Electrochemical quartz crystal microbalance

FIGURE 2-20 The quartz crystal microbalance a, the quartz crystal b, the gold electrode c 

FIGURE 2-21 EQCM (a) and cyclic voltammetry (b) profiles at an ion exchanger-coated electrode in the presence of 6 x 10 3 M Ru(NH3)6C16. (Reproduced with permission from reference 65.) 

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

Rudolph, D. Reddy and S.W. Feldberg, Anal. Chem., 66, 589A (1994). 

Michael, E. Travis and R.M. Wightman, Anal. Chem., 70, 586A (1998). 

An electrochemical quartz crystal microbalance (EQCM) follows changes in frequency of a quartz crystal resonator, typically of disk form, during an electrochemical reaction. The frequency change is imposed through the piezoelectric effect, as two 

polyethylene body 7, glass cell 8, O rings 9, electrical contacts 10, glass tube. Reproduced with permission from [15] copyright 1995, The Electrochemical Society 

W Heineman, F. Hawkiidge and H. Blount, Spectroelectrochemistiy at Optically Transparent Electrodes in A.I Bard, Ed., Electroanalytical Chemistry, Vol. 13, Marcel Dekker, New York, 1986. 

SECM instruments (77,78) will undoubtedly increase the scope and power of SECM. Further improvements in the power and scope of SECM has resulted from its coupling scanning probe or optical imaging techniques, such as AFM (57,79) or single-molecule fluorescence spectroscopy (80). The combined SECM-AFM technique offers simultaneous topographic and electrochemical imaging in connection to a probe containing a force sensor and an electrode component, respectively. 

Electrochemical quartz crystal microbalance (EQCM) is a powerful tool for elucidating interfacial reactions based on the simultaneous measurement of electrochemical parameters and mass changes at electrode surfaces. The microbalance is based on a quartz crystal wafer, which is sandwiched between two electrodes, used to induce an electric held (Fig. 2.21). Such a held produces a mechanical oscillation in the bulk of the wafer. Surface reactions, involving minor mass changes, can cause perturbation of the resonant frequency of the crystal oscillator. The frequency change (A/) relates to the mass change (Am) according to the Sauerbrey equation  

Ru(OOOl) obtained by a conventional electrodeposition process from AnClj soln-tions. The insert shows an atomically resolved image of a X Cl adlayer that 

The electrochemical quartz crystal microbalance (EQCM) is a very useful technique for detecting small mass changes at the electrode surface that accompany electrochemical processes. In 1880, Jacques and Pierre Curie discovered that when stress was applied to some crystals, such as quartz, it resulted in an electrical potential across the 

If an electric held of the proper frequency is applied across the quartz crystal, the crystal wiU oscillate in a mechanically resonant mode. These condihons correspond to the creation of a standing acoustic shear wave that has a node midpoint between the two faces of the crystal and two antinodes at both faces of the disk. This is depicted schematically in Eig. 21.20b. In an EQCM experiment the crystals are operated at the fundamental resonant frequency that is a function of the thickness of the crystal. A crystal with a thickness of 330pm has a resonant frequency of 5 MHz. Crystals with these characteristics are commercially available. In an EQCM experiment, an alternating electric field of 5 MHz is applied to excite the quartz crystal into 

FIGURE 27.20 (a) Top and edge views of quartz crystal with keyhole-shaped vapor- 

Any mass changes that occur on the working elechode are reflected in changes in the frequency. The quantitative relationship is given by the Sauerbrey equation  

Counteranion effects on the [Os(bipy)2(PVP)ioCl] redox polymer were stud-ied 052,153) para-toluene sulphonate (pTS ), NOJ, SO4, and Cl electrolytes, significant solvent transfer was observed that was thought to be related to the increased solvent content of the polymer layers in the initial state when converted into these salt forms. The large movement of solvent in pTS electrolytes was confirmed from isotopic substitution of H2O with In perchlorate no 

The importance of polymer swelling and solvation was clearly demonstrated in the break-in and memory effects observed in many electroactive polymer systems. Break-in effects in tetracyanoquinodimethane 

FIGURE 8.15. The EQCM data for an [Os(bipy)2(PVP)ioCl] film in a 0.1 M p-TSA solution. The film was previously exposed to a 1 M HCIO4 solution. Main figure shows selected mass-(lrequency-) potential curves after (a) 0, (b) 45, (c) 120, (d) 180, and (e) 240 minutes of potential cycling. Inset shows simultaneously acquired I—E curves scan rate 50 mV s Os surface coverage 2 x 10 mol cm (From Ref 160.) 

Studied by the combined use of EQCM and ellipsometry measurements. In nitrated polystyrene films, increased solvation of the polymer with increasing redox cycling was observed/ The effect of electrolyte concentration and temperature on polymer swelling in TCNQ films was studied at the EQCM. In TCNQ films cation motion maintains electroneutrality within the polymer during redox cycling, and mass changes observed were found to be dominated by the concomitant movement of water of hydration.  

The following sections highlight more pertinent aspects of the EQCM tech-nique, its application to analysis, and results obtained for the [Os(bipy)2(PVP)ioCl]Cl polymer in perchloric acid electrol) e. For a more extensive discussion of this technique, the reader is referred to Refs. 135—138. 

An example of the use of an EQCM is in the deposition of Cu from a solution of CUSO4 in 1M H2SO4. Eigure 15.50 is a cyclic voltammogram showing both current and change in mass versus E. 

Electropolymerization of 1 mM bithiophene. Details may be found at www.gamry.com. (Courtesy of Gamry Instruments, Inc., Warminster, PA, www.gamry.com.) 

Mass change plotted against charge for a cycle in monomer-free electrolyte provides information about mobile species during oxidation and reduction. Information about rate of solvent ingress/ egress in the film can be obtained. Details on this and other applications of the EQCM can be found at www.gamry.com. 

1 Run a DC polarogram with a known volume of 1M KNO3 electrolyte that has not been deaerated. Observe and identify the two reduction waves of dissolved oxygen. 

2 Purge the electrolyte in Problem 15.1 with purified nitrogai gas for 20 min or so. Add suffidait lead nitrate solution to make the electrolyte 1.0 x 10 M in Pb + ion. Record the DC polarogram and measure the limiting current and the half-wave potential (EjJ for the lead ion reduction wave. 

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An electrochemical quartz crystal microbalance (EQCM or QCM) can be used to estimate the surface roughness of deposited lithium [43],... 

EC mechanism, 34, 42, 113 E. Coli, 186 Edge effect, 129 Edge orientation, 114 Electrical communication, 178 Electrical double layer, 18, 19 Electrical wiring, 178 Electrocapillary, 22 Electrocatalysis, 121 Electrochemical quartz crystal, microbalance, 52 Electrochemihuiiinescence, 44 Electrodes, 1, 107... 

Saloniemi H, Kemell M, Ritala M, Leskela M (2000) PbTe electrodeposition studied by combined electrochemical quartz crystal microbalance and cyclic voltammetry. J Electroanal Chem 482 139-148... 

In the case of Ni(OH)2 and conductive polymer electrodes, solvent and anions intercalate into the electrode at anodic potentials. Electrochemical quartz crystal microbalance (EQCM) is a useful technique for monitoring the ingress and egress of solvent and anions in these materials. 

Electrochemical Quartz Crystal Microbalance Fntnre advances will require the coupling of EQCM with spectroscopic techniqnes that yield chemical information. EQCM has been conpled with ellipsometry (Gottesfeld et al., 1995). However, ellip-sometry does not yield chemical information. 

Ward, M. D., Principles and applications of the electrochemical quartz crystal microbalance, in Physical Electrochemistry, I. Rubenstein, Ed., Marcel Dekker, New York, 1995, p. 293. 

Leopold et al. and Nyholm et al. have investigated this oscillatory system by in situ confocal Raman spectroscopy [43], and in situ electrochemical quartz crystal microbalance [44], and in situ pH measurement [45] with the focus being on darification of the osdllation mechanism. Based on the experimental results, a mechanism for the oscillations was proposed, in which variations in local pH close to the electrode surface play an essential role. Cu is deposited at the lower potentials ofthe oscillation followed by a simultaneous increase in pH close to the surface due to the protonation... 

Bohannan, E. W., Huang, L. Y Miller, F. S., Shumsky, M. G. and Switzer, J. A. (1999) In situ electrochemical quartz crystal microbalance study of potential oscillations during the electrodeposition of CU/CU2O layered nanostructures. Langmuir, 15, 813—818. 

Studies have shown that the Pt oxides are not hydrated [Birss et al., 1993 Harrington, 1997 Jerkiewicz et al., 2004]. Electrochemical quartz crystal microbalance [Birss et al., 1993] and nanobalance [Jerkiewicz et al., 2004] experiments... 

We have found new CO-tolerant catalysts by alloying Pt with a second, nonprecious, metal (Pt-Fe, Pt-Co, Pt-Ni, etc.) [Fujino, 1996 Watanabe et al., 1999 Igarashi et al., 2001]. In this section, we demonstrate the properties of these new alloy catalysts together with Pt-Ru alloy, based on voltammetric measurements, electrochemical quartz crystal microbalance (EQCM), electrochemical scanning tunneling microscopy (EC-STM), in situ Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). 

Gao, G., Y. Wurm et al. (1997). Electrochemical quartz crystal microbalance, voltammetry, spectroelectrochemical, and microscopic studies of adsorption behavior for (7E,7 Z)-diphenyl-7,7 -diapocarotene electrochemical oxidation product. J. Phys. Chem. B 101 2038-2045. 

The Electrochemical Quartz Crystal Microbalance d 2.2.7—FTIR and Related Techniques... 

The first application of the quartz crystal microbalance in electrochemistry came with the work of Bruckenstein and Shay (1985) who proved that the Sauerbrey equation could still be applied to a quartz wafer one side of which was covered with electrolyte. Although they were able to establish that an electrolyte layer several hundred angstroms thick moved essentially with the quartz surface, they also showed that the thickness of this layer remained constant with potential so any change in frequency could be attributed to surface film formation. The authors showed that it was possible to take simultaneous measurements of the in situ frequency change accompanying electrolysis at a working electrode (comprising one of the electrical contacts to the crystal) as a function of the applied potential or current. They coined the acronym EQCM (electrochemical quartz crystal microbalance) for the technique. 

Kemell, M. Saloniemi, H. Ritala, M. Leskela, M. 2001. Electrochemical quartz crystal microbalance study of the electrodeposition mechanisms of CuInSe2 thin films. /. Electrochem. Soc. 148 010-018. 

An application of an electrochemical quartz crystal microbalance (EQCM) in the study of the A11/HCIO4 system shows that even at a potential about 0.5 V more negative than the onset of AuO formation (the so-called preoxide region), the resonant frequency of the Au-covered quartz crystal decreases as that of the surface mass increases. A comparison of a voltammogram with the potential dependence of the micro-balance frequency for an Au electrode is shown in Figs. 6a and 6b. 

The electrochemical quartz crystal microbalance (EQCM) method was first used to study underpotential deposition in 1988 for Pb, Bi, Cu,... 

Fig. 14 Set-up of an electrogravimetric experiment with an electrochemical quartz crystal microbalance.

A technique for such measurements is the electrochemical quartz crystal microbalance (EQCM figure 14) [71]. Here, the working electrode is part of a quartz crystal oscillator that is mounted on the wall of the electrochemical cell and exposed to the electrolyte. The resonance frequency / of the quartz crystal is proportional to mass changes Am A/ Am. With base frequencies around 10 MHz, the determination of Am in the ng range is possible. 

Electrochemical quartz crystal microbalance studies at Sn-modified Pt and Au electrodes allowed a further insight into the kinetics and mechanism of the reduction process [58, 59]. The problems connected with the chemisorption of N03 ions were discussed in [30, 60]. 

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