| Recently,TiO2 semiconductor has received continuous attention in the field of photoelectrochemical(PEC)water splitting and PEC hydrogen production due to its superior physical and chemical properties,excellent photocorrosion resistance and nontoxicity.However,as a wide band gap semiconductor(3.2 eV),TiO2 can only absorb UV light and its charge recombination rate is high,resulting in low utilization of solar energy.Therefore,improving visible light harvesting ability,effective separation of charge carriers and substantial prolongation of charge carrier lifetime are vital issues for a TiO2-based photoanode.In this thesis,TiO2 nanowire array photoanode was fabricated via hydrothermal methos,then binary TiO2/CdS and ternay TiO2/CdS/Cu2O nanowire array photoanodes were fabricated by growing CdS nanoparticles on TiO2 nanowire arrays and Cu2O nanoparticles on TiO2/CdS nanowire arrays,respectively.The composition,crystalline phase,morphology and size of the nanowire arrays were characterized.Light absorption ability,transfer and separation process of photoproduced charge carriers,charge carrier lifetime,PEC performanec and PEC H2 production of the nanowire arrays were studied.The main contents and conclusions of this thesis are give as following:(1)A modified hydrothermal method was employed to prepare TiO2 nanowire arrays on fluorine-doped tinoxide(FTO)glasses using tetrabutyl titanate as Ti sources.Then,the TiO2 nanowire arrays were annealed at different temperatures.The effect of annealing temperature on the crystal quality was studied.The results show that the crystal quality of the nanowire arrays increas with the increase of annealing temperature.And the prepared sample is composed of rutile TiO2 nanowire arrays with a diameter of about 100 nm.Light absorption measurements show that absorption edge the TiO2 nanowire arrays is about 400 nm.The PEC performance show that the highest current density of 0.59 mA cm-2 is achieved for the TiO2 nanowire arrays,which were prepared by annealing at 450? for 30 min.(2)An improved successive ionic layer adsorption and reaction(SILAR)was used to prepare TiO2/CdS nano wire arrays by growing CdS nanoparticles on the surface of TiO2 nano wire arrays using Cd(NO3)2·6H2O and Na2S·9H2O as Cd and S sources,respectively.The effect of SILAR cycles on the light absorption ability and PEC performance of the TiO2/CdS nanowire arrays was investigated.The results demonstrate that the prepared TiO2/CdS nanowire arrays exhibit improved visible light absorption capability with an absorption edge of 550 nm.In addition,a three-electrode electrochemical workstation was employed to evaluate the PEC performance of the nanowire arrays.The experimental results show that the heterogeneous TiO2/12CdS nano wire array photoanode fabricated via 12 SILAR cycle times obtains the highest photocurrent density.The photocurrent density of this heterojunction photoanode reaches up to 5.3 mA cm-2,which is 9 times that of the TiO2 nanowire array photoanode.Electrochemical impedance spectroscopy(EIS)was used to evaluate the trannsfer and separation process of photoproduced charge carriers.The results demonstrate that the enhanced PEC performance of the TiO2/12CdS is attributed to the effective transfer and separation of the photoproduced charge carriers.(3)A modified chemical bath deposition(CBD)was employed to prepare TiO2/12CdS/Cu2O nano wire arrays by growing Cu2O nanoparticles on the surface of TiO2/CdS nanowire arrays using Cu2SO4 as Cu source.Light adsorption measurements show that the obtained TiO2/12CdS/Cu2O nanowire arrays display superior visible light capture capability with an absorption edge of 650 nm.PEC measurements demonstrate that the prepared TiO2/12CdS/Cu2O nanowire arrays exhibit significantly enhanced PEC water splitting ability.The photocurrent density can reach 6.4 mA cm-2,1.2 times that of TiO2/12CdS and 10.5 times higher than TiO2 nanowire arrays,respectively,under simulated light irradiation.Moreover,the prepared TiO2/12CdS/Cu2O nanowire arrays achieve the maximum solar-to-hydrogen(STH)energy conversion efficiency of 4.3%and the highest incident photon to current efficiency(IPCE)of as high as 32.3%.And the H2 production rate of the TiO2/12CdS/Cu2O nano wire array photoanode is greatly increased to 214.3 ?mol h-1 cm-2,which is 8.1 and 1.8 times higher than that of TiO2(26.04 ?mol h-1 cm-2)and TiO2/12CdS(120.8 ?mol h-1 cm-2)nanowire array photoanodes,respectively,under bias-free simulated light irradiation.The measurements of EIS and photoluminescence(PL)were used to evaluate the transfer ansd separation process of charge carriers in TiO2/12CdS/Cu2O heterojunction nano wire arrays.In addition,the charge carrier lifetime of TiO2/12CdS/Cu2O heterojunction nanowire arrays was evaluated via measuring transient open-circuit voltage decay(OCVD),showing that the average charge carrier lifetime within the TiO2/12CdS/Cu2O nanowire array photoelectrode is substantially prolonged,compared to that of the bare TiO2 and heterogeneous TiO2/12CdS nanowire array photoelectrodes.The experimental results of light absorption,photoluminescence and electrochemical spectra show that the improved PEC H2 generation is ascribed to(i)significant enhancement for visible-light harvesting ability and(ii)effective space charge separation and substantial prolongation of charge carrier lifetime,which are achieved by synergetic effects of the type-II band alignment with a stair-like structure and the p-n junction. |
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