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 (ii) dependence of coverage by adsorbed intermediates, such as H, with pressure. Methods of 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 found for the cathodic 
evolution reaction under some conditions are attributed to increasing electrostriction of the proton in the
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.