Production of Hydrogen by Photo-electrochemical methods

 

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.

Design and development of metal hydride storage devices


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.

Diffusion of hydrogen in alloys


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

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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