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On the surface oxidation of a gold electrode in 1N H2SO4 electrolyte
A205 515
Surface Science 141 (1984) 515-532 North-Holland, Amsterdam
THE SURFACE OXIDATION H *SO4 ELECTROLYTE
ON
M.. PEUCKERT,
F.P. COENEN
OF A GOLD
11 January
1984; accepted
IN 1N
and H.P. BONZEL
Institut ftir Grenzjliichenforschung und Vakuumphysik, Postfach 1913, D -5170 Jiilich, Fed. Rep. of Germany Recieved
ELECTRODE
for publication
Kernforschungsanlage 8 March
Jiilich GmbH,
1984
A single crystal Au(100) electrode in 1N H,SO, electrolyte has been potentiostatically polarized at potentials from 0.8 to 4.0 V versus standard hydrogen electrode (SHE). Cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) analysis of the surface gave evidence for water adsorption up to 1.5 V. An 0 1s signal with an electron binding energy of 532.4 eV was found. Beyond the region of transition from OH adsorption to bulk gold oxidation, i.e. 1.4 to 2 V, thick oxidic adlayers were grown. The Au 4f,,, and 4f,,, levels with binding energies of 86.1 and 89.8 eV, respectively, the 0 1s signal at 530.8 eV, as well as the O-to-Au stoichiometry of two, suggested an oxyhydroxide AuOOH for the chemical composition of these thick adlayers. This assignment is in accordance with two cathodic reduction peaks in the cyclic voltammograms, one being interpreted as hydrogenation of an oxidic species and the other as of a hydroxidic species. Thermal decomposition at 400-500 K led to a mixture of Au,O, and Au metal. The measured 0 1s binding energy was 530.0 eV. Above 600 K all oxygen was desorbed.
533
Surface Science 141 (1984) 533-548 North-Holland, Amsterdam
ADSORPTION AND DECOMPOSITION OF METHANOL STUDIED BY ELECTRON ENERGY LOSS AND THERMAL DESORPTION SPECTROSCOPY F. SOLYMOSI,
A. BERKb
and T.I. TARN&Z1
Reaction Ktnetics Research Group, The Unioersity, P. 0. Box 105, H-6701 Received
1 August
1983; accepted
ON Rh(ll1)
for publiCation
15 March
Sreged, Hungary
1984
Methanol adsorbs readily on the Rh(ll1) surface at 100 K, with a high sticking probability, which decreases only slightly up to monolayer coverage. The adsorption occurs in a random fashion, as no long-range order was found by LEED measurements. Four adsorption states can be distinguished: a condensed layer which exhibits fractional kinetics ( Edes = 37 kJ/mol), a physisorbed layer (Ed_ = 39 kJ/mol), and two chemisorption states. The methanol is initially adsorbed dissociatively to the accompaniment of the appearance of a loss feature at 13.7 eV in the EEL spectrum of Rh(ll1) in the electronic range. This process is followed by an associative chemisorption of methanol with a bonding energy of 48 kJ/mol; the corresponding loss feature in the EEL spectrum is at 12.1-11.2 eV. The surface concentration of chemisorbed methanol at monolayer formation is - 7~ lOI molecules/cm’. The methoxy species is not stable on the Rh(ll1) surface; some of it reacts with adsorbed hydrogen and desorbs as methanol at 210-250 K, in a second-order process with an activation energy of 58 kJ/mol. The remaining methoxy decomposes at around 200 K to produce CO and H on the surface. This process is indicated in the EEL spectra by the appearance of a loss at 13.1 eV due to chemisorbed CO. There are no indications of the formation of stable methoxy species.
Surface Science 141 (1984) 515-532 North-Holland, Amsterdam
THE SURFACE OXIDATION H *SO4 ELECTROLYTE
ON
M.. PEUCKERT,
F.P. COENEN
OF A GOLD
11 January
1984; accepted
IN 1N
and H.P. BONZEL
Institut ftir Grenzjliichenforschung und Vakuumphysik, Postfach 1913, D -5170 Jiilich, Fed. Rep. of Germany Recieved
ELECTRODE
for publication
Kernforschungsanlage 8 March
Jiilich GmbH,
1984
A single crystal Au(100) electrode in 1N H,SO, electrolyte has been potentiostatically polarized at potentials from 0.8 to 4.0 V versus standard hydrogen electrode (SHE). Cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) analysis of the surface gave evidence for water adsorption up to 1.5 V. An 0 1s signal with an electron binding energy of 532.4 eV was found. Beyond the region of transition from OH adsorption to bulk gold oxidation, i.e. 1.4 to 2 V, thick oxidic adlayers were grown. The Au 4f,,, and 4f,,, levels with binding energies of 86.1 and 89.8 eV, respectively, the 0 1s signal at 530.8 eV, as well as the O-to-Au stoichiometry of two, suggested an oxyhydroxide AuOOH for the chemical composition of these thick adlayers. This assignment is in accordance with two cathodic reduction peaks in the cyclic voltammograms, one being interpreted as hydrogenation of an oxidic species and the other as of a hydroxidic species. Thermal decomposition at 400-500 K led to a mixture of Au,O, and Au metal. The measured 0 1s binding energy was 530.0 eV. Above 600 K all oxygen was desorbed.
533
Surface Science 141 (1984) 533-548 North-Holland, Amsterdam
ADSORPTION AND DECOMPOSITION OF METHANOL STUDIED BY ELECTRON ENERGY LOSS AND THERMAL DESORPTION SPECTROSCOPY F. SOLYMOSI,
A. BERKb
and T.I. TARN&Z1
Reaction Ktnetics Research Group, The Unioersity, P. 0. Box 105, H-6701 Received
1 August
1983; accepted
ON Rh(ll1)
for publiCation
15 March
Sreged, Hungary
1984
Methanol adsorbs readily on the Rh(ll1) surface at 100 K, with a high sticking probability, which decreases only slightly up to monolayer coverage. The adsorption occurs in a random fashion, as no long-range order was found by LEED measurements. Four adsorption states can be distinguished: a condensed layer which exhibits fractional kinetics ( Edes = 37 kJ/mol), a physisorbed layer (Ed_ = 39 kJ/mol), and two chemisorption states. The methanol is initially adsorbed dissociatively to the accompaniment of the appearance of a loss feature at 13.7 eV in the EEL spectrum of Rh(ll1) in the electronic range. This process is followed by an associative chemisorption of methanol with a bonding energy of 48 kJ/mol; the corresponding loss feature in the EEL spectrum is at 12.1-11.2 eV. The surface concentration of chemisorbed methanol at monolayer formation is - 7~ lOI molecules/cm’. The methoxy species is not stable on the Rh(ll1) surface; some of it reacts with adsorbed hydrogen and desorbs as methanol at 210-250 K, in a second-order process with an activation energy of 58 kJ/mol. The remaining methoxy decomposes at around 200 K to produce CO and H on the surface. This process is indicated in the EEL spectra by the appearance of a loss at 13.1 eV due to chemisorbed CO. There are no indications of the formation of stable methoxy species.