Rapid Screening Methods And Applications Of Photo-Catalysts Based On Scanning Electrochemical Microscopy

Solar energy is the most abundant nature resource and plays important roles in the sustainable developments of energy and environment domains.With the upspring of photoelectrocatalytic nanomaterials,the photovoltaic devices are widely used from water splitting for hydrogen production,through solar cells for energy conversion and storage,to pollutant decomposition in environmental protection.In general,photoelectrocatalysis involves charge separation,recombination,and transfer when the semiconductors are well-illuminated.Each of them can be the rate-determining step(rds)for photoelectrocatalytic reactions.To improve photoelectrocatalytic efficiency,organic dyes or quantum dots are often adopted as "sensitizers" for the titanium dioxide(TiO2)nanomaterial-based solar cells.However,the electrolyte,redox couple,as well as the counter electrode should be selected carefully to match the sensitized TiO2 photoanode.All of these factors make the photoelectrocatalysis a complex system.Because of the lack of theoretical guidance,huge workload has to be tried to optimize the technical formula of photocatalysts with the demo photovoltaic devices.Thus,in order to investigate the kinetics of photoelectrocatalysis,one has to screen and find out the optimized photoelectrochemical system.Scanning electrochemical microscopy(SECM),in which an ultramicroelectrode(UME)is used as the scanning probe,has the advantage of obtaining the information on chemical reaction with high spatial resolution.Thus,SECM has become a high-throughput imaging technique for the screening of catalysts.The thesis is mainly base on scanning electrochemical microscopy and combinational chemistry to achieve rapid and high detection of photocatalysts with excellent properties and higher photocatalytic activity.The main work and results are summarized as follows:(1)Based on the method for rapid screening of photocatalysts using scanning electrochemical microscopy,we adopt a facile microfabrication method to isolate the substrate area other than the catalyst array from not only the electrolyte solution but also the light illumination.Consequently,the imaging quality has been promoted dramatically due to suppressed background current.Then,this method is applied to characterize the performance of the quantum dots sensitized solar cell(QDSSC)system,in which the QD sensitizers were loaded on the TiO2 nanoparticles through SILAR.The experimental results show this method is also useful to optimize the technical processing route of QDSSCs,such as the SILAR procedures,illumination intensity,and so on.(2)Combining SECM imaging mode with combinatorial chemistry methodology,we proposed a high-throughput and high signal/noise ratio screening method for the optimization of the binary QDs co-sensitized solar cells.On the basis of the optimized technical protocols screened by SECM,the PbxCd1-xS/CdS QDs co-sensitized TiO2 solar cell achieves a short circuit current density of 24.47 mA/cm2,an open circuit potential of 421 mV,and a photovoltaic conversion efficiency of 5.33%.Therefore,the proposed highthroughput screening method based on SECM imaging mode has a prospective potential in optimizing the technical protocols of QDSSCs.(3)A comparative study was performed using SECM in imaging mode,the transient photocurrent time spectrum(i-t)and electrochemical impedance spectroscopy(EIS),demonstrating that crystal facets play an important role in the action of hematite as a photocatalyst for water splitting.The mass specific activity of the facets was found to be in the order {110}>{012}>>{001},regardless of whether the hematite was sensitized by cadmium sulfide quantum dots(CdS QDs).However,the photocatalytic performance of 2D nanoplates with {001} and {110} facets improved dramatically on sensitization with CdS QDs.This was attributed to spatially separated transport of photogenerated charges on different facets,as shown by the selective deposition of CdS QDs and platinum clusters on the {110} facet.The work demonstrates the importance of crystal facet engineering in nanocatalysis.(4)Based on the photoelectric conversion effect of TiO2,the organic semiconductor Ag-TCNQ was synthesized by photocatalytic coupling reaction.The morphology,structure and electrochemical properties of Ag-TCNQ were also studied.