Frumkin mechanism

Hydrogen evolution reaction, mechanism, 1135, 1151, 1163, 1164, 1189 catalytic pathway, 1163,1194, 1255 electrocatalysis, 1280 Frumkin-Temkin isotherm, 1194 Langmuir isotherm, 1194 Hydrogen coadsorption... 

B. Kabanov, R. Burshstein, and A. Frumkin, Disc. Faraday Soc. 1 259 (1947). First suggestion of a mechanism of Fe in alkaline solution that was compatible with modem ideas. 

Refs. [i] Frumkin A (1925) Zphys Chem 116 466 [ii] Fowler R, Guggenheim EA (1956) Statistical mechanics. Cambridge University Press, Cambridge [iii] Parsons R (1964) J Electroanal Chem 7 136 [iv] Levi MD,... 

For one-electron transfer reactions occurring via outer-sphere mechanisms, wp and ws can be estimated on the basis of electrostatic double-layer models. Thus, if the reaction site lies at the outer Helmholtz plane (o.H.p.), wp = ZFd and ws = (Z - 1 )Fcharge number of the oxidized species and (j>d is the potential across the diffuse layer. Rewriting eqn. (7) in terms of rate constants rather than free energies yields the familiar Frumkin equation [8]... 

In mixed (0.8 - x) M NaClO4 + x M NaF supporting electrolyte the electroreduction of Cd(II) was also studied by Saakes etal. [25]. The kinetic parameters were analyzed using CEE mechanism. The obtained chemical rate constants at both steps, fcg 1 and fcg 2, decreased with increasing NaF concentration. The data were corrected for nonspecific double-layer effect (Frumkin correction). The interpretation of CEE mechanism with parallel pathways connected with coexisting cadmium complexes was presented. 

The studies into the electrochemical kinetics of solvated electrons were to some extent stimulated by the hypothesis put forward in the second half of 6O s (see Sect. 8) for explaining the role of solvated electrons as intermediate products of electrode reactions, and also by the development made at that time in organic synthesis involving the participation of solvated electrons (see Sect. 9). Undoubtedly, knowledge of the mechanism of electrode generation of solvated electrons is of fundamental importance. Electrochemistry is the chemistry of the electron , Professor A. N. Frumkin once said. In fact, electron reactions at the interface of electronic and ionic conductors are inevitably associated with the electron addition or detachment process. In a solvated electron reaction no heavy particle (atom or molecule) acts as electron acceptor, or donor. In this sense, the electrode reactions of solvated electrons are the most simple electrode processes. Therefore, an insight into the solvated electron reaction mechanism is necessary for electrochemical kinetics as a whole. 

An early investigation of the mechanism of the methanol oxidation was made by two Russian workers, Bagotskii and Vasiliev [23], from the famous Moscow group directed by Frumkin. They suggested that the r.d.s. is not an electron-transfer reaction such as water discharge (40H >... 

There are two different ways of deriving the Langmuir adsorption isotherm. One of the derivations is based on kinetic transfer mechanisms of adsorption/desorption of adsorbing molecules. The second, thermodynamic derivation starts from the equivalence of the chemical potentials of adsorbing molecules in the bulk phase and in the adsorbed state. Frumkin (1925) introduced additional interaction forces between adsorbed molecules into the Langmuir adsorption isotherm. 

The equations given above, based on the Frumkin isotherm, assume a random distribution of O and R sites in the film. If the film is structured, such as in an organized mono-layer deposited by the L-B technique, there will be an ordered distribution of the sites. Under these conditions, a statistical mechanical approach is needed to account for the interactions and to find the i-E curve (38). For negative values of the interaction parameter in a structured film, a double wave results, even for a single electrode reaction, while the random distribution produces only a single broadened wave. 

As the theoretical models are comparatively complex, only numerical methods allow to interpret experimental data. A software package is available that allows to make model calculations for any type of the above discussed diffusion-controlled mechanism [223]. In addition to the theory for a Langmuir isotherm, where the collocation solution by Ziller and Miller can serve as analytical solution, the programme gives access also to calculations based on the Frumkin, the reorientation and aggregation isotherms. 

For a modelling of adsorption processes the well-known integro-differential equation (4.1) derived by Ward and Tordai [3] is used. It is the most general relationship between the dynamic adsorption r(t) and the subsurface concentration e(0,t) for fresh non-deformed surfaces and is valid for kinetic-controlled, pure diffusion-controlled and mixed adsorption mechanisms. For a diffusion-controlled adsorption mechanism Eq. (4.1) predicts different F dependencies on t for different types of isotherms. For example, the Frumkin adsorption isotherm predicts a slower initial rate of surface tension decrease than the Langmuir isotherm does. In section 4.2.2. it was shown that reorientation processes in the adsorption layer can mimic adsorption processes faster than expected from diffusion. In this paragraph we will give experimental evidence, that changes in the molar area of adsorbed molecules can cause sueh effectively faster adsorption processes. 

The experimental study of the adsorption of organic compounds on electrodes began in the first decade of the previous century with Gouy s electrocapillary work. Since then it has attracted considerable attention, mainly because it affects the mechanism of most of the processes occurring on electrodes. The first attempts to present a theoretical description of the effect of the electric field on adsorption appeared in 1925 and 1926 by Frumkin, who formulated the macroscopic model of condensers in parallel. The interpretation of the electrosorption of organic compounds at a molecular level was initiated by Butler" in 1929, but it was the work of Bockris and co-workers in 1963 that put the bases of the contemporary microscopic modelling. The main contribution by Bockris et al. was the introduction of the concept of the competition between solvent and adsorbate molecules for adsorption and the reorientation of the adsorbed molecules on the electrode upon the variation of the electric field. ... 

However, we have endless results that r = 1 in the vast majority of the experimental systems. Thus the wide applicability of the Frumkin isotherm is an indirect evidence that r = 1. Indeed, if we adopt r = 1, assume an adsorbed layer with a two-dimensional lattice structure and a random distribution of the adsorbed molecules, then statistical mechanics readily yields the Frumkin isotherm, Eq. (1). ° A direct indication that r is close to unity comes from the thermodynamic method we have proposed for the determination of This method is applicable to monolayers composed of solvent and constant orientated solute molecules. These conditions can be safely detected experimentally and if they are fulfilled, r can be obtained from surface pressure data by means of two extrapolations. Due to these extrapolations the method is extremely sensitive to experimental errors and for this reason it is applicable only to air / solution and liquid / liquid interfaces. All applications of this method gave the value r = 1 0.2, despite the considerable differences in the size of the adsorbates used. ... 

The value r 1 may be explained by the work of Guidelli et which shows that a strict statistical mechanical treatment of an adsorbed layer composed of adsorbate and solvent molecules distributed over a two-dimensional lattice yields roughly linear plots of F = ln 6/x(l-0) vs.. 6 even when the dimensions of the solute molecules are greater than those of the solvent molecnles, provided that H-bonding among the solvent molecules is taken into account. Note that the linearity of the F= ln 9/x(l-6) vs.. 0 plots shows the validity of the Frumkin isotherm, which in turn indicates that r w 1. 

Up to now the model has been applied with monomeric, dimeric and trimeric solute molecules. Although the study of these cases is not complete, possibly due to computational difficulties, it seems that some of the adsorption features are satisfactorily predicted only in the case of non-polar monomeric and polar dimeric solute molecules, provided that the latter exhibit certain orientations on the electrode surface. " In the case of polar monomeric and dimeric molecules that may adsorb either vertically or flat, the model does not give satisfactory predictions. This is shown in Figure 3 where the solid lines represent adsorption isotherms predicted by the model and the dotted lines represent the best Frumkin s isotherms that describe them. In the case of the trimeric solutes, the model predicts the existence of a surface phase transition. However, the transition properties, due to the use of an inappropriate statistical mechanical treatment, contradict thermodynamic and experimental data. Thus, despite its novelty the three-dimensional lattice approach has not given the expected results yet. 

Large-scale, systematic research in colloid chemistry began in the Soviet Union in the 1920s. Among the prominent chemists in this field are Dumansky (lyophilic colloids), Peskov (stable disperse systems). Rebinder (surface-active substances, physicochemical mechanics), Zhukov (electro-surface phenomena), and Deryagin (surface forces). Fundamental interdisciplinary research was carried out by Frumkin, Balandin, Boreskov, Chmutov, Laskorin, and others. The outstanding schools in the former Soviet Union in the field of adsorption developed under the leadership of Dubinin, A. V. Kiselev, and Neimark. 

Bagotskaya [18], and later Frumkin [19], proposed a mechanism where hydrogen atoms directly enter a metal membrane without going through an intermediate adsorbed state. 

Surfactant keeps emulsion droplets and latex particles colloidally stable against coalescence/aggregation. The surfactant plays another important role in emulsion polymerisation besides stabilisation. Surfactant is critically involved in the nucleation mechanism (i.e., how the particles are formed) of the polymer latex particles (418,419). The amount of surfactant used is critical in controlling the latex particle size distribution. As surfactant is added to an emulsion, some remains dissolved in the aqueous phase, and some adsorbs onto the surface of the emulsion droplets according to an adsorption isotherm (e.g., Langmuir, Freundhch, or Frumkin adsorption isotherms) (173). 

Age of material characterization (1970-present) (R.A. Huggins, J.R. Macdonald, W. Weppner) Age of reaction mechanism analysis (1970-present). The real power of EIS (A.N. Frumkin, R.D. Armstrong, I. Epelboin, M. Keddam, C. Gabrielli, D.D. Macdonald)... 

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