High electron density favours better reduction reaction of subject in interest (for eg. CO2 photoreduction into fuels like CO,CH4 etc or Proton reduction to H2).
In cass of bandgap: Smaller band gap is always beneficial for photocatalytic reaction because of maximum solar light absorbing capacity of the photocatalyst and in turn generating excess charge carriers in conduction and valence band BUT the conduction band edge should be higher and valence band edge should be lower wrt redox potentials of CO2, water oxidation and proton reduction.
If these conditions are well satisfied, the photocatalyst will have an efficient photocatalytic activity.
Regards.
Hello,
In order to increase the electronic densities on photocatalyst must load a metal, that act as collector of electron and declined the recombination process by increasing the separation between e-h pair, hence, the activity of semiconductor will improve. From the other hand, the band gap may be increasing or decreasing depended on the crystal sizes that produced according to the different amount and type of loaded metal.
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