K. Wiesener

Influence of metal ions on the electrocatalytic oxygen reduction of carbon materials prepared from pyrolyzed polyacrylonitrile

Abstract The influence of transition metal ions during a thermal process in which electrocatalysts are made from polyacrylonitrile is discussed. The electrocatalysts were applied on appropriate carbon supports and used for the cathodic oxygen reduction in acid and alkaline electrolytes. Results concerning the electrocatalitic properties of these materials in self-breathing oxygen electrodes as well as the long-term behaviour and the metal dissolution are compared.

The effect of additives on the positive lead-acid battery electrode

Abstract The effect of the additives carboxymethylcellulose (CMC), carbon black, silica gel, and fibres on the manufacture of positive active material and on the cycle life was investigated by means of porosimetry, inner surface (BET) determination, X-ray diffractometry, chemical analysis, and by measuring the course of the potential, by testing the low rate and high rate capacities and by overcharge cycling tests. It was shown that the additives can be classified, according to their mode of action, into additives (a) increasing the water accumulating capacity of the paste, (b) influencing the crystallization of the mass, (c) increasing the electronic conductivity of the mass, (d) stabilizing the mass. Types (a), (b), and (c) affect the manufacture of active material and the initial capacities, whereas additive (d) improves the cycle life.

The electrochemical oxidation of sulphur dioxide at porous catalysed carbon electrodes in sulphuric acid

Abstract The electrochemical oxidation of sulphur dioxide has been studied in sulphuric acid solution at porous carbon electrodes coated with catalysts consisting of aluminum-vanadium mixed oxides with traces of platinum. Catalyst activity and stability in acid electrolytes are determined by the preparation conditions and the V 2 O 5 : Al 2 O 3 ratio. Potentiodynamic measurements were made for investigating the mechanism of the anodic oxidation of sulphur dioxide. When catalysts are present, sulphur dioxide is anodically oxidized at the porous carbon electrodes. Direct electron transfer from the sulphur dioxide to the anode takes place at low potentials, whereas at more positive potentials reaction takes place between the sulphur dioxide and the electrolytically produced surface oxides on the platinum.

Vanadium oxides in electrodes for rechargeable lithium cells

Abstract In principle, vanadium pentoxide can be used as an active material for positive electrodes in rechargeable lithium cells. Cyclability is possible when the discharge is limited to a value of y = 2.35 (in Li y V 2 O 5 ). The cycling behaviour is comparatively good up to a discharge level of y = 1.

Influence of phosphoric acid on both the electrochemistry and the operating behaviour of the lead/acid system

Abstract The addition of phosphoric acid to the electrolyte or the positive active material of the lead/acid battery yields different results. For antimony-free batteries, the capacity is reduced but the lifetime is improved under deep-discharge service. Both effects at the positive electrode appear to originate from the same cause, namely, the crystal size of PbSO 4 is decreased considerably in the presence of phosphoric acid. The utilization of the positive active material is reduced because the resulting fine-grained PbSO 4 covers the PbO 2 . On the other hand, the PbSO 4 protects the corrosion layer against further discharge. The action of phosphoric acid is demonstrated through cyclic voltammetric, potential-step, impedance and microscopic investigations.

On the hydrogen balance in sealed lead/acid batteries and its effect on battery performance

Abstract An overview is provided on the basic principles of decreasing hydrogen pressure in sealed lead/acid batteries. Approaches that are basedon present technology, as well as other possibilities for suppressing hydrogen evolution and oxidizing hydrogen, are studied and discussed. The results emphasize the relevance of so-called hydrogen-evolution inhibitors for industrial applications.

Influence of H3PO4 on the electrochemical behaviour of the PbO2 electrode

Abstract Passivation caused by sulfate formation within corrosion layers during cyclic deep discharge of PbO 2 electrodes with grids free of antimony can be diminished by addition of phosphoric acid to the electrolyte. The mechanism was studied by means of cyclovoltammetric and potential-step measurements, X-ray diffraction and scanner electron microscopy (SEM). It was observed that phosphate ions adsorbed specifically on lead dioxide influence nucleation and nuclei growth of PbO 2 . During discharge of PbO 2 formed in this manner a PbSO 4 of extremely fine grain and dense structure was found, which protects PbO 2 against further discharge and thus prevents an irreversible sulfation of the corrosion layer.

Noble metal-free catalysts for the hydrogen/oxygen recombination in sealed lead/acid batteries using immobilized electrolytes

Abstract In order to remove hydrogen in sealed lead/acid batteries operating on oxygen cycle the facility to recombine hydrogen and oxygen at a catalyst in the gas phase was studied. Based on the assumption of an electrochemical mechanism, several catalytic materials were investigated. It has been shown that noble metal-free composite materials based on tungsten carbide (WC) and carbon can be applied as catalysts for this purpose. The working conditions for their application in model cells were discussed. The efficiency of such catalysts in sealed lead/acid batteries was also demonstrated.

Zum einfluss von zinn auf das passivationsverhalten der bleidioxidelektrode

Zusammenfassung Wahrend der stromlosen Standzeit (Hochtemperaturtrocknung, Batterielagerung) verandert sich die Korrosionsschicht der PbO 2 -Elektrode. Das fuhrt zu einem betrachtlichen Spannungsabfall (Passivation) bei der Entladung der Elektrode uber die Korrosionsschicht. Nichtohmsche Eigenschaften sowie eine Potential- und Polaritatsabhangigkeit des Elektrodenwiderstandes werden durch potentiodynamisch erhaltene U—I -Kurven von passivierten und trocken-vorgeladenen PbO 2 -Elektroden nachgewiesen. Durch Impedanzmessungen an diesen Elektroden konnte gezeigt werden, dass die Passivschicht zusatzlich zu einem nichtlinearen Widerstandsanteil durch eine kapazitive Komponente beschrieben werden kann. Eine Passivation der PbO 2 -Elektrode wahrend der Trocknung und Lagerung kann durch Auftragen einer Sn-Schicht auf das Elektrodengitter vermieden werden. Die Ursachen fur die Nichtpassivierung der Elektrode in Gegenwart von Sn ist nicht klar. Verschiedene Moglichkeiten werden jedoch diskutiert, z.B. eine starke Dotierung des PbO n , die zu einem betrachtlichen Leitfahigkeitsanstieg des PbO n und moglicherweise zu einer Anderung des Halbleitertyps fuhrt.

On thermopassivation of positive lead—acid battery electrodes: Part I: The influence of drying positive, dry-charged lead—acid battery electrodes on thermopassivation and its causes

Abstract The influence on thermopassivation (η T ) of the drying time (τ) and drying temperature (ϑ) of formed positive electrodes for dry-charged lead—acid batteries has been investigated. It has been shown that there is no thermopassivation in the case of τ ⩽ 4 min up to approx. ϑ = 250 °C, while drying temperature has a different influence on thermopassivation at 4 min