Konrad Mund

Titanium‐Containing Raney Nickel Catalyst for Hydrogen Electrodes in Alkaline Fuel Cell Systems

In alkaline hydrogen-oxygen fuel cells Raney nickel is employed as catalyst for hydrogen electrodes. The rate of anodic hydrogen conversion has been increased significantly by using a titanium-containing Raney nickel. The properties of the catalyst powder, the influence of particle diameter, and the behavior of electrodes under load are described. Impedance measurements have been used to characterize the electrodes. In fuel cell systems the supported electrodes are normally operated at current densities up to 0.4 A . cm/sup -2/; the overload current density of 1 A . cm/sup -2/ can be maintained for several hours. (15 fig.)

Electrochemical Properties of Platinum, Glassy Carbon, and Pyrographite as Stimulating Electrodes

Presently, platinum, platinum‐iridium, and carbon (glossy and pyrographite) are the preferred materials to be used as stimulating electrodes. Electrochemical tests revealed higher thresholds with Pt‐Ir, which possibly are a result of excessive connective tissue growth. A porous structure appears to be preferred especially if the electrode materials are smooth and activated glassy carbon. When comparing power consumption, glassy carbon was found to be a superior electrode material.

A new principle for an electrochemical oxygen sensor

Abstract An electrochemical oxygen sensor using a smooth glassy carbon electrode for continuous monitoring of oxygen has been developed, which can find a wide range of application. Two different potential levels of preset durations are imposed on the sensing electrode in a cyclic manner. The current flow due to O 2 reduction at a negative potential is integrated after a time lag. The charge is proportional to the oxygen concentration. The electrode is then held at a positive potential for a longer period before repeating the cycle. Thus, oxygen is consumed only during the short pulse duration. This sensor principle is unique, since the sensing electrode operates without a covering membrane. This is possible because of the low electrocatalytic activity of glassy carbon. The response is immediate and reproducible even at a low consumption of oxygen. The long-term response is stable over 60 h and sensitive to a change of about 0.5 hPa partial pressure of oxygen in saline solution. Measurements with the sensor in bovine serum demonstrated the negligible influence of other substances on the response to oxygen. The sensor has been tested in animal experiments, and shows a good response in blood as well as in tissue.

Equivalent circuit diagram and power consumption of stimulating electrodes

Abstract In order to compare different stimulating electrodes for cardiac pacemakers, impedance measurements have been carried out in physiological saline solution. Classical circuit diagrams are not able to describe the results. The impendance Z with reference to its frequency dependence can be expressed by the equations Z = Z1(ν/ν1x, where α = const. = (π/2)x. As an example of a porous electrode, a sintered tantalum electrode has been investigated; its behaviour is characterized by the volume capacity and the diaphragm resistance. In vitro and in vivo measurements have been compared. Stimulating electrodes were implanted in a cat and the threshold of the muscle was measured. The impedance of the Pt-Ir electrode had changed during the implanted period. Connective tissue had grown in the porous system of a sintered Ta-electrode. Porous electrodes are superior to smooth ones as far as the economic utilization of energy is concerned.

A NEW PRINCIPLE FOR AN ELECTROCHEMICAL OXYGEN SENSOR

An electrochemical O2-sensor using a smooth glassy carbon electrode for a continuous monitoring of oxygen has been developed, which can find a wide range of application. Two different potential levels of preset durations are imposed on the sensing electrode in a cyclic manner. The current flow due to O2-reduction at a negative potential is integrated after a time lag. The charge is proportional to the oxygen concentration. The electrode is then held at a positive potential for a much longer period before repeating the cycle. Thus, oxygen is consumed only during the short pulsing duration. This principle of sensor is unique for in vivo application since the sensing electrode operates without a covering membrane [1]. The response is immediate and reproducible at a low consumption of oxygen. The long-term response is stable over 60 h and sensitive to a change of about 0.5 hP partial pressure of oxygen in saline solution. Measurements with the sensor in bovine serum demonstrated the negligible influence of other substances on the response to oxygen. Continuous monitoring of oxygen is of vital interest in intensive care, during surgery under general anaesthesia, in obstetrics and others. Therefore, the sensor was tested in animal experiments. In an experiment with a flow-through-cell in the circulation of a minipig, the sensor response showed a good correlation with the O2-content in blood. It was also the case in a measurement of the oxygen partial pressure in the tissue of a cat. At present stage, the in vivo response to absolute values of oxygen concentration with time is not very precise. However, the sensor responds very sensitively to relative changes in O2-concentration so that it could be developed to a very useful instrument in monitoring the oxygen partial pressure in blood of a patient.