Acta Chim. Slov. 2003, 50, 601-618. 601 IN-SITU RESONANCE RAMAN MEASUREMENTS OF A HYBRID ELECTROCHROMIC CELL WITH A GEL REDOX (IT/T) ELECTROLYTE Angela Šurca Vuk, Boris Orel,* National Institute of Chemistry, Hajdrihova 19, SI—1000 Ljubljana, Slovenia Philippe Colomban LADIR UMR 7075 CNRS & Pariš VI University, 2 Rue Henry Dunant, 94320 Thiais, France Received 11-09-2003 Abstract A hybrid electrochromic (HEC) device was constructed from opticallv active nanocrystalline W03 film and transparent platinised Sn02:F-glass electrodes encapsulating a gel redox electrolyte. The electrolvte was prepared from an organic-inorganic ICS-PPG precursor that was synthesized from bis end-capped triethoxy silane and poly(propyleneglycol)-bis-(2-amino-propyl)ether (MW = 4000). KI and I2 in a molar ratio KI:I2 = 10:1 were a source of an I3~/T redox pair while valeric acid was used as a catalyst for the solvolysis reactions of the ICS-PPG precursor. The stability and kinetics of colouring/bleaching changes of the HEC device were determined by using in-situ UV-visible spectroelectrochemical measurements betvveen +2 and -2 V (CV, CC). In-situ micro-Raman spectroscopic technique was used to follow the functioning of the HEC device. The excitation line of 647.1 nm was focused in the redox electrolyte, closer to the platinised Sn02:F-glass electrode and the resonance Raman spectra were recorded during the cyclovoltammetric scanning of the potential betvveen +2 and -2 V. The resonance Raman spectra were dominated by the symmetric vs(l3~) stretching of 13" ions at 111 cm"1. Its relative intensity changes revealed the course of the redox reaction 3F <-» I3~ + 2e~ in the electrolyte and were accompanied by the intensity changes of the background Rayleigh scattering. The latter were assigned to the dissociation/association of the KI microcrystallites in the gel redox electrolyte during the intercalation and deintercalation ol K ions in electrochromic W03 film. Introduction Conventional - batterv type ' - EC devices with two films with intercalation properties are well established as “smart windows”, ' enabling the control of heat-loads and the illumination levels inside the buildings simplv by the application of the potential pulse at the will of the occupant. The battery-type EC device consists of two optically transparent and electronically conducting (TCO) electrodes supporting active films with intercalation properties. One film possesses electrochromic properties (usually W03) and * r* + r* colours under cathodtc voltage and intercalation 01 Li ions due to the redox reaction 01 A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 602 Acta Chim. Slov. 2003, 50, 601-618. W + + e~ —> W +. After the opposite voltage is applied, Li+ ions moved from W03 to counter-electrode film which should remain optically passive (V/Ti-oxide, M VO4, M = Ce, In, Fe,...) ' or should colour complementary (Ni-oxide, Ir-oxide,...). ' The space betvveen both electrodes is nlled with an electrolyte containing H , Li or other small cations in a solvent, polymer matrix (laminated design) or thin film (all-film design). Such EC devices exhibit an extended open-circuit memory since the electrolyte is electronically non-conducting. Beside the battery-like also a solution-type and a hybrid-type of EC devices exist, having in common that a constantly applied voltage is needed to retain the coloured state (self-erasing devices). The chromophore-based devices, for example, with the chromophore dissolved in solution or deposited in polymeric form on TCO electrode have the colouring/bleaching times in the range of seconds or less. As a support for the redox chromophore recently also TiC>2 film was used. ' Typical examples of molecular redox chromophores are viologens, conducting polymers, metallopolymers and some metallophthalacyanines. The construction of a hybrid EC device was recently reported by Lin et al. They used Prussian blue as an electrochromically active film in contact + with the heptyl viologen (V ) dissolved in aqueous electrolvte. The first aim of the present study was the preparation of a hybrid EC device consisting of a nanocrystalline W03 film as an optically active film and a gel redox electrolyte containing If/T redox pair (Figure 1). ' A platinized Sn02:F-glass served as a counter-electrode. In this device the change from the optically transparent to the absorbing state is achieved by the simultaneous insertion of electrons and cations into optically active WC>3 film as in standard battery-type EC devices. However, the charge entering the WC>3 is compensated by the redox reaction 3T —» 13" + 2e~ at the Pt-electrode. Bleaching is achieved by the application of an opposite voltage: cations leave the structure of the WC>3 film and enter the electrolyte, in which at Pt electrode T are formed again. Hybrid-type EC devices, that do not need a counter-electrode with intercalation properties for their functioning, represent a step-forward in simplicity of EC device design. The number of active layers is diminished compared to the standard battery-type EC devices and the colouring/bleaching speeds are increased. Due to the latter property and the self-erasing effect, the hybrid EC devices are more suitable for the rear-view EC mirrors for cars than for “smart windows”. A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 603 Laser & Spectrometer 1 Sn02:F Pt Focused volume Electrolyte W03 Sn02:F Figure 1. Schematic representation of a hybrid EC cell and in-situ resonance Raman measurements. In the hybrid EC devices we used a gel redox electrolyte that we developed during our investigations of dye-sensitised photoelectrochemical (Grätzel) cells. " We used a Class II organic-inorganic hybrid based on bis-end-capped triethoxysilane covalently bonded via urea bridges to poly(alkyleneoxide) chains (ICS-PPG). Instead of the more ionophilic and commonly used poly(ethyleneglycol) we used poly(propyleneglycol) (PPG) with the molar weight of 4000. Recently, we prepared ICS-PPG containing KI and h, gelled it with acetic acid and used it as a redox gel If/T electrolyte in dye-sensitised photoelectrochemical (DS PEC) celi " ' giving an efficiency of 4-5%. This value is lower than the efficiency of DS PEC cells employing liquid redox electrolytes (-10%), but is the highest reported up to date for the semi-solid DS PECs. In this paper we present the properties of a hybrid EC device in which the gel If/T redox electrolyte was catalysed by valeric instead of acetic acid. The electrochemical properties were assessed by in-situ UV-visible spectroelectrochemical techniques and calculation of photopic transmittances. A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 604 Acta Chim. Slov. 2003, 50, 601-618. The second main aim of this study was to obtain a better insight into the functioning of the hybrid EC device by in-situ resonance Raman measurements. This technique exploits the strong resonance Raman effect of I3- ions and is therefore a suitable tool to follow the course of the redox reaction 3T <-> 13" + 2e~ in the space between two electrodes. The micro-Raman technique was already used to study the interactions of If ions with a ruthenium bipyridyl dye attached to Ti02 film in a DS PEC celi and also to study the 3T <-> 13" + 2e~ process in DS PECs under open- and short-circuit conditions. " In this study we focused the laser ex citation line (413.1 and 647.1 nm) on the redox electrolyte in the hybrid EC device and collected the spectra during its cyclovoltammetric cycling. From these experimental data, by following the changes in the relative intensity of the symmetric Vs(l3~) stretching of I3- ions, we inferred how the intercalation and deintercalation from the WC>3 film influenced the course of the redox reaction 3T <-> 13" + 2e~. Apart to vs(l3~) mode intensity changes we observed also the variation in the background Rayleigh scattering with potential that we ascribed to a reversible dissociation/association of the KI microcrystallites of submicrometre dimensions. Experimental Optically active WC>3 films were nanocrystaline with the grain size of 30 nm and were prepared by using peroxo sol-gel route. A drop of the redox electrolyte was placed on the WC>3 film and immediately covered with the platinised SnC^F glass substrate. The redox electrolyte was prepared from organic-inorganic silicon precursor ICS-PPG that was synthesised from 3-isocyanatopropyltriethoxy silane (ICS) and poly(propyleneglycol)-bis-2-amino-propyl)ether (PPG) with a molar weight of 4000 g mol" . ICS-PPG was first dissolved in ethanol (EtOH), then KI and I2 were added in molar ratio KLI2 = 10:1. Finally, the valeric acid (CH3(CH2)3COOH; VaOH for short) was added as a catalyst for the gelation of ICS-PPG via aprotic solvolysis reactions. ' C — /1--- + The tinal product was a sol-gel network with incorporated I3 /1 redox pairs, K ions, some residual EtOH and ester of valeric acid as a side product of the solvolysis reactions. The redox electrolytes did not gel when kept refrigerated (4 °C). In-situ UV-visible spectroelectrochemical measurements of the hybrid EC cells were made using the HP 8453 diode-array spectrophotometer in combination with an A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 605 EG&G PAR model 273 potentiostat-galvanostat. The cyclovoltammetric (CV) curves were obtained by the scan rate of 20 mV s" and were scanned from 0 V to -2 V, reversed to 2 V and then finished at 0 V. The kinetics of the coloration and bleaching was obtained by applying a chronocoulometric (CC) technique by performing the r* T7-+ * C intercalation oi K lons at -2 V tor 100 s and deintercalation at 2 V (100 s). Reported potentials correspond to the potential applied to the WC>3 film (working electrode) with respect to the platinised Sn02:F-glass substrate (counter-electrode). Due to the presence of l3~/r couple in the electrolyte may the platinised counter electrode function as a quasy reference electrode with a definite constant potential according to the actual activity of the redox h~/T pair close its surface. The potentials of working and counter electrode are not know exactly. This problem can be solved with the use of the micro-reference electrode incorporated in the electrolyte betvveen both electrodes and this work is under progress. In addition, it might be assumed that the potential shifts of the counter electrode in the HEC celi may influence the background changes in the in-situ Raman spectra since the KI microcrystallite formation depends on potential. However, such an effect should be small compared to reactions KI (microcrystallites) <-> KIi_x + xK+ + xr and I3- + 2e~ <-> 3 T occurring in the measured part of the electrolyte. Prior to resonance Raman spectra measurements of ICS-PPG/EtOH/KI/VVaOH sol s EtOH solvent was partly evaporated in a rotary evaporator. The Raman spectra were then recorded by the ex citation lines of 413.1 and 647.1 nm on two different XY DILOR spectrographs. For the measurement of the HEC cells with the 647.1 nm line the spectrograph was equipped with mixed Ar-Kr ion plasma. The HEC celi was positioned under the laser beam in such a way that the WC>3 film was on the bottom and platinised SnC^F on the top (Figure 1). The laser beam was then focused on the electrolyte closer to the Pt-covered counter-electrode. For in-situ resonance Raman measurements we used HEC devices that were 50 \±m thick. Results and discussion In-situ UV-visible spectroelectrochemical characterisation The colouring/bleaching changes of the hybrid EC device with the redox electrolyte catalysed with VaOH are shown in Figure 2. The spectra revealed that the optical change is lower than 30% for wavelengths below 500 nm, while it can even A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 606 Acta Chim. Slov. 2003, 50, 601-618. exceed 50% at higher wavelengths. The cross-section of the optical modulation at ? = 634 nm (Figure 2C) revealed that colouring is slower (-20 s) then bleaching (5 s) for this HEC device. Optical response can be expressed also in term of a photopic transmittance Tvis: The calculation of the photopic transmittance showed that its values were 35.0%, 31.2% and 28.9% after 10 s, 20 s and 100 s of colouring, respectivelv, confirming that the device coloured mostlv during the first 20 s of the experiment. After bleaching the photopic transmittance achieved was 69.1. 100 80 60 40 20 100 80 60 40 20 400 600 800 ? [nm] 1000 50 100 t [s] 150 200 100 80 60 40 20 0.4 0.2 0.0 -0.2 400 600 800 ? [nm] 1000 20 40 60 t [s] 80 100 Figure 2. In-situ UV-visible spectroelectrochemical measurements of a hybrid EC cell with the electrolyte catalysed with the VaOH acid during chronocoulometric colouring/bleaching: A) spectra during colouring, B) spectra during bleaching, C) monochromatic transmittance at 634 nm and D) chronocoulometric curves. The interesting feature of the chronocoulometric experiment is the linear response of the charge vs. tirne curves (Figure 2D). For the usual battery-type EC device with two films with intercalation properties is the characteristic CC response the saturation 0 0 0 0 0 A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 607 plateau due to the limited ion-storage of the intercalation electrodes. ' . The linear CC • + curves of HEC cells, however, do not reflect only the lntercalation/deintercalation of K ions in WC>3 film but also the fact that the redox reaction 3T <-> l3~ + 2e~ may occur at either Pt-covered or WC>3 electrode (Figure 1). Therefore, by taking 20 s as the most appropriate tirne for the evaluation of the electrochromic efficiency, this becomes 6.3 cm2 C1. The intrinsic property of the hybrid EC devices is the self-erasing effect. For the FLEC with VaOH it is demonstrated in Figure 3. The device was first charged at -2 V for 100 s and then disconnected from the electrical contacts. The UV-visible spectra were recorded every 3 s during the first 1000 s of the measurement, later every 600 s. It is clearly visible that most of the bleaching at A, = 634 nm occurred by 1000 s. 100 80 60 40 20 0 0 1000 2000 3000 4000 5000 t [s] Figure 3. Self-erasing properties of a hybrid EC celi with the electrolvte catalysed with VaOH acid: the celi was charged at -2.0 V for 100 s and then disconnected from electrical contact. Monochromatic transmittance changes were followed at 634 nm. Cyclovoltammetric (CV) curves are shown in Figure 4 together with the monochromatic transmittance response at 634 nm. When a scan rate of 20 mV s" was c + ta used the current peaks ot intercalation and deintercalation of K ions in WC)3 film could not be discerned (Figure 4A). They can be observed, however, between -1 and -2 V (intercalation) and in a reverse scan between 0 and 1 V (deintercalation) when either a thicker layer of the electrolyte or a longer tirne aged electrolyte is used in the HEC 100 s of charging A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 608 Acta Chim. Slov. 2003, 50, 601-618. device (see section on in-situ Raman measurements). In contrast, the CV curves in Figure 4A revealed an increase in current densitv at approximately -0.3 V and simultaneouslv the device began to colour (Figure 4B). The maximal coloration is achieved between -2 and -1.5 V in a reverse scan, while bevond this potential the transmittance started to increase to an initial value that was reached up to 2 V. The current densitv at -2 V decreased with the number of cvcles. Stabilitv of this device was tested up to 1210 cycle and is represented with photopic transmittances in Figure 5. It is clearlv visible that the photopic transmittances in the bleached state were approximately 68% throughout the whole cycling, while the values in the coloured state varied between 30 to 40%. 100 80 60 40 20 0 -2 -2 -1 0 ?E [V] -1 ?E [V] Figure 4. In-situ UV-visible spectroelectrochemical measurements of a hybrid EC cell: A) CV curves and B) monochromatic transmittance at 634 nm. The scan rate used was 20 mV s-1. 1 2 0 2 A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 609 100 80 60 40 20 400 800 Number of cycles 1200 Figure 5. Photopic transmittance of a hybrid EC device in a coloured and bleached state during CV cvcling with a scan rate of 20 mV s"1. Resonance Raman spectra of sols Resonance Raman spectra of an ICS-PPG/EtOH/KI/I2/VaOH (partly evaporated EtOH) sol were measured by the excitation lines of 413.1 and 647.1 nm (Figure 6). Positions of both excitation lines are marked on UV-visible reflection-absorption spectrum of the ICS-PPG/EtOH/KI/I2 gel showing the two absorptions of I3- at 290 and 360 nm and absorption of I- ions at 225 nm.24,25 During our investigation of sols and gels having various KI:I2 molar ratios we found out that for the functioning of the HEC devices the ratio of the I3- and I- UV-visible absorptions should tend towards one. In the Raman spectra recorded with either of the excitation lines we observed the symmetric (?s(I3-)) stretching of I3- ions at 111 cm-1 as the dominating band and its asymmetric (?a(I3-)) counterpart at 139 cm-1.12-16,25-28 In addition, in the spectrum recorded with 413.1 nm line higher harmonics at 222, 336, 452 cm-1, … of the symmetric ?s(I3-) mode at 111 cm-1 can be observed. This is due to the strengthening of the resonance Raman effect26,27 because this excitation line lies closer to the maximum of the genuine absorption of I3- ions at 360 nm than the 647.1 nm line (Figure 7). The reason for the comparable intensities of the 111 cm-1 band in both Raman spectra (Figure 6) is the longer time of excitation and higher power used for measurements with the 647.1 nm line (180 s, 20 W) than for 413.1 nm line (35 s, 15 W), although should be – 0 0 A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 610 Acta Chim. Slov. 2003, 50, 601-618. according to the theory of the resonance Raman intensive when measured with 413.1 nm line. 26,27 -1 the 111 cm" significantly more 100 200 300 400 500 Raman shift [cm ] Figure 6. Resonance Raman spectra of an ICS-PPG/EtOH/KI/I2/VaOH (EtOH partly evaporated prior to measurement) sol measured by the excitation lines 413.1 and 647.1 nm. Time of collection was 35 s at 413.1 nm and 180 s at 647.1 nm. 1.2 0.8 0.4 0.0 200 400 600 ? [nml 800 Figure 7. UV-visible reflection-absorption spectrum of an ICS-PPG/EtOH/KI/l2 (EtOH partly evaporated prior to measurement) redox electrolvte with indicated excitation lines of 413 and 647.1 nm. A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 611 In the resonance Raman spectrum measured with the 647.1 nm excitation line the overtones betvveen 150 and 500 cm" were not visible (Figure 6). This spectrum is dominated by an intense symmetric Vs(l3~) stretching at 111 cm" and therefore suitable to obtain information about the course of the redox reaction 3T <-> l3~ +2e~ in the electrolyte betvveen the W03 and platinised Sn02:F-glass electrodes in a HEC device. In-situ resonance Raman spectra of a hybrid EC device A schematic presentation of the in-situ resonance Raman measurements of the hvbrid EC devices is depicted in Figure 1. The spectra were measured by focusing laser radiation (k = 647.1 nm) through the SnC^F glass substrate and sputtered Pt layer on the redox gel electrolyte encapsulated in the HEC device. In order to follow the redox reaction that occurred in the electrolyte closer to the Pt counter-electrode, thicker EC devices than usual (-10 |im) were prepared (-50 |im). The results of the in-situ resonance Raman measurement of the 12* cyclovoltammetric (CV) potential scan of a hybrid EC device are shown in Figure 8. The CV was performed with a scan rate of 20 mV s" , starting from 0 V to -2 V, then reversed to 2 V and finished at 0 V (Figure 8A). Raman spectra, dominated with the symmetric Vs(l3~) stretching at 111 cm" (Figure 11B), were measured every 50 s for a duration of 30 s, as depicted with arrows in Figure 8A. Two main features were noted in the corresponding in-situ resonance Raman spectra: (i) the absolute and relative intensity of the I3- mode at 111 cm" changed with potential, and (ii) the background scattering averaged over the range 200 - 500 cm" varied with potential as well. At cathodic potentials the intensity of 111 cm" band changed in the opposite direction than the background (Figure 8B,C). The absolute integral intensity of the 111 cm" mode increased during cathodic potentials (-1 and -2 V in Figure 8C), attained minimal values at -1 V in a reverse scan and then increased again at anodic potentials. However, due to the high background intensity compared to the intensity of the Vs(l3~) stretching and its pronounced changes during the CV measurement, the absolute integral intensity of Vs(l3~) could not give an exact insight into the reactions taking plače in the HEC celi. Therefore, the relative intensity of the 111 cm" band corrected for the intensity of the background (Figure 8C) was calculated, and this varied according to expectations. During cathodic potentials A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 612 Acta Chim. Slov. 2003, 50, 601-618. when K+ ions intercalated in the WC>3 film the redox reaction 3 T —» h~ + 2e~ took plače at the Pt counter-electrode, leading to an increase in the relative intensity of 111 cm" band (-2 V in Figure 8C). Due to the applied potential, the reverse reaction (I3- + 2e~ —> ^1--- + TTT P 1 31) could take plače in addition to K intercalation at the VVO3 side 01 the HEC celi. Expectedly, the minimal relative integral intensitv of the 111 cm" band was reached at 0 V in a reverse scan. At anodic potentials its intensitv remained approximately the same (2 V in Figure 8C). 0 -2 1000 A t = 300 s 2 V * t = 100 s t = 200 s t = 250 S //,: -1 V 0 V , ;____» ^X^ ^^cSv ////' ~ = 0 s, 400 s t = 350 s III / t = 50 s 0 V 1 V II1/ "^ ^ y *l= 100 s -2 V 1000 750 500 250 -2 0 AE [V] 1000 2000 3000 4000 t [s] 750 250 C IP Average background intensity betvveen 200 and 500 cm1 -2 AE [V] Figure 8. In-situ resonance Raman measurements (k = 647.1 nm) of a hybrid EC celi with electrolyte catalysed with VaOH: A) CV curve (12th cycle; 20 mV s"1), B) ali measured in-situ Raman spectra between 50 to 500 cm"1 and C) intensity changes of the vs(I3~) stretching band and the background. In CV curve the arrows denote the starting potential and the duration (30 s) of the Raman measurement. -i The background intensity averaged over the range 200 – 500 cm-1 had at cathodic potentials the opposite behaviour than the relative intensity of 111 cm-1 mode: its intensity decreased from 0 V to –2 V then remained the same up to 0 V in a reverse scan. Beyond 0 V the intensity of the background increased again, but did not reach the initial 1 -1 0 -1 1 2 0 Absolute intensitv of v (I,) ' s* 3 ' Relative intensitv of v (L) ' s* 3 ' 0 -1 0 1 2 A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 613 value. Such a variation of the background scattering intensity (Figure 8B,C) was noted also for the HEC devices in which the electrolyte was catalysed by acetic acid ' and in in-situ resonance Raman spectra of the electrolyte encapsulated in DS PEC cells. " In analogy with the interpretation of the latter spectra we assumed that also in HEC devices the background intensity changes occurred due to the reaction KI (microcrystallites) <-> T7- T + i 1— P C T Kli_x + xK + 1 . Namely, because oi the relatively high amount ot KI and I2 in the 1CS-PPG/EtOH/KI/12/VaOH redox electrolyte we found out that after gelation and r* r* + i— r* r* evaporation 01 EtOH part 01 the K and 1 in the electrolyte already existed in the torm 01 KI microcrystallites having submicrometer dimensions. The appearance of the crystalline or amorphous KX precipitates (X = Cl~ C104~, T, NO2 ) is already mentioned in the literature and was found in siloxane-polyoxypropylene (PPO) hybrids doped with KI, KCIO4 and KNO2. In this čase the existence of crystallites was proved by X-ray diffraction. Figure 9. SEM micrograph of the microcrystallites that formed in the redox gel electrolyte catalysed with AcOH acid in a hybrid EC device cycled over 1830 cycles (100x magnification). Insert: EDX spectra of the squarish- and round-shaped microcrystallites. A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 614 Acta Chim. Slov. 2003, 50, 601-618. The presence of KI microcrystallites we evidenced for the HEC device with the electrolvte catalvsed with acetic acid (ICS-PPG/EtOH/KI/12/AcOH). This HEC device was opened and the redox electrolyte examined under an SEM microscope (Figure 9). Two kinds of defects were observed: squarish- and round-shaped crvstallites. The dimensions of the larger crvstallites were in the range 25 and 40 |im, the smaller between 1 to 5 |im. EDX measurements showed that the squarish crvstallites corresponded to KI and the round-ones to potassium acetate. This was inferred from the EDX-analysis shovving 50 at.% K and 50 at.% I for the squarish crystallites (Figure 9A) and 87 at.% of K and 13 at.% of I for the round crvstallites (Figure 9B). The formation of the microcrvstallites was undoubtedlv connected to the evaporation of the volatile components, i.e. EtOH esters of AcOH or VaOH acids, from the electrolvte. Reaction KI (microcrvstallites) <-> KIi_x + xK+ + xr is consistent with the background changes in the HEC device (Figure 8). During the cathodic scan (0 V to -2 PT7-+ * V) when the intercalation 01 K lons in the WO3 film took plače, the KI microcrvstallites dissociated, therefore diminished the concentration of the KI scattering centres and the background intensitv decreased to minimal value (Figure 8C). After deintercalation of K+ • r* lons that was completed at approximately 1.3 V the intensity 01 the background increased again. Direct confirmation that the KI microcrystallites contributed to the background Raman scattering was obtained from in-situ Raman spectra measurements of a svmmetric celi (not shovvn here). This celi was composed of two Pt-covered SnC^F- glass electrodes facing each other vvhile the space betvveen them was filled with the redox electrolyte. When the potential was changed in the same manner as shovvn in Figure 8A, no variation of the background intensity with potential was noted. This signalled that the concentration of the scattering centers, i.e. KI microcrystallites, did not change during the potential svveep. The reason for that lies in the fact that in the symmetric celi no WC>3 film is incorporated and the intercalation/deintercalation reaction r* T7-+ * C 01 K lons are therefore not possible. The concentration 01 KI microcrystallites, irrespective of their absolute initial concentration, did not change during the vvhole potential scanning of the symmetric celi. The variations of the intensity of the vs(l3~) mode and the background follovved the described pattern (Figure 8C) also when 32 CV cycles were measured successively (Figure 10). The cycling was performed with the scan rate of 5 mV s" and for each A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 615 0.8 0.4 0.0 -0.4 -0.8 -2-10 1 2 AE [V] 3000 2000 1000 0 10000 20000 30000 40000 50000 t [s] 3000 2000 1000 30400 32000 33600 35200 t [s] Figure 10. In-situ resonance Raman measurements (k = 647.1 nm) of a hybird EC celi with electrolyte catalysed with VaOH: A) CV curve (12th cycle; 5 mV s"1) and B,C) intensity changes of the vs(I3~) stretching mode and the background during CV cycling (32 cycles; dashed lines separate the cycles). In CV curve the arrows denote the starting potential and the duration (120 s) of the Raman measurement. 0 0 A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... 616 Acta Chim. Slov. 2003, 50, 601-618. separate cycle four Raman spectra were recorded (every 400 s for 120 s) as shown by arrows in Figure 10. The higher intensity changes compared to those in Figure 8 can be explained by the longer tirne used for collection of the Raman spectra (120 s vs. 30 s) in the čase of continuous measurement (Figure 10). In addition, the intensity vs. tirne plot showed that the intensity of the I3- stretching band decreased during the initial cycles, but then became more stabilised. This signified that the FtEC celi needed some pre-cycling until a persistent electrochromic response developed. However, due to the inherent instability of the sol-gel redox electrolytes a small fading remained throughout the whole cycling of the device (more then 1000 cycles). Conclusions The hybrid EC device with gel redox electrolvte catalysed with valeric acid revealed quick colouring/bleaching performance. Most of the colouring was achieved in 20 s, while bleaching was even faster (5 s). The reason is that the FtEC devices do not need the counter-electrode with the intercalation properties and therefore the kinetics of the coloration and bleaching, as well as the coloration efficiency, depends solely on the active electrochromic WC>3 film. The counter-electrode is in FtEC devices platinised SnC>2:F-glass and the second redox pair is present in the gel redox electrolvte. The FtEC device was characterised by the self-erasing effect contrary to the battery-type of the EC devices, which are due to their memory effect appropriate for the “smart windows” applications. Main application area of FtEC devices is “rear-windows for cars” and important is that also reflective FtEC devices can be prepared, simply by changing the thickness of the Pt-layer on the Sn02:F-glass substrate. The main emphasis in the present work was on in-situ resonance Raman spectroelectrochemical measurements. The resonance Raman spectra were found an excellent tool to follow the variation in the intensity of the symmetric Vs(l3~) stretching at 111 cm" . These intensity changes directly reflected the course of the redox reaction 3T <-> 13" +2e~ closer to the Pt-side of the FtEC device where we measured. At the same tirne we noted also the changes in the background intensities that were ascribed to dissociation/association of the KI microcrystallites in the gel redox electrolyte matrix. The presence of KI in the electrolyte is related to the evaporation of the volatile species as EtOH and ester of valeric acid from the sol-gel network during its ageing and was proved by SEM and EDX analysis. A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Raman Measurements of a Hybrid... Acta Chim. Slov. 2003, 50, 601-618. 617 Acknowledgements The authors wish to thank the Ministry for Education, Science and Šport of the Republic of Slovenia for financial support under Programme P-506 and project Jl-2125. Special thanks to Helena Spreizer, National Institute of Chemistry, for her technical assistance. Thanks also to Dr. Andreas Georg for the Pt covered glass electrodes. The paper was presented at the 13n International “Symposium Spectroscopy in Theory and Practice” in Nova Gorica, Slovenia, 27 - 30 August, 2003. References 1. R. D. Rauh, Electrochim. Acta 1999, 44, 3165–3176. 2. C. G. Granqvist, Handbook of Inorganic Electrochromic Materials; Elsevier Science, Amsterdam, 1995. 3. U. Opara Krašovec, A. Šurca Vuk, B. Orel, Solar Energy Mater. Sol. Cells 2002, 73, 21–37. 4. A. Šurca, B. Orel, B. Pihlar, P. Bukovec, J. Electroanal. Chem. 1996, 408, 83–100. 5. R. J. Mortimer, Electrochim. Acta 1999, 44, 2971–2981. 6. R. Cinnsealach, G. Boschloo, S. N. Rao, D. 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Stabilnost sklopa in hitrost obarvanja oz. razbarvanja smo določili z in-situ UV-vidnimi spektroelektrokemijskimi meritvami med +2 in -2 V. Z in-situ mikro Ramansko spektroskopijo smo zasledovali delovanje hibridnega sklopa. Svetlobo z valovno dolžino 647.1 nm smo usmerili v elektrolit v bližino Pt-elektrode in nato snemali Ramanske spektre med spreminjanjem potenciala s ciklovoltametrično elektrokemijsko tehniko. V Ramanskih spektrih je bil najbolj izražen trak simetričnega valenčnega nihanja I3~ ionov. Na osnovi sprememb relativne intenzitete tega traku smo sklepali na potek reakcije 3I <-» I3~ + 2e~ v elektrolitu. V Ramanskih spektrih smo opazili tudi spremembe intenzitete ozadja, ki smo jih pripisali disociacij i/asociacij i KI mikrokristalitov v redoks elektrolitu med interkalacijo in deinterkalacijo K ionov v elektrokromno tanko plast WO3. A. Šurca Vuk, B. Orel, Ph. Colomban: In-situ Resonance Roman Measurements of a Hybrid...