聚合物材料中成分检测方案(电化学工作站)

Bruker Optics is continually improving its products and reserves the right to change specifications without notice.◎ 2015 Bruker Optics BOPT-40004000757-01 Application Note #AN125 In Situ FT-IR Spectroelectrochemistry： Experimental Set-up for the Investigations of Solutes and Electrode Surfaces Electrochemical investigations are a very current topic inresearch. In recent times advancement in technology andindustry results in a world-wide increasing energy consump-tion. A future requirement to face this trend is the develop-ment of high capacity and as well low weight rechargeablebatteries for energy storage. Therefore studies of electrolytesystems or electrode surfaces are of great importance forpossible further improvements. Also in other fields， like biochemistry or catalysis，electroche-mistry is of great benefit to get access to information of mo-lecules， depending on an applied electrochemical potential.For example of the redox-active center in biomolecules [1]，the reaction behavior of catalysts or the formation of carbonoxides during alcohol oxidation. The combination of FT-IR spectroscopy with electrochemi-stry offers insight in the molecular change and the reactionprocess of the studied molecules in addition to the electro-chemical response of the experiment. This valuable me-thod can be applied for investigations of electrolytes or ofelectrode surfaces.With the BRUKER A530/x reflection unitprepared for electrochemical cells the opportunity is givento study both [2]. For an external IR reflection-absorbancespectroscopy (IRRAS) set-up a thin layer configuration isused which allows the study of the electrolyte and theelectrode surface. Alternatively an internal reflection ATRset-up can be used to analyze the electrode surface direct-ly with limited influence of the electrolyte (see figure 1). Keywords Instrumentation and Software Electrode surface VERTEX Electrolyte A530/x reflection unit Internal reflection Potentiostat External reflection CAN-ADI board Potential modulation VB-script potentiostat control FT-IR spectroelectro- chemistry Figure 1： Different measurement modes of the A530/x reflection unit.On the left side external reflection (materials： CaF，， BaF，)， on the rightside internal reflection (materials： Ge， Si). Furthermore for the IR spectroelectrochemical investigationof dissolved molecules in solution Optically Transparent ThinLayer Electrochemical Cells (OTTLE) are also well known fortransmission measurements [3， 4]. Therein the working elec-trode consist of a semi-transparent metal minigrid.Thereforethe molecules can be studied directly in the vicinity of theelectrode surface with transmission measurements. In this application example we will study the oxidation of ferrocyanide [Fe(CN)]4 and the dependance of the CN- li- gand stretching vibration on the oxidation state of the iron center (Fe"or Fe). This system is also discussed in detail in the literature [5].Additionally we will determine the layer thickness within the external reflection mode. Instrumentation The experiments were conducted with a purged VERTEXFT-IR spectrometer equipped with the A530/P accessoryand a mid-band MCT detector. A representation of thereflection cell A530/P as used in the experiment is depictedin figure 2， showing the installation of the different com-ponents， a glass body and electrodes. The measurementparameters were 4 cm1 resolution and 100 scans. A MIRpolarizer was installed and p-polarized light was used forthe investigations. The experiments were controlled by theFT-IR spectrometer using a software script and a connectionwith the CAN-ADI board to a Gamry 600 reference potenti-ostat. A thin gold plate disk was used as working electrode，and silver and platin wires as quasi-reference and counterelectrodes. Figure 2： Design of the reflection cell A530/x with installed glass tube. Investigations were performed on a 20 mmol/l solution ofpotassium ferrocyanide K [Fe(CN) ] in water and additional 1mol/l potassium chloride KCl as supporting electrolyte. Forthe study of the dissolved metal complex the solution wasmeasured using a silicon hemispherical window (F530-8)in the ATR mode with the working electrode placed 1 mmabove the window. Figure 3： First and second run of a cyclic voltammogram with 0.1 V/sof ferrocyanide [Fe(CN)]4 in 1 M KCI solution. Figure 4： Pictures of the experimental setup. Reflection unit withpolymeric flask installed (left)， complete cell installed and connected(right). Investigation in the external specular reflection mode wereperformed using a barium fluoride hemispherical window(F530-17) and a gold electrode pressed against the windowcreating a thin layer between them. Results and discussion A cyclic voltammogram (current at the working electrodeplotted versus the working electrode potential)， which isdepicted in figure 3， of this redox system was recorded toget an overview of the oxidation and reduction potentials.Afterwards the solution of potassium ferrocyanide wasinvestigated with in situ FT-IR spectroelectrochemistry. Figure 5： Potential change during an experimental run. Depicted likegiven in chronoamperometry. IR spectra are measured at the definedpotential levels. The quasi-revesible redox process for the reaction [Fe(CN) ]4=[Fe(CN)+e can be seen in this system and the oxida-tion and reduction peak are well resolved. The in situ FT-IRspectroelectrochemical experimental setting is depictedin figure 4. The experiment can be controlled in a way thatthe potential is set in steps to a desired value. Betweenevery potential increase the value can return to a specifiedreference potential to control the reversibility of the electro-chemical process. A diagram of one experimental run is shown infigure 5 exemplarily， starting from Estart =-0.3V to Eend=0.8Vandreturning after every step to a reference potential E =0V. Aftera certain delay， which is also specified in the control script，at every level shown in the graph， a defined number of IRspectra are co-added and averaged. Figure 6： IR spectra of the ferrocyanide solution measured at potenti-als ranging from -0.3 V to 0.8 V shown as SNIFTIRS type spectra. After the start the experiment runs independently with aduration of approximately twenty minutes in this example.Afterwards the collection of IR spectra can be analysed andpresented in different ways. One common possibility is theuse of SNIFTIRS type diagrams (Subtractively NormalizedInterfacial Fourier Transform IR Spectroscopy) [6]， in whichthe y-scale of the graph represents the following R/R=(R -R )/R. An example of it is shown in figure 6 for the oxidationof [Fe(CN) ]4 in the spectral range between 2200 and 1950cm- and with cell potentials ranging from -0.3 V to 0.8V. Ascan be seen clearly the decrease of the reduced form of themolecule [Fe(CN) ]4 in solution is indicated in this repre-sentation by the increasing band at 2039 wavenumbers.The formation of the oxidized form ferricyanide[Fe(CN)] insolution can be seen by the decreasing band at 2115 cm1.Additionally a slightly yellow color of the solution could beobserved.When the potential returns to a value of -0.3 V the spectrum resembles again the spectrum of the starting potential，which points out the reproducibility of the experiment. Soagain the reduced form [Fe(CN)]4 is present is solution. Figure 7： Three dimensional representation of the oxidation of aferrocyanide solution at potentials ranging from -0.3 V to 0.8V， shown as3D-plot as offered in the OPUS software. Alternatively the course of the reaction can be illustratedwith a 3D-plot showing directly the change in absorbanceof the infrared bands during the measurement. Thereforethe Time-Resolved-Spectroscopy (TRS) postrun window ofthe OPUS software offers useful functionality. A plot forthe oxidation of the ferrocyanide solution measured in ATRconditions is shown in Figure 7. Figure 8： IR spectra of the empty electrochemical cell measured inthe external reflection mode using a barium fluoride hemisphericalwindow. The layer thickness in this measurement between electrodesurface and window is determined to 27 um. For the study of small layers on electrode surfaces and elec-trolytes， alternatively to the ATR mode， a thin layer experi-mental set-up can be used. For this external reflection modeof the electrochemistry accessory one of the important pa-rameters to know is the thickness of the layer， created bet-ween the electrode surface and the hemispherical window.The thickness can be determined easily after the positioning of the metal working electrode on top of the hemisphericalwindow (low refractive material) and prior to the addition ofthe electrolyte. For the determination the interferences areused which arise from the IR beam path going through theflat surface of the hemispherical window of the cell. Figure 7shows the interference pattern without electrolyte in the cellwhich calculates a layer thickness of 27 pm. The path lengthcan be determined easily with the Layer Thickness functionas integrated in the OPUS software.By doubling this valuefor the IR path (in and out of the electrochemical cell)， theIR beam would penetrate about 50 pm of the electrolytesolution during the measurement. The electrochemical oxidation of a metallic complex， ferrocy-anide [Fe(CN)]4 was studied with FT-IR spectroelectroche-mistry. This combined analysis method offers the possibilityto investigate the molecular change of this compounddepending on the applied electrochemical potential. Theoxidation to ferricyanide [Fe(CN)]-was illustrated in theform of a SNIFTIRS spectrum and a 3D-plot with the OPUSsoftware. One main advantage of the set-up reported hereis， that the potentiostat and the spectrometer are connectedby the CAN-ADI board and a VB-script for an all-over commu-nication is used. After setting the experimental parametersand the desired potential procedure， the measurement canbe simply started in OPUS and will run automatically. Theresulting spectra will be well sorted and assigned to theircorresponding potential for subsequent evaluation. In theend， the technical realization of the combination of FT-IRspectroscopy and electrochemical investigations makes thein situ monitoring of electrochemical processes easy andreliable. ( References ) ( [ 1 ] C . Berth o mi e u ， L . M a rbo u t i n ， F . D u pe y ra t， P . Bo u y er，Bio po ly mer s 2 006 ， 82(4)， 3 63 - 367 . ) ( [ 2 ] Br u ke r Prod u ct No t e M 14 0 -0 8 / 1 2 ： A 5 3 0/P o r A 53 0/ V Refl e ction U nit p repared fo r E l ectrochemica l Cell. ) ( [ 3 ] B ru ker Ap pl i c a ti on N ote AN40 (D . A . M o ss ， W. M ante l e )： F T -IR S p ec tro e le c tr och e m is t r y of P r ot e ins； ) [4] S. R. Domingos， H. Luyten ，F. van Anrooij， H.J. Sanders，B. H. Bakker， W. J. Buma， F. Hartl， S. Woutersen， Rev. Sci.Instrum. 2013，84，033103. ( [5] S. M. R os end ahl， F. B o r o nd i cs， T . E . M a y， T . M . Pede r s en an d l . J . Bu r gess Ana l . C he m. 2 011， 8 3 (10)，3 63 2 -363 9 . ) ( [6] A. Ka bbabi， R . F a u re ， R. D ur a nd ， B . Bede n ， F. Hahn， J. - M. Leg e r ， C. L a m y， J . E lec t roan a l . C hem. 19 9 8 ， 444， 1 -5 3. ) Bruker Optics Inc. Billerica， MA· USAPhone +1 (978) 439-9899Fax +1 (978) 663-9177info@brukeroptics.com www.bruker.com/optics Bruker Optik GmbH Ettlingen· DeutschlandPhone +49 (7243) 504-2000Fax+49 (7243)504-2050info@brukeroptics.de Bruker Hong Kong Ltd. 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