Javier Garrido

Proton Transport in Membranes Prepared from Sulfonated Polystyrene-Poly(vinylidene fluoride) Blends

The preparation of new cation-exchange membranes from polymer composites based on poly(vinylidene fluoride), sulfonated polystyrene-co-divinylbenzene, and antimonic acid is reported. The thermal properties of the composites have been characterized by differential scanning calorimetry. Values of the transport number of protons in the membranes were obtained from the observable electric potential. It is defined from the potential difference measured between the electrodes reversible to one of the constituent ions in equilibrium with the system. When compared with Nafion cation-exchange membranes, the membranes described in this work exhibit interesting proton transport properties that could make them suitable as polymer electrolytes in fuel cells.

A finite-difference method for numerical solution of the steady-state Nernst-Planck equations with non-zero convection and electric current density

Abstract A computer algorithm has been developed for digital simulation of ionic transport through membranes obeying the Nernst—Planck and Poisson equations. The method of computation is quite general and allows the treatment of steady-state electrodiffusion equations for multiionic environments, the ionic species having arbitrary valences and mobilities, when convection and electric current are involved. The procedure provides a great flexibility in the choice of suitable boundary conditions and avoids numerical instabilities which are so frequent in numerical methods. Numerical results for concentration and electric potential gradient profiles are presented in the particular case of the ternary system NaClHClH2O.

Kinetics and Compositional Dependence on the Microwave Power and SiH4 / N 2 Flow Ratio of Silicon Nitride Deposited by Electron Cyclotron Resonance Plasmas

The archival version of this work was published in Journal of The Electrochemical Society. Hernandez, M. J., Garrido, J., Martinez, J. and J. Piqueras. Kinetics and compositional dependence on the microwave power and DiH4/N flow ratio of silicon nitride deposited by electron cyclotron resonance plasmas. Journal of The Electrochemical Society 141.11 (1994): 3234-3237

Observable variables of the transport processes in discountinuous systems

Abstract A new formulation for the transport processes across membranes in isothermal processes is derived. The study is carried out within the frame of the thermodynamics of irreversible processes. The fundamental variables of this formulation are the pressure difference, the difference in electrical potential between two reversible electrodes and the concentration dependent par of the chemical potential of the solutes. All these variables can be directly measured. The development includes the study of systems with gas electrodes. The connections of this formulation with others described before is also shown.

Rapid Thermal Annealing Behavior of Amorphous SiC Layers Deposited by Electron Cyclotron Resonance Plasma

The archival version of this work was published in Journal of the electrochemical society 143.1 (1996): 271-277

Thermodynamics of electrokinetic processes—II. systems with different kinds of electrodes

Abstract In this work Haases Formulation of Electrokinetic Processes is applied to special systems: those working with two different electrodes and those where gaseous phases are formed. Phenomenological equations are always written in terms of directly observable variables. The extrinsic character of Haases Formulation is clearly shown. Some special results on streaming current in dielectric liquids are explained.

Peltier’s and Thomson’s coefficients of thermoelectric phenomena in the observable formulation

Four transport coefficients characterize the thermoelectric properties of materials. Three of them are widely measured and studied. But the number of references on the Peltier coefficient are very limited. This unequal result is a consequence of the Onsager reciprocal relation (ORR). A review on the preciseness and accuracy of Peltier coefficient measurements has been developed in this paper. Thus we can appreciate a low level in the experimental confirmation for the ORR. In order to describe the thermoelectric processes in an advantageous way, the observable formulation has been used. This is characterized by the electric potential measured at the probe terminals and for the heat flux which the conductor laterally dissipates. The energy balance provides the basic relationships among the observables and the Peltier and Thomson coefficients. A new way for measuring the Peltier coefficient has been suggested.

Thermodynamics of electrokinetic processes—I. Formulations

Abstract The phenomenological equations of electrokinetic processes are studied according to five different formulations. Transformation matrices with Haases formulation are given. A study of the measurable character of fluxes, forces and phenomenological coefficients in those formulations is also made. The extrinsic character, if so, of the formulations is examined and a general definition of formulations established only for binary solutions is given. Finally, a review of the literature is included, aiming to clarify the possible misunderstandings arising from the application of these five formulations.

Observable quantities for electrodiffusion processes in membranes.

Electrically driven ion transport processes in a membrane system are analyzed in terms of observable quantities, such as the apparent volume flow, the time dependence of the electrolyte concentration in one cell compartment, and the electrical potential difference between the electrodes. The relations between the fluxes and these observable quantities are rigorously deduced from balances for constituent mass and solution volume. These relations improve the results for the transport coefficients up to 25% with respect to those obtained using simplified expressions common in the literature. Given the practical importance of ionic transport numbers and the solvent transference number in the phenomenological description of electrically driven processes, the transport equations are presented using the electrolyte concentration difference and the electric current as the drivers of the different constituents. Because various electric potential differences can be used in this traditional irreversible thermodynamics approach, the advantages of the formulation of the transport equations in terms of concentration difference and electric current are emphasized.

Observable Electric Potential in a KCl Salt Bridge

The theoretical description of nonequilibrium electrochemical systems involves nonobservable variables such as diffusion potential (dp). In the recent years, a new way based on the observable electric potential (oep) has been developed. In this work we provide an illustration of the potential applications of the oep formalism by considering a system of great practical interest: the salt bridge. This system has been chosen because, in spite of its widespread use for many decades, a sound theoretical base for the salt bridge concept is still lacking. The oep is offered as a good alternative in the salt bridges. Moreover, it involves a ternary electrolyte system, with a common anion at uniform temperature and pressure, which complexity is enough to make useful this application example of the oep formalism.