A team of researchers from the Universitat Politècnica de Catalunya · BarcelonaTech (UPC) collaborated with the experts from the Catalan Institute of Nanoscience and Nanotechnology (ICN2) to design a stable and efficient photocatalyst that can produce hydrogen directly using sunlight. Their findings are discussed in the paper "Facet-engineered TiO2 drives photocatalytic activity and stability of supported noble metal clusters during H2 evolution."
Hydrogen Production Using Titanium Dioxide
Hydrogen is vital for energy transition as long as it is derived from renewable sources. It has been known that electrons in some semiconductor devices can participate in chemical reactions when illuminated with sunlight.
This happens in titanium dioxide, a cheap and harmless material widely used as a white pigment in papers, cosmetics, paints, inks, and plastics. The excited electrons in this compound can generate hydrogen from the photons in water and other organic materials. However, hydrogen production is deficient because electrons prefer to relax rather than react. As a result, the efficiency of the process is too low from a practical point of view.
Most efforts to improve titanium dioxide's photocatalytic activity are directed toward synthesizing highly exposed anatase surfaces. It is well known that the photocatalytic activity of noble metal-loaded titanium dioxide heavily relies on the interactions between the co-catalysts and titanium dioxide support, which are specific to the anatase surfaces and metal species.
Harnessing the Power of Light
Overcoming this limitation has been the goal of experts from UPC and ICN2. They tried to achieve this by bringing titanium dioxide into contact with metal nanoparticles, which function as electron filters. This extends the life of the electrons in an excited state to allow them to react and produce hydrogen. Such a mechanism allows the team to achieve hundreds of times higher yields.
This study is considered a step forward for sustainable hydrogen production. Led by professor Jordi Llorca from the ENCORE-NEMEN and Ramón y Cajal researcher Lluís Soler, the researchers used a mechanochemical process to deposit metal clusters on titanium dioxide nanoparticles of different morphologies.
The team discovered that titanium dioxide's different exposed crystallographic faces also play an essential role in producing hydrogen. The stability of the photocatalyst and the strength of electron transfer between the semiconductor and the metal nanoparticles are related to the semiconductor's exposed faces. These faces are responsible for atom mobility and aggregation.
Llorca and Soler obtained precise results from their investigations. Upon depositing platinum clusters on octahedral titanium dioxide nanoparticles, they got a photocatalyst that produces higher quantities of hydrogen and is much more stable than any other combination.
To understand the collected data, Ramón y Cajal researcher Claudio Cazorla conducted quantum mechanical calculations to investigate the electronic structure of the photocatalysts. It was further compared with the X-ray photoelectron spectroscopy results taken from UPC's Research Center in Multiscale Science and Engineering.
The research team is hopeful that the outcomes of their research will allow the creation of novel catalysts for the efficient and sustainable production of clean fuel in the form of green hydrogen.
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