Hydrogen
fuel
cell
(HFC)
vehicles
are
currently
becoming
a
popular
choice among the
people
who
prefer driving
their car
under
an 'emission
free'
label.
In
fact,
today
leading
automobile
manufacturers
such as Toyota, Honda and BMW are now in this business and
conduct further research
to develop
much
more
efficient
hybrid
HFC
cars. This recent report in CNN shows that the commercial HFC cars will emerge in near future not only to cater this niche market but also for general public. http://edition.cnn.com/2012/11/25/business/eco-hydrogen-fuel-cell-cars/index.html
 |
| http://www.ornl.gov/info/ornlreview/v38_1_05/article06.shtml |
In
a HFC,
chemical
energy
in
hydrogen
is
converted
into
electricity by
combining
with
oxygen
in
a electrochemical cell and producing
water
as
the
only
by
product.
Hence,
it has
zero
emissions
unlike
in
the
case
of
fossil
fuel
driven vehicles, which
produces
CO2
and
various
other
harmful
chemicals.
It has
also
revealed that
fuel
efficiency
of
HFC
driven
vehicles
are
much
higher
than
conventional
petroleum
vehicle.
Despite
the
immense
research
carried out during the last
couple
of
decades, there
are still a number of major challenges for
practical onboard HFC applications including production
and
storage of hydrogen.
 |
http://autotechsforum.com/archives/448
|
Even
though hydrogen
is
one
of
the
most
abundant
elements
on
earth
(in
the
form
of
water),
molecular
hydrogen
(H2
gas) is
not
freely
available,
hence
has
to be
produced
using
another
energy
source.
Therefore,
hydrogen
used
in
HFCs
is not described
as
a
energy
source
but
only
as
a
energy
carrier. Currently
most
hydrogen
is
produced
from
coal and natural gases,
which
should
not
be
a sustainable long
term
solution,
because they produce
green
house
gases in the
process. Use of nuclear
power
to
produce
hydrogen
is
another
possibility despite
the inherent risk associated with nuclear plants. Nevertheless most research is focused on the production of hydrogen from renewable sources such as biomass, photolytic and fermentative micro-organism systems, and photoelectrochemical systems.1,2
Another
speculated method
is to split
water
by
electrolysis
in order to
produce
hydrogen
using
the
solar
energy. 1,2,3
 |
Jena,
P.; J. Phys. Chem. Lett. 2011, 2, 206-211
|
Currently, hydrogen is stored in HFC driven vehicle in high pressure tanks which is not a efficient way of storing hydrogen because it has much less energy density. Onboard hydrogen storage systems must have reasonable storage capacity [5.5 wt% , accordingly to US Department of Energy (DOE) 2017 target], reversibility, fast kinetics, safety, and cost effectiveness. Furthermore, mild operating conditions such as a temperature between -40 to 60 0C and delivery pressure not exceeding 12 bar have been recommended by the DOE for such a system.1,2
Hydrogen
storage
research
mainly
focuses
on
developing
chemical
hydrogen
storage
materials.
Sorbent
materials
and
complex
hydrides
are
two
main
categories
of
chemical
hydrogen
storage.
Sorbent
materials,
physisorb
molecular
hydrogen
through
weak
dispersion
forces,
hence
it
has
a
low
hydrogen
binding
energy
typically
in
the
range
of
4
-
8
kJ/mol.4
As
a
result,
these
materials
have
good
reversibility
and
fast
kinetics,
but
have
limited
hydrogen
storage
capacity
at
ambient
temperature. Examples
in this
category
are
fullerines, graphenes, carbon aerogels, metal organic frameworks, etc. Recent
research
revealed
that
imposing
heterogeneity
in
the
porous
structure
by
adding
transition
metals (e.g.
Ni,
Pt,
Ru,
Ti
and
etc),
alkali
and
other
metal
ions,
and
surface
modification
with various functional
groups can
enhance
the
hydrogen
binding
energy.
Further
improvements
in
hydrogen
storage
can
be
obtained
by
optimizing
pore
sizes
and
increasing
the
specific
surface
area.
In
contrast
to
hydrogen
physisorption
in
the
sorbent
materials,
hydrogen
is
chemisorbed
(dissociated
atomic
hydrogen
is
chemically
bonded)
into
the
bulk
of
the
material
in
complex
hydrides.
This
requires
much
more
energy
to
desorb
hydrogen
and
results
in
slower
sorption
kinetics.
Hence,
much
higher
temperatures
are
required
for
sorption
process
(adsorption
/
absorption
and
desorption).
However, none of the storage systems studied so far have satisfied the entire
onboard hydrogen storage requirements listed above.
Scientists
and
engineers
in
various
laboratories
are
still
working
to
develop
solid
state
materials
for
on-board
hydrogen
storage,
to find the most efficient
way
to
produce
hydrogen
using HFC technology.
If
everything
goes
well
there
can
there
be
a
day
in
future,
when water
(hydrogen) powered car is a reality.
 |
| http://www.gasdetection.com/news2/health_news_digest131.html |
References
2.
Broom,
D. P., Hydrogen Storage Materials The Characterisation of Their Storage
Properties, 1st ed.; Springer: New York, 2011.
3.
Jena,
P., Materials for Hydrogen Storage: Past, Present, and Future. The Journal
of Physical Chemistry Letters 2011 2, 206-211.
4.
Bhatia,
S. K.; Myers, A. L., Optimum Conditions for Adsorptive Storage. Langmuir 2006,
22, 1688-1700.
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