gaskets and seals: seals around edge of structure
SOFC Componets
Anode: Ni/YSZ Cermet
Electrolyte: Yttrium Stabilized Zirconia
(YSZ)
Cathode: Lanthanum Strontium
Manganite (LSM)
MCFC Components
Anode is a highly porous sintered nickel
powder, alloyed with chromium
Electrolyte is a liquid in a lithium—
Aluminum Oxide matrix
Cathode is a porous nickel oxide material
doped with lithium.
AFC Components
Electrodes:
>porous (and catalyzed) graphite electrodes
>semi-permeable, Teflon coated carbon
material
>heavily catalyzed as compared with other
types of fuel cells
Electrolyte: potassium hydroxide (KOH) solution
retained in a porous stabilized matrix
PAFC Components
Electrodes: porous carbon containing Pt or its alloys
as catalysts
Electrolyte: liquid phosphoric acid in Teflonbonded silicon carbide matrix