Zur kenntnis des elektrochemischen verhaltens von raney-nickel preβ-körpern in 5 N Kalilauge

Abstract

A new pressing procedure has been developed to obtain highly active Raney nickel electrodes. Electrodes pressed at 450 Kp/cm 2, pre-heated at various temperatures in high vacuum, have been studied. The overvoltage for cathodic hydrogen evolution has been measured up to 500 mA/cm 2. The rest potential was independent of the pre-heating in 5N KOH solution and corresponds approximately to the reversible value. Measurable overvoltage was observed only above 1 mA/cm 2, when the IR drop was eliminated. The polarization behaviour was the same for the samples sintered between 100 and 300°C in high vacuum and unsintered samples. The overvoltage was about 10 mV at 10 mA/cm 2 and 90 mV at 200 mA/cm 2. The E/log i plot was rectilinear for all samples between 80 and 500 mA/cm 2, with slope 120 mV almost independent of the temperature of the pre-heating. This corresponds to the value for a metal hydrogen electrode. The exchange cd for all samples was between 10 and 30 mA/cm 2. A compact nickel-electrode polarized in the same way has a b-value of 117 mV and an exchange cd of 2 μA/cm 2. It is concluded that the electrochemical activity of the Raney-nickel electrode, apparent through its extremely small cathodic overvoltage, is due chiefly to the high surface area, as measured by the BET method, and by electron-microscope and X-ray determinations of the size of the primary particles.