Recent applications of hard x-ray photoelectron spectroscopy

Rumaiz, Abdul K.; Pianetta, P.; Woicik, J. C.

doi:10.1116/1.4946046

Cited by 43 publications

(38 citation statements)

References 155 publications

(186 reference statements)

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“…Λ e is the inelastic mean free path determined through the Tanuma–Powell–Penn algorithm 53 , since the single scattering albedo is negligible for excitation energies above 2.0 keV 54 55 ; Λ e (for an incoming photon energy of 4.0 keV and a 1.0 M pyrazine aqueous solution as attenuating medium) is equal to 8.8 nm and to 9.3 nm for an N 1 s (BE=400.6 eV) and an O 1 s (BE=532.8 eV) escaping photoelectron, respectively.…”

Section: Methodsmentioning

confidence: 99%

Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

et al. 2016

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The electrochemical double layer plays a critical role in electrochemical processes. Whilst there have been many theoretical models predicting structural and electrical organization of the electrochemical double layer, the experimental verification of these models has been challenging due to the limitations of available experimental techniques. The induced potential drop in the electrolyte has never been directly observed and verified experimentally, to the best of our knowledge. In this study, we report the direct probing of the potential drop as well as the potential of zero charge by means of ambient pressure X-ray photoelectron spectroscopy performed under polarization conditions. By analyzing the spectra of the solvent (water) and a spectator neutral molecule with numerical simulations of the electric field, we discern the shape of the electrochemical double layer profile. In addition, we determine how the electrochemical double layer changes as a function of both the electrolyte concentration and applied potential.

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Section: Methodsmentioning

confidence: 99%

Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

et al. 2016

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“…Recoil is present in all photoemission processes and the corresponding loss of photoelectron kinetic energy (ΔE K ) is given by ΔE K = E K (m e /M), where E K is the photoelectron kinetic energy, m e is the electron rest mass, and M the emitting atom mass (49). Therefore, recoil effects are not negligible for high photoelectron kinetic energy and light elements (49,57) and the energy difference observed here is a consequence of the larger photon energy used in the present work (4 keV) compared to typically used soft X-rays (< 2 keV). A detailed analysis of the VB photoemission spectra from the biphasic coating is reported in Figure 2d for the cases of measurement under pristine, hydrated, and electrochemical conditions.…”

Section: Operando Spectroscopic Investigation Of the Biphasic Coo X Smentioning

confidence: 99%

“…To perform a detailed surface and near-surface spectroscopic investigation, we have used ambient pressure X-ray photoelectron spectroscopy (APXPS) coupled with intermediate energy, or "tender", X-rays (hν = 4.0 keV). Taking advantage of the high photoelectron kinetic energy (49,50) it is possible to probe 10 -30 nm of a liquid phase and 2 -10 nm of a solid phase, while simultaneously undergoing electrochemical reactions (39, 42-44, 46, 48).Previously, we observed a significant improvement of OER electrocatalytic activity in a biphasic CoO x system, in which a disordered outer-surface layer of Co(OH) 2 is introduced atop a nanocrystalline spinel Co 3 O 4 phase via PE-ALD, relative to pure phase spinel Co 3 O 4 (37). However, the electrochemical and ex situ spectroscopic measurements utilized in that study were incapable of characterizing the extent of conversion from Co(OH) 2 to CoO(OH), the degree to which spinel Co 3 O 4 may undergo parallel chemical transformations, the composition of the film under real operational conditions, or the validity of the current mechanistic models for OER on CoO x formed via PE-ALD.…”

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confidence: 99%

Understanding the Oxygen Evolution Reaction Mechanism on CoO_x using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy

et al. 2017

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ABSTRACT:Photoelectrochemical water splitting is a promising approach for renewable production of hydrogen from solar energy and requires interfacing advanced water splitting catalysts with semiconductors. Understanding the mechanism of function of such electrocatalysts at the atomic scale and under realistic working conditions is a challenging, yet important, task for advancing efficient and stable function. This is particularly true for the case of oxygen evolution catalysts and, here, we study a highly active Co 3 O 4 /Co(OH) 2 biphasic electrocatalyst on Si by means of operando ambient pressure X-ray photoelectron spectroscopy performed at the solid/liquid electrified interface. Spectral simulation and multiplet fitting reveal that the catalyst undergoes chemical-structural transformations as a function of the applied anodic potential, with complete conversion of the Co(OH) 2 and partial conversion of the spinel Co 3 O 4 phases to CoO(OH) under pre-catalytic electrochemical conditions. Furthermore, we observe new spectral features in both Co 2p and O 1s core level regions to emerge under oxygen evolution reaction conditions on CoO(OH). The operando photoelectron spectra support assignment of these newly observed features to highly active Co 4+ centers under catalytic conditions. Comparison of these results to those from a pure phase spinel Co 3 O 4 catalyst supports this interpretation and reveals that the presence of Co(OH) 2 enhances catalytic activity by promoting transformations to CoO(OH). The direct investigation of electrified interfaces presented in this work can be extended to different materials under realistic catalytic conditions, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design. Introduction Sustainable solutions are required to mitigate the impact of increasing world energy demand on the environment and avoid depletion of natural energy sources (1). While transduction of solar energy to electricity has already made a significant impact on the renewable energy sector, the intermittent nature of sunlight imposes critical storage challenges (2,3,4,5,6). Furthermore, addressing broader energy needs, particularly in transportation, requires new technologies for the next generation of renewable fuels. Within this context, (photo)electrochemical conversion of sunlight to hydrogen -or other chemical fuels -represents an appealing approach to both solar energy conversion and high energy density storage. An essential step in such artificial photosystems is the oxygen evolution reaction (OER), in which the protons and electrons required for the fuel formation reaction are harnessed from water (2-7, 8, 9). However, OER pathways can be complex and impose significant kinetic bottlenecks. To address this challenge, increasing efforts have been devoted to developing OER catalysts possessing high activity, long-term durability, and low cost, a combination of attributes that is most commonly obtained with first row transition metal oxides (10,11,12,13,14,15...

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“…This might be due to recoil effects when momentum is transferred from the ejected photoelectron to the emitting atom. Recoil is present in all photoemission processes and its effects are non-negligible for high photoelectron KEs and light elements [51,52]. At a photon energy of 4000 eV the calibration performed on gold using the Au 4f 7/2 core level signal (KE~3916 eV) is essentially not influenced by the recoil (the corresponding loss is about 10 meV).…”

Section: Evolution Of the Physical/chemical Properties Of The Solid/lmentioning

confidence: 99%

Interface Science Using Ambient Pressure Hard X-ray Photoelectron Spectroscopy

et al. 2019

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The development of novel in situ/operando spectroscopic tools has provided the opportunity for a molecular level understanding of solid/liquid interfaces. Ambient pressure photoelectron spectroscopy using hard X-rays is an excellent interface characterization tool, due to its ability to interrogate simultaneously the chemical composition and built-in electrical potentials, in situ. In this work, we briefly describe the "dip and pull" method, which is currently used as a way to investigate in situ solid/liquid interfaces. By simulating photoelectron intensities from a functionalized TiO 2 surface buried by a nanometric-thin layer of water, we obtain the optimal photon energy range that provides the greatest sensitivity to the interface. We also study the evolution of the functionalized TiO 2 surface chemical composition and correlated band-bending with a change in the electrolyte pH from 7 to 14. Our results provide general information about the optimal experimental conditions for characterizing the solid/liquid interface using the "dip and pull" method, and the unique possibilities offered by this technique.Surfaces 2019, 2 79 perturbation of the junction itself. Therefore, several spectroscopic methods based on photon in/photon out or photon in/electron out approaches have been applied to investigate solid/liquid interfaces. Among them, synchrotron-based techniques such as surface X-ray diffraction, X-ray absorption/emission and photoelectron spectroscopy, and "laboratory-based" techniques, such as infrared, Raman and non-linear optical spectroscopies have been recently developed [10].In this context, X-ray photoelectron spectroscopy (XPS) stands as an excellent characterization tool, since it offers elemental and chemical sensitivity, simultaneously measuring local built-in electrical potentials via the detection of rigid photoelectron kinetic energy shifts in both core and valence levels [11][12][13][14][15][16][17]. Due to the high vapor pressure of many liquids of interest, differential pumping schemes have to be used in photoelectron analyzers to minimize the elastic and inelastic scattering of electrons in the gas phase above the liquid side of the junction [18][19][20]. In addition, small sample-to-analyzer aperture working distances (WDs) must be used, for the same purpose [18][19][20]. A reasonable trade-off needs to be found between limiting the electron scattering by the gas phase molecules and keeping the pressure at the sample surface above 90-95% of the nominal pressure in the chamber. Usual WDs (at which the analyzer focus is optimized) are about the diameter of the aperture itself [18][19][20]. Modern state-of-the-art electron analyzers are capable to operate at pressures of and above 30 mbar (the vapor tension of water at room temperature) and at high photoelectron kinetic energies (KEs, up to 12 keV) [11]. The extension of AP-XPS to high photon energies (i.e., high photoelectron KEs) has two main advantages: the reduced photoelectrons/gas molecules scattering provides higher signal intensity at...

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Recent applications of hard x-ray photoelectron spectroscopy

Cited by 43 publications

References 155 publications

Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

Understanding the Oxygen Evolution Reaction Mechanism on CoO_x using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy

Interface Science Using Ambient Pressure Hard X-ray Photoelectron Spectroscopy

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Recent applications of hard x-ray photoelectron spectroscopy

Cited by 43 publications

References 155 publications

Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

Unravelling the electrochemical double layer by direct probing of the solid/liquid interface

Understanding the Oxygen Evolution Reaction Mechanism on CoOx using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy

Interface Science Using Ambient Pressure Hard X-ray Photoelectron Spectroscopy

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Understanding the Oxygen Evolution Reaction Mechanism on CoO_x using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy