Significance of Effects of High Pressure on Kinetics of Electrode Reactions: I . Applications to Transition States in Hydrogen Evolution Reaction Mechanisms

Abstract

The effects of high hydraulic pressures on electrode reactions are complex because of (i) the variation of reference electrode potentials with pressure so that only an apparent volume of activation can be directly measured experimentally/, and (U) dependence of coverage by adsorbed intermediates, such as H, with pressure. Methods o5 dealing with these problems are treated and the significance of measured apparent volumes of activation for the hydrogen evolution reaction is discussed in terms of the nature of the transition state for proton transfer and neutralization. The negative true volumes of activation iound for the cathodic H2 evolution reaction under some conditions are attributed to increasing electrostriction of the proton in the H~O4 + complex as the transition state is formed. The significance of applications to ionic redox reactions is pointed out where pressure effects may be able to distinguish activation associated with long-range Born polarization from that associated more specifically with reorganization of the primary solvation shell or inner coordination sphere of ions.