Publications

In this paper we present a mathematical model of a sealed nickel-cadmium cell that includes proton diffusion and ohmic drop through the active material in the nickel electrode. The model is used to calculate sensitivity coefficients for various parameters in the model. These calculations show that the discharge voltage of the cell is affected mostly by the kinetics of the nickel reaction. Toward the end of discharge, proton diffusion also becomes important, because the proton diffusion process affects the active material utilization significantly. During charge; the cell voltage is mainly affected by the kinetics of the nickel reaction until the oxygen evolution reaction begins, after which time the kinetics of the oxygen evolution has the largest effect. The oxygen evolution reaction is also the most influencing factor on the actual charge uptake of the cell by the end of a charge operation (charge efficiency). Compared to the rates of reaction and proton diffusion, the ohmic drop in the active material of the nickel electrode and the mass transport and ohmic drop in the electrolyte have negligible effect on the behavior of the cell studied here.

A mathematical model for the discharge of a metal-hydride electrode was developed. The model was used to study the effect of various parameters on predicted;discharge curves. The simulations obtained using the model show the expected decrease of charge utilization as the rate of discharge is increased. Increasing the particle size of the alloy and decreasing the diffusion coefficient of the hydrogen atoms in the hydride showed a similar effect on the discharge curves. The model simulations also show the critical role that the kinetic and transport parameters play in determining the overall shape of the predicted discharge curves for a metal-hydride electrode. The kinetic parameters used in the model predictions are those for TiMn1.5Hx (x \textless 0.31).

It is shown that the underpotential deposition of zinc on AISI 4340 steel and Inconel 718 alloys inhibits the hydrogen evolution reaction and the degree of hydrogen ingress. In the presence of monolayer coverage of zinc on the substrate surfaces, the hydrogen evolution current densities are reduced 46% and 68% compared with the values obtained on bare AISI 4340 steel and Inconel 718 alloy, respectively. As a consequence, the underpotential deposition of zinc on AISI 4340 steel and Inconel 718 alloy membrane reduces the steady state hydrogen permeation current density by 51% and 40%, respectively. © 1995 Chapman & Hall.

The initial current density distribution in lead acid batteries with tubular lead dioxide electrodes and flat lead electrodes has been studied by means of a two-dimensional model and experimental verification by polarization curves and potential transients during galvanostatic discharge. The cell geometry was modelled with and without separators and a tubular electrode envelope. The governing equations were solved with a finite element method. It was found that the tube envelope has a large impact on the current density distribution and had to be incorporated into the model to fit the experimental results. Although the envelope increases the ohmic losses, it has the positive effect of giving a more uniform current distribution around the electrode tube. A lead acid cell with tubular positive electrodes and flat negative electrodes can therefore be approximated by a one-dimensional model consisting of a positive electrode tube placed concentrically in a cylindrical lead electrode. The two-dimensional model was further used to study the effects of different design factors, for example, cell width and kinetic parameters of the lead dioxide electrode. © 1995 Chapman & Hall.

Polarization and permeation experiments showed that a thin layer of electroplated bismuth (1 $μ$m to 2 $μ$m) inhibited the evolution and penetration of hydrogen through nickel-chromium alloy 718 (UNS N07718) and type 4340 (UNS G43400) steel. Inhibition effects were due to the kinetic limitations of the hydrogen discharge reaction and to the suppression of hydrogen adsorption on the deposited layers. The hydrogen evolution reactions on alloy 718 and type 4340 steel were inhibited by 28% and 85%, respectively. The hydrogen permeation rates through these alloys were reduced by 76% and 65%, respectively.

The constant potential and constant current discharge techniques were used to determine the hydrogen diffusion coefficients in an LaNi 4.25 Al o.75 electrode. The values obtained were 2.97 X 10 -11 and 3.30 X 10- 11 cm 2 /s, respectively. The advantages and disadvantages of these two techniques are discussed. © 1995, The Electrochemical Society, Inc. All rights reserved.

Iron-nickel (Fe-Ni) plating bath solution chemistry was studied by determining the Fe-Ni equilibrium concentrations at various pH levels. It was found that the alloy composition is determined by solution equilibria, mass transfer of the electroactive species within the diffusion layer and by the surface coverage of the additives on the electrode. The effect of the rotation speed of the disc electrode and the presence of organic additives on the deposition of Fe-Ni alloys are evaluated. Boric acid increases the absolute iron deposition rate, while it inhibits the rate of nickel reduction. Saccharin and ethylene diamine influence the metal deposition rate but are not as effective as boric acid. © 1995 Chapman & Hall.

The hydrogen-atom direct-entry mechanism is used to explain why the steady-state hydrogen permeation current density through a metal membrane is directly proportional to the cathodic current density i c , and is independent of the membrane thickness when i c is small. © 1994, The Electrochemical Society, Inc. All rights reserved.

A parallel-plate electrochemical reactor model with multiple reactions at both electrodes and anolyte and catholyte recirculation tanks was modeled for the electrochemical destruction of nitrate and nitrite species in an alkaline solution. The model can be used to predict electrochemical reaction current efficiencies and outlet concentrations of species from the reactor, given inlet feed conditions and cell operating conditions. Also, predictions are made for off-gas composition and liquid-phase composition in the recirculation tanks. The results of case studies at different applied potentials are shown here. At lower applied potentials, the model predictions show that the destruction process is more energy efficient, but the time required to destroy a given amount of waste is increased.