G. Zheng

Electrochemical Determination of the Diffusion Coefficient of Hydrogen Through an LaNi4.25Al0.75 Electrode in Alkaline Aqueous Solution

Metal hydrides are being used as electrodes in nickel/metal-hydride batteries because of their ability to store large quantities of hydrogen and because of their many advantages over conventional lead-acid and nickel-cadmium batteries. The performance of a metal hydride electrode is determined by both the kinetics of the processes occurring at the metal/electrolyte interface and the rate of hydrogen diffusion within the bulk of the metal. The constant potential and constant current discharge techniques were used to determine the hydrogen diffusion coefficients in an LaNi{sub 4.25}Al{sub 0.75} electrode. The values obtained were 2.97 {times} 10{sup {minus}11} and 3.30 {times} 10{sup {minus}11} cm{sup 2}/s, respectively. The advantages and disadvantages of these two techniques are discussed.

Determination of Transport and Electrochemical Kinetic Parameters of Bare and Copper‐Coated LaNi4.27Sn0.24 Electrodes in Alkaline Solution

Electrochemical properties of bare and copper-coated LaNi{sub 4.27}Sn{sub 0.24} electrodes were investigated in alkaline solution. The exchange current density, polarization resistance, and equilibrium potential were determined as functions of the state of charge in the electrodes. The symmetry factors for bare and copper-coated electrodes were estimated to be 0.53 and 0.52, respectively. By using a constant current discharge technique, the hydrogen diffusion coefficient in bare and coated LaNi{sub 4.27}Sn{sub 0.24} was estimated to be 6.75 {times} 10{sup {minus}11} cm{sup 2}/s.

Mathematical modeling of hexavalent chromium decontamination from low surface charged soils

Abstract A new electrokinetic technology has been developed for in-situ decontamination of hexavalent chromium in sand. Imposition of a constant potential gradient across the soil matrix through a graphite cathode and iron anode resulted in successful migration of chromate towards the anode. The hexavalent chromium ions are reduced to the harmless trivalent form by chemical reaction with the anodic electrochemical dissolution product, Fe2+. The alkaline front generated at the cathode due to water reduction flushes across the cell and favors faster transport of chromate by enhancing its conductivity. The acidic front generated due to water oxidation at the anode remains adjacent at the electrode-sand interface due to its consumption by the corrosion reaction with iron. The lower production rate of H+ is also due to the competing anodic dissolution reaction. The low pH at the anodic region favors the reduction of hexavalent chromium to its trivalent state. The experimental results are compared with a theoretical model developed from first principles. The water electrolysis reactions at both electrodes, the sorption processes in sand and the water hydrolysis reaction have been included in the model. Concentration profiles for the movement of ionic species under a potential field were simulated for different times. The model predicts the sweep of the alkaline front across the cell due to the transport of OH− ions. Comparison of the chromate concentration profiles with experimental data after 28 days of electrolysis shows good agreement. The potassium cations are positively charged and remained at the cathode where they had been placed initially. The good agreement between the model and the data demonstrates that the analysis is likely to be an accurate estimation of the physical situation, within the limits of the assumptions made.

Application of Porous Electrode Theory on Metal Hydride Electrodes in Alkaline Solution

Porous electrode theory was applied to estimate the exchange current density, the polarization resistance, and symmetry factor for LaNi 4.27 Sn 0.24 hydride electrode in alkaline solution. The exchange current density, polarization resistance, and symmetry factor were determined from polarization curves which were obtained at low overpotentials.

Determination of transport and electrochemical kinetic parameters of M-H electrodes

AbstractElectrochemical and transport properties of La0.65Ce0.35Ni3.55Co0.75Mn0.4Al0.3 electrode were investigated in alkaline solution. The exchange current density, polarization resistance and the symmetry factor were determined from polarization curves obtained at low overpotentials. The symmetry factor was estimated to be 0.55 ± 0.01 and is independent of the state of charge. The equilibrium potential of the electrode was found to depend upon the hydrogen content in the alloy. The constant current discharge technique was used to determine the hydrogen diffusion coefficient in the alloy. The estimated value of

Electrochemical Investigations of Bare and Pd-Coated LaNi 4.25 Al 0.75 Electrodes in Alkaline Solution

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Surface Treatment for Mitigation of Hydrogen Absorption and Penetration into AISI 4340 Steel

/a2 at 0.1 C discharge rate was 1.39 × 10−4s−1.

Use of Underpotential Deposition of Zinc to Mitigate Hydrogen Absorption into Monel K500

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[sub c], and is independent of the membrane thickness when i[sub c] is small. The Devanathan-Stachurski permeation technique was used to investigate the rate of hydrogen permeation through a HY-130 steel and through palladium membranes with an area of approximately 4 cm[sup 2] with thicknesses of 0.15 and 0.025 mm, respectively.