Question

?n-type semi-conductor contacts with aqueous electrolyte in dark, the equilibrium condition is shown in the diagram. Please explain what is going to happen when the system is under illumination? Also explain why reaction is significant in Green Chemistry.

Answer 1

It's about the photoelectric effect and water splitting with sunlight using photoelectrochemical cell (PEC) to produce hydrogen.

Extraction work for Platinum is (according to some sources): 6.35 eV (this corresponds to a wavelength of ~195 nm. This in the UV region of the spectrum).

Contact between two electrodes immersed in the electrolyte (no illumination) results in charge transfer until the work functions of both electrodes equilibrate. Under light illumination, the excited electrons move to cathode (Pt) where water reduction occurs. The generated holes move towards anode/electrolyte interface (left side electrode) where water oxidation takes place.

For Green Ch: no residues appear in this reaction.