Highlights

Electrodeposition and pyrolysis of Mn/polypyrrole nanocomposites: a study based on soft X ray absorption, fluorescence and photoelectron microspectroscopies

Electrodeposition of manganese/polypyrrole (Mn/PPy) nanocomposites has been recently shown to be a technologically relevant synthesis method for the fabrication of Oxygen Reduction Reaction (ORR) electrocatalysts. In this study …
Bozzini et al., J. Mater. Chem. A (2015).

… such composites have been grown with a potentiostatic anodic/cathodic pulse-plating procedure and characterized by a multi-technique approach, combining a suite of in situ and ex situ spectroscopic methods with electrochemical measurements, in view of improving their electrocatalytic ORR activity and durability. In particular the pyrolysis process has been monitored in situ by micro-XPS: Mn, initially present in a core–shell structure with a metallic core and a Mn(II, III) shell, tends to oxidise achieving a final composition in which Mn(III) and Mn(IV) dominate; the partial decomposition of Mn/PPy results in a rearrangement of the chemical structure of PPy with the formation of novel Me–N bonds

and graphitic-N functionalities, that can be regarded as the active sites of this class of electrocatalysts. In terms of the same electrocatalytic figures of merit, our electrocatalyst outperforms MnOx supported on a range of carbons, such as C- powders, vulcan, and nanocarbon.

Retrieve article
Electrodeposition and pyrolysis of Mn/polypyrrole nanocomposites: a study based on soft X ray absorption, fluorescence and photoelectron microspectroscopies. Bozzini B, Bocchetta P, Aleman B, Amati M, Gianoncelli A, Gregoratti L, Sezen H, Taurino A, Kiskinova M J. Mater. Chem. A (2015)


 


Spatially resolved chemical characterization with scanning photoemission spectromicroscopy: towards near ambient pressure experiments

The first measurements of core level photoemission spectroscopy and imaging obtained with spatial resolution of the order of 100 nm at near ambient pressure have been achieved at the SPEM of Elettra.
Sezen H et al., ChemCatChem (2015).


The unique combination of surface and chemical sensitivity has ranked X-ray photoelectron spectroscopy (XPS) as one of the most important experimental methods for characterization of catalytic systems. The success of the first near ambient pressure SPEM experiments manifests that the developed novel solutions can pave the road to ambient pressure photoelectron spectromicroscopy. In the present review using representative examples we demonstrate the power of chemical surface sensitivity with a submicron spatial resolution to study nanostructured matter and/or processes occurring at surfaces and interfaces at their natural length scales. The reported exemplary results have provided evidence that due to structural differences sub-regions of nanoparticles exert different reactivity

and catalysts supported by nanostructures can be easily characterized. Responding to the increasing demand to use SPEM for in situ and even in operando studies the recently developed DHP and high pressure cell solutions allow the SPEM at Elettra to overcome the pressure constraints and to operate up to mbar range, opening new frontiers for this technique.

Retrieve article
Spatially Resolved Chemical Characterization with Scanning Photoemission Spectromicroscopy: Towards Near-Ambient-Pressure Experiments Sezen H, Alemán B, Amati M, Dalmiglio M, Gregoratti L , ChemCatChem (2015)

 


Tuning electronic properties of carbon nanotubes by nitrogen grafting: Chemistry and chemical stability

The effect of adding nitrogen atoms via plasma treatment on the electronic properties of both v-CNT tips and sidewalls has been investigated by using ultraviolet and X-ray photoemission spectroscopy and spectromicroscopy. Site selective nitrogen grafting near the tips, up to a depth of 4mm, was evaluated, beyond which the properties of the v-CNTs remain unperturbed.
Scardamaglia M, Carbon, Vol. 83, pp. 118-127 (2015).


In this work the effect of the nitrogen doping of carbon nanotubes by means of a post synthesis plasma treatment has been investigated by using advanced photoemission spectromicroscopy. Thanks to the nanoscale spatial resolution achieved by the scanning photoelectron microscope we were able to investigate the side walls of the nitrogen doped nanotubes, where the pyrrolic-N is practically absent, confirming its origin from the intrinsic disorder present at the v-CNT closed tips. We evaluated the nitrogen grafting region which extends in a few mm from the tips, leaving the other whole length of the nanotubes unperturbed. The tuning of the nitrogen bonding configuration by

means of temperature treatments allows a continuous tuning of the density of states at the Fermi level region, which makes this nitrogen doping strategy appealing for field emission applications.

Retrieve article
Tuning electronic properties of carbon nanotubes by nitrogen grafting: Chemistry and chemical stability, Scardamaglia M, Struzzi C, Aparicio Rebollo FJ, De Marco P, Mudimela PR, Colomer J, Amati M, Gregoratti L, Petaccia L, Snyders R, Bittencourt C, Carbon, Vol. 83, pp. 118-127 (2015)

 


Photoelectron spectroscopy of wet and gaseous samples through graphene membranes

This report proposes an alternative ambient pressure approach that can be applied to a broad class of samples and be implemented in conventional PES instruments. It uses ultrathin electron transparent but molecular impermeable membranes to isolate the high pressure sample environment from the high vacuum PES detection system.
Kraus J, Vol. 6 - 23, pp. 14394-14403 (2014).


A novel APPES approach using graphene as an electron-, X-ray-, and optically transparent window separating the UHV analyzer chamber from the sample environment that allows for acquiring photoelectron spectra from fully hydrated interfaces has been developed and tested. Photoelectron spectroscopy (PES) and microscopy are highly important for exploring morphologically and chemically complex liquid–gas, solid–liquid and solid–gas interfaces under realistic conditions, but the very small electron mean free path inside dense media imposes serious experimental challenges. Currently, near ambient pressure PES is conducted using dexterously designed electron energy analyzers coupled with differentially pumped electron lenses which make it possible to conduct PES measurementsat a few hPa. In this work it has

been demonstrated that the separating graphene membrane windows are both mechanically robust and sufficiently transparent for electrons in a wide energy range to allow soft X-ray PES of liquid and gaseous water. The performed proof-of-principle experiments confirm the possibility to probe vacuum-incompatible toxic or reactive samples placed inside such hermetic, gas flow or fluidic environmental cells.

Retrieve article
Photoelectron spectroscopy of wet and gaseous samples through graphene membranes Kraus J, Reichelt R, Gunther S, Gregoratti L, Amati M, Kiskinova M, Yulaev A, Vlassiouk I, Kolmakov A, Vol. 6 - 23, pp. 14394-14403 (2014)

 


Microchemical inhomogeneity in eutectic Pb-Bi alloy

The structure of quenched liquid Pb–Bi eutectic alloy has been studied with photoemission microscopy to investigate transformations occurring to the alloy in the liquid state at different temperature.
Mezzi A et al., Surface and Interface Analysis (2014).


Liquid Pb–Bi eutectic alloy is a good candidate as a coolant and neutron spallation source for the development of new accelerators driven system, one of the possible solutions for the nuclear waste problem, but liquid metal corrosion and embrittlement are the main issue.
The structure of the liquid alloy is not stable but undergoes relevant changes as the temperature increases (elemental clustering). To understand transformations occurring in the liquid state, the alloy has been water quenched from the liquid at different temperature. SPEM results evidenced a structural and microchemical rearrangement of the atoms in the melt consisting in the evolution of cluster size and composition.

The distribution of the two metals is characterized by the following: (i) Pb-enriched clusters, (ii) Bi-enriched clusters and (iii) a matrix in near eutectic composition. The average size of clusters is reduced by increasing temperature: it is in the range of 1 ÷ 3 μm at 313 °C and passes to 0.5 ÷ 0.9 μm at 518 °C.

Retrieve article
Microchemical inhomogeneity in eutectic Pb-Bi alloy quenched from melt, Mezzi A, Kaciulis S, Balijepalli SK, Montanari R, Varone A, Amati M, Aleman B , Surface and Interface Analysis (2014)

 


Graphene oxide windows for in situ environmental cell photoelectron spectroscopy

We develop a simple environmental cell with graphene oxide windows that are transparent to low-energy electrons (down to 400 eV), and demonstrate the feasibility of X-ray photoelectron spectroscopy on samples such aqueous salt solution.
Kolmakov et al., Nature Nanotechnology, 6, 651 (2011).
 


X-ray photoelectron spectroscopy generally require high-vacuum conditions. The state-of-the-art approach to increase the base pressure up to ambient condition relies on unique and expensive apparatus sophisticated differentially pumped electron lenses. We develop a simple environmental cell with graphene oxide windows that are transparent to low-energy electrons and demonstrate the feasibility of XPS measurements on model samples such aqueous salt solution placed on the back side of a window. These proof-of-principle results show the potential of using graphene oxide, graphene and other emerging ultrathin membrane windows.
for the fabrication of low-cost, single-use environmental cells compatible with commercial X-ray and Auger microprobes as well as scanning or transmission electron microscopes.

Retrieve article


Graphene oxide windows for in situ environmental cell photoelectron spectroscopy. A. Kolmakov, D. A. Dikin, L. J. Cote, J. Huang, M. Kazemian Abyaneh, M. Amati, L. Gregoratti, S. Günther & M. Kiskinova. Nature Nanotechnology, Published online (2011)

 


In Situ X-Ray Investigation of the SOFC Stability in Operating Condition

in situ study of electrochemically induced processes occurring in Cr/Ni bilayers in contact with a YSZ electrolyte aims at a molecular-level understanding of the aspects related to the durability of metallic interconnects in solid oxide fuel cells (SOFCs).
Bozzini et al., ChemSusChem 4, 8, 1099 (2011).


The present in situ study of electrochemically induced processes occurring in Cr/Ni bilayers in contact with a YSZ electrolyte aims at a molecular-level understanding of the fundamental aspects related to the durability of metallic interconnects in solid oxide fuel cells (SOFCs). The results demonstrate the potential of scanning photoelectron microspectroscopy and imaging to follow in situ the evolution of the chemical states and lateral distributions of the constituent elements (Ni, Cr, Zr, and Y) as a function of applied cathodic potential in a cell working at 650 °C in 10−6 mbar O2 ambient conditions. 

The most interesting findings are the temperature-induced and potential-dependent diffusion of Ni and Cr, and the oxidation–reduction processes resulting in specific morphology–composition changes in the Ni, Cr, and YSZ areas..

Retrieve article
In  Situ X-Ray Spectromicroscopy Investigation of the Material Stability of SOFC Metal Interconnects in Operating Electrochemical Cells. B. Bozzini, E. Tondo, M Prasciolu, M. Amati, M. Kazemian Abyaneh, L. Gregoratti, and M. Kiskinova. ChemSusChem 4, 8, 1099-1103 (2011).


Imaging and Spectroscopy of Multiwalled Carbon Nanotubes during Oxidation: Defects and Oxygen Bonding

The gasification process, which increases the number of broken C = C bonds and the abundance of particular oxygenated functional groups, is shown to destroy carbon nanotubes (CNTs). The expansion of the defect density and dimensions leads to nonlinear consumption of the CNTs with increasing O dose.
A. Barinov et al., Adv. Mater. 21, 1916 (2010).


 The interaction with atomic oxygen converts the initially metallic CNTs into semiconducting, and that depending on the oxygen dose and reaction temperature the type and abundance of oxygenated functional groups formed changes significantly, including gasification and consumption of the CNTs at elevated temperatures. The most important finding is that the type and abundance of the groups formed and the gasification rate are strongly influenced by the density and size of vacancy defects in the graphene layers of the carbon nanotube. On one hand, this introduces uncertainties when analogous procedures are employed for

functionalization of CNTs with undefined density and types of defects, but on the other hand it prompts an approach for tailoring CNTs via controlled introduction of defects, which can favor the formation of a preferred functional group.

Retrieve article
Imaging and Spectroscopy of Multiwalled Carbon Nanotubes during Oxidation: Defects and Oxygen Bonding A. Barinov, L. Gregoratti, P. Dudin, S. La Rosa, and M. Kiskinova Adv. Mater. 2009, 21, 1916–1920.

 

Ultima modifica il Giovedì, 07 Ottobre 2021 18:34