Components of overvoltage of hydrogen electrode reaction on nickel

Abstract

For the case of hydrogen evolution reaction (HER) in alkaline solutions on nickel, the overvoltage of the electron transfer step (the first step of HER) was separated from that of the overall reaction on the basis of the results obtained by the galvanostatic transient method, which has been developed by us earlier. The difference of the overall-reaction overvoltage and electron-transfer overvoltage, which is considered as the overvoltage of the step of an adsorbed hydrogen atom recombination (the last step of HER), was also determined. It is known that on nickel, during cathodic polarization in alkaline solutions, the intermetallic compound M(I) of an alkali metal with nickel is formed as practically the main intermediate. In this case, the Tafel line, corresponding to the last step, shows a slope of 70–80 mV, and the observed overvoltage can be explained in terms of the decrease of the work function of the surface component, caused by the M(I) formation. On the other hand, on a cobalt-deposit-modified nickel, the Tafel line shows a slope of 30 mV, even in alkaline solutions. The nickel surface may be completely covered with the cobalt deposit. Therefore, no intermetallic compound seems to be formed on the surface, and the main intermediate is likely to be an adsorbed hydrogen atom, as in the case of HER on platinum in acid solutions.