Statistical Aspects of Electrochemical Arrhenius Analysis in the Study of Overpotential-Derived Compensation Effects

High Resolution Image Download MS PowerPoint Slide Electrochemical Arrhenius analysis provides the pre-exponential factor, log 10 A (η), and apparent activation energy, E A (η), as a function of free energy driving force, i.e., the kinetic overpotential (η). In this context, our team observed a very prevalent compensation effect between the overpotential-dependent log 10 A (η) and E A (η) and related it to entropy−enthalpy compensation for interfacial ion solvation kinetics and, more generally, the inherent multistep nature of (electro)catalytic reactions. Importantly, in general, this overpotential-derived compensation is distinct from the case of a kinetic (Constable−Cremer) log 10 A − E A compensation that was observed for a series of closely related reactions or catalysts along a slope given by the isokinetic temperature, T iso . In this case, a set of compensating log 10 A and E A values along the isokinetic slope of 1/ RT iso produce the same rate constant at the specific isokinetic temperature. This kinetic compensation effect can have real physical origins, such as the presence of multiple active sites, but was simultaneously subject of intense debates about possible random or systematic error artifacts in the Arrhenius analysis, which has negatively influenced views in the electrochemistry community. Here, we use the hydrogen evolution reaction on Au/C nanoparticles in acid under high mass transport conditions to shed light onto statistical aspects of electrochemical Arrhenius analysis and overpotential-derived compensation effects. We show that for high quality data, the random errors are too small to cause the overpotential-derived compensation. Further, the latter is a natural consequence of overpotential- and temperature-dependent Tafel analysis and can be derived from the charge transfer coefficients. Overall, the work rejects tendencies in the community of dismissing overpotential-derived log 10 A (η)− E A (η) compensation as an artifact and drawing unwarranted parallels to problems in other fields. The physiochemical origins of ubiquitous log 10 A (η)− E A (η)-compensation are at the core of the overpotential-dependent kinetics over overpotential-dependent interfaces, which includes the subset of entropy-enthalpy compensation.