Desorption, scanning electrochemical

The preparation and application of SAM systems patterned by STM and their use in catalysis was demonstrated by Wittstock and Schuhmann [123]. The patterning (local desorption) of SAMs from alkane thiols on gold was performed by scanning electrochemical microscopy (SECM), followed by the assembly of an amino-deriva-tized disulfide and coupling of glucose oxidase to form a catalytically active pattern of the enzyme. The enzymatic activity could be monitored/imaged by SECM. 

The SECM can be used in the feedback mode to probe lateral mass-charge transfer [79-83]. The theory of SECM feedback surveyed in Section IV.A.2 assumes that the substrate surface is uniformly reactive. When lateral mass and/ or charge transfer occurs on the substrate surface, or within a thin film, the surface reactivity of the substrate becomes non-uniform and the SECM feedback theory must be modified. Unwin and Bard [79] developed the theory for adsorption-desorption of a redox species at the substrate that allowed for surface diffusion of the adsorbate. They introduced a new approach, the scanning electrochemical microscope induced desorption (SECMID), as a way to probe surface diffusion. The set of differential equations for the diffusion problem comprise Eqs. (8a,b), and Eq. (26), which relates the redox concentration at the substrate surface and the surface coverage by adsorbed species... 

Scanning electrochemical microscopy (SECM) - Direct mode - Feedback mode - Generation/collection mode Scanning reference electrode technique (SRET) Scanning vibrating electrode technique (SVET) Scanning photoelectrochemical microscopy (SPECM) Scanning electrochemical induced desorption (SECMID)... 

Wilhelm, T. and Wittstock, G. (2000) Localised electrochemical desorption of gold alkanethiolate monolayers by means of scanning electrochemical microscopy (SECM). Microchimica Acta, 133 (1-4), 1-9. 

For the investigation of adsorption/desorption kinetics and surface diffusion rates, SECM is employed to locally perturb adsorption/desorption equilibria and measure the resulting flux of adsorbate from a surface. In this application, the technique is termed scanning electrochemical induced desorption (SECMID) (1), but historically this represents the first use of SECM in an equilibrium perturbation mode of operation. Later developments of this mode are highlighted towards the end of Sec. II.C. The principles of SECMID are illustrated schematically in Figure 2, with specific reference to proton adsorption/desorption at a metal oxide/aqueous interface, although the technique should be applicable to any solid/liquid interface, provided that the adsorbate of interest can be detected amperometrically. 

Unwin PR, Bard AJ (1992) Scanning electrochemical microscopy. 14. Scanning electrochemical microscope induced desorption - a new technique for the measurement of adsorption desorption-kinetics and surface-diffusion rates at the solid liquid interface. J Phys Chem 96(12) 5035-5045... 

Yang Y, Denuault G (1996) Scanning electrochemical microscopy (SECM). Study of the adsorption and desorption of hydrogen on platinum electrodes in Na2S04 solution (pH = 7). J Electroanal Chem 418(l-2) 99-107... 

Cyclic voltammograms of PtSn microelectrodes in 0.5 M sulfuric acid solution are shown in Fig. 15.6. The potential range was -200 to 800 mV (vs. SCE) and the scan rate was 100 mV/s. It can be seen clearly that hydrogen desorption from the PtSn-2 electrode is seriously inhibited compared with that from the PtSn-1 electrode. From the hydrogen desorption peak areas in the CV curves and the Pt single crystallite hydrogen desorption constant of 210 /xC/cm Pt, the electrochemical surface areas (ESA) for PtSn-1 and PtSn-2 were calculated to be 391 and 49 cm /mg, respectively. However, it is evident from XRD and TEM results that the two catalysts have similar particle size and so they should possess the similar physical surface area. The difference... 

The spontaneously deposited mthenium layer has to be electrochemically stabilized by potential cycling in the hydrogen adsorption/desorption region at low scan rates. Thus, the following situation can occur [124] ... 

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