John O’M. Bockris

The Electrocatalysis of Oxygen Evolution on Perovskites

Measurements of the oxygen evolution reaction have been made on eighteen substituted perovskites containing first‐row transition metal ions. Rates are reported at equilibrium and at an overpotential of 0.3V. Electrode kinetic parameters are given, including roughness factors. The rate does not depend on semiconductor‐type properties. It increases as the pH of zero charge, at which the occupancy of OH− and H+ at the interface becomes equal, moves in an alkaline direction, with decrease of magnetic moment, with decrease of stability of the perovskite lattice, with decrease of the enthalpy of formation of the transition metal hydroxides, and with increase in the number of d‐electrons in the transition metal ion. The accuracy of the roughness factor measurements are affected by weakness in knowledge of true double layer capacities. The value assumed here, 60 μF cm−2, may be accurate to only ± 100%. Models are given which suggest that the pores are active throughout. The correlations between the rate and electronic properties are consistent with rate‐determining steps which involve desorption of OH radicals, e.g., . An MO discussion suggests that the electrocatalysis increases with increased occupancy of the antibonding orbitals of MZ‒OH. Earlier interpretations include the concept that an increase of the rate occurs because of increasing overlap between the orbitals of the transition metal ion and the spσorbital of O. However, this theory is based on only three different materials, in which rate‐determining step changes. An interpretation based upon nonstoichiometry is shown to be consistent with observed trends, but insufficient to explain their magnitude. The electrical and chemical contributions to the rate are analyzed. The value of agr; is related via bond strength considerations to the MZ‒OH bond strengths. The relative electrocatalysis discussed is limited to an overpotential which corresponds to a practical range of rates on the faster catalysts. A volcano relation for oxygen evolution on perovskites seems likely. Future electrocatalysts are predicted.

Exact ellipsometric measurement of thickness and optical properties of a thin light-absorbing film without auxiliary measurements

Abstract It is shown, by exploring film optics, that the thickness and optical constants (refractive and absorption indices) of a light absorbing film can be determined from optical measurements alone made by an ellipsometer without the necessity of an auxiliary non-optical measurement. Use is made of an extra equation, relating the intensity of the reflected light to the three parameters pertaining to the film, in addition to the equations used in conventional ellipsometry. A surface film on cobalt in the state of electrochemically induced passivity was analyzed using this approach.

Studies of the mechanism of the anodic oxidation of ethylene in acid and alkaline media

Abstract The ethylene oxidation reaction on smooth and platinized platinum has been studied at 80°C in solutions of H 2 SO 4 + K 2 SO 4 and NaOH + K 2 SO 4 of constant ionic strength = 1.5. Reaction rates were measured as a function of potential, pH and partial pressure of ethylene. Coulombic efficiency of the reaction was determined by measurements of CO 2 production in acidic solutions, and of C 2 H 4 consumption in alkaline solutions. The following parameters have been found: Coulombic efficiency is 100 ± 1% in acidic and 90 ± 5% in alkaline solutions, i 0 = 10 −8 A cm −2 on platinized and 10 −10 A cm −2 on smooth Pt respectively. Activation energy A = 17 ± 2 kcals. At higher overpotentials diffusion limiting current was obtained. At V = 0.9 (R.H.E.), the current drops to negligible values due to the oxide formation. Coverage of the electrode with the ethylenic radical at 1 atm has been evaluated by two independent methods as θ E = 0.55 ± 0.2. The reaction mechanism in the Tafel potential range was interpreted in terms of water discharge as the rate-determining step over the complete pHrangeinvestigated. In the potential range higher than that of the Tafel region the rate control is shifted to mass transport of ethylene. At P E = 1 atm, the Tafel potential range is limited by oxide formation before diffusion control sets in. A possible explanation of the anomalous pH effect in reactions concerning water discharge has been given.

Stacked thin‐film photoelectrode using iron oxide

For photoanodes of materials with low mobilities it is advantageous to use several layers of thickness less than the space‐charge region, thereby decreasing recombination. To compensate losses due to lack of absorption, several layers should be placed successively in the light path. Some experimental verification is described.

The mediation of the photoelectrochemical reduction of carbon dioxide by ammonium ions

Donnees sur la reduction photoelectrochimique de dioxyde de carbone en presence de CdTe, avec comme intermediaires des ions ammonium, dans un electrolyte constitue de perchlorate de tetrabutylammonium, dans du DMF

Photoelectrocatalysis on silicon in solar light

Photoelectrochemical measurements have been carried out on p‐Si electrodes which contained islands of Pb, Cd, Au, Ni, Co, and Pt. These islands cause the photocurrent density of some of the Si systems to increase greatly (10×) in the middle region of the photocurrent potential curve. A plot of the change in potential observed for this region against log i0 for the dark hydrogen evolution on the metals concerned is linear with a slope close to that expected for a rate determining step at the metal‐solution interface.

Electrochemical Reductions of Hg(II), Ruthenium‐Nitrosyl Complex, Chromate, and Nitrate in a Strong Alkaline Solution

The electrochemistry of low-level nuclear wastes, the reductions of Hg(II), [RuNO(NO{sub 2}){sub 4}OH]{sup 2{minus}}, CrO{sub 4}{sup 2{minus}}, and NO{sub 3}{sup {minus}} in 1.33 M NaOH solution have been studied primarily at nickel electrodes for electrocatalytic advantages. Hg(II) was reduced to Hg metal [equilibrium potential of 0.099 V vs NHE (normal hydrogen electrode)]. The ruthenium-nitrosyl complex, [RuNO(NO{sub 2}){sub 4}OH]{sup 2{minus}}, was reduced to Ru metal (half-wave potential of {minus}0.38 V vs NHE). Chromate was reduced to chromic hydroxide (equilibrium potential of {minus}0.24 V vs NHE). Nitrate reduction has two different regions of Tafel behavior from which reduction mechanisms are proposed. The exchange current densities for the nitrate reduction at Ni, Pb, Fe, and graphite were measured and the competition of the nitrate reduction with the hydrogen evolution investigated.

Reflectance and ellipsometric study of anodic film on platinum electrode

Abstract The anodic films on platinum electrode in 0.05 M sulfuric acid solution were examined by means of ellipsometry. By measuring the relative phase retardation (Δ), relative amplitude reduction (tanψ) and also the intensity of the reflected polarized light, the optical constants of the films ( n , k ) and thickness (τ) at various potentials were obtained. The results showed that the optical properties of the film remain nearly constant ( n = 2.8, k = 1.7) while the thickness increases from 2 A to 5 A with anodic potential. From this evidence, it is concluded that the film is made of an oxide of platinum forming a definite phase.

On an electrode producing massive quantities of tritium and helium

A Pd electrode has been examined which produced a concentration of tritium in a 0.1 M LiOD solution around 103 times above background. Tritium production at a given potential ceased after a few days, but could be restarted by a small increase of the deuterium overpotential. Correspondingly, He4 was found in 9–10 pieces of the Pd electrode at 2–100 times background. Addition of fresh amounts of D2O quenched the T production which began again spontaneously after 1–2 days. If the T had come from contamination, 3He would have been found in the electrode: it was absent. Loss of charge by the nucleus takes place when the fugacity of D in voids exceeds 1017 atm (Lifshitz and Pitaevskii, 1963). Sporadicity of function arises from the state of the surface, which is difficult to reproduce. The surface state controls the mechanism of D2 evolution; only some mechanisms give a fugacity high enough to cause fusion. Only one electrode out of four examined produced T and 4He. The surface of this electrode contained a Cu-mosaic structure, not seen on the inactive electrodes.

A Solar-Hydrogen Energy System for Environmental Compatibility

Our Biosphere, the only one known to exist, is under attack by various factors. Major culprits amongst these include fossil-fuel-produced air pollution, acidic precipitation (acid rains), and CO 2 . As we run out of petroleum and natural gas, the question becomes: what should the new energy-system be, so that the damage to The Biosphere and life can be stopped? In view of the rapid depletion of the main energy sources of the present, the fluid fossil-fuels, this paper analyses the various primary energy-options (such as coal, breeder reactors, fusion reactors, and solar energy), and also considers such possible energy-carriers as synthetic fossil-fuels and hydrogen. In this analysis, the environmental effects of various options are considered both qualitatively and quantitatively. It is concluded that the Hydrogen Energy-system is the most efficient and economical energy-system possible, and that it results in the environmentally most compatible and permanent energy-system when coupled with solar energy as the primary energy-source. It is important now that this information be disseminated among the public in general, and environmentalists in particular, so that the implementation of the solar-hydrogen economy can be started without delay, in order to minimize any further damage to The Biosphere and its living components.