In situx-ray photoelectron spectroscopy studies of water on metals and oxides at ambient conditions

Abstract

E d i t i o n o f a c t i v e P D F S o f t w a r e . V i s i t w w w . a c t i v e P D F . c o m f o r m o r e d e t a i l s .1In-situ X-ray photoelectron spectroscopy studies of water on metals and oxides at ambient conditions Abstract. X-ray photoelectron spectroscopy (XPS) is a powerful tool for surface and interface analysis, providing the elemental composition of surfaces and the local chemical environment of adsorbed species. Conventional XPS experiments have been limited to ultrahigh vacuum (UHV) conditions due to a short mean free path of electrons in a gas phase. The recent advances in instrumentation coupled with third-generation synchrotron radiation sources enables in-situ XPS measurements at pressures above 5 Torr. In this review, we describe the basic design of the ambient pressure XPS setup that combines differential pumping with an electrostatic focusing. We present examples of the application of in-situ XPS to studies of water adsorption on the surface of metals and oxides including Cu(110), Cu(111), TiO 2 (110) under environmental conditions of water vapor pressure. On all these surfaces we observe a general trend where hydroxyl groups form first, followed by molecular water adsorption. The importance of surface OH groups and their hydrogen bonding to water molecules in water adsorption on surfaces is discussed in detail. E v a l u a t i o n E d i t i o n o f a c t i v e P D FS o f t w a r e . V i s i t w w w . a c t i v e P D F . c o m f o r m o r e d e t a i l s .2

High-Voltage Symmetric Supercapacitor Based on 2D Titanium Carbide (MXene, Ti2CTx)/Carbon Nanosphere Composites in a Neutral Aqueous Electrolyte

“…The obtained values of the binding energy (BE) after deconvolution are comparable with previous studies. [80][81][82] For the MXene, the O 1s core level consists of three photoelectron peaks (Figure 7b). The lower BE, located at 529.38 eV, which comprises 57.59% of the photoemission in the O 1s core level is assigned to TiO 2 formed by oxidation of the MXene surface.…”

“…86 The results are in good agreement with the literature. [80][81][82][83][84][85] Indeed, the XPS results show the existence of the expected functional groups and oxidation of the surface and also prove that MXene is made up of mostly carbon. If we consider that the electrode was constructed with extra carbons (4% CNS and 15% carbon black), it can easily be inferred that the high-voltage operation of this supercapacitor may be partly related to the high carbon content.…”

Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars

“…The dissociative adsorption of water on metals surfaces produces OH species, and consequently the metal surface carries a partial negative charge. Analogous to OH − ions in solution, OH γ − species adsorbed on metal surfaces act as Brłnsted bases (51,52) and may facilitate the formation and precipitation of carbonates. The in situ formation of CO 2 on iron oxide surfaces in the presence of adsorbed water and CO 2 has been demonstrated using 18 O labeled water (15) and labeled C 16 O 2 , C 18 O 2 on zeolite surfaces (53).…”

Effect of key parameters on the photocatalytic oxidation of toluene at low concentrations in air under 254+185nm UV irradiation

“…Instead, dry air conditions did not favor the formation of formaldehyde in either case, suggesting that the presence of surface OH groups may play an important role in the pathways leading to formation of this byproduct, presumably through oxidative cleavage of the methyl group (side chain), as opposed to the oxidation of the aromatic ring [46]. The population of surface OH is regenerated through dissociative chemisorption of water vapor under humidified air, thus becoming a limiting factor under dry air [39,40,43]. On the other side, the multilayer water film formed at 66% RH on the surface of the photocatalyst [41] has the potential capacity to retain larger amounts of polar oxidation byproducts and reduce their gas-phase levels.…”

“…As RH increased further to 33% and 66%, the net effect was an inhibition that led to reaction rates lower than those measured with dry air. The effect of low levels of water can be interpreted as a contribution of adsorbed water to the regeneration of active surface species at low water coverage (i.e., 10% RH), since H 2 O molecules adsorb dissociatively to TiO 2 surfaces at low RH, generating surface OH groups [39,40]. For RH > 15-20%, the amount of water adsorbed on the surface of TiO 2 amounts to more than a monolayer [41], and the net effect is likely a competition with toluene for adsorption to the active surface sites that leads to a 17 decline in toluene reaction rates with increasing RH.…”