The Mechanism of the Cathodic Hydrogen Evolution Reaction

Abstract

Some of the outstanding problems of concept and mechanism in the fieldof cathodic hydrogen evolution kinetics are discussed and clarified. Afull derivation and correlation of kinetic equations which assume nomechanism reveals expressions for several parameters which take valuesspecific to one or more mechanisms. The use of statistical methods oftreatment of data proves indispensable in estimating the values ofthese parameters. A further method of ascertaining the mechanism of thehydrogen evolution reaction is to examine the kinetics of theindividual reaction paths, so that the expected values of parameterscommon to all paths may be deduced. A number of mechanisms important inacid and alkaline solutions are thus treated, and are shown to bedistinguishable experimentally. Using already published data, theactual conditions under which various reaction paths take place at Hg,Ag, Ni and smooth Pt cathodes are calculated. It is not only possibleto compare these deduced data with observation, and thereby verify theoccurrence of a particular reaction path, but also to demonstrate theimpossibility of some mechanisms in specific cases. The recent advanceswhich the foregoing methods have made possible are discussed inrelation to data which have recently become available.