Identification and Quantification of Oxygen Species Adsorbed on Pt(111) Single-Crystal and Polycrystalline Pt Electrodes by Photoelectron Spectroscopy

Abstract

We have positively identified oxygen species on Pt(111) single-crystal and polycrystalline Pt electrodes in N2-purged 0.1 M HF solution by X-ray photoelectron spectroscopy combined with an electrochemical cell. Four oxygen species (Oad, OHad, and two types of water molecules) were distinguished. The binding energies of each species were nearly constant over the whole potential region and independent of the single- or polycrystalline electrodes. The coverages, however, varied considerably and were dependent on the electrode potential. We have for the first time demonstrated clear differences in the surface oxidation processes for Pt(111) and polycrystalline Pt electrodes.

Volcano Plots and Effective Reversible Potentials for Oxygen Electroreduction

“…In recent years, it has become well-established that platinum electrodes immersed in acidic or basic aqueous electrolytes react with water when the potential is increased from the edge of the hydrogen under potential deposition potential region,~0.35 V on the reversible hydrogen electrode scale, which will be used in this paper, to around 0.6 V. At 0.6 V, water begins to be oxidized to OH(ads), and at around 0.8 V OH(ads), it begins to be oxidized to O(ads) [1][2][3]. Even before the careful work in these recent references, it was well-known that water oxidizes on platinum cathodes in acid or base as the potential is increased out of the double-layer region, beginning around 0.6 V. It has been long assumed that these adsorbates control the kinetics and current densities of oxygen cathodes by blocking active adsorption sites for O 2 .…”

“…The first showed that both OH and H 2 O bond more weakly to the (111) Pt skin on Pt 3 Cr alloy surfaces, but the weakening was greater for OH, and from this, it was deduced that the shift of the reversible potential for reducing OH(ads) to H 2 O(l) would be about 110 mV positive [7]. The implication was that the skin surface would be clear of OH(ads) at 110 mV higher potential than on pure Pt(111).…”

Direct observation of the oxygenated species during oxygen reduction on a platinum fuel cell cathode

“…The application of vibrational spectroscopy is also limited by the strong absorbance of both the electrolyte solution and the electrolyte membrane, which makes the weak vibrational signature of the OH species virtually undetectable 13,14 . X-ray photoelectron spectroscopy (XPS), which probes all oxygenated surface species with equal sensitivity, has been used to study Pt single-crystal electrodes 15,16 in ultra-high vacuum. The challenge with these ex situ measurements is to minimize decomposition and contamination during sample transfer, as surface water species on Pt all desorb above 200 K in ultra-high vacuum 17 .…”

Research and Development of Highly Active and Durable Electrocatalysts Based on Multilateral Analyses of Fuel Cell Reactions

“…[1][2][3][4] For PEFC anode and cathode catalysts, the activity and its degradation have been analyzed by multilateral techniques such as X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-XPS), 2,[5][6][7][8] in situ Fourier-transform infrared spectroscopy (FTIR), [9][10][11][12][13][14][15][16][17][18][19][20][21][22] electrochemical quartz crystal microbalance (EQCM), [23][24][25][26] in situ scanning tunneling microscopy (STM), [27][28][29][30][31] in addition to conventional electrochemical measurements such as rotating disk electrode (RDE), [32][33][34] channel flow electrode (CFE), 21,35,36 and channel flow double electrode (CFDE) methods. [37][38][39][40][41][42] Based on these results, new practical catalysts have been synthesized.…”