Development Of Electrochemical Reflective Absorption Microscopy For Probing Local Electrochemical Response

The electrochemical interfacial processes and their kinetics are complex systems,involving charge transfer,conversion and storage of energy,and transport of ions.To characterize the electrochemical interfacial structure,reaction process and mechanism,it is necessary in-situ characterize the electrochemical interfacial microstructure and composition during electrochemical reaction.However,conventional electrochemical methods that can only provide the current or potential information for the whole electrode could not meet the demand to obtain the local electrochemical information on the electrode surface for understanding the problem in the field of solar energy,lithium ion battery,and corrosion etc.Therefore,it is important to develop techniques to allow the electrochemical imaging.Among the existed methods,scanning probe techniques are powerful way to provide spatial resolution at the nanometer scale.But they sacrifice the information in the time domain,and the probe may impact the electrochemical reaction processes.Optical microscopic techniques can provide spatial resolution at submicron scale and the time-resolved information at the same time.But the imaging mechanisms of SPR,fluorescence,and surface reflectivity limit their application.UV-Vis absorption spectroscopy has sensibility with single molecular layer level,and its application range is not confined by electrode material because it does not need special substrate to enhance the signal and has flexible spectrum acquisition modes including transmission and reflection mode.It has found application in various fields like lithium ion battery,photoelectric material,and is has not limited by special molecular system.However,the development of electrochemical imaging technique on the basis of UV-Vis absorption spectroscopy is slow,and there are enough rooms for development.Derivative Cyclic Voltabsorptometry(DCVA)was proposed by Bancroft’s group at 1981,they took the derivative of absorption intensity of potential(dA/dE),which they plot against potential to obtain the DCVA curve.For a simple single electron reaction,the DCVA curve has the same shape as the conventional CV curve.DCVA was found to be valid for the thin layer and finite space condition.But in these work,it is proposed that the absorbance is proportional to the total charge of the electrochemical reaction and obtain the relationship between dA/dE and potential from 1D diffusion equation.Strictly speaking,it is only suitable to large planar electrode and not suitable to electrode with special shape and microelectrode.In this thesis,we used develop the technique of electrochemical reflective absorption spectrum on a commercial Witec instrument,and electrochemical reflective absorption microscopy(EC-RAM)that has high temporal-spatial resolution on a high temporal-spatial resolution microimaging system.Reassess DCVA method by electrochemical imaging.The main results are outlined as follows:1.We developed the technique of electrochemical reflective absorption spectrum on a commercial Witec instruments,expand the application range of this instrument;2.We develop reflective absorption microimaging technique based on home-built developed high temporal-spatial resolution microimaging system.This technique improves the spatial resolution of UV-Vis absorption imaging.We utilized the BNC connector to achieve the syncronization between reflective absorption microimaging and conventional electrochemical method.Eventually we were able to construct electrochemical reflective absorption microscopy(EC-RAM);3.We used EC-RAM to study the electrochemical reaction at electrodes with different size and reassessed DCVA,and demonstrate that DCVA is only suitable for the center of large planar electrode.Current reconstructed by derivation were not suitable for edge of electrode and micro-/nano-scale.But the dA/dt imaging also gives our useful information.4.We found that the current reconstruction method that utilizes absorption spectrum obtained by our technique is quite different from conventional DCVA.CVA curve is similar to the conventional CV at micro-/nano-scale and DCVA curve is quite different from it.We proposed a simple model to validate our method.