Ni(OH)2 As a Hole Mediator for Visible Light-Induced Urea Photo-Oxidation

Urea, a major component of human urine, has been proposed as a source of electrolytic hydrogen. We describe here CdS-sensitized TiO₂ assembled with urea electrocatalyst, Ni(OH)₂, on fluorine-doped tin oxide (FTO) coated glass (FTO/TiO₂/CdS/Ni(OH)₂) used as photoanode to realize simultaneous urea oxidation and water reduction using visible light irradiation. A photoelectrochemical reactor is employed to demonstrate the Ni(OH)₂ can serve as hole mediator to drive urea oxidation. The steady-state response of the semiconductor-catalyst electrode in the photoelectrochemical system is investigated, and the photoelectrode transient charge dynamics are studied by employing transient absorption spectroscopy. The obtained carrier dynamics can provide useful information on the competitive processes such as charge transfer and/or recombination within the photoanode.