|
What is a
hydrogen battery?
Hydrogen
Battery Technology for Portable Devices
Unlike a conventional primary
battery, where the entire battery is replaced once
discharged, in a hydrogen battery only the compact,
inexpensive energy module needs to be replaced.
Unlike a conventional secondary
battery, which must be plugged into the grid for recharge
for hours at a time, a hydrogen battery provides instant
recharge.
|
A hydrogen battery is a combination of a fuel cell
power module and an energy module based on Hydrogen on
Demand® technology.
Like a traditional battery, a hydrogen battery converts
chemical energy into electrical energy. However, there are
important differences.
Traditional batteries are sealed systems. The volume of
the battery limits the amount of energy the device can
supply, which is in turn limited by the amount of active
“fuel” material the battery contains. Once that fuel is
consumed, the entire battery must either be replaced or
recharged.
In a hydrogen battery the amount of energy the device can
supply is not limited by the volume of the device. Because
the hydrogen battery has separate power and energy modules,
the hydrogen battery can be refueled and used over and over
simply by replacing the energy module (refueling the
system). The energy module can be more compact and less
expensive than a primary, single use, battery and can be
replaced in a moment, instead of recharged for an hour or
more.
Advantages for hydrogen batteries vs. traditional
batteries:
| • |
The amount of energy
possible is easily variable. For a traditional battery
to supply energy for a longer time, the size of the
entire sealed battery system must increase. A hydrogen
battery system sized for a particular power can supply
energy as long as it is refueled, keeping the size of
the power module constant. |
|
|
| • |
Because the fuel for a
hydrogen battery packs more energy per unit volume and
weight (energy density) than traditional batteries, the
size of a hydrogen battery energy supply increases less
with runtime than does a traditional battery. |
|
|
| • |
The cost of obtaining
additional energy from a hydrogen battery is simply the
cost of the fuel. The cost of additional energy when
using traditional primary batteries is that of
purchasing more batteries, which can be many times the
cost of the fuel. |
|
|
| • |
A hydrogen battery can be
“recharged” virtually instantaneously by supplying
additional fuel; traditional battery recharging can take
considerably longer, and is impossible in the absence of
an auxiliary source of electrical power. |
Inside the Millennium Cell Hydrogen
Battery – Power and Energy
Power
The power module half of the hydrogen battery is a fuel
cell. Of existing fuel cell technologies, the proton
exchange membrane fuel cell (PEMFC, or sometimes just PEM)
has received significant attention for portable electronic
device applications. These fuel cells operate at low
temperature (< 80 °C) and use a solid polymer electrolyte.
PEM fuel cells have a number of advantages vs. alternative
technologies that make them particularly suitable for use in
a hydrogen battery.
Unlike direct methanol fuels cells (DMFC), which operate
on methanol and water and use a complicated process that
requires more platinum at the electrodes, PEM systems use a
simpler process requiring less costly electrodes. In
addition, PEMs are more efficient, deliver higher voltages,
and are more compact than a DMFC system of equivalent power.
Energy
The energy half of a hydrogen battery is, as one
might expect, hydrogen. Hydrogen is an ideal fuel for fuel
cells because the conversion of hydrogen and oxygen to
energy is simple and uncomplicated by side reactions. The
only byproduct of a hydrogen fuel cell is water, which
typically vanishes into the atmosphere as harmless water
vapor. The key practical issue is storing enough hydrogen in
the hydrogen battery for it to be useful.
There are a several options for storing hydrogen for use
in hydrogen batteries, but many have important draw-backs:
| • |
Compressed hydrogen—the
object of great attention for transportation, cannot
supply enough fuel from a sufficiently small and light
package for a portable device. |
|
|
| • |
Metal hydrides, which
absorb hydrogen on charging and release it on use are
too heavy for portable use; they also require a local
source of hydrogen for reuse and are too expensive to
discard after only one use. |
| |
|
| • |
Because PEM fuel cells
require hydration (wetting) of the membrane, both
compressed hydrogen and hydrogen from a metal hydride
source require humidification subsystems. |
| |
|
| • |
Hydrogen from methanol or
other hydrocarbons, formed via a “reformation” process,
requires high internal temperatures, complicated fuel
processors, slow start-ups and results in carbon dioxide
emissions. Purification is also usually required for use
on PEM fuel cells.
|
In contrast, reacting chemical hydrides with water is a great way to
generate hydrogen. Millennium Cell has developed and
publicly demonstrated systems (known as Hydrogen on Demand®
or HOD™ systems) utilizing sodium borohydride (NaBH4)
as a hydrogen storage medium at power levels ranging from as
low as 2 W up to 65 kW.
These systems are light, do not require purifiers,
complicated fuel processors or high temperatures; they start
quickly and do not emit greenhouse gasses.
This information is from
http://www.millenniumcell.com/fw/main/Overview-27.html