M.V. Sangaranarayanan

A new analysis of the metal/electrolyte interface using jellium model for metal surfaces and Bethe approximation for dipolar interactions is carried out. The total surface energy taking into account the metal-solvent interactions is then solved using a one-parameter family of trial functions for the electronic density profile, and a systematic investigation of the metal-solvent bond length (X1) and its dependence on electrode charge density (OM) is presented. The crucial role played by x1 in double-layer analysis is also pointed out using the variation of inner layer capacitance with OM at the Hg/NaF interface. The model is then used to analyze the effect of temperature, bulk electron density of the metal, and electron-ion coupling terms using Ashcroft pseudopotential on the capacitance-potential plots. The position of the image plane and its variation with electric field, electron density of metals, etc., have also been outlined. The influence of external field on work function changes pertaining to solvent adsorption at electrochemical interfaces is discussed.

The analysis of transient chronoamperometric current response for various ultramicroelectrode geometries is carried out by solving the mixed boundary value problem for short and long time regimes. A two-point Padé approximant valid for entire time domain is developed. Tabular compilations of dimensionless current for ring and disc electrodes are reported.

The conductance and transport number expressions are derived for the ion-involved electron-hopping (IIEH) mechanism taking into account the ion pairing between fixed redox ions and the mobile electroinactive counterions. Under the steady-state condition, the effects of ion pairing, the ratio of diffusivity associated with electron hopping and the mobile electroinactive counterion, and the applied potential are studied both in the presence and in the absence of supporting electrolyte. The main effect of ion pairing is to decrease the charge transport rate, and that of the diffusivity rake is to change the mechanism of the conductance process from ohmic (electronic) to redox (or nonohmic). This change in the conductance behavior from ohmic to nonohmic is shown to be due to the change in the rate-limiting process from electron transport to counterion movement. A direct correlation between the proposed theory and experimental results obtained earlier using poly(benzimidazobenzophenanthroline) and [Os(vbpy)3]2+/[Zn(vbpy)3]2+ copolymer coated electrodes is demonstrated.

The consequences of employing the Bethe approximation for dipolar interactions in the inner part of the electrical double layer are examined. Apart from providing explicit results for order parameters, dipolar potential, and differential capacitance for a two-state polarizable point dipole model, a nonlinear regression analysis using experimental data is carried out in order to estimate interfacial constants such as permanent dipole moment, polarizability, effective coordination number, etc. This indicates that the simultaneous agreement of dipole potential and differential capacitance variations with charge density on the metal surface cannot be obtained using conventional discrete multistate orientational state models, thereby pointing to the need for explicit introduction of a metal surface into the double layer theories.

The generalised master equation approach is employed in conjunction with the spin- 1 2 Ising Hamiltonian to formulate different types of diffusion migration equations. The methodology involving Kawasaki dynamics for the transition probabilities is demonstrated for electron hopping between nearest-neighbour redox centres in chemically modified electrodes and the classical Nernst-Planck equation. © 1995.

A comprehensive analysis of electron hopping between spatially separated redox centres pertaining to supramolecular structures is carried out by taking into account different mechanistic pathways. Spin exchange dynamics due to Kawasaki is invoked to study the transport phenomena for the more appropriate, thermodynamically favored ion pairing mechanism. The generalized master equation and its reduced form are presented and the dynamics of electron hopping is analyzed both under spin-1/2 and spin-1 Ising versions. Transition probabilities chosen for the present study satisfy the condition of detailed balancing and is a function of spin exchange jump frequencies and spin variables. Energetics of electron hopping process is obtained from the Ising Hamiltonian under molecular field approximation and incorporated into the spin exchange frequencies. The apparent diffusion coefficient that emerges along with the transport equation reflects the dynamics of electron propagation in the films. The importance of blocking factor and potential independent terms in the apparent diffusion coefficient expression overlooked in hitherto known phenomenological approaches is emphasized.

The analysis of two-dimensional condensation of organic compounds at the mercury|aqueous solution interface is carried out using a two-state Ising model formalism. Explicit results for the transition potential in terms of surface coverage, temperature and adsorbate concentration are reported. A methodology for estimating critical temperatures using the classical formula of dispersion forces is proposed, and the calculation of critical concentration is discussed. The estimated critical parameters are compared with the experimental data for various organic adsorbates.

The mixed boundary value problem for the two dimensional diffusion equation pertaining to ultramicrodisc electrodes, is analysed and a two-point Padé approximation result is derived for the non steady-state chronoamperometric current. A satisfactory agreement with the available digital simulation data is noted. © 1995.

The methodology for deriving the differential capacitance at electrochemical interfaces using quasi-chemical approximation is demonstrated for adsorption of solvent dipoles in two configurational states. Explicit results for dipole potential (g(dip)) and the inner layer capacitance (C(i)) are reported. The experimentally observed linear correlation between (1/C(i)) and g(dip), the negative temperature coefficient of the dipole potential at the potential of zero charge, and the occurrence of capacitance maximum at positive charge densities are discussed.

A comprehensive analysis starting from the formalism of irreversible thermodynamics, incorporating activity coefficients and interparticle interactions, is developed to derive expressions for mixed conductance, transport numbers, etc., for diffusive and electric field assisted electron hopping through polymer matrixes attached to electrode surfaces. The transport equation obtained is a combination of Dahms-Ruff diffusion and the Levich migration terms and includes short-range interparticle interactions under molecular field approximation as well as activity coefficient terms. The derived dynamical equation for electron flux follows a second-order law in species concentrations in contrast to the classical Nernst-Planck equation for ion migration. Applicable systems are thought to be organic π-conjugated electroactive polymers, electronically conducting polymers with covalently linked redox groups, i.e., metal ion redox site membranes, and ion-exchange polymers. The concept of self and tracer diffusion coefficients is brought into the formalism of charge transport in supramolecular structures. Some new insights regarding the identification of Onsager's coefficient in diffusion through supramolecular structures are also provided.