Coadsorption of D₂O and CO on Pt(111) Studied by in Situ High-Resolution X-ray Photoelectron Spectroscopy

Abstract

The adsorption of D2O on Pt(111) and the coadsorption with CO have been revisited by quantitative and in situ high-resolution X-ray photoelectron spectroscopy (XPS). During D2O adsorption at 110 K, O 1s spectra clearly show the known formation of a bilayer and multilayers. As indicated by a binding energy change of the multilayer peak in the XP spectra recorded during heating, a structural change in the D2O multilayer at the onset of multilayer desorption (∼145 K) is observed. Coadsorption of CO and D2O leads to occupation of bridge and on-top sites by CO, with the order in site occupation reversed as compared to the clean surface, as previously observed. In addition, a new CO species is clearly resolved in C 1s spectra, which may be identified with CO on hollow sites. Upon D2O desorption, this new species disappears and the CO site occupation changes to the value observed on the clean Pt(111). Induced by CO coadsorption, partial replacement of D2O from the surface into higher layers is observed, indicated by a reduced desorption temperature of water and an O 1s binding energy shift toward the value of the multilayer signal. Our results suggest an intermixed first layer of CO and D2O molecules; D2O on top of this layer also influences the CO site distribution. On a surface precovered with 0.5 monolayer (ML) of CO, D2O molecules can only adsorb on top of the CO layer and no mixed layer is formed; hence, no site change is observed. The preadsorbed D2O bilayer lowers the initial CO sticking coefficient by a factor of ∼13 as compared to the clean surface; this reduction is larger than previously detected.

Mechanism of an Enhanced Oxygen Reduction Reaction at Platinum‐Based Electrocatalysts: Identification and Quantification of Oxygen Species Adsorbed on Electrodes by X‐Ray Photoelectron Spectroscopy

“…The BEs of the four oxygen species were found to be nearly constant at 529.6, 530.5, 531.1, and 532.6 eV, with variations of AE0.2 eV. The species at 529.6 and 530.5 eV can be assigned to OH ad and O ad , in agreement with the assignments of these species on Pt(111) formed in UHV [36][37][38]. The species at 532.6 eV can be assigned to H 2 O ad , also in good agreement with the value found for Pt(111) in UHV [36,[39][40][41].…”

CO oxidation on Pt(111) at near ambient pressures

“…The experiment started by admitting CO to the chamber with a pressure of 0.66 mbar and the sample at 300 K. This leads to a gas phase peak at 536.6 eV and to two peaks at ∼532.8 and ∼531.1 eV due to CO adsorbed in on-top sites (pink) and in bridge sites (purple) on the Pt(111) surface. 20,35,39 Please note that due to the limited resolution of our setup, these two peaks are not well resolved. In Figure 1(b), exemplary fits are shown, where three successively measured O 1s spectra were added up in order to get a better signal-to-noise ratio.…”

Unveiling the Oxidation Processes of Pt3Ni(1 1 1) by Real‐Time Surface Core‐Level Spectroscopy

“…Previously, a peak at a BE of 531.1 eV was associated with CO molecules in the bridge sites of Pt(1 1 1) . However, the presence of coadsorbed CO molecules would imply the presence of an additional feature related to CO in on‐top sites, with a BE of 533.0 eV . The preferential adsorption site for CO is the on‐top site, but in principle, the presence of oxygen could result in site blocking .…”

“…The Pt 3 Ni surface at room temperaturei sh ighly reactive toward residual CO in the vacuum chamber,w hich could in principle induce the appearanceo ft he above-mentioned peak at aB Eo f5 31.7 eV.P reviously,apeak at aB Eo f5 31.1 eV was associated with CO molecules in the bridge sites of Pt(111). [32] However,t he presence of coadsorbed CO molecules would imply the presence of an additional feature related to CO in on-top sites, with aBEo f533.0 eV. [32,33] The preferentialadsorption site for CO is the on-top site, [15] but in principle, the presence of oxygen could result in site blocking.…”

“…[32] However,t he presence of coadsorbed CO molecules would imply the presence of an additional feature related to CO in on-top sites, with aBEo f533.0 eV. [32,33] The preferentialadsorption site for CO is the on-top site, [15] but in principle, the presence of oxygen could result in site blocking. [34] Nonetheless, the thermal behavioro ft he Pt 3 Ni(111)s urfaces aturated with ad ose of 100 Lo fO 2 at 353 Ka nd successively heated in UHV, in the absence of an oxygen environment, gives important hints (Figure 4).…”