New efficient nanocatalysts for producing hydrogen energy produced by sunlight
The University of Oulu’s NANOMO research unit has developed three efficient heterogeneous composites that use sunlight as an energy source and water as a raw material to produce hydrogen gas.
Hydrogen is the cleanest fuel used by humans. If hydrogen is still produced as cleanly as possible, for example directly from sunlight, it is also completely renewable. In practice, hydrogen would thus be a completely carbon-free option and could displace the use of carbon-based energy sources with a more sustainable option. Today, commercially available hydrogen is produced almost entirely from non-renewable natural gas through reform. Hydrogen produced from natural gas brings with it climate-changing carbon dioxide (CO2) emissions.
The tremendous potential of hydrogen as a completely clean and renewable energy source has been identified half a century ago, when scientists originally managed to photocatalytically produce pure hydrogen with ultraviolet light. On a large scale, the utilization of photocatalysis has not progressed because the efficiency of photocatalysis has so far been too low.
However, researchers around the world have been researching and developing a variety of synthetic photocatalyst materials at an accelerating pace to improve efficiency and make the price of solar hydrogen competitive. The interest is specifically in the development of catalysts operating with visible light, as this would allow a significant part of the energy contained in the light to be utilized.
The catalysts developed by NANOMO researchers are based on nanoscale heterocoupling semiconductor composite structures. The catalyst collects energy from visible light, uses the energy to break down water molecules (H2O) and form two hydrogen atoms to form a hydrogen molecule. The process also releases a small amount of oxygen. The catalyst is based on a semiconductor material and a conductive metal. The semiconductor collects energy from light and oxidizes water and transfers electrons across the semiconductor-conductor interface to a conductor where a hydrogen ion pair (2H +) is reduced to a hydrogen molecule (H2). It is important for the operation of the catalyst that all steps work as well as possible.
In the studied catalysts the challenges of photocatalytic hydrogen production are efficient capture of sunlight, ie the photons contained in the light, into the semiconductor, the ability to convert photon energy into semiconductor electron excitation state, for a long time (to reduce hydrogen ions). Water molecules must adhere well to the semiconductor for oxidation and, correspondingly, hydrogen ions must be attracted to the metal for reduction. It is about optimizing quantum mechanical and chemical phenomena, which requires theoretical and experimental research in atomic-level physics. The process must also maintain balance, i.e. oxidation and reduction must take place in the right proportions.
So far, the three most promising composites of NANOMO are based on MoS2-Ag-Ni, Bi2O2CO3 / Bi2WO6 (iodine doped) and TiO2-Ag-Ni structures. All three have shown good photocatalytic properties in the production of hydrogen by sunlight (visible). The quantum efficiency of MoS2-Ag-Ni and Bi2O2CO3 / Bi2WO6 has been 7% and 14.9%, respectively. The efficiency is approaching that of commercial photovoltaic panels. 1 gram of TiO2-Ag-Ni catalyst has produced 86 moles of hydrogen per hour in experiments under 1 watt white LED lighting. The research conducted by NANOMO covers applied experiments, experiments on the development of photocatalysis scaling, and sheds light on the function and mechanisms of catalysts at the level of quantum mechanics not only experimentally but also theoretically.
Recent research demonstrates the role of the NANOMO research unit at the world’s leading level in the development and research of photocatalysts. The unit is pioneering work that uses fundamental new concepts for research and innovation in functional materials. Pilot experiments on photocatalysts have been carried out and developed in a project for which the unit has received funding from the European Regional Development Fund. The project is led by Associate Professor Wei Cao and Professor Marko Huttula.
Materials solutions have already been granted patents in Finland and the latest results have been published at the top level in the Chemical Engineering Journal and RSC Advances.
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