M. Fleischmann

Calorimetry of the palladium-deuterium-heavy water system

Abstract It is shown that accurate values of the rates of enthalpy generation in the electrolysis of light and heavy water can be obtained from measurements in simple, single compartment Dewar type calorimeter cells. This precise evaluation of the rate of enthalpy generation relies on the non-linear regression fitting of the “black-box” model of the calorimeter to an extensive set of temperature time measurements. The method of data analysis gives a systematic underestimate of the enthalpy output and, in consequence, a slightly negative excess rate of enthalpy generation for an extensive set of blank experiments using both light and heavy water. By contrast, the electrolysis of heavy water at palladium electrodes shows a positive excess rate of enthalpy generation; this rate increases markedly with current density, reaching values of approximately 100 W cm−3 at approximately 1 A cm−2. It is also shown that prolonged polarization of palladium cathodes in heavy water leads to bursts in the rate of enthalpy generation; the thermal output of the cells exceeds the enthalpy input (or the total energy input) to the cells by factors in excess of 40 during these bursts. The total specific energy output during the bursts as well as the total specific energy output of fully charged electrodes subjected to prolonged polarization (5–50 MJ cm−3) is 102–103 times larger than the enthalpy of reaction of chemical processes.

Development of the theory for the interpretation of steady state limiting currents at a microelectrode: EC' processes: first and second order reactions

Equations are developed to describe the radius dependence of the steady state limiting current at a microelectrode for the case where the electron transfer process is followed by a homogeneous chemical reaction regenerating the electroactive species. Following a brief discussion of systems where the coupled chemical reaction may be considered to be pseudo-first order, the theory is extended to the more general, second order case by seeking an asymptotic solution to the differential equation. This allows the study of fast chemical reactions and systems where the reactants are present in similar concentrations.

The behavior of microdisk and microring electrodes: application of Neumann's integral theorem to the prediction of the steady state response of microdisks

Abstract It is shown that Neumanns integral theorem can be used to derive the steady-state behavior of microdisk electrodes. Results obtained previously using other methods for uniform surface concentration and uniform flux boundary conditions are derived as limiting cases of a general equation which describes irreversible and quasi-reversible reaction kinetics. It is shown that the approach can be used to assess the effects of the tertiary current distribution and to predict the behavior for electrode reactions which are non-linear in the concentration terms.

The behavior of microdisk and microring electrodes: application of Neumann's integral theorem to the prediction of the steady state response of microdisks. Numerical illustrations

Abstract We illustrate numerical examples of the application of Neumanns integral theorem to the steady state behavior of microdisk electrodes. Results obtained previously using other methods for uniform surface concentration and uniform flux boundary conditions are derived as limiting cases of a general equation which describes irreversible and quasi-reversible reaction kinetics. It is shown that the approach can be used to assess the effects of the tertiary current distribution. Comparisons are made with previous approximate analyses.

A microelectrode study of the mechanism of the reactions of silver(II) with manganese(II) and chromium(III) in sulphuric acid

Abstract The variation of the steady state limiting current for the Ag(I)/Ag(II) oxidation wave with the radius of the microdisc electrode, concentration and temperature has been used to probe the kinetics and mechanisms for the reactions of silver(II) with manganese(II) and chromium(III) in 10 mol dm −3 sulphuric acid. It is shown that the current density for the silver(I) mediated oxidation of manganese(II) is controlled by the diffusion of manganese(II) to the surface except for microelectrodes with radii below 5 μm. On the other hand, the current density for the mediated oxidation of chromium(III) is determined by the rate of the Ag(II)/Cr(III) reaction over a range of conditions. In contrast to the Ag(II)/water reaction, its kinetics can be fitted to a mechanism where the initial electron transfer from Cr(III) to the Ag(II) is the rate determining step.

Gas phase electrochemistry on dispersions of microelectrodes

Abstract It is shown that dilute mixtures of small platinum particles supported in a matrix consisting of alumina particles may be used for electrochemical experiments in the gas phase. The results are compared with measurements using platinum dispersions in conductivity water.

Electrodeposition and electrocatalysis: The deposition and dissolution of single catalyst centres

Abstract It is confirmed that it is possible to obtain a mathematical solution to the problem of the nucleation and three-dimensional growth at constant potential of single growth centres of a new phase on a microelectrode substrate under all conditions ranging from kinetic to diffusion control of the growth process under the assumption that diffusion is in a quasi-steady state. The results are extended to double-potential-step experiments and it is shown that similar complete descriptions can be derived for experiments where the growth centre acts as a catalyst site for an electrocatalytic reaction. Cyclic voltammetry of the two types of processes is discussed for a more restricted range of conditions, namely pure kinetic or diffusion control of the growth of the catalyst centre. It is shown that it should be possible to detect catalytic reactions at a single atom of the new phase.