Time-differential frequency response of electrochemical quartz crystal electrode during the dissolution and deposition processes of Au in H2SO4 solution containing chloride ion

Time-differentiation of the frequency response observed with electrochemical quartz crystal microbalance (EQCM) was applied for the analysis of the electrode processes for the Au electro-dissolution and deposition in acidic aqueous solution containing free chloride ion (Cl−). Evaluation for the values of the apparent equivalent molar mass per second proved the generation of the Au(I) species during the oxidation and reduction reactions of Au electrode in the presence of Cl− at a level of 10 mM, which has not been reported so far. It was found that the electron-transfer reactions composed of Au(0), Au(I) and Au(III) species are participated in the overall Au electro-dissolution and deposition reactions in the applied potential range from −0.10 to 1.50 V (vs. Ag/AgCl).

Graphical abstractCV (a), frequency vs. potential (b), and apparent equivalent molar mass (λ) vs. potential (c) obtained at Pt-QCE in 0.10 M H2SO4 solution containing 1.36 mM K[AuCl4] and 4.21 mM HCl. The potential scanned at 5 mV s−1; (●): 1st potential scan (0.932 → 1.50 → 0.932 V; (○): 2nd scan (0.932 → −0.10 V), (Δ): 2nd scan (−0.10 → 1.50 V) and (1.50 → 0.932 V). The main reactions assigned to the λ responses.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Electrochemistry of Au in acidic media containing less than 10 mM of Cl− was examined. ► Time-differential frequency response of EQCM was analyzed. ► The analysis proved the generation of the Au(I) species during redox reaction of Au.