Christoph Fabjan

Die kathodische Reduktion von Ozon in alkalischen Elektrolyten

AbstractThe cathodic reduction of ozone according to the overall reaction O3+H2O+2e→O2+2OH− was studied on bright platinum electrodes in KOH electrolytes. The rest potentials deviate from the theoretical values by −300 to −350 mV. They are determined by a mixed potential mechanism involving anodic evolution of O2 and cathodic reduction of O3 as half reactions. Steady-state polarization measurements were carried out. Extrapolation of Tafel-lines to zero over-voltage and the determination of the charge transfer resistance give current densities at the rest potential, which are analogous to exchange current densities. A single electron transfer reaction is found to be the rate controlling step, which is occurring twice for the reduction of one molecule of ozone. A cathodic reaction order of approximately zero is evaluated with respect to OH−-ion concentration. The reaction mechanism is proposed according to

Untersuchungen über die selektive Katalyse der Elektrodenreaktionen im Aasserstoff-Brom-Speichersystem

\begin{gathered} O_3 + e \to O_3 - / \cdot 2 \hfill \\ 2O_3 - + H_2 O \to 2 OH - + O_2 + O_3 \hfill \\ \end{gathered}

Elektrochemische Untersuchungen des Systems Ozon/Sauerstoff an verschiedenen Elektrodensubstraten

which is consistent with experimental data.

Gegenwärtiger Entwicklungsstand und Versuch einer Beurteilung der Zukunftsaussichten

The dependence of the rate of the oxygen reduction on the nature of cations [Li+, Na+, K+, Rb+, Cs+, (CH3)4N+] is studied at smooth platinum and porous carbon loaded with a platinum catalyst in alkaline solutions.The rest potentials are shifted to more negative values from Li+ to (CH3)4N+, likewise the cathodic polarization is increased with the size of the cations. A change of the potential drop within the diffuse double layer caused by increasing cation concentration with growing size of ions is of minor importance in 0.5N alkaline solutions. Specific adsorption of (Rb+), Cs+ and (CH3)4N+ has to be considered, which would give rise to a decrease of the rate of the electrochemical reaction.Secondly the observed effect can be attributed to ion pairing of charged species (O2−) involved in the overall reaction and the cations. The stability of the hyperoxide ion is increased from (CH3)4N+ to Li+ by interaction with the cations. Consequently the velocity of the rate determining charge transfer step is accelerated in this direction.The experimental findings are in favour of the second interpretation, because the effect is not enhanced in more dilute solutions.

Grundlegende Technologische Fragen

SummaryConsiderable rates are obtained for the hydrogen electrode reactions using WC-gas-diffusion electrodes which are not impaired by active Br2 in the solution. Tafel-lines withb-values of appr. 30 mV for both, anodic and cathodic current density potential curves, can be attributed to the Tafel-reaction as the rate controlling step. High reversibility (very low polarization) of the Br2/2 Br− redox couple is observed at activated carbon plastic composite material. The presence of H2 does not influence the electrode behavior. The use of both substrates in the H2/Br2 storage system provides definite advantages of the conceptual design and operation due to their electrocatalytic selectivity.

In‐situ‐Ramanspektroskopie am Elektrolyten des Zink/Brom‐Batteriesystems

In den folgenden Abschnitten sollen die grundlegenden Beziehungen der Thermodynamik, der Elektrodenkinetik und des Massentransportes besprochen werden, die fur ein Verstandnis der Wirkungsweise galvanischer Zellen unentbehrlich sind.

Die kathodische Reduktion von Sauerstoff an pyrolytisch abgeschiedenem Kohlenstoff und Graphit in alkalischen Elektrolyten

The cathodic reduction of O3 and O2 in O3/O2 gas mixtures was studied at Pt−Pt/Au-alloy-, Au−Ir and Rh-electrodes in 1N-H2SO4.The steady state polarization curves exhibitTafel-regions withb-values from 110–160 mV (260–280 mV at Rh). A single electron transfer reaction is found to be the rate determining step. In a region of high cathodic polarization limiting currents are observed which are controlled by diffusion. Platinum is the only electrode material at the O3-electrode which is stable against corrosion.In the presence of O3 a decrease of the cathodic polarization of +300 to +400 mV for the O2 reduction is observed on Pt.This activation of the O2-electrode is only quasi-stationary because the reduction of the Pt−O layer, which is electrocatalytically effective, proceeds at a low rate for the potentials concerned.The triangular voltage sweep curves show that formation and reduction of oxygen layers and the electrochemical reactions of O3 and O2 respectively occur independently of each other.

Bromine‐Storage Materials

Eine gultige, absolute Sicherheit beanspruchende Vorhersage uber die Zukunft des elektrischen Kraftfahrzeuges ist zum gegenwartigen Zeitpunkt nicht moglich. Um die zukunftige Entwicklung mit grostmoglicher Wahrscheinlichkeit abschatzen zu konnen, mussen die wesentlichen Aspekte aus verschiedener Richtung kritisch beleuchtet und entsprechend ihrem Gewicht gewertet werden.