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    Catalysis: Route toward green hydrogen

    Solar-driven catalytic ultra-thin films and protective layers: Cutting-edge Technology for Provision of Green Hydrogen production
    Nowadays, hydrogen is mainly produced by the steam reforming of natural gas (50%), a process which leads to massive emissions of greenhouse gases . About 30% is from oil/naphtha reforming from refinery/chemical industrial off-gases, 18% from coal gasification, 3.9% from water electrolysis, and 0.1% from other sources . Electrolytic and plasma processes demonstrate a high efficiency for hydrogen production, but unfortunately they are considered as energy intensive processes .

    By considering the green hydrogen project, photoelectrolysis which work withn the same principle of photocatalysis, is one of the renewable ways of hydrogen production, exhibiting promising efficiency and costs, although it is still in the phase of experimental development. Currently, it is the least expensive and the most effective method of hydrogen production from renewable resources.

    In this research project, green hydrogen initiative, we are proposing the use of photoelectrolysis techniques, the work extends of a promising recent results from the fabrication of thin film semiconductor materials at the UNAM Material Science Research Centre (UMSRC) to be used as the photoelectrodes. These photoelectrodes will then act as semiconducting device absorbing solar energy and simultaneously creating the necessary voltage for the direct decomposition of water molecule into oxygen and hydrogen.

    Photoelectrolysis utilizes a photoelectrochemical light collection system for driving the electrolysis of water. If the semiconductor photoelectrode is submerged in an aqueous electrolyte exposed to solar radiation, it will generate enough electrical energy to support the generated reactions of hydrogen and oxygen. When generating hydrogen, electrons are released into the electrolyte, whereas the generation of oxygen requires free electrons.The reaction depends on the type of semiconductor material and on the solar intensity. So far we manage to fabricate Ag/TiO2 thin films photoelectrodes which produce current density of 10–30 mA/cm2 depend on the Ag/TiO2 molar fraction . At these current densities, the voltage necessary for electrolysis is approximately 1.35 V.

    The photoelectrode can be also comprised of thin film semiconductors layer sush as pure TiO2 or Cu2O thin films, currently fabricated at UNAM using the molecular precursor methods and spin-coating at our UMSRC. Thus, the solar-driven technology ultra-thin film paves the way for overcoming two reasons behind the low overall process efficiencies of past photoelectrolysis treatment concepts including:
    • * Absorbing a broad enough range of wavelengths of sunlight; and
    • * Speeding up the slow reaction times that have been typically reported.

    The other important component of a photoelectrolysis techniques is the presence of a catalytic layer. The catalytic layers of the photoelectrochemical cell influence the performance of the electrolysis and require suitable catalysts for water splitting. The catalyst layer has a microstructure of ionomer, Pt-deposited carbon, and pores and this can be changed by various means. The catalytic layer can be prepared with the assistance from the Institute for Microstructure Technology (IMT), Germany. The preparation of the microstructures for the Pt-carbon can be done using any of the two most common Physical Vapor Deposition (PVD) coating processes: Sputtering or Thermal Evaporation.

    The protective layers and encased layers are another important components of the photoelectrolysis which prevents the semiconductor from corroding inside the aqueous electrolyte. This layers must be highly transparent in order to be able to provide the maximum solar energy, so that it could reach the thin film semiconducting layer. These layers can be prepared in collaboration with the Institute of Advanced Membrane Technology (IAMT). In this current research project, researchers at two institutes within KIT (IMT & IAMT) in Germany and UNAM have partnered together to further develop a solar-driven water treatment technology based on a combination of membrane filtration and photocatalysis.
    The students involved in this project will be able to in rolled in either of the following academic programs that are already offered at UNAM:
    • Msc/ PhD in Chemistry
    • Msc in Renewable Energy (Material Science)