Synthesis Of Nanocatalyst Supported On TiO₂ Photoanodes And Study Of Their Photoelectrochemical Water Splitting Performance

To solve the increasingly serious resource shortage and environmental pollution problems,hydrogen energy is becoming more and more popular as a green energy source.Hence,photoelectrochemical(PEC)water splitting using semiconductor materials has attracted great attention as a reliable approach to produce hydrogen.As is known,TiO2 is widely used as photoanodes in PEC applications due to its nontoxicity,lost cost and good stability.However,some inherent problems still need to be solved.First of all,TiO2 only absorb sultraviolet light(it only holds a proportion of 4% in the whole solar spectrum)because of its wide band gap.Moreover,it always suffers from electron-hole recombination,which decreases its photo conversion efficiency.Thus expanding absorption region and accelerating separation of photogenerated carriers are pivotal ways to enhance the PEC performance of TiO2.In this paper,three-dimensional(3D)TiO2 nanoflowers(NFs)were used as photoanode,and a suitable narrow-bandgap nanophotocatalyst was loaded thereon to construct a heterojunction to improve light absorption and suppress combination of photogenerated carriers.The specific research contents are as follows:1.TiO2 seed solution was spin-coated on the FTO conductive glass by a sol-gel method to prepare TiO2 film,and the 3D flower-like structure of TiO2 was further grown on the TiO2 film by hydrothermal method.TiO2 NFs have a larger specific surface area,which increase the active site of the reaction,facilitate the loading of the catalyst and expand the contact interface of electrode/electrolyte.In view of the fact that TiO2 has no visible light response,we deposited narrow band gap CdS quantum dots(QDs)on TiO2 NFs as a photocatalyst to sensitize TiO2 NFs by a facile successive ionic layer adsorption and reaction(SILAR)method,and formed TiO2 NFs/CdS photoanodes.The experimental results show that the PEC performance of the samples was significantly improved.The improved PEC performance results from the broader absorption range of TiO2 NFs/CdS and effectively separation of photogenerated electron-hole pairs due to a reasonable loading amount of CdS QDs on TiO2 NFs.Under AM 1.5G and visible light illumination,the highest photocurrent density of the TiO2 NFs/CdS was about 48 times and 118 times compared with that of pure TiO2 NFs,respectively.By coupling electron collector and transferlayer into the TiO2 NFs/CdS photoanodes,charge recombination in Pt/TiO2 NFs/CdS photoanodes were efficiently suppressed since the Pt layer facilitate the electrons to the opposite directions,which is the key to further improve the PEC performance of the samples.2.The preparation of TiO2 NFs and the deposition of CdS QDs were the same as in the previous section.MoS2 nanosheets(NSs)were prepared by hydrothermal method.Through dipping method,we designed and constructed ternary TiO2/CdS/MoS2 hybrids,which was composited with CdS photocatalyst and MoS2 co-catalysts.The design of two type II junction between CdS QDs/MoS2 NSs and TiO2 NFs/CdS built up a multi-step separation of photogenerated carriers,which further increased the PEC performance of TiO2/CdS/MoS2.The outer layer is MoS2 NSs with the smallest band gap and good light stability.The middle layer is CdS QDs and the inner layer is TiO2 NFs.Through the characterization and PEC measurements,it was found that due to the wide absorption of visible light,the separation and transfer speed of carriers was fast,and the PEC performance was greatly improved.Under AM 1.5G and visible light illumination,the highest photocurrent density of the TiO2/CdS/MoS2 was about 3 times and 10 times compared with that of pure TiO2/CdS,respectively.3.TiO2 NFs and MoSe2 NSs were prepared by hydrothermal method,and the TiO2 NFs were modified by MoSe2 NSs through a simple dipping method.Compared with MoS2,layered structure MoSe2 with 1T phase shows better conductivity and favors the electrochemical reactions,and thus has the ability to serve as a catalyst for hydrogen evolution reaction.Ultraviolet-visible absorption(UV-VIS)and photoluminescence(PL)spectra indicated that the formed TiO2 NFs/MoSe2 structure exhibited higher visible light absorbance and effectively accelerated the charge separation and transportation.The PEC test showed that the highest photocurrent density of TiO2 NFs/MoSe2 samples was significantly improved under AM 1.5G and visible light illumination,which was about 5 times and 10 times that of pure TiO2 NFs,respectively.Moreover,all samples showed good stability during the period of 450 s.