Photocatalytic water splitting
A photon with an energy greater than 1.23 eV is needed to generate an electron–hole pairs, which react with water on the surface of the photocatalyst.
In the laboratory, this challenge is typically overcome by coupling the hydrogen production reaction with a sacrificial reductant other than water.
[6] Materials used in photocatalytic water splitting fulfill the band requirements and typically have dopants and/or co-catalysts added to optimize their performance.
A sample semiconductor with the proper band structure is titanium dioxide (TiO2) and is typically used with a co-catalyst such as platinum (Pt) to increase the rate of H2 production.
A key principle is that H2 and O2 evolution should occur in a stoichiometric 2:1 ratio; significant deviation could be due to a flaw in the experimental setup and/or a side reaction, neither of which indicate a reliable photocatalyst for water splitting.
The prime measure of photocatalyst effectiveness is quantum yield (QY), which is: To assist in comparison, the rate of gas evolution can also be used.
The treatment ultimately reduced the amount of surface Zn and O defects, which normally function as recombination sites, thus limiting photocatalytic activity.
[11] Proton reduction catalysts based on earth-abundant elements[12][13] carry out one side of the water-splitting half-reaction.
[14] Ru(II) with three 2,2'-bipyridine ligands is a common compound for photosensitization used for photocatalytic oxidative transformations like water splitting.
In 2014 researchers announced an approach that connected a chromophore to part of a larger organic ring that surrounded a cobalt atom.
Transient absorption optical spectroscopies indicate that charge recombination occurs through multiple ligand states within the photosensitizer modules.
[40] An Indium gallium nitride (InxGa1-xN) photocatalyst achieved a solar-to-hydrogen efficiency of 9.2% from pure water and concentrated sunlight.
The effiency is due to the synergistic effects of promoting hydrogen–oxygen evolution and inhibiting recombination by operating at an optimal reaction temperature (~70 degrees C), powered by harvesting previously wasted infrared light.
[42] Textural, structural and surface catalyst properties were determined by N2 adsorption isotherms, UV–vis spectroscopy, SEM and XRD and related to the activity results in hydrogen production from water splitting under visible light.
It was reported that the crystallinity and energy band structure of the Cd1-xZnxS solid solutions depend on their Zn atomic concentration.
Variation in photoactivity was analyzed for changes in crystallinity, level of the conduction band and light absorption ability of Cd1-xZnxS solid solutions derived from their Zn atomic concentration.
