Microcalorimetric Determination of the Exchange Current Density and the Reaction Entropy of Fast Electrochemical Processes: Hydrogen Evolution on Pt

A common way to benchmark catalysts is to perform a Tafel analysis on the current-overpotential relationship obtained by potential sweep methods and extract the exchange-current density. However, especially for fast reactions this analysis underestimates the reaction rate. In this contribution, we introduce an alternative way to determine the activation overpotential from the irreversible part of the heat exchanged during the electrode reaction, which was measured with electrochemical microcalorimetry (ECM). In addition, the reversible part of the exchanged heat allows access to the reaction entropy. We evaluate the proposed procedure using the fast hydrogen evolution at platinum in acidic solution as model reaction.