Analysis of the Surface Oxidation Process on Pt Nanoparticles on a Glassy Carbon Electrode by Angle-Resolved, Grazing-Incidence X-ray Photoelectron Spectroscopy

Abstract

We have analyzed the surface oxidation process of Pt nanoparticles that were uniformly dispersed on a glassy carbon electrode (Pt/GC), which was adopted as a model of a practical Pt/C catalyst for fuel cells, in N-purged 0.1 M HF solution by using angle-resolved, grazing-incidence X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-ARGIXPS). Positive shifts in the binding energies of Pt 4f spectra were clearly observed for the surface oxidation of Pt nanoparticles at potentials E > 0.7 V vs RHE, followed by a bulk oxidation of Pt to form Pt(II) at E > 1.1 V. Three types of oxygen species (HO, OH, and O) were identified in the O 1s spectra. It was found for the first time that the surface oxidation process of the Pt/GC electrode at E < ca. 0.8 V (OH formation) is similar to that of a Pt(111) single-crystal electrode, whereas that in the high potential region (O formation) resembles that of a Pt(110) surface or polycrystalline Pt film.

Redox Behavior of Pt/Co3O4(111) Model Electrocatalyst Studied by X-ray Photoelectron Spectroscopy Coupled with an Electrochemical Cell

“…As discussed in the literature, ,, the mechanism of electrochemical oxidation of Pt under alkaline conditions involves the formation of Pt δ –OH ads species, where the oxidation state of the activated Pt δ adsorption site varies between Pt 0 and Pt 2+ . In the next step, deprotonation of OH ads yields Pt δ –O ads species, which are converted to surface Pt oxides. ,, The formation of surface PtO and PtO 2 is typically detected at potentials above 1.0 V RHE . ,,,,, Noteworthy, no substantial differences were detected in the oxidation onsets of Pt particles supported on carbon substrates with respect to single crystalline and polycrystalline Pt surfaces. , In the present study, the onsets of surface PtO and PtO 2 in Pt/Co 3 O 4 (111)/Ir­(100) at 1.0 and 1.1 V RHE , respectively, are in good agreement with the literature.…”

“…We note that the size of Pt nanoparticles supported on the Co 3 O 4 (111) system is similar to the Pt particle sizes in Pt/C systems, , enabling direct comparison of Pt oxidation in systems with and without EMSI. In particular, the absence of interfacial Pt oxide in the Pt/C system suggests that EMSI effects are involved in the Pt oxidation in Pt/Co 3 O 4 (111).…”

“…Here, the formation of OH and O ads species was observed above 0.3 and 0.7 V RHE , respectively, followed by the formation of bulk Pt oxide above 1.1 V RHE . Although shifts of Pt 4f core levels toward higher binding energies were observed in Pt/C systems above 0.7 V RHE , 37 these shifts are small (less than 0.5 eV) 37 and do not support the formation of Pt oxide below 1.1 V RHE . In fact, they rather point to chemisorption of atomic oxygen species.…”

“…Quasi in situ studies come with the advantage that, in contrast to many in situ approaches, the conditions (e.g., pH, potential, electrolyte concentration) are well-defined in the electrochemical experiment. The disadvantage is that the electrochemical interface is not investigated under working conditions, that is, only the information on permanent changes of the chemical composition or structure of the catalyst associated with the thermodynamic state that is stable after emersion from the aqueous electrolyte can be obtained as a function of electrode potential. − …”

Atomically Flat Pt Skin and Striking Enrichment of Co in Underlying Alloy at Pt3Co(111) Single Crystal with Unprecedented Activity for the Oxygen Reduction Reaction

“…Figure 3 shows the Co 2p 3/2 spectra for the Pt 73 Co 27 (111) after H 2 annealing by angle-resolved, grazing-incidence X-ray photoelectron spectroscopy (ARGI-XPS). 22 The incident angle of the X-rays (Al Kα) was between 1 and 2°, whereas the detection angles of the photoelectrons were adjusted to 75 and 0° for the detection of signals from the surface (ca. 4 layers) and the bulk (ca.…”