Electroadsorption processes

As is widely known, bulk species which have chromophores that absorb in the UV-Vis can be analyzed quantitatively and qualitatively by this spectroscopy. The study of electrodes or species adsorbed as thin layers by UV-Vis is more difficult, due to sensitivity problems and the availability of the appropriate chromophores [50], Another use of this type of analysis is electroreflectance [51,52], Adsorption of species on reflective electrode surfaces changes their reflectivity. Thus, this method can indicate electroadsorption processes very sensitively, in situ, although it does not provide specific information on the structure and composition of surface layers. 

The glucose electroadsorption process (measured through potentio-static current transients ) and the interaction between the electro-adsorbed species and H-adatoms, suggest a quite complex reaction pattern... 

At the electrochemical interface, adsorption of either charged or neutral molecules and charge transfer processes may occur simultaneously. Electroadsorption and electrodesorption processes play a key role in electrocatalytic reactions [2],... 

Two different stages for silver deposition on platinum can be described one at 1.1 V vs. RHE responding to a silver-platinum alloy electrodissolution (overlapped with the oxygen electroadsorption at free platinum sites) and the other at 0.65 V due to the silver oxidation (from the onset of the bulk deposition process) deposited on the former surface alloy [88,89]. The former process splits into two peaks when the potentiostatic ageing is performed. The spectroscopic techniques such as XPS and ARXPS (angle resolved x-ray photoelectron spectroscopy) were used to determine the chemical composition of the silver films on the platinum in an acid solution [92], The technique was not able to discern between the presence of silver oxides and sulfates, only an energy shift of the clean silver 3d5/2 band at a upd level of —0.5 eV was detected. 

Formhals A (1934) Process and apparatus for preparing artificial threads, U.S. patent 1975504. Huang Z M, Zhang Y Z, Kotaki M and Ramakrishna S (2003) A review on polymer nanofibers by electrospinning and their applications in nanocomposites. Compos Sci Technol 63 2223-2253. Rodney K (2009) Four commercial applications for electroadsorptive filter media in water filtration. In Conf Proc Nanofibers for the Millenium - Nano for Life , March 11-12, Prague, Czech Republic, pp.168-171. 

Cyclic voltammetry (CV) is one of the most widely used electrochemical techniques for acquiring qualitative information about electrochemical reactions. Measurement using cyclic voltammetry can rapidly provide considerable information about the thermodynamics of redox processes and the kinetics of heterogeneous electron-transfer reactions, as well as coupled chemical adsorption and reactions. Cyclic voltammetry is often the first experiment performed in an electroanalytical study. In particular, it can rapidly reveal the locations of the redox potentials of the electroactive species. CV is also used to measure the electrochemical surface area (ECSA, m /g catalyst) of electrocatalysts (e.g., Pt/C catalyst) in a three-electrode system with a catalyst coated glass carbon disk electrode as a working electrode [52]. Figure 21.9 shows a typical CV curve on Pt/C. Peaks 1 and 2 correspond to hydrogen electroadsorption on Pt(lOO) and Pt(l 11) crystal surfaces, respectively. The H2 electroadsorption can be expressed as Equation 21.35 ... 

Figure 3.4 shows a typical CV curve recorded from a fuel cell catalyst layer catalyzed by a carbon-supported Pt catalyst. A total of six peaks are apparent on the CV curve. Peaks 1 and 2 correspond to the hydrogen electroadsorption induced by the reduction of H" " on the Pt(lOO) and Pt(lll) crystal surfaces, respectively. The process can be expressed as follows ... 

This equation provides the correspondence between adsorption / absorption equilibria in the gas phase and electroadsorption / electroabsorption equilibria in solution [28,73] (for example, the H coverage or bulk solubility at OV / RHEl is equal to the coverage or solubility at an H2 pressure of 1 atm). However, this relation applies only to electrosorption processes in equilibrium or at least in quasi-equilibrium and is not valid not at large overpotentials where coupled mechanisms prevail. 

The process of reversible hydrogen electroadsorption occurs at the smface of metal electrodes of the platinum group at potentials anodic with respect to the reversible hydrogen electrode at the given pH and at a pressure of 1 atm (half-standard reversible H+/H2 electrode at 1 atm. 

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