Production
of Hydrogen by Photo-electrochemical
methods
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Major hydrogen production method as of now is
by
steam reforming of methane which results in the emission of
CO2.
Any
form of dependence on the fossil fuels cannot be considered as
environmentally
friendly and is not an assured source in the long run. Electrolysis of
water is
an ideal method of distributed hydrogen production if one can derive
the
electrical energy from renewable and non polluting sources.
Photoelectrochemical (PEC) water electrolysis is a single step hydrogen
production method, where in light energy is directly converted to
chemical
energy thus |
eliminating the inherent losses of the naive water
electrolysis. In
a typical PEC cell, the semiconducting photoanode, on shining with light,
develops holes and electrons thus causing reduction of water to
genarate oxygen
at anode and oxidation of H+ ions to generate hydrogen at
cathode.
An ideal photoanode material must be stable in the corrosive alkaline
or acidic
electrolyte medium, should have energy band gap such that “solar
energy” is
utilized to its fullest. Such materials have to be engineered upon due
to the
fact that the presently available materials are not suiting these
requirements.
At IIT Madras, a PEC hydrogen production setup has been developed and
preliminary studies on TiO2 thin films, grown
using
reactive RF magnetron sputter technique at different substrate
temperature, as
photoanode material have been carried out. We are in the
process
of developing novel photoanode materials which can utilize the maximum
solar
energy. |
Hydrogen in metals, composites and carbon
nanotubes
|
From
the
studies of hydrogen storage properties
of various types of alloys, we have already developed Zr and Mm (Mm =
Mischmetal) based materials having storage properties comparable to the
materials used in commercial hydrogen storage. Even though Magnesium
and Mg
based alloys have high hydrogen storage capacity, they have hard
activation
process, slow reaction kinetics and thigh work temperature. Currently
we are
focusing on the hydrogen absorption and kinetics of hydrogen absorption
studies of Mg-based composite materials, prepared by reaction ball
milling Mg
powder and catalytic alloy particles. |
High reversible adsorption of molecular hydrogen in carbon nanotubes (CNTs), have stimulated tremendous interests in the research community to exploit the lightweight novel carbon materials as ideal candidates for hydrogen storage devices. Due to the wetting properties of carbon nanotubes, their inner hollow cavityan serve as a storage medium for hydrogen. At IIT Madras, multiwalled carbon nanotubes (MWNTs) are synthesized by a novel technique by the catalytic decomposition of acetylene over alloy-hydride catalysts. |
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Design
and development of metal hydride storage devices
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A metal hydride based hydrogen storage device
has been designed
and fabricated. The device made of stainless steel (SS) can withstand high operating
pressure.
A porous sintered SS filter acts as a barrier for the alloy powder
through which hydrogen is distributed or collected from the alloy .Inbuilt heat
exchanger are provided to facilaite hydrogen charging and discharging.
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Diffusion
of hydrogen in alloys
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Apart from
the three major steps involved in the
hydrogen technology, the fundamental studies of hydrogen interstitial
diffusion
in materials is being carried out. The bulk diffusion
coefficients
of hydrogen have been measured from the kinetics of hydrogen absorption
reaction. An experimental facility working on the principle of
pressure reduction method has been specially designed and developed
using
stainless steel tube (NOVA), high pressure needle valves (NOVA) and
pressure
transducers for the measurements of diffusion coefficients in materials. |
Development of hydrogen
sensors and optical shutters
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Apart from the
three major steps involved in the hydrogen technology, the electrical
resistivity and
the optical properties of metal hydride thin films are being carried
out in
order to develop hydrogen sensors and optical shutters. An
experimental facility for the measurements of the electrical
conductivity of bulk and thin film metal hydrides is developed and is
used for
the identification of materials showing metal-semiconductor transition
upon
hydrogen interstitials accompanied by an optical effect in the visible
spectrum. |
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