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Recent studies of the Au leaching process have employed thiosulfate as the alternative complexing ligand to cyanide for gold extraction from ores containing carbonaceous components which preferentially absorbs gold and gold-cyanide complexes ( the so called preg-robbing). Thiosulfate, in the presence of an appropriate oxidant such as dissolved oxygen, is well known to complex Au(I) ions and form a soluble [Au(S2O3)2]3- complex. However, the kinetics of this process are inhibited by the formation of a passivating layer of species on the Au surface that block the lixiviant reagents from reaching the underlying Au atoms, thereby preventing full recovery of Au from the ore. To determine the composition of this passive layer, the interfacial behaviour of tetrathionate, trithionate, the [Au(S2O3)2]3- complex and thiosulfate upon immersion of a Au nanorods electrode into each of the electrolyte solutions was investigated using surface enhanced Raman spectroscopy (SERS). Raman bands indicative of adsorbed tetrathionate, trithionate, and [Au(S2O3)2]3- were identified at early immersion times. However, bands assigned to decomposition products such as elemental sulfur, were observed in all SERS spectra at longer immersion times. The SERS spectra for tetrathionate, trithionate, the [Au(S2O3)2]3- complex were compared to SERS spectra collected in a thiosulfate electrolyte in an attempt to better identify the passivating species that accumulate on the Au surface in typical gold leaching conditions. In thiosulfate solution, Au surface passivation by elemental sulfur did not occur to the same extent relative as in the three other electrolytes in the time period studied. This behavior indicates that complexation of the oxidized Au atoms by thiosulfate and its subsequent mass transportation into the bulk electrolyte is the predominantly favoured pathway at early immersion times. However, the disappearance of the Raman bands characteristic of the [Au(S2O3)2]3- complex and the appearance of bands indicative of elemental sulfur on the Au surface at longer immersion times confirms the growth of a passivating film of elemental sulfur on the gold surface in the thiosulfate electrolyte, albeit at much longer immersion times.

This lecture will review our research involving IR spectroscopy at the solid –liquid interface. After a brief review of basic principles of IR spectroscopy and the laws of reflection of light at interfaces, three methods of Infrared Reflection Absorption Spectroscopy (IRRAS) will be described. The first is subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) or in short potential difference IR spectroscopy. This technique finds application to study reversible adsorption of soluble molecules at electrode surfaces. The methods of optimisation of the SNIFTIRS experiment will be discussed. Its application will be illustrated by the case of adsorption of a soluble surfactant such as sodium dodecyl sulphate (SDS) at a gold electrode surface.1 The second technique to measure IR spectra at interfaces is the photon polarization modulation infrared reflection absorption spectroscopy (PM IRRAS). This technique is used to study films of insoluble molecules a various interfaces. I will discuss application of this technique to study model biological membranes supported at a gold electrode surface.2 The third technique is the surface enhanced infrared reflection absorption spectroscopy (SEIRAS). It is performed using attenuated total internal reflection (ATR) element covered by nanoparticles of gold. The intensity of the IR signal is then enhanced by a factor of 100. In addition, since the film of metal nanoparticles is conductive it is used to study phenomena at electrified interfaces. I will describe application of this technique to study structure of water in model biological membrane supported at a gold electrode surface.3 I will emphasize complementarity of SEIRAS and PMIRRAS in application to bio-electrochemical research. Literature 1.Jay Leitch, John Collins, K. Andreas Friedrich, Ulrich Stimming, John R. Dutcher, Jacek Lipkowski “Infrared Studies of the Potential Controlled Adsorption of Sodium Dodecyl Sulfate at the Au(111) Electrode Surface”, Langmuir, 2012,28,2455-2464. 2. Jacek Lipkowski, “Building model biomimetic membrane at a gold electrode surface”, Phys. Chem. Chem. Phys., 2010,12,13874-13887. 3. Taro Uchida, Masatoshi Osawa and Jacek Lipkowski, “SEIRAS studies of water structure at the gold electrode surface in the presence of supported lipid bilayer”, J.Electroanal.Chem. DOI:10.1016/j.jelechem.2013.10.015

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Chronocoulometry recorded during the first 100 ms of double layer charging has been used to study the physical adsorption of neutral organic molecules on solid electrodes. The adsorption of cyclohexanol on gold is used to illustrate the method. The film pressure and the Gibbs surface excess for this system are determined as functions of potential from charge densities obtained by the analysis of the potentiostatic transients. Charge densities determined by chronocoulometry are compared with results obtained from the integration of differential capacities, which were independently measured at 25 Hz. Film pressures determined from these differential capacity measurements are shown to be unrealistically low and inconsistent with changes in bulk cyclohexanol concentration. In contrast, chronocoulometry gives consistent results and allows the determination of results that are comparable to those obtained on mercury.

The adsoption of hydrogen and the kinetics of the hydrogen evolution reaction (HER) on the vitreous Pt 77 Si 23 alloy have been investigated. Five differently treated samples of the alloy have been studied and their electrocatalytic activities have been compared with those of pure polycrystalline Pt