Preparation Of Metal-semiconductor Composite Nanomaterials And Study On Their Performance For Photoelectrocatalysis

Hydrogen is a clean and efficient new energy that can be used to replace traditional energy.Semiconductor photoelectrochemical（PEC）water splitting to produce H₂ has become one of the most promising hydrogen production methods.However,due to the wide band gap and high photo-generated electron-hole pair recombination rate,pure semiconductor has a narrow photoresponse range and low photocatalytic efficiency.Noble metal nanoparticles have been widely used to improve the photocatalytic efficiency of semiconductors due to the unique surface plasmon resonance（SPR）effect.There are three main enhancement mechanisms for the composite system of precious metal nanoparticles（NPs）and semiconductors:（1）photon enhancement（light trapping）,（2）direct electron transfer（DET）,and（3）plasmon-induced resonance energy transfer（PIRET）.Photon enhancement is ubiquitous in precious metal-semiconductor composite systems,but Schottky contact and spectral overlap are two key factors that control the DET and PIRET processes,respectively.Based on the principles of DET and PIRET,we designed and synthesized three nanocomposites（NCs）,and studied their PEC water splitting performance and influencing factors.In particular,the designed materials are all sorted in the structure of metal core and semiconductor shell,which not only protects the precious metal nanoparticles from damage,but also maximizes the active interface.In addition,TEM,UV-Vis,SEM,EDS,XRD and other methods are used to characterize the microstructure and performance of NCs.The research in this article is mainly divided into the following three parts:（1）The ascorbic acid-assisted method was used to prepare precious metal nanoparticles@ZnO core-shell structure NCs,and the shape of precious metal NPs（spherical and rod-like）were adjusted.The PEC water splitting properties of NCs were studied.The results show that the metal@ZnO NCs exhibits significantly better photocurrent response than pure ZnO or a mixture of metal NPs and ZnO,which is related to the effective DET mechanism.Meanwhile,the photocurrent of metal@ZnO NCs varies with the thickness of ZnO,and has an optimal thickness for each metal core.In addition,compared with pure Au NP,Au@Ag NP has higher PEC activity,which can be attributed not only to the lower Schottky barrier between Ag and ZnO,but also to the wider SPR band of Au@Ag NP.（2）The AgNS@SiO₂@ZnO triple core-shell NCs were prepared by the ascorbic acid-assisted method,and their PEC activity under visible light was studied.The study found that the photocurrent response of AgNS@SiO₂@ZnO NCs is related to the thickness of the SiO₂ middle layer and the ZnO outer layer.AgNS@SiO₂（8nm）@ZnO（15 nm）NCs showed the highest photocurrent density and the smallest EIS radian,indicating that their PEC water splitting performance is better.In addition,AgNS@SiO₂@ZnO NCs has significantly enhanced PEC performance compared with pure ZnO and AgNS@SiO₂ NPs under visible light irradiation.We attribute the enhanced PEC activity to the transfer of plasmon resonance induced energy transfer from the metal core to the ZnO,increasing the effective separation of electrons and holes.（3）A series of novel AgNS@SiO₂@Cu₂O triple core-shell structure NCs were prepared by a simple aqueous solution method,and the thickness of the SiO₂intermediate layer and the Cu₂O outer layer were adjusted.Driven by visible light,AgNS@SiO₂@Cu₂O NCs exhibits a sensitive photocurrent response.In addition,the photocurrent response of AgNS@SiO₂@Cu₂O NCs is affected by the thickness of the SiO₂ intermediate shell and the Cu₂O outer shell.AgNS@SiO₂（5 nm）@Cu₂O（29 nm）NCs show the highest photocurrent and smallest EIS radian,indicating that their photo-generated carrier yield and PEC performance are better.Meanwhile,compared with pure Cu₂O,pure AgNS and AgNS@SiO₂ NPs,AgNS@SiO₂（5 nm）@Cu₂O（29 nm）NCs has better PEC water splitting activity.This indicates that the enhanced PEC activity of NCs is the result of the synergistic effect of AgNS and Cu₂O,and the PIRET mechanism was used to explain this result.