Hydrogen Fuel Cell versus Hydrogen
on Demand
A hydrogen fuel cell and hydrogen on demand (HOD) are two very
different technologies. A hydrogen fuel cell (often called a proton
exchange membrane or PEM cell) uses compressed hydrogen and oxygen
from the ambient air to create an electrical current to run one
or more electric motors in a car.
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Hydrogen Fuel Cell
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Hydrogen on demand inside a vehicle is a very different process.
Let's start with the example of creating hydrogen on demand from
water. In this scenario, hydrogen will be used to supplement a gasoline
or diesel powered vehicle. The hydrogen will be sucked into the
vehicle's intact system where it will mix with the other fuel and
burn more cleanly and completely inside the cylinders.
Hydrogen on demand is created by electrolyzing water as needed.
No compressed hydrogen is stored onboard the vehicle, only a small
amount of water, which is inert and is non-flammable and non-explosive.
Compressed hydrogen is another story altogether.
The hydrogen fuel cell is what most people speak of when they talk
about the hydrogen highway system and the hydrogen economy. Massive
amounts of hydrogen will need to be created, stored, transported
perhaps and then pumped inside of vehicles.
With hydrogen on demand technology, some other substance such as
water will need to be generated, stored, transported and put inside
vehicles. If the substance for hydrogen on demand is not water,
but some other hydrogen chemical substance such as sodium borohydride
(NaBH4), or magnesium borohydride, then the remaining chemicals
may need to be recycled as well.
Purdue University has been developing hydrogen on demand technology
that uses aluminum plus the inert gallium, indium and tin alloy
that reacts with water to create H2. In this case, over time, the
metals alloys will need to be recycled as they become degraded.
But, the technology on this is very promising and no electrical
current will be needed, just a chemical reaction to produce hydrogen
inside the vehicle.
So, you can see that the sole purpose of a hydrogen fuel cell is
to create an electrical current to turn a motor and the sole purpose
of hydrogen on demand is to extract H2 as needed and either run
it through a fuel cell or more likely an internal combustion engine.
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