Determination of the concentration of surface hydroxyl groups on metal oxide films by a quantitative XPS method

McCafferty, E.; Wightman, J. P.

doi:10.1002/(sici)1096-9918(199807)26:8<549::aid-sia396>3.0.co;2-q

Cited by 822 publications

(323 citation statements)

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“…The TiO 2 water interface 29 can be probed with a range of experimental techniques. Important examples include determining the amount of surface OH groups with x-ray photoelectron spectroscopy (XPS), 30 measuring the water oxygen-to-surface bond length with xray photoelectron diffraction (XPD), 31 and/or imaging the interface with scanning tunneling microscopy (STM). 32 Computational work has focused on determining whether water dissociates or stays intact when adsorbed to low-energy TiO 2 a) Author to whom correspondence should be addressed: erik.brandt@ mmk.su.se surfaces, which is of particular interest to water splitting applications.…”

Section: Introductionmentioning

confidence: 69%

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Agosta

Brandt

Lyubartsev

2017

The Journal of Chemical Physics

104

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Ab initio molecular dynamics simulations are reported for water-embedded TiO2 surfaces to determine the diffusive and reactive behavior at full hydration. A three-domain model is developed for six surfaces [rutile (110), (100), and (001), and anatase (101), (100), and (001)] which describes waters as “hard” (irreversibly bound to the surface), “soft” (with reduced mobility but orientation freedom near the surface), or “bulk.” The model explains previous experimental data and provides a detailed picture of water diffusion near TiO2 surfaces. Water reactivity is analyzed with a graph-theoretic approach that reveals a number of reaction pathways on TiO2 which occur at full hydration, in addition to direct water splitting. Hydronium (H3O+) is identified to be a key intermediate state, which facilitates water dissociation by proton hopping between intact and dissociated waters near the surfaces. These discoveries significantly improve the understanding of nanoscale water dynamics and reactivity at TiO2 interfaces under ambient conditions.

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Section: Introductionmentioning

confidence: 69%

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Agosta

Brandt

Lyubartsev

2017

The Journal of Chemical Physics

104

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“…The 532.2 and 531.9 peaks are attributed to TiÀOH, which are reported to be located at binding energies 1.5-1.8 eV higher than the O 1s signal for TiO 2 . [24] The TiÀOH peak intensity for the H-TNTs is substantially higher than that of the air-TNTs, indicating that the surface of TNTs was functionalized by hydroxyl groups after hydrogenation.…”

Section: Synthesis and Characterization Of H-tntsmentioning

confidence: 98%

Supported Noble Metals on Hydrogen‐Treated TiO₂ Nanotube Arrays as Highly Ordered Electrodes for Fuel Cells

Zhang

et al. 2013

ChemSusChem

103

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Hydrogen‐treated TiO2 nanotube (H–TNT) arrays serve as highly ordered nanostructured electrode supports, which are able to significantly improve the electrochemical performance and durability of fuel cells. The electrical conductivity of H–TNTs increases by approximately one order of magnitude in comparison to air‐treated TNTs. The increase in the number of oxygen vacancies and hydroxyl groups on the H–TNTs help to anchor a greater number of Pt atoms during Pt electrodeposition. The H–TNTs are pretreated by using a successive ion adsorption and reaction (SIAR) method that enhances the loading and dispersion of Pt catalysts when electrodeposited. In the SIAR method a Pd activator can be used to provide uniform nucleation sites for Pt and leads to increased Pt loading on the H‐TNTs. Furthermore, fabricated Pt nanoparticles with a diameter of 3.4 nm are located uniformly around the pretreated H–TNT support. The as‐prepared and highly ordered electrodes exhibit excellent stability during accelerated durability tests, particularly for the H–TNT‐loaded Pt catalysts that have been annealed in ultrahigh purity H2 for a second time. There is minimal decrease in the electrochemical surface area of the as‐prepared electrode after 1000 cycles compared to a 68 % decrease for the commercial JM 20 % Pt/C electrode after 800 cycles. X‐ray photoelectron spectroscopy shows that after the H–TNT‐loaded Pt catalysts are annealed in H2 for the second time, the strong metal–support interaction between the H–TNTs and the Pt catalysts enhances the electrochemical stability of the electrodes. Fuel‐cell testing shows that the power density reaches a maximum of 500 mW cm−2 when this highly ordered electrode is used as the anode. When used as the cathode in a fuel cell with extra‐low Pt loading, the new electrode generates a specific power density of 2.68 kW gPt−1. It is indicated that H–TNT arrays, which have highly ordered nanostructures, could be used as ordered electrode supports.

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“…47 By performing isobaric and/or isothermal measurements to access a range of relative humidities, the oxygen spectra of model oxide surfaces have been deconvoluted into hydroxyls (OH − ), oxy-carbonaceous species such as carbonate (CO3 2− ), bulk oxygen, and adsorbed water (H2O). Using a multilayer electron attenuation model, [48][49][50] the coverage of each species can be deduced. In the case of TiO2, the relation between the coverage of OH − and Ti 3+ sites suggests hydroxylation of the surface proceeds by dissociation of water molecules, where the OH − group fills an O 2− vacancy and the remaining H + binds to a bridging O 2− , forming a second OH − group.…”

Section: The Oxide/h2o Vapor Interfacementioning

confidence: 99%

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

et al. 2015

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ConspectusThe understanding of fundamental processes in the bulk and at the interfaces of electrochemical devices is a prerequisite for the development of new technologies with higher efficiency and improved performance. One energy storage scheme of great interest is splitting water to form hydrogen and oxygen gas, and converting back to electrical energy by their subsequent recombination with only water as a by-product. However, kinetic limitations to the rate of oxygen-based electrochemical reactions hamper the efficiency in technologies such as solar fuels, fuel cells, and electrolyzers. For these reactions, the use of metal oxides as electrocatalysts is prevalent due to their stability, low cost, and ability to store oxygen within the lattice. However, due to the inherently convoluted nature of electrochemical and chemical processes in electrochemical systems, it is difficult to isolate and study individual electrochemical processes in a complex system. Therefore in situ characterization tools are required for observing related physical and chemical processes directly at the places where and while they occur, and can help elucidate the mechanisms of charge separation and charge transfer at electrochemical interfaces.X-ray photoelectron spectroscopy (XPS), also known as ESCA (electron spectroscopy for chemical analysis) has been used as a quantitative spectroscopic technique that measures the elemental composition, as well as chemical and electronic state of a material. Building from extensive ex situ characterization of electrochemical systems, initial in situ studies were conducted at (near) UHV conditions (≤10 −6 Torr) to probe solid-state electrochemical systems. However through the integration of differential-pumping stages, XPS can now operate at pressures in the Torr range, comprising a technique called ambient pressure XPS (AP-XPS).In this Account, we briefly review the working principles and current status of AP-XPS. We use several recent in situ studies on model electrochemical components as well as operando studies performed by our groups at the Advanced Light Source (ALS) at Lawrence Berkeley National Lab to illustrate that AP-XPS is both a chemically and electrically specific tool since photoelectrons carry information on both the local chemistry and electrical potentials. The applications of AP-XPS to oxygen electrocatalysis shown in this Account span well defined studies of (1) the oxide/oxygen gas interface, (2) the oxide/water vapor interface, and (3) operando measurements of half and full electrochemical cells. Using 2 specially designed model devices, we can expose and isolate the electrode or interface of interest to the incident X-ray beam and AP-XPS analyzer to relate the electrical potentials to the composition/chemical state of the key components and interfaces. We conclude with an outlook on new developments of AP-XPS endstations, which may provide significant improvement in the observation of dynamics over a wide range of time scale, higher spatial resolution, and improved characteri...

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Determination of the concentration of surface hydroxyl groups on metal oxide films by a quantitative XPS method

Cited by 822 publications

References 13 publications

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Supported Noble Metals on Hydrogen‐Treated TiO₂ Nanotube Arrays as Highly Ordered Electrodes for Fuel Cells

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

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Determination of the concentration of surface hydroxyl groups on metal oxide films by a quantitative XPS method

Cited by 822 publications

References 13 publications

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Supported Noble Metals on Hydrogen‐Treated TiO2 Nanotube Arrays as Highly Ordered Electrodes for Fuel Cells

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

Contact Info

Product

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Supported Noble Metals on Hydrogen‐Treated TiO₂ Nanotube Arrays as Highly Ordered Electrodes for Fuel Cells