Effect of Temperature on Gold Dissolution in Acidic Media

Abstract

Temperature has a tremendous effect on the rate and amount of gold dissolution. In potentiodynamic experiments the total amount of dissolved gold increases by a factor of 4.5 when the temperature is increased from 25 to 75 • C. Moreover, the previously reported correlation between the onset of oxide formation and the commencement of the dissolution process is found to be correct for all studied temperatures. Negative shift in the advent of oxidation is accompanied by a similar shift in the dissolution onset potential. Similarly, the dissolution rate rises significantly with temperature during potentiostatic and galvanostatic polarization steps. A correlation between the temperature-dependent oxygen evolution reaction (OER) and gold dissolution is found. Arrhenius plots for the OER and gold dissolution are used to obtain information on the apparent activation energy E A for both processes. It is found that for OER and Au dissolution E A = 57 kJ mol −1 . The later finding suggests that there is a common intermediate for both reactions, the formation of which constitutes the rate-determining step. Over the past few years, our group has published a number of papers on electrochemical dissolution of noble metals (coinage and precious) such as copper, 1 rhodium, 2 platinum, 3,4 gold 5,6 and alloys. 7,8Unlike most base metals, noble metals are usually resistant toward significant oxidation and corrosion in moisture, air and most acidic and alkaline electrolytes. However, they do dissolve at positive potential excursions in parallel to surface oxidation. The relatively low rates of noble-metal corrosion impose severe restrictions on the range of techniques which can be used to reliably investigate these processes. Nevertheless, over the last forty or fifty years, numerous approaches have been proposed, with some providing integral values on the amount of dissolved material during relatively long polarization time and others providing information on the rate of the process directly. The former are based on the post-analysis of the electrolyte by atomic absorption spectroscopy, 9 inductively coupled plasma mass spectrometry (ICP-MS), 10,11 radiotracer technique, 12,13 etc. As an example of the latter we should mention pure electrochemical methods based on comparison of oxide formation and reduction charge, 9 utilization of rotating ring disk electrodes 14,15 or double electrode flow cell [16][17][18][19][20] and coupled techniques like electrochemical quartz crystal nano(micro)balance. [21][22][23] Having extremely small detection limits, along with the ability to detect many elements over a wide linear detection range, ICP-MS is extensively utilized in different areas ranging from forensic to nuclear science. 24 Using an ICP-MS to detect traces of noble metals and coupling it directly to a so-called scanning flow cell (SFC) allowed us to extend ICP-MS applicability further; now including on-line investigation of metals dissolved during an electrochemical treatment. This technique allowed us to precisely quantify the diss...

Oxygen evolution activity and stability of iridium in acidic media. Part 2. – Electrochemically grown hydrous iridium oxide

“…As for the OER, however, a constant dissolution rate should be observed. Such constant dissolution was found for OER on gold at elevated temperatures [70]. Moreover, it was shown that dissolution increases linearly with oxygen evolution current.…”

A Flexible Nafion Coated Enzyme‐free Glucose Sensor Based on Au‐dimpled Ti Structures

“…Analogous measurements, were performed for electrode without Nafion and it can be seen that the TiND|Au sample has significantly lower electrochemically active area than the one with the membrane. The cause of this phenomenon might be ascribed to the partial degradation of bare gold during positive potentials scan in strongly acidic conditions .Therefore, it can be concluded that Nafion is a suitable protection layer.…”

Pt Sub-Monolayer on Au: System Stability and Insights into Platinum Electrochemical Dissolution

“…In order to clarify if indeed Pt can be stabilized against dissolution by Au, and to improve our understanding of the involved processes, in the current work a supposedly more stable Au-supported Pt sub-monolayer (Pt@Au) system is investigated using a scanning flow cell inductively coupled plasma mass-spectrometry (SFC-ICP-MS) setup, described in more detail in our previous works. 23,24 Experimental Two electrochemical setups were utilized in the current work. The first setup (Setup I) was based on a conventional three-electrode onecompartment electrochemical cell made of glass.…”