THE INFLUENCE OF H-ABSORPTION ON THE CATHODIC RESPONSE OF HIGH AREA NICKEL ELECTRODES IN ALKALINE-SOLUTIONS

Anomalous low values of the Tafel slope and of its temperature depende nce have been frequently reported for the hydrogen evolution reaction (her) in alkaline solutions on high area nickel and nickel alloy elect rodes and are the subject of much controversy. A systematic investigat ion carried out in this laboratory using Ni and Ni-Co deposits with ro ughness factors of the order of 10(3) have shown that slopes of 118 m V dec(-1) at 25 degrees C can be obtained in concentrated alkaline sol utions by means of rapid data acquisition (4 ms point(-1)). The measur ed values follow very closely the relationship 2.3 x 2RT/F in the 25-7 5 degrees C temperature range. In contrast, slow measurements (200 ms point(-1)) resulted in slopes of 80 m V dec(-1) or lower that were alm ost independent of temperature. Cyclic voltammetry of the electrode su rface in the Ni(O)/Ni(II) region showed marked differences for the two experiments suggesting the participation of absorbed hydrogen and the formation of surface hydrides in parallel with the her at low current densities.