Preparation And Research On Photoelectrochemical Properties Of TiO₂ And TiO₂-based Composite Photoelectrodes

In the field of photoelectrochemical?PEC?water splitting for the evolution of H₂and O₂,TiO₂ as an n-type semiconductor has attracted much attention because of its low cost,non-toxicity,good stability,and suitable conduct/valence band positions for splitting water.However,the wide band gap,slow charge separation and migration efficiency severely limit the practical application of TiO₂.Therefore,developing TiO₂-based photoelectrodes with visble light absorption abiliy,high carrier separation and utilization efficiency is vital in the research of TiO₂ for PEC water splitting.At present,coupling another semiconductor can not only broaden the photoresponse range of TiO₂ in practical application,but also improve its carrier separation and transfer efficiency.Therefore,in this work,rutile TiO₂ nanorod array films were prepared by hydrothermal method,and TiO₂/Cu₂O core-shell structure and anatase TiO₂/rutile TiO₂?r-TiO₂/a-TiO₂?three-dimensional structure hetero-/homojunction were successfully fabricated.Then,the hetero-/homojunction photoelectrodes were further modified with non-noble metal Al and oxygen vacancies,respectively.The stability and catalytic activity of TiO₂-based composite electrodes in practical applications are improved.The results show that the photocurrent density of TiO₂/Cu₂O core-shell structure modified with non-noble metal Al is up to 4.52 mA?cm^-2?1.23 V vs.RHE?,5.95 times than that of bare TiO₂.Through PEC measurements,it is proved that Al with SPR effect and narrow bandgap semiconductor Cu₂O siginificantly improve the visible light absorption of TiO₂,and the built-in electric field of the TiO₂/Cu₂O p-n heterojunction can accelerate the separation and transmission of carriers.At the same time,owing that the Al and the dense Al₂O₃ layer formed naturally on the Al surface can protect the Cu₂O from corrosion,stability and catalytic activity in applications of photoanodes show significant improvements.Moreover,the urchin-like anatase TiO₂ was loaded on r-TiO₂ nanorods by a two-step hydrothermal method,and then the r-TiO₂/a-TiO₂ was treated with acid to introduce abundant oxygen vacancies.The photocurrent density reaches 1.14 mA·cm^-2?1.23 V vs.RHE?,1.6 times than that of r-TiO_2.Comparative experiments show that the improvement of performance in practical application is due to the highly matched lattice of the homojunction which could effectively reduce the content of internal defects,thus inhibiting the recombination of photogenerated electrons and holes.The formed gradient energy level can promote the separation and transfer of carriers and the introduction of oxygen vacancies could provide abundant electrons and improve the conductivity of the electrodes.Meanwhile,the introduction of oxygen vacancies can provide plenty of reaction sites and promote surface water oxidation reaction kinetics.