Electrode SEIRA

Figure 6.16 Attenuated total reflection surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS) spectra for the oxidation of 0.1 M HCOOH in 0.5 M H2SO4 on a polycrystaUine electrode. The bands at 2055 -2075 and 1800-1850 cm are assigned to linear- and bridge-bonded CO, whereas the band at 1323 cm corresponds to adsorbed formate. (Reproduced from Samjeske et al. [2006].)...

Figure 9.2 SEIRAS spectra for a Pt thin film electrode in 02-saturated 0.1 M NaC104 + NaOH (pH 11). The reference spectmm at 0.4 V was taken before the potential sweep started. The scan rate was 10 mV/s. (Reproduced with permission from Shao et al. [2006a].)...

Delgado JM, Orts JM, Rodes A. 2005. ATR-SEIRAS study of the adsorption of acetate anions at chemically deposited silver thin film electrodes. Langmuir 21 8809-8816. 

Pronkin S, Wandlowski T. 2004. ATR-SEIRAS—An approach to probe the reactivity of Pd-modified quasi-single crystal gold film electrodes. Surf Sci 573 109-127. 

The structure and orientation of water molecules on quasi single-crystalline Au(lll -20 nm) thin film electrodes in contact with aqueous sulfuric acid solution were studied by surface-enhanced infrared reflection absorption spectroscopy employing an ATR configuration (ATR-SEIRAS) [22,31]. The spectrum of interfacial water is strongly dependent on electrode potential, ionic strength and pH. Figure 4A shows a series of SEIRA spectra recorded within the potential range of an ideally polarizable Au(lll) electrode in... 

In the following paragraphs we will describe results of a comprehensive electrochemical study employing cychc voltammetry, STM and ATR-SEIRAS on the potential-controlled assembly and on structure transitions of TMA adlayers on Au(lll) electrodes in 0.1 M H2SO4. For comparison we will also discuss data for benzoic acid (BA), isophthalic acid (lA) and terephthalic acid (TA). 

Fig. 13 A Selected SEIRA spectra of Au(lll-25nm)/0.1M HCIO4 in the absence gray traces) and in the presence of 3 mM TMA (black traces) recorded simultaneously during a positive-going potential from - 0.20 to 0.90 V, scan rate 10 mV s . The background spectra were measured at - 0.20 V. The data represent different potential regions of the various adlayer phases of TMA start (- 0.20 V), 11a (0.11 V), 11b (0.39 V), IV (0.53 V) and IV (0.88 V). B Equilibrium SEIRA spectra of TMA (3 mM), isophthalic acid (lA, saturated solution) and benzoic acid (BA, 3 mM) in 0.05 M H2SO4 obtained at 0.80 V in region IV. The reference spectra were taken at = - 0.20 V. The insets illustrate the derived interfacial orientations of the three molecules chemisorbed on a positively charged Au(lll-25nm) film electrode [68]...

The high sensitivity of SEIRAS (see above) allows measurements in real time during a slow electrode potential scan [303-305] for particularly fast acquisition, step-scan interferometers may be used [306]. A series of time-resolved SEIRA spectra recorded during reduction of heptyl viologen to HV + at a silver electrode in an aqueous solution of 0.3 M KBr is displayed in Fig. 5.60 [274]. 

Fig. 5.60. Time-resolved SEIRA spectra of the reduction of to HV + at a silver electrode in an aqueous solution of 0.3 M KBr (based on data in [274])...

Fig. 5.61. Time-resolved SEIRAS. Pump pulse 532 nm, 35 ps duration, 3 mJ cm , temporal profile indicated by dotted line position and infrared absorption intensity of CO stretch mode plotted as a function of time, platinum electrode, aqueous solution of 0.1 M HCIO4 (based on data in [310])...

Further reported examples include electrocatalytic processes and their intermediates [313, 314]. Formate could be identified as an active intermediate of methanol electrooxidation at a polycrystalline platinum electrode [315]. Water molecules coadsorbed during methanol adsorption on platinum were identified as those species that react subsequently with COad that was formed as a result of methanol chemisorption [316]. The high sensitivity of SEIRAS allows mapping of two-dimensional spectra (for selected examples, see [285]). Finally, two-dimensional correlation analysis of electrochemical reactions becomes possible [317]. 

Mechanism and reaction intermediates of the hydrogen oxidation reaction on platinum have been studied with SEIRAS [324]. A band observed around 2090 cm was assigned to adsorbed hydrogen species and the band height dependency on electrode potential and hydrogen overpressure was found to match values predicted on the basis of the Volmer-Tafel mechanism. 

The interface platinum/NAFION monomer in the presence of perchloric acid was investigated with SEIRAS [325]. A band showing electrode potential depen-... 

To prevent denaturation of redox proteins and enzymes upon immobilization on an electrode surface that is necessary for electrochemical investigations, electrodes may have to be modified with suitable biocompatible membranes. Studies of redox processes and associated non-electrochemical processes of bound species with both SEIRAS and SERS have been reviewed [326]. 

These ions undergo only weak perturbations upon adsorption. Thus, it can be difficult to discriminate species in solution, or in the diffuse doublelayer, from ions at the electrode surface [54]. Better selectivity for adsorbed electrolyte anions has been achieved through use of the surface-enhanced infrared absorption spectroscopy (SEIRAS) technique [22, 54, 89, 90]. Methods for the preparation of quasi-single crystalline thin films are enabling the study of electrolyte adsorption on structurally well-defined surface sites by SEIRAS [22, 89,... 

SEIRAS is emerging as a powerful technique for interfacial studies in electrochemistry and electrochemical catalysis. Chapter 9 of this volume is devoted to SEIRAS and describes experimental aspects and many applications. Highlights are presented below, and the reader is referred to Chapter 9 for details regarding cell design, working electrode characteristics, and preparation techniques and applications. 

Fig. 7.3 SEIRAS spectra obtained from an Au(lll) film electrode in 0.5 M HCIO4. Spectra were recorded at potentials of 0.12 Vrhe (3)1 0.77 Vrhe (b), and 1.22 Vrhe W-A spectrum recorded near the potential of...

Fig. 7.S SEIRAS spectra obtained from a Pt film electrode in 0.1 M HCIO4 containing 0.5 M CH3OH. Spectra were recorded in sequence starting from 0.05 Vrhe aud progressing positive. The scan rate was 5 mVs . Adapted with permission from Ref [21].

In addition to electrocatalysis and double-layer phenomena, SEIRAS has proved particularly useful in the study of organic adsorption on electrodes [99, 146-149]. This is an area where SEIRAS can have an especially important impact, as traditional in-situ infrared methods are often limited by the low absorption cross-sections of organic adsorbates. Along these same lines, SEIRAS is... 

Figure 7.6 A shows SEIRAS spectra that foUow the adsorption of the protein cytochrome c oxidase onto the surface of a chemically modified Au electrode. Bands of the amide I and amide II modes of the protein backbone appear at 1658 cm" and 1550 cm", respectively. The peak intensity of the bands increases with time. The amide II band was shown to grow according to an exponential rate law with a time constant of 213 s [151]. The amide I band position is characteristic of an a-helical protein, consistent with the structure of cytochrome c oxidase. The protein was adsorbed onto the Au surface via affinity for a chemical layer that was constructed in a step-wise fashion upon exposure of the surface to a series of reagents. Initially, the metal surface was modified by self-assembly of DTSP [difhiobis-(suc-...

In early in-situ infrared spectroscopy studies of catalyst supported on reflective Au substrates, it was recognized that spectral bands develop distortions due to anomalous optical effects as the catalyst coverage becomes greater than a few monolayers [17, 18, 158]. Different procedures were adopted to ensure that catalyst coverages on Au remained low [15, 17, 18, 157, 158]. Related to these efforts are experiments that examine the electrochemical and optical properties of nanostructured metal electrodes prepared by chemical, vapor, or electrochemical deposition methods (cf. Refs. [79, 137, 141, 170-179] and references therein). Much of the work in this area has targeted SEIRAS measurements. 

The understanding of factors that lead to enhanced band intensities and dispersive band shapes is of central interest in studies with nanostructured electrodes. Effective medium theory has often been employed to identify mechanisms for enhanced infrared absorption [28, 128, 172, 174, 175]. Osawa and coworkers applied Maxwell-Garnett and Bruggeman effective medium models in early SEIRAS work [28, 128]. Recently, Ross and Aroca overviewed effective medium theory and discussed the advantages and disadvantages of different models for predicting characteristics of SEIRAS spectra [174]. When infrared measurements on nanostructured electrodes are performed by ATR sampling, as is typically the case in SEIRAS experiments, band intensity enhancements occur, but the band shapes are usually not obviously distorted. In contrast, external... 

Typical electrochemical cells used for ATR-SEIRAS are shown in Fig. 8.4 [28, 29). The cell can be made of either glass or plastics such as Kel-F. The prism works as the cell window as well as the substrate on which a thin-film electrode is deposited. Infrared-transparent materials with high reflective indices such as... 

Thin-film electrodes that exhibit the SEIRA effect can be deposited on the total-reflecting plane of the prism by vacuum evaporation or electroless plating of the desired metal. Electrochemical deposition cannot be used for non-doped (and thus non-conducting) Si windows, but is possible for Ge. 

Vacuum-evaporated very thin ( 20 run) Au and Ag electrodes suitable for SEIRAS show pale blue to purple colors, while chemically deposited film electrodes show the colors of the corresponding massive metals and are as shiny as a well-polished surface. Both thin-film electrodes have enough conductivity for electrochemistry. These film electrodes are usually polycrystaUine. In the case of Au films,... 

SEIRAS usually gives spectral features of the adsorbed molecules the same as those observed by IRAS on massive bulk electrodes, but the band intensity and... 

Fig. 8.7 SEIRA spectra of CO adsorbed on vacuum-evaporated (a) and chemically deposited (b) Au film electrodes measured in CO-saturated H2SO4 at OV (vs SCE). The reference spectrum of each spectrum was acquired at the same potential in the pure supporting electrolyte without CO [22].

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