By Will Soutter
Introduction - Hydrogen Fuel
Issues with Hydrogen
Production of Hydrogen
Storage of Hydrogen
Introduction - Hydrogen
Hydrogen is an extremely promising form of energy storage. It is not
an inherently renewable source of energy like solar power, nor is it a naturally occurring fuel like methane or coal. However, the process by which it releases its energy is very efficient, and the only exhaust gas
produced is pure water.
Figure 1. Hydrogen could power fuel
cells in vehicles and combined heat and power (CHP) systems. Top image
Bottom image credit: ORNL.gov
Whilst hydrogen can be burnt like any other fuel (it is the fuel of
choice for space rockets), it can also be used to produce electricity
directly in a hydrogen fuel
cell. Whilst fuel cells will run on other fuels (methanol, natural gas,
etc.), they run less cleanly than on hydrogen, and require higher
operating temperatures, more
expensive materials, and more careful design to avoid fouling and
achieve good long-term
The problems with adoption of hydrogen thus far have resulted from
production and storage of hydrogen gas. Existing processes for
producing hydrogen require a large amount
of energy which typically comes from fossil fuels, negating the
environmental benefits of the otherwise carbon-free and pollution-free
Storage of hydrogen is also an issue, as it is highly flammable in its
free gaseous form. Storing and transporting the fuel safely is
therefore a priority. Much research effort has gone into developing a
viable commercial solution to these problems, but so far to no avail.
Nanotechnology could provide more of the answers, however. The most
promising recent developments in hydrogen production and storage have
involved the use of novel nanomaterials to produce hydrogen from water
more efficiently, and to enhance the performance of hydrogen storage
Production of Hydrogen
The majority of hydrogen is currently produced by steam reformation
of natural gas. Despite being a well developed, relatively efficient
process when operating on a large scale, steam reformation is highly
energy intensive, and obviously requires a source of non-renewable
Hydrogen can also be produced by electrolysis of water. This also
requires large amounts of energy, typically a combination of heat and
As the energy for these processes is most likely to come from fossil
fuel sources, hydrogen is not an especially "green" way to store
energy. There has been a major push in the last few years to develop
some methods of using renewable energy - primarily solar energy - to
directly produce hydrogen, thereby making the fuel what it should be:
an efficient alternative to batteries for storing clean energy on a
Some kinds of nanoparticles (titanium dioxide, which is a common
white pigment in its bulk form) have shown very strong photocatalytic
activity - the ability to use the energy from sunlight to decompose
molecules. So far, this has mostly been applied to self-cleaning
surfaces, but a good deal of research has gone into investigating and
optimizing the photocatalytic properties of various nanomaterials for
splitting water into hydrogen and oxygen.
In 2009, researchers at Northeastern University and NIST discovered
that titanium dioxide nanotubes have extremely good photocatalytic
activity - much more so than what should be expected from the simple
increase in available surface area over nanoparticles. The cause was
found to be a very small amount of potassium ions on the nanotube
surfaces, left accidentally by the fabrication process.
Figure 2. Titanium Dioxide
nanotubes can convert water into hydrogen and oxygen using the power of
sunlight. Further research will try to optimize the technology so it
can compete with established natural gas-based routes for manufacturing
hydrogen. Image Credit: Menon, Northeastern University.
Storage of Hydrogen
Safe, practical storage of hydrogen has been a major roadblock to
widespread use of the fuel. Storing hydrogen as a compressed gas or
liquid requires extremely high pressures, which results in expensive
tanks and risks of leaks or explosions.
Locking hydrogen into solid materials has long been seen as the way
forward. Hydride-forming materials can absorb hydrogen and store it
securely at much higher densities than are available by other means.
However, conventional materials cannot store very large amounts of
hydrogen, and require extremes of temperature to make the capture and
release of hydrogen efficient enough for commercial applications.
Nanostructured materials have unique and tunable properties which
are much more suited to this application. Research teams around the
world have hunted down nanomaterials which are capable of storing
hydrogen at high densities. The key is to find a material which has
controllable hydrogen affinity, and can absorb and release its full
capacity of fuel in the shortest time possible.
In 2011, scientists at Lawrence Berkley National Laboratory
developed a composite material composed of magnesium nanoparticles
embedded in a flexible organic polymer matrix. The material is capable
of selectively absorbing hydrogen gas, storing it safely at high
densities as magnesium hydride, and releasing it rapidly when required.
Figure 3. Magnesium
nanoparticles in a polymer matrix could contain hydrogen safely and in
high density, allowing it to be stored and transported efficiently. Image credit: Lawrence Berkeley National Laboratory.
Nanotechnology seems to hold the key to viable solutions to the two
biggest problems holding back the hydrogen economy: production of
hydrogen using renewable energy sources, and safe storage and
distribution of hydrogen around the world.
Photocatalytic production of hydrogen from water and storage of
hydrogen using novel nanomaterials could form the basis of a viable
distribution infrastructure, effectively allowing vehicles and local
combined heat and power (CHP) systems to run on solar energy, stored as
clean and efficient hydrogen fuel.