Heat Effects upon Electrochemical Copper Deposition on Polycrystalline Gold

Abstract

Heat effects upon Cu deposition on polycrystalline Au surfaces from sulphuric acid electrolytes were calorimetrically measured. By combination of pyroelectric temperature detection at the backside of a thin electrode foil with pulsed electrochemistry, sensitivities to electrochemical conversions of a few percent of a Cu monolayer (ML), corresponding to about 1 microJ cm(-2) were achieved. We compared the heat evolution upon Cu under potential deposition (UPD), Cu deposition onto a fully developed Cu UPD layer and bulk Cu deposition onto a 300 ML thick Cu layer on Au. The heat effects were measured dependent on the amplitudes of the applied potential steps, that is, the driving forces of the respective reactions. From the differences of the heat effects among the Cu deposition processes, we deduced implications on the reaction mechanisms. For Cu UPD, the heat effects were explicable by the deposition of 1.3 Cu atoms per two electrons flowing to the electrode accompanied by sulphate coadsorption, similar to Cu UPD from sulphuric acid solutions on Au(111). Upon Cu deposition on a Cu UPD layer the heat effects signal considerable anion coadsorption up to the deposition of about 0.5 ML of Cu. At higher conversions the deposition mechanism gradually changes towards bulk Cu deposition, accompanied by reduction of the sulphate coverage.

In-situ Thermoelectrochemistry

“…[104,311]. Generally, microcalorimeters are of growing interest [314][315][316][317][318]. lithium cells, have been studied to test the thermal behaviour under practical conditions.…”

Microcalorimetric Measurements of the Solvent Contribution to the Entropy Changes upon Electrochemical Lithium Bulk Deposition

“…It should be noted that all of the above cited studies required rather high electrochemical conversions of the order of several 10 to 10 000 monolayers, referenced to the electrode surface, to obtain reliable heat measurements. Only recently reactions with submonolayer conversions, such as oxide formation on a Au surface, [11] hydrogen adsorption on a platinized Pt foil, [12] or Cu underpotential deposition on a Au surface, [13] became accessible. Herein we apply our microcalorimetric approach [14] to the study of Li deposition.…”

An improved sensor for electrochemical microcalorimetry, based on lithiumtantalate

“…1. The sensor signal steeply rises during the electrochemical Cu dissolution, which is at the first sight conceivable from evolution of Peltier heat, due to the positive Peltier coefficient of the Cu-UPD formation, 8 and heating up of the electrode sensor assembly. When the reaction was switched off, the sensor charge decreased on a time scale of a few 100 ms, in accordance with the dissipation of the deposited heat to the electrolyte and the surrounding.…”

“…6 By this method, heat effects of electrochemical surface reactions, e.g., the formation of a Cu underpotentially deposited adlayer on Au or the adsorption of sodium dodecyl sulfate, could be calorimetrically studied. 7,8 The method is based on the pyroelectric detection of the temperature changes at the back of a thin working electrode (WE) during a short (≈10 ms) potential step. During such short pulses, the heat loss into the electrolyte and the surrounding may be neglected.…”