Hydrogen adsorption rate and discharge mechanism on palladium-carbon suspension electrode

Summary The activity of a palladium-carbon suspension electrode in hydrogen gas electro-oxidation was investigated in 2 M H 2 SO 4 solution. The main feature of the work was the attempt to separate experimentally the various kinetic steps. Thus the rate of hydrogen adsorption was studied by connecting the electrochemical cell to a volumetric system, while a four-electrode system was used for current-potential relationships. It was possible to show that the rate of adsorption of hydrogen is determined by the dissolution of gas if the powder suspension concentration is higher than 0.5 weight percent. The charge transfer was 3 to 4 orders of magnitude lower than the rate of adsorption, indicating that the average collision frequency and the contact time of the particles with the collector electrode was the slowest step. A critical analysis of these two parameters is given, relying mainly on some other works. This showed that the double layer charge is completely transferred to the collector electrode during the short time of collision. Hence, electrode particles of high surface area, such as catalyst-impregnated carbon black, are preferable. It is concluded that in order to accelerate the slowest step of charge transfer. an extremely thick suspension electrode had to be used. This approximates the above electrode closely to the well-known porous electrode.