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operation is important. Modern devices need to be as or more reliable than the internal combustion engine—it is essential that with little upkeep they will last for an
extended time period (for example 50 years or more in the case of satellites), and
can be cycled repeatedly. Often, the limitation is due to the electrodes, rather than
the membrane, such as in proton exchange fuel cells. However, in other cases, such
as hydroxide-conducting fuel cells, the membrane itself is the limiting technology.
In any case, the electrolyte is crucial. By improving the electrolyte, the conductivity
and lifetime itself can improve, and this may also allow for less caustic conditions
that accommodate the chemical sensitivity of the electrodes.
Water Many modern materials require anhydrous conditions, where others require
a specific humidity range. Materials that work only at high relative humidity need a
separate water system, making those that operate under anhydrous or low humidity
conditions very attractive in comparison for certain applications. With waterassisted ionic conductivity, the mechanism involves a hydrated charge for transport.
Polymer nanocomposites might hold onto water more effectively to reduce the need
for external humidification. MOFs can provide the water molecules as part of their
structure in some cases, thus lowering the requirements for humidity conditions.
Further, removal of water may induce a structural change in the MOF, yielding different mechanisms to allow for ion transport. These types of electrolytes can operate
at impressively large variations in humidity. Even more fundamentally important,
water has limited voltage stability, so these materials may help to improve the
potential voltage range of non-aqueous devices.
4 Fuel Cells
Fuel cells utilize membranes that allow for proton conductivity (in proton exchange
membranes, PEMs) or hydroxide ion conductivity (within anionic exchange membranes). Fuel cells combine an oxidant and a fuel, but rather than initiating a combustion reaction (which is inherently a redox reaction), electrons are transferred in
a circuit between an anode and cathode, making these true electrochemical reactions. Therefore, an electrolyte/membrane is needed to balance charge. There are
many reasons why fuel cells are one of the most sought after green energy solutions,
the most touted being a significant reduction in the production of toxic and greenhouse gases and the production of water as a potable byproduct. They also release
heat (as does any combustion reaction), which can be captured and used, allowing
for high efficiency of energy conversion. They find application in remote locations
and places where the emission of gases would be unsuitable, such as inside residential and commercial buildings. Most famously, they have been used to provide electrical power to spacecraft, where the electricity is utilized and the produced water
can be consumed by astronauts.
Fuel cells require a continuous supply of both the fuel and an oxidant, hence they
are not enclosed systems (compared to batteries). Hydrogen is the most commonly
Polymer Nanocomposites for Ion Transport
operation is important. Modern devices need to be as or more reliable than the internal combustion engine—it is essential that with little upkeep they will last for an
extended time period (for example 50 years or more in the case of satellites), and
can be cycled repeatedly. Often, the limitation is due to the electrodes, rather than
the membrane, such as in proton exchange fuel cells. However, in other cases, such
as hydroxide-conducting fuel cells, the membrane itself is the limiting technology.
In any case, the electrolyte is crucial. By improving the electrolyte, the conductivity
and lifetime itself can improve, and this may also allow for less caustic conditions
that accommodate the chemical sensitivity of the electrodes.
Water Many modern materials require anhydrous conditions, where others require
a specific humidity range. Materials that work only at high relative humidity need a
separate water system, making those that operate under anhydrous or low humidity
conditions very attractive in comparison for certain applications. With waterassisted ionic conductivity, the mechanism involves a hydrated charge for transport.
Polymer nanocomposites might hold onto water more effectively to reduce the need
for external humidification. MOFs can provide the water molecules as part of their
structure in some cases, thus lowering the requirements for humidity conditions.
Further, removal of water may induce a structural change in the MOF, yielding different mechanisms to allow for ion transport. These types of electrolytes can operate
at impressively large variations in humidity. Even more fundamentally important,
water has limited voltage stability, so these materials may help to improve the
potential voltage range of non-aqueous devices.
4 Fuel Cells
Fuel cells utilize membranes that allow for proton conductivity (in proton exchange
membranes, PEMs) or hydroxide ion conductivity (within anionic exchange membranes). Fuel cells combine an oxidant and a fuel, but rather than initiating a combustion reaction (which is inherently a redox reaction), electrons are transferred in
a circuit between an anode and cathode, making these true electrochemical reactions. Therefore, an electrolyte/membrane is needed to balance charge. There are
many reasons why fuel cells are one of the most sought after green energy solutions,
the most touted being a significant reduction in the production of toxic and greenhouse gases and the production of water as a potable byproduct. They also release
heat (as does any combustion reaction), which can be captured and used, allowing
for high efficiency of energy conversion. They find application in remote locations
and places where the emission of gases would be unsuitable, such as inside residential and commercial buildings. Most famously, they have been used to provide electrical power to spacecraft, where the electricity is utilized and the produced water
can be consumed by astronauts.
Fuel cells require a continuous supply of both the fuel and an oxidant, hence they
are not enclosed systems (compared to batteries). Hydrogen is the most commonly
Polymer Nanocomposites for Ion Transport