ABSTRACT
We measured the heat which is reversibly exchanged during the course of an electrochemical surface reaction, i.e., the deposition/dissolution of the first two monolayers of Ag on a Au(111) surface in (bi)sulfate and perchlorate containing electrolytes. The reversibly exchanged heat corresponds to the Peltier heat of the reaction and is linearly related to its entropy change, including also non-Faradaic side processes. Hence, the measurement of the Peltier heat provides thermodynamic information on the electrochemical processes which is complementary to the current-potential relations usually obtained by conventional electrochemical methods. From the variation of the molar Peltier heat during the various stages of the deposition reaction we inferred that co-adsorption processes of anions and Ag do not play a prominent role, while we find strong indications for a charge neutral substitution reaction of adsorbed anions by hydroxide, which would not show up in cyclic voltammetry.
ABSTRACT
We have developed a pyroelectric sensor for electrochemical microcalorimetry, based on LiTaO3, which provides unprecedented sensitivity for the detection of electrochemically induced heat effects. Deterioration of the heat signal by electrostriction effects on the electrode surface is suppressed by a multilayered construction, where an intermediate sapphire sheet dampens mechanical deformations. Thus, well textured thin metal films become viable candidates as electrodes. We demonstrate the sensor performance for Cu underpotential deposition on (111)-textured Au films on sapphire. The sensor signal compares well with a purely thermal signal induced by heating with laser pulses. The high sensitivity of the sensor is demonstrated by measuring heat effects upon double layer charging in perchloric acid, i.e., in the absence of electrochemical charge- or ion-transfer reactions.
