David R. Flinn

Comparative Activity of (111), (100), (110), and Polycrystalline Platinum Electrodes in H2‐Saturated 1 M H 2 SO 4 under Potentiostatic Control

Potentiostatic measurements of the three principle faces of oriented single Pt crystals and polycrystalline Pt showed some interesting comparisons. True areas are based on Pt atom densities, and under the electrochemical treatment used, no changes in these areas were found once the initial surface cleaning was completed. The hydrogen overvoltage was independent of crystal orientation or other metallurgical factors; however, the passivation of the hydrogen oxidation reaction and the oxygen generation reactions were different for each single crystal orientation with a large difference between these faces and a polycrystalline bead electrode. Steady‐state relations between potential and amounts of associated H atoms and number of sites available for coverage with O atoms were determined also. These steady‐state values are generally less than the comparative amounts found under transient conditions. Oxygen evolution on the Pt faces was not observed below a potential of 1.8V. It appears that grain boundaries, stress, and impurity inclusions may have more effect in determining the catalytic activity for some reactions than does the actual atomic density or geometry of Pt atoms.

Chemical and electrochemical studies of the oxide ion-oxygen reaction in equimolar sodium nitrate+potassium nitrate

Abstract Manometric and potentiometric studies of the oxide ion+oxygen reaction in molten alkali nitrate are reported. Sufficient oxygen was found to be absorbed by alkali nitrate melts after addition of Na2O to convert virtually all of the added O2− ion to O22− and O2− ions. The equilibrium constant and the temperature dependence of the reaction 2 O2−=O2+O22− was determined over a temperature range of 250–400°C. The value of the equilibrium constant determined by the method used was found to depend on whether Na2O, Na2O2, or NaO2 was used as the starting material. Stabilized zirconia tubes were studied for use as oxide ion probes in these melts. In oxygen-containing melts the zirconia/melt interface was shown to respond to added Na2O or NaO2 in a manner similar to the response of a platinum wire dipped into the melt. This response is shown to be the expected one, for the cells studied. When nickel chloride was added to oxygen-saturated melts which contined Na2O, a reaction was found to occur which resulted in the effective loss of two oxide ions from the melt for each nickel ion which was added.

The rate of the hydrogen discharge reaction on platinum in sulfuric acid solution

Abstract The io for the H+/H exchange on Pt was found to be dependent on H2SO4 concentration, giving a linear log—log relation with a slope of 0·5. For any given H2SO4 concentration, io was virtually independent of potential to an anodic value at which the Pt-associated H concentration dropped to a low value. Comparisons are made with literature results. The influence of the dilute double layer on io appeared to be minimal over a wide range of H2SO4 concentrations.

Electrochemical Properties of Sodium Beta‐Alumina in ZnCl2 ‐ NaCl Melts

On the basis of membrane potential measurements, sodium ..beta..-alumina is shown to be almost completely selective for sodium ions in NaCl--ZnCl/sub 2/ melts. However, the continuous electrolysis of ..beta..-alumina in these melts decreases its conductivity. These results are interpreted in terms of the movement of mobile sodium ions becoming impeded by nearly immobile zinc ions introduced into the ceramic under the applied electric field. Beta-alumina is therefore not useful in battery applications where ions other than sodium are present. It can, however, be used in the construction of sodium ion specific membrane electrodes. 6 figures.

Characterization of platinum electrodes in H2-saturated sulphuric acid solution under steady-state potentiostatic conditions

Abstract The character of platinum-bead and -(111) electrodes at anodic steady-state potentials was determined by analysing with cathodic galvanostatic pulses for reducible, Pt-associated species. There was a considerable amount of potential overlap in the reduction of adsorbed and dermasorbed O. The θ so 2− 4 - dependence on potential and the effects of adsorbed SO 2− 4 on H and O sorption were shown. SO − 4 adsorption passivated the surface for H 2 oxidation below 1·0 V and stabilized the associated oxygen species at higher potentials. Pre-saturation of Pt with dermasorbed oxygen caused a hysteresis effect requiring potentiostating at or below 0·85 V for its removal. H 2 has a strong effect on the steady-state character below 1·0 V, but has essentially no effect for the transient formation of Pt—O, Pt-bead and -(111) electrodes showed important differences.

The Pt—O + H2 reaction from initial steady-state potentiostatic conditions☆

Abstract H 2 reactivity with steady-state formed Pt—O is far slower and more complex than H 2 reactivity with transient formed Pt—O ad . Under steady state, dermasorbed oxygen, adsorbed sulphate ions, and the uncertainty in the types and total quantities of associated oxygen make the relationship between the concentration of oxygen and time, or potential, too complex for direct kinetic evaluation. The early, diffusion-independent, open-circuit potential decay from steady state, however, can be described using a model of two capacitive discharges. One process is a double-layer capacitance discharge plus complex adsorption/desorption effects, while the second is the chemical removal of Pt—O by reaction with H 2 .

Application of time-domain reflectometry to electrochemical studies—a critique

Summary A critical analysis of the application of Time-Domain Reflectometry (TDR) to electrochemical studies is made. Since this technique could appeal to investigators interested in measurements in the nanosecond time region, the recent work of Payne on the Pt/H 2 electrode is closely examined. Present electrochemical cell design is the limiting factor in short-pulse work rather than the band-width of available real-time oscilloscopes. The possible disadvantages of the relatively high-frequency repetitive pulses necessary for sampling oscilloscopes are shown. It is concluded that, at present, the TDR technique does not offer any real advantage over direct pulse techniques.