Photoelectron Spectroscopy at the Graphene–Liquid Interface Reveals the Electronic Structure of an Electrodeposited Cobalt/Graphene Electrocatalyst

Velasco-Vélez, Juan-Jesús; Pfeifer, Verena; Hävecker, Michael; Weatherup, Robert S.; Arrigo, Rosa; Chuang, Cheng‐Hao; Stotz, Eugen; Weinberg, Gisela; Salmerón, Miquel; Schlögl, Robert; Knop‐Gericke, Axel

doi:10.1002/anie.201506044

Cited by 147 publications

(130 citation statements)

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“…Photoelectron spectroscopy can be conducted from the solid side of the solid/liquid interface using few layer graphene membranes supporting the solid phase [30,31]. Although this technique is appealing for the fact that gases or liquids can be flown through the system thereby providing facile mass transport, it limits the investigation to thin solid films since the photo-emitted electrons must travel through the solid phase/graphene membrane to reach the photoelectron analyzer.…”

Section: The Challenge Of Preparing a Realistic Solid/liquid Interfacementioning

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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Section: The Challenge Of Preparing a Realistic Solid/liquid Interfacementioning

confidence: 99%

Interface Science Using Ambient Pressure Hard X-ray Photoelectron Spectroscopy

et al. 2019

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“…the solid or the liquid side [23,30,31]. Using supported membranes, such as graphene on a silicon nitride grid, or coated membranes, where the total thickness of the solid material is less than two to three times the mean free path of electrons, photoemission experiments can be conducted from the solid side of the solid/liquid interface (see Figure 2A) [30,31]. When combined with a flow cell, this approach has the advantage that the liquid electrolyte can flow through the system thereby providing facile mass transport in the liquid electrolyte.…”

Section: General Aspects Of Studying Semiconductor/aqueous Electrolytmentioning

confidence: 99%

Combined soft and hard X-ray ambient pressure photoelectron spectroscopy studies of semiconductor/electrolyte interfaces

Starr

Favaro

Abdi

et al. 2017

Journal of Electron Spectroscopy and Related Phenomena

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The development of solar fuel generating materials would greatly benefit from a molecular level understanding of the semiconductor/electrolyte interface and changes in the interface induced by an applied potential and illumination by solar light. Ambient pressure photoelectron spectroscopy techniques with both soft and hard X-rays, AP-XPS and AP-HAXPES respectively, have the potential to markedly contribute to this understanding. In this paper we initially provide two examples of current challenges in solar fuels material development that AP-XPS and AP-HAXPES can directly address. This will be followed by a brief description of the distinguishing and complementary characteristics of soft and hard X-ray AP-XPS and AP-HAXPES and best approaches to achieving monolayer sensitivity in solid/aqueous electrolyte studies. In particular we focus on the detection of adsorbed hydroxyl groups in the presence of aqueous hydroxyls in the electrolyte, a common situation when investigating photoanodes for solar fuel generating applications. The paper concludes by providing an example of a combined AP-XPS and AP-HAXPES study of a semiconductor/aqueous electrolyte interface currently used in water splitting devices specifically the BiVO 4 /aqueous potassium phosphate electrolyte interface.2

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“…However, EY has been recently realized in liquid cell studies, thanks to the newly developed graphene membranes. 13 Another recently developed detection method in liquid cells is to measure the electric current induced by X-ray excitation. This electric-current detection which was categorized as total electron yield (TEY) [9][10][11] is further explored and discussed in detail in this study.…”

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confidence: 99%

Introducing Ionic-Current Detection for X-ray Absorption Spectroscopy in Liquid Cells

Schön

Xiao

Golnak

et al. 2017

J. Phys. Chem. Lett.

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Photons and electrons are two common relaxation products upon X-ray absorption, enabling fluorescence yield and electron yield detections for X-ray absorption spectroscopy (XAS).The ions that are created during the electron yield process are relaxation products too, which are exploited in this study to produce ion yield for XA detection. The ionic currents measured in a liquid cell filled with water or iron(III) nitrate aqueous solutions exhibit characteristic O K-edge and Fe L-edge absorption profiles as a function of excitation energy. Application of two electrodes installed in the cell is crucial for obtaining the XA spectra of the liquids behind membranes. Using a single electrode can only probe the species adsorbed on the membrane surface. The ionic-current detection, termed as total ion yield (TIY) in this study, also produces an undistorted Fe L-edge XA spectrum, indicating its promising role as a novel detection method for XAS studies in liquid cells.Key words: total ion yield (TIY), ionic current, liquid flow-cell, total electron yield (TEY), X-ray absorption spectroscopy (XAS) TOC GraphicPage 2 of 17 ACS Paragon Plus EnvironmentThe Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 Studying the electronic structure of liquid water and aqueous solutions by soft X-rays has attracted much attention in recent years, 1-6 and continues to be a vital research field. Resonant excitation by X-rays is highly element-specific, which makes X-ray absorption spectroscopy (XAS) a widely used tool in many scientific disciplines. Due to the vacuum requirement for soft X-ray propagation, detection of XA spectra for liquid (volatile) samples in vacuum is very challenging. One of the most applied techniques to introduce liquid samples into a vacuum chamber is a liquid flow-cell with an ultra-thin membrane separating the liquid from the vacuum. 7,8 When equipped with multiple electrodes, such a liquid cell can act as a standard electrochemical cell. It is therefore of great interest to combine XAS and the liquid cell technique for in situ/operando investigations on liquid-based materials. [9][10][11][12] When a sample's thickness exceeds the penetration depth of soft X-rays, which is the case for the liquid cell adopted in this study, detection of XA spectra in the transmission mode is not applicable. Therefore, fluorescence yield (FY) or electron yield (EY) must be employed to acquire XA spectra. Due to the significant thickness of typical membranes, e.g. Si 3 N 4 and SiC membranes (~ 100 nm), the electrons created within liquid solutions cannot penetrate the membrane and escape into vacuum. The FY was thus considered the only feasible way to probe the liquid-phase species behind membranes. However, EY has been recently realized in liquid cell studies, thanks to the newly developed graphene membra...

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Photoelectron Spectroscopy at the Graphene–Liquid Interface Reveals the Electronic Structure of an Electrodeposited Cobalt/Graphene Electrocatalyst

Cited by 147 publications

References 54 publications

Interface Science Using Ambient Pressure Hard X-ray Photoelectron Spectroscopy

Interface Science Using Ambient Pressure Hard X-ray Photoelectron Spectroscopy

Combined soft and hard X-ray ambient pressure photoelectron spectroscopy studies of semiconductor/electrolyte interfaces

Introducing Ionic-Current Detection for X-ray Absorption Spectroscopy in Liquid Cells

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