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Surfaces
Volume 2
Issue 4
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Surfaces, Volume 2, Issue 4 (December 2019) – 3 articles

Cover Story (view full-size image): One of the most pressing needs of the emerging hydrogen economy is the development of sustainable catalysts for the electrochemical production of hydrogen from water. Transition metal chalcogenides, given their large availability and low cost, represent an excellent choice; however, their catalytic performance is still inadequate for practical devices. Here, we demonstrate that nickel can be used to boost the catalytic activity of MoS2 both in alkaline and acid media. By combining different characterization techniques to the study of the electrochemical performances, we deduced that NiSx species help the hydrogen evolution in alkaline conditions by facilitating water dissociation, whereas in acid conditions, nickel dopants (Ni–Mo–S) improve catalytic activity through a combination of structural and electronic effects. View this paper.
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14 pages, 4357 KiB  
Article
UV Light Driven Selective Oxidation of Cyclohexane in Gaseous Phase Using Mo-Functionalized Zeolites
by Vincenzo Vaiano and Diana Sannino
Surfaces 2019, 2(4), 546-559; https://doi.org/10.3390/surfaces2040040 - 9 Dec 2019
Cited by 2 | Viewed by 2584
Abstract
Heterogeneous photocatalysis in the gas phase has been applied as a promising technique for organic syntheses in mild conditions. Modified zeolites have been used under UV irradiation as novel photocatalysts. In this study, we preliminarily investigated the photoxidation of cyclohexane on ferrierite and [...] Read more.
Heterogeneous photocatalysis in the gas phase has been applied as a promising technique for organic syntheses in mild conditions. Modified zeolites have been used under UV irradiation as novel photocatalysts. In this study, we preliminarily investigated the photoxidation of cyclohexane on ferrierite and MoOx-functionalized ferrierite in a gas–solid continuous flow reactor. In the presence of UV light, MoOx-functionalized ferrierite showed the formation of benzene and cyclohexene as reaction products, indicating the occurrence of photocatalysed cyclohexane oxydehydrogenation. By contrast, unmodified ammonium ferrierite exhibited relevant activity for total oxidation of cyclohexane to carbon dioxide and water. The influence of Mo loading on cyclohexane conversion and products selectivity was evaluated. Full article
(This article belongs to the Special Issue Surface Aspects of Semiconductor Photochemistry)
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15 pages, 3534 KiB  
Article
Effect of Ni Doping on the MoS2 Structure and Its Hydrogen Evolution Activity in Acid and Alkaline Electrolytes
by Dario Mosconi, Paul Till, Laura Calvillo, Tomasz Kosmala, Denis Garoli, Doriana Debellis, Alessandro Martucci, Stefano Agnoli and Gaetano Granozzi
Surfaces 2019, 2(4), 531-545; https://doi.org/10.3390/surfaces2040039 - 3 Dec 2019
Cited by 34 | Viewed by 4995
Abstract
We have investigated three-dimensional (3D) MoS2 nanoarchitectures doped with different amount of Ni to boost the hydrogen evolution reaction (HER) in alkaline environment, where this reaction is normally hindered. As a comparison, the activity in acidic media was also investigated to determine [...] Read more.
We have investigated three-dimensional (3D) MoS2 nanoarchitectures doped with different amount of Ni to boost the hydrogen evolution reaction (HER) in alkaline environment, where this reaction is normally hindered. As a comparison, the activity in acidic media was also investigated to determine and compare the role of the Ni sites in both media. The doping of MoS2, especially at high loadings, can modify its structural and/or electronic properties, which can also affect the HER activity. The structural and electronic properties of the Ni doped 3D-MoS2 nanoarchitecture were studied by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electronic microscopy (SEM; TEM), and X-ray photoemission Spectroscopy (XPS). XPS also allowed us to determine the Ni-based species formed as a function of the dopant loading. The HER activity of the materials was investigated by linear sweep voltammetry (LSV) in 0.5 M H2SO4 and 1.0 M KOH. By combining the physicochemical and electrochemical results, we concluded that the Ni sites have a different role in the HER mechanism and kinetics in acidic and in alkaline media. Thus, NiSx species are essential to promote HER in alkaline medium, whereas the Ni-Mo-S ones enhance the HER in acid medium. Full article
(This article belongs to the Special Issue Surface Science and Catalysis of Graphene-Related 2D Materials)
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11 pages, 3028 KiB  
Article
A Comparative Study of the Electro-Assisted Grafting of Mono- and Bi-Phosphonic Acids on Nitinol
by Bastien Arrotin, Corentin Libioulle, Tatiana Issakova, Laetitia Mespouille, Philippe Dubois, Joseph Delhalle and Zineb Mekhalif
Surfaces 2019, 2(4), 520-530; https://doi.org/10.3390/surfaces2040038 - 29 Sep 2019
Viewed by 2900
Abstract
Over the last few years, Nitinol (NiTi) has become one of the most attractive alloy materials for industrial applications. However, its implementation is still problematic due to its surface nickel content, making it sensitive to pitting corrosion. In applications, it is often necessary [...] Read more.
Over the last few years, Nitinol (NiTi) has become one of the most attractive alloy materials for industrial applications. However, its implementation is still problematic due to its surface nickel content, making it sensitive to pitting corrosion. In applications, it is often necessary to modify NiTi surfaces by using organic coatings, which provides new physico-chemical properties as well as functionalities and often contributes to a reinforcement of the alloy corrosion resistance. In this work, we assess the differences between the molecular layers made out of methylphosphonic acid (C1P) and the bi-phosphonic acid derivatives: (methylimino)dimethylene-bisphophonic acid (MIP2) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEP2) using conventional (CG) and electro-assisted (EG) graftings. The surface modifications with the bi-phosphonic derivatives (MIP2) and (HEP2) carried out with the EG process lead to denser layers and a reinforced NiTi corrosion resistance. Full article
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