Establishing new reactivity map descriptor of TOF–SD for PGM-free Fe–N–C catalysts ORR activity.

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The pivotal importance of TiO2 as a technological material involves most applications in an aqueous environment, but the single‐crystal TiO2/bulk‐water interfaces are almost completely unexplored, since up to date solid/liquid interfaces are more difficult to access than surfaces in ultrahigh vacuum (UHV). Only a few techniques (as scanning probe microscopy) offer the opportunity to explore these systems under realistic conditions. The rutile TiO2(110) surface immersed in high‐purity water is studied by in situ scanning tunneling microscopy. The large‐scale surface morphology as obtained after preparation under UHV conditions remains unchanged upon prolonged exposure to bulk water. Moreover, in contrast to UHV, atomically resolved images show a twofold periodicity along the [001] direction, indicative of an ordered structure resulting from the hydration layer. This is consistent with density‐functional theory based molecular dynamics simulations where neighboring interfacial molecules of the first water layer in contact with the bulk liquid form dimers. By contrast, this dimerization is not observed for a single adsorbed water monolayer, i.e., in the absence of bulk water.

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The hydrogen evolution reaction (HER) is a fundamental process that impacts several important clean energy technologies. Great efforts have been taken to identify alternative materials that could replace Pt for this reaction or that may present additional functional properties such as optical activity and advanced electronic properties. Herein, a comparative study of the HER activity for ultrathin films of MoTe2, MoSe2, and their solid solutions on highly oriented pyrolytic graphite is reported. Combining advanced characterization techniques and density functional theory calculations with electrochemical measurements, it is shown that the chemical activity of the scarcely reactive 2H phases can be boosted by the presence of metallic twin boundaries. These defects, which are thermodynamically stable and naturally present in Mo‐enriched MoTe2 and MoSe2, endow the basal plane of the 2H phase with a high chemical activity, which is comparable to the metastable 1T polymorph.

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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.