| Solar energy is abundant and clean renewable energy,and converting it into chemical energy such as hydrogen energy through photocatalysis is an ideal way to utilize clean energy.Efficient photogenerated charge separation is the key to the smooth progress of the photocatalytic reaction,but it is restricted by bulk recombination or defect trapping.The polarization field of ferroelectric materials has been shown to facilitate the efficient separation of photogenerated charges and accelerate the migration of photogenerated charges from the bulk to the surface.However,the insufficient surface electrocatalytic activity and narrow light absorption range caused by the surface electronic structure,polarization shielding and energy band structure of ferroelectric PbTiO3 make it unable to exert efficient photocatalytic water splitting activity.In order to solve the above two problems,this paper explores the regulation mechanism of bifunctional cocatalyst RuO2 modification,interface modification of rutile TiO2 between PbTiO3 and RuO2,the regulation of oxygen vacancies on water splitting over PbTiO3 and the construction of CdS/PbTiO3/TiO2 three-phase structure,as a result of realizing photocatalytic total water splitting and the formation of different oxidized products by oxygen vacancies and effectively broadening the light absorption range.Bifunctional cocatalyst RuO2 modifies PbTiO3.The polarized surfaces of PbTiO3 can spontaneously adsorb external species in solution to shield the surface polarization,which affects the transport of photogenerated charges across the interface between photocatalyst and aqueous solution.Moreover,the water splitting reaction on the surface of perovskite oxide is sluggish.The poor crystalline RuO2 has excellent electrocatalytic activity for water splitting and can be used as a bifunctional cocatalyst to modify the surface of PbTiO3 and improve the catalytic activity.Such RuO2 was grown on the polarized surfaces of ferroelectric PbTiO3 by a one-step hydrothermal method.By controlling the content of RuO2,its distributions on the positive and negative polarities of PbTiO3 as hydrogengenerating and oxygen-generating cocatalysts,respectively,can effectively demonstrate the bifunctionality of RuO2 and achieve the photocatalytic overall water splitting of PbTiO3.To further improve the activity of photocatalytic water splitting of PbTiO3/RuO2,the interface modification of these two materials is also a powerful way.Based on the selective adsorption of H+ions on negatively polarized facet of PbTiO3 and their selective etching to Pb element,TiO2 is epitaxially precipitated on the negatively polarized surface of PbTiO3 as the interface layer between PbTiO3 and RuO2.Meanwhile,the highly close lattice constant of RuO2 and rutile TiO2 can promote the growth of rutile TiO2.Benefiting from the directionally distributed microstructure and high-quality interface,the construction of PbTiO3/TiO2/RuO2 further enhances the activity of photocatalytic overall water splitting.The stabilization of single domain in ferroelectric PbTiO3 is inseparable from the shielding of intrinsic defects particularly oxygen vacancies.However,the regulation of water splitting by oxygen vacancies in ferroelectrics has rarely been considered.A detailed experimental study together with theoretical calculations was conducted to establish oxygen vacancies dependent photocatalytic water splitting activity and product species.By comparing the water splitting activity and reaction product species of co-catalyst modified PbTiO3 with different oxygen vacancy contents,one can conclude that oxygen vacancies on the negatively polarized facets of PbTiO3 facilitate the oxidation of H2O to O2,while the defect-free sites prefer the oxidation of H2O to H2O2.Furthermore,the interplay coupling between oxygen vacancies and polarization strength affects absolute photocatalytic activity of water splitting by affecting photo-generated charge separation.Based on the intrinsic features of polarized surfaces of PbTiO3,CdS and TiO2 were selectively deposited on the positively and negatively polarized facets of PbTiO3 by a two-step hydrothermal process to construct a three-phase junction of CdS/PbTiO3/TiO2.This junction not only extends the absorption range of PbTiO3 but also lowers the Schottky barrier between PbTiO3 and cocatalyst.The combination of matched band structures,suitable spatial distribution and strong interfaces can greatly promote the separation of photo-generated electrons and holes in the junction.Consequently,compared to the counterpart PbTiO3/TiO2 without CdS,the visible light photocatalytic hydrogen production activity of CdS/PbTiO3/TiO2 is enhanced by two orders of magnitude. |
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