Differential electrochemical

In situ analysis of the reaction products can also be carried out by mass spectrometry, using the differential electrochemical mass spectrometry (DBMS) technique.This technique permits the detection of gaseous products since they are produced and captured through a porous electrode. It has been confirmed that carbon dioxide is the main reaction product. With this technique, it is also possible to determine the production of CO2... 

At present, most workers hold a more realistic view of the promises and difficulties of work in electrocatalysis. Starting in the 1980s, new lines of research into the state of catalyst surfaces and into the adsorption of reactants and foreign species on these surfaces have been developed. Techniques have been developed that can be used for studies at the atomic and molecular level. These techniques include the tunneling microscope, versions of Fourier transform infrared spectroscopy and of photoelectron spectroscopy, differential electrochemical mass spectroscopy, and others. The broad application of these techniques has considerably improved our understanding of the mechanism of catalytic effects in electrochemical reactions. 

K. and Enyo, M. (1989) Surface species produced on Pt electrodes during HCHO oxidation in sulfuric add solution as studied by infrared reflection-absorption spectroscopy (IRRAS) and differential electrochemical mass spectroscopy (OEMS)./. Electroanal. Chem., 258, 219-225. 

Jusys Z, Behm RJ. 2001. Methanol oxidation on a carbon-supported Pt fuel cell catalyst—A kinetic and mechanistic study by differential electrochemical mass spectrometry. J Phys ChemB 105 10874-10883. 

Heinen M, Jusys Z, Behm RJ. 2009. Reaction pathways analysis and reaction intermediate detection via simultaneous differential electrochemical mass spectrometry (DBMS) and attenuated total reflection Bourier transform infrared spectroscopy (ATR-BTIRS). In Vielstich W, Gasteiger HA, Yokokawa H, eds. Handbook of Buel Cells. Volume 5 Advances in Electrocatalysis. Chichester John Wiley Sons, Ltd., in press. 

Jambunathan K, Jayataman S, HiUier AC. 2004. A multielectrode electrochemical and scanning differential electrochemical mass spectrometry study of methanol oxidation on electrodepos-ited PORUy. Langmuir 20 1856 1863. 

JusysZ. 1994. H/D substitution effect on formaldehyde oxidation rate at a copper anode in alkaline medium studied by differential electrochemical mass spectrometry. J Electroanal Chem 375 257-262. 

Recently the proposed Oz evolution mechanism was supported by the results of a DEMS (Differential Electrochemical Mass Spectrometry) study performed by Wohlfahrt-Mehrens and Heitbaum [71] on Ru electrodes. Using this mass spectroscopic technique and lsO labeling for the determination of reaction products during 02 evolution, it could be verified that the oxygen of the oxide formed on Ru takes part in the 02 evolution process. The same observation was made for Ru02 electrodes when using labeled H2lsO. 

Mass spectrometry (MS) is an extremely powerful method of chemical analysis and the possibility of measuring electrochemical reaction products via MS was first suggested by Grambow and Bruckenstein (1977). The technique of differential electrochemical mass spectroscopy (DEMS) was later perfected and pioneered by Wolter and Heitbaum (1984). 

Figure 2.115 Experimental system for differential electrochemical mass spectroscopic (DEMS) measurements with automatic data acquisition. TP = turbo pump, IC = inlet chamber, A = analysis chamber, S — screw mechanism to control aperture between both chambers. After Iwasita and...

A long disputed issue of the nature of strongly bound species in this reaction has been recently revived with the vibrational spectroscopy studies of Bewick et al. (30) using EMIRS technique and of Kunimatsu and Kita (31) using polarization modulation IR-reflection-absorption technique. These data indicated the only CO is a strongly bound intermediate. Heitbaum et al. (32) on the other hand advocate COH, and most recently HCO (33), as the poisoning species on the basis of differential electrochemical mass spectroscopy (DEMS). 

N. Fujiwara, K. A. Friedrich, and U. Stimming, Ethanol oxidation on PtRu electrode studied by differential electrochemical mass spectrometry, J. Electroanal. Chem. 472, 120—125 (1999). 

Study of fhe mechanism of MeOH oxidation over Pt and PtRu surfaces has recenfly been given new insights using a combination of experimental and theoretical approaches. The use of electrochemically linked mass spectroscopy techniques (e.g., differential electrochemical mass spectroscopy— DBMS) has allowed the quantification of the MeOH oxidation reaction in terms of comparing CO2 yields with electrons passed. In addition, detection and quantification of reaction intermediates has also been demonstrated. In addition, use of theorefical fechniques such as DFT has allowed calculation of adsorbafe energies, probing reaction pathways, and activation of H2O to provide active OH species. 

Bagdonoff P, Friebe P, Alonso-Vante N (1998) A new inlet system for differential electrochemical mass spectroscopy applied to the photocorrosion of p-InP (111) single crystals. J Electrochem Soc 145 576-582... 

A series of pubKcations was devoted to the electrocatalytic reduction of nitrate by the Eindhoven group [50-54]. On the basis of these works, a comparative study was performed to determine the reactivity of nitrate ions in 0.1 mol dm concentration on eight different polycrystaUine electrodes (platinum, palladium, rhodium, ruthenium, iridium, copper, silver, and gold) in acidic solution using cyclic voltammetry, chronoamperometry, and differential electrochemical mass spectroscopy (DEMS) [50]. 

Similar studies on palladium/copper electrodes was carried out using differential electrochemical mass spectroscopy (DBMS), rotating ring-disk electrodes and EQCM [144]. In acidic electrolytes, the activity increased linearly with Cu coverage in alkaline electrolytes, a different dependence on coverage was observed. 

Oxidation of thiourea adsorbed on Au(lll) and pc-Au electrode in 0.1 M HCIO4 has been investigated using CV, in situ Fourier transform infrared spectroscopy, and differential electrochemical mass spectrometry [165]. Two reaction mechanisms were proposed for the oxidation of the adsorbed and nonadsorbed thiourea. For both types of Au electrodes, similar results were obtained. 

Equation (7.116) indicates that the charge-potential curves for reversible processes are only dependent on the square wave amplitude Sw and are independent of the frequency / = 1 jh and the staircase amplitude AEs. As a consequence, they are superimposable on those obtained at any differential electrochemical technique, such as DSCVC, provided that the differences between the successive potential pulses coincide (AE = 2 sw)- Moreover, when this difference is much less than RT/F (i.e., less than 25 mV at T = 198 K), the responses obtained in Cyclic Voltammetry (CV), Alternating Current Voltammetry, Potentiometric Stripping Analysis (PSA) and also in any Reciprocal Derivative Chronopotentiometry (RDCP) fulfill [5, 74, 75] ... 

The mechanisms of the oxidation of solvents such as THF and PC were studied by several groups, utilizing FTIR and XPS spectroscopy [107-109] and on-line mass spectrometry (DEMS-differential, electrochemical mass spectroscopy [110-112]). For example, using ex situ FTIR spectroscopy, Lacaze et al. [46] showed that THF in FiC104 solutions are polymerized on electrodes biased to high potentials. The proposed mechanism involves oxidation of C104 as an initial step, as shown in Scheme 7 [46,102], ESR measurements also support such a mechanism. However, there are also suggestions for possible direct oxidation... 

Although the data of Herrero et al. [34] were interpreted in terms of a parallel reaction scheme model, such a model is certainly not established by their treatment, and Vielstich and Xia [36] have criticised such a model on the basis of their Differential Electrochemical Mass Spectroscopy (DEMS) data [37]. At least below a potential of 420 mV, the very sensitive DEMS technique detects no C02 evolved from a polycrystalline particulate Pt electrode surface on chemisorption of methanol indeed, the only product detected other than adsorbed CO, in very small yield (one or two orders of magnitude smaller), is methyl formate from the intermediate oxidation product HCOOH. This is graphically illustrated in Fig. 18.2 in which the clean electrode is maintained at 50 mV, a 0.2M methanol/O.lM HCIO4 electrolyte introduced, and the electrode swept at 10 mV s I anod-... 

Refs. [i] (1972) Definition, terminology and symbols in colloid and surface chemistry, Part I. Pure Appl Chem 51 77 [ii] Horanyi G (2002) Specific adsorption. State of art Present knowledge and understanding. In Bard AJ, Stratmann M, Gileadi M, Urbakh M (eds) Thermodynamics and electrified interfaces. Encyclopedia of electrochemistry, vol. 1. Wiley-VCH, Weinheim, pp 349-382 [Hi] Calvo EJ (1986) Fundamentals. The basics of electrode reactions. In Bamford CH, Compton RG (eds) Comprehensive chemical kinetics, vol. 26. Elsevier, Amsterdam, pp 1-78 [iv] Baltruschat H (1999) Differential electrochemical mass spectrometry as a tool for interfacial studies. In Wieckowski A (ed) Interfacial electrochemistry, theory, experiment, and applications. Marcel Dekker, New York, pp 577-597... 

Jusys, Z., Kaiser, J., and Behm, R.J., Simulated air bleed oxidation of adsorbed CO on carbon supported Pt. Part I. A differential electrochemical mass spectrometry study, J. Electroanal. Chem., 554/555, 427, 2003. 

We will first describe briefly the main experimental techniques coupled with electrochemical methods Infrared Reflectance Spectroscopy (IRS), Electrochemical Quartz Crystal Microbalance (EQCM), Differential Electrochemical Mass Spectrometry (DEMS), Chemical Radiotracers and High Performance Liquid Chromatography (HPLC). 

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