Enhancement Effects of Cobalt Phosphate Modification
on Activity for Photoelectrochemical Water Oxidation of TiO<sub>2</sub> and Mechanism Insights
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Abstract
Cobalt
phosphate-modified nanocrystalline TiO<sub>2</sub> (nc-TiO<sub>2</sub>) films were prepared by a doctor blade method using homemade nc-TiO<sub>2</sub> paste, followed by the post-treatments first with monometallic
sodium orthophosphate solution and then with cobalt nitrate solution.
The modification with an appropriate amount of cobalt phosphate could
greatly enhance the activity for photoelectrochemical (PEC) water
oxidation of nc-TiO<sub>2</sub>, superior to the modification only
with the phosphate anions. It is clearly demonstrated that the enhanced
activity after cobalt phosphate modification is attributed to the
roles of cobalt(II) ions linked by phosphate groups with the surfaces
of nc-TiO<sub>2</sub> mainly by means of the surface photovoltage
responses in N<sub>2</sub> atmosphere. It is suggested that the linked
cobalt(II) ions could capture photogenerated holes effectively to
produce high-valence cobalt ions, further inducing oxidation reactions
with water molecules to rereturn to cobalt(II) ions. This work is
useful to explore feasible routes to improve the performance of oxide-based
semiconductors for PEC water splitting to produce clean H<sub>2</sub> energy