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The oxide films produced by anodic oxidation of gold and platinum have been studied by X-ray photoelectron spectroscopy. The change in the amount of each species present, with electrode potential, has been investigated. It is demonstrated that X-ray reduction occurs for these systems but that it can be minimised by a suitable choice of experimental conditions.A study of the intensities of the photoelectron peaks demonstrates how the thickness of an oxide layer and the true surface area of the electrode may be determined. * Amount of water not known exactly under high vacuum conditions of spectrometer. t Adjusted to our calibration scale where necessary. Pt 4f3 electron peak for platinum compounds, Au 4f4 electron peak for gold compounds. 1 Run at -150°C to prevent X-ray decomposition.Decomposes to metallic gold above 350°C. 7 The sample was prepared by dipping a platinum rod in fused potassium nitrate at 400°C.16

The presence and nature of surface species formed on a nickel electrode after polarisation in 0.5 mol dm-3 sulphuric acid and 0.5 mol dm-3 sulphuric acid+0.005 mol dm-3 nickel sulphate has been investigated by X-ray photoelectron spectroscopy. The film produced in the active, prepassive, passive and transpassive regions was studied. Nine different species were detected including two sulphur species. In all cases the electrode was transferred to the spectrometer under nitrogen to 327 328 DISSOLUTION A N D PASSIVATION O F Ni of undetermined impurities has been suggested as the cause of the double-peak behavi0ur.l X-ray photoelectron spectroscopy (X.P.S., E.S.C.A.) has been used to study several electrochemically produced o x i d e ~, ~~-l ~ and much information has been obtained from detailed studies of the oxidation of gold and platinum l 8 and the reduction of chromium (VI) on a gold e1e~trode.l~ The elements present, their oxidation state and the thickness of the film at different potentials may be deduced. This may enable mechanisms to be proposed or disproved.lg Two X.P.S. studies of electrochemically treated nickel alloys have been reported.16* 2o They were, however, only studied over a limited potential range and were not transferred to the spectrometer anacrobically, thus the oxide film studied was not necessarily that due to the electrochemical treatment. X.P.S. studies of the oxidation of nickel by gaseous oxygen 21* 22 have shown discrepancies in the values of the binding energies for both the metal and the oxides produced. The spectra are complex in some cases due to multiplet splitting and other satellite peaks.The aim of this work was to characterize the species present on a nickel electrode after a variety of treatments, including treatment in the active, prepassive, passive and iranspassive regions shown diagrammatically in fig. 1. The correlation of the electrochemical behaviour with the nature of the species on the surface is attempted. All experiments were performed with anaerobic transfer of the sample to the spectrome tcr . EXPERIMENTALThe nickel was either Goodfellows nickel foil (99.995 % pure) or Johnson Matthey " specpure ". AristaR sulphuric acid and AnalaR nickel sulphate were used for the electrolyte solutions. Doubly distilled water l 8 was used for both the electrolyte solution and the washing procedure. The electrochemical cell consisted of three compartments and has been described previous1y.lg All potentials were measured and are quoted with respect to a saturated calomel reference electrode (s.c.e.) in 0.5 mol dm-3 sulphuric acid. The working electrode was a rectangular piece of nickel about 1 CM x 0.5 cm (to facilitatc mounting in the spectrometer) with a 1.5 cm handle, and was suspended from a platinum wire such that the platinum was above the level of the electrolyte solution.The whole cell was mounted in a glove-box which was continually flushed with white-spot nitrogen. A fresh electrode, degreased in acetone and then rinsed in doubly-distilled water, was used for each run. Pr...

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