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The development of noble-metal-free electrocatalysts with high electrocatalytic performance and stability by adopting a scalable route is key to solving the energy crisis. We report a P Ni co-doped Mo 2 C-based electrocatalyst with high hydrogen evolution reaction (HER) catalytic activity prepared by a molten-salt method. Using phosphating times of 2 h and 4 h yielded P-Ni-Mo 2 C-2h and P-Ni-Mo 2 C-4h, respectively, both of which exhibited nanoflower-like structures that provided abundant active sites for the reaction. P-Ni-Mo 2 C-2h possessed good electrocatalytic properties with a low overpotential of only 140.5 mV at j = 10 mA cm−2 and a small Tafel slope of 50.7 mV dec−1 in an alkaline environment. P-Ni-Mo 2 C-2h exhibited excellent stability after 20 h of continuous hydrogen production. The use of an excessively long phosphating time caused a narrow down of spaces formed by nanoflakes, thereby reducing the HER performance of the electrocatalyst. The results of this study provide guidelines for the preparation of high-efficiency P Ni co-doped electrocatalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

In the paper, we prepared a hydrogenated nanocrystalline diamond (NCD-H) film by the chemical vapor deposition (CVD) method. A variable degree of NCD-H surface destruction and surface graphitization was achieved by Ar ion bombardment using monoatomic beam (Ar+) and cluster ion beam (ArCIB). Bombardment with ArCIB manifests itself by the formation of a very thin altered layer on the surface of NCD-H accompanied by no Ar atoms embedded in the surface region. In contrast, bombardment with Ar+ beam leads to the creation of thicker, homogeneous altered layer characterized by dominating C sp2 hybridization, by the embedded Ar atoms, and by the reduced dimensions of diamond grains located near the surface of the samples. A combination of multiple microscopy and spectroscopy methods enabled us to evaluate the contribution of the C-H x bonds to the asymmetry of the C 1s core level line shape and to measure the H concentration on the surface. The limitation of Auger spectroscopy (D-parameter) analysis for the sp2/sp3 phase concentration measurement on rough, NCD-H surface is demonstrated. The controllable amorphization or graphitization of diamond surface can further extend its functionality in detectors, electrochemical sensing or supercapacitor uses. [Display omitted] • Hydrogen-terminated nanocrystalline diamond (NCD-H) surfaces were bombarded by the monoatomic Ar+ ions and the Ar ion clusters. • The NCD-H surfaces were studied using several microscopy and spectroscopy methods: ARXPS, AES, Raman spectroscopy, REELS, EPES, SEM. • The Ar+ ion beam increased the sp2 content, decreased the grain size and led to Ar implantation into the sub-surface of the diamond. Ar clusters had minimal affect on the sp2 content and showed unchanged grains size and Ar-free diamond surface. • Hydrogen concentration was quantified and lower values were found for the diamond surface bombarded with Ar+ ions. • Ar+ ions reduced the mass density from diamond to amorphous carbon films. [ABSTRACT FROM AUTHOR]

Abstract: Detonation nanodiamond (DND) is an attractive class of diamond material, which has a great potential to be used for a wide range of applications. In this paper, untreated DND was employed to perform hydrogen passivation process using microwave plasma enhanced chemical vapor deposition in order to investigate the influence of hydrogen-terminated surface on the DND''s electrical properties. Impedance spectroscopy (IS) has been used to characterize the electrical properties of DND samples using a newly-developed measurement set-up. It is found that hydrogen-passivation process has increased the electrical conductivity of the DND by up to four orders of magnitude when compared with the untreated sample. An RC parallel equivalent circuit with a Warburg element has been proposed to model the DND''s impedance characteristics. [Copyright &y& Elsevier]

Abstract: Hydrogen-free and predominantly tetrahedrally bonded amorphous carbon thin films (ta-C) are excellent coatings to protect surfaces from wear due to their low coefficient of friction and high hardness. Since these coatings may be several times harder than common engineering materials counterpart wear can be significant. Therefore the surface texture of the ta-C coating is critical to wear applications. While the surface roughness is an important factor, the paper shows that other surface texture parameters have to be considered as well to predict the wear performance of the coating. Wear data are compared of as deposited, polished and brushed ta-C coatings. The results show that typically referenced average values for the surface roughness such as R a and R z may prove insufficient to reliably predict the wear behavior of the coating. Additional parameters describing the surface texture such as the “Skewness” (R sk) and “Kurtosis” (R ku) can provide relevant information. For example, a brushed ta-C surface with an average roughness of R a =31nm showed a tenfold improved wear performance over a polished ta-C surface with an average roughness of R a =10nm. This phenomenon is explained by analyzing the R sk and R ku data, which prove to more closely capture the post-treatment specific changes to the surface texture of the coatings. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the study of electrochemical preconditioning on moderately boron doped diamond electrodes. Samples were submitted to an isothermal annealing at 1100 °C in order to outgas the hydrogen introduced into the layer during the deposition process. Consequences of anodic and cathodic galvanostatic steps (1 C cm−2), in H2SO4 0.5 M, have been studied on both as-deposited samples and annealed ones, by capacitance measurements, cyclic voltammetry in presence of Ce4+/3+ redox system and XPS measurements. The results of Mott–Schottky plots and current voltage curves show that the electrochemical responses of BDD electrodes are strongly influence by annealing. After preconditioning, an enhancement of charge transfer is observed for as-deposited samples, while a more and more passivated behavior is recorded for annealed electrodes. On as-deposited samples a “new” superficial conductive layer linked to the creation of surface defects high above the valence band, is suggested after a specific electrochemical treatment which is not possible on annealed ones. [Copyright &y& Elsevier]

Abstract: This paper reports on green chemical functionalization of hydrogen-terminated boron-doped diamond (BDD) surfaces with aryldiazonium salts in the presence of ionic liquids. The reaction takes place at room temperature in air without any external bias in either hydrophobic (1-butyl-3-methylimidazolium hexafluorophosphate) or hydrophilic (1-butyl-3-methylimidazolium methyl sulfate) ionic liquids. The resulting surfaces were characterized using X-ray photoelectron spectroscopy and electrochemical measurements. [Copyright &y& Elsevier]

Abstract: Recently, many studies have been reported about a variety of carbon materials in adsorbing hydrogen. Regarding that, hydrogen adsorption in different carbonaceous materials was investigated at room temperature, 298 K and three different pressures which were 6.5, 8.5 and 9.5 bar. Pressure drop of hydrogen was measured and the amount it adsorbed was calculated by using ideal gas law and it was presented in weight percent, wt.%. In this paper, the effect of a purification process on hydrogen adsorption was also discussed. Along with that, pretreatment also gave a major influence in hydrogen adsorption because it affected the adsorption behavior of the carbon nanotubes surfaces. The highest result obtained during this work was 0.195 wt.% for purified carbon nanotubes. [Copyright &y& Elsevier]

Abstract: This paper is concerned with the study of the influence of electrochemical pre-treatments on the behavior of highly boron doped diamond electrodes. Anodic and cathodic preconditioning, performed during 10 s either with 10−4 A/cm−2 (10−3 C cm−2) or 10−1 A/cm−2 (1 C cm−2), has been studied. Cyclic voltammetry at as-deposited, anodically and cathodically treated electrodes, in presence of 2 redox couples serving as electrochemical probes is analyzed in the light of the surface characterization given by XPS chemical analysis. Ce4+/3+ redox couple in 0.5 M H2SO4 medium and Fe(CN)6 3−/4− redox couple in 0.1 M KOH medium, have been studied before and after the different treatments. The results of Mott–Schottky plots and current voltage curves are reported and show that the electrochemical response of BDD electrodes is very dependent on the current density involved in the electrochemical preconditioning. The modification of surface bond termination – either hydrogen or oxygen – studied by XPS analyses is also strongly dependent on electrochemical pre-treatment. In particular, it is evidenced that the most important conversion of surface functionalities from hydrogen to oxygen is obtained when the anodic treatment is performed with the smallest current density. Finally, a correlation between surface terminations and charge transfer is evidenced. [Copyright &y& Elsevier]

Abstract: Intrinsic CVD diamond is well known as insulator, however if the surface is hydrogen terminated, a surface conduction can be detected if exposed to air and covered by an adsorbate layer. In this paper we show that hydrogen terminated intrinsic single crystalline CVD diamond undergoes an insulator metal transition if immersed into redox electrolyte solutions with chemical potentials below the valence-band maximum. We have applied cyclic voltammetry experiments using different redox couples to characterize this phenomenon. The experiments reveal a large chemical window (>4.6 V) of undoped diamond. We detect the same formal potentials as reported in the literature for H-terminated boron doped polycrystalline diamond. The peaks show comparable symmetries but are shifted towards higher and lower potentials, and are significantly broadened. We attribute this to the rate limited electron transfer at the interface. The results are discussed based on the transfer doping model. [Copyright &y& Elsevier]

Abstract: Most studies on the electrochemistry of boron doped diamond electrodes deal with highly doped materials which generally act as semi-metallic electrodes. This paper is concerned with the study of the electrochemical behavior of moderately boron doped diamond. The behavior of as-deposited, annealed, and oxidized electrodes in a 2 M H2SO4 medium containing the Ce4+/Ce3+ redox couple as an electrochemical probe is analyzed in the light of the material surface characterization given by XPS analysis. The results of Mott–Schottky plots and cyclic voltammetry are reported and show that the electrochemical response of these moderately doped electrodes is characteristic of semiconductors. The p+-type conductivity of the surface hydrogenated layer present on as-deposited samples and the influence of surface bond termination—either hydrogen or oxygen—on charge transfer are evidenced. [Copyright &y& Elsevier]

Abstract: The elements of nitrogen and hydrogen are the main impurities in natural and synthetic diamond and can significantly affect the physical properties of diamond. In this paper, the effects of nitrogen and hydrogen, which came from decomposition of melamine (C3N6H6) at 5.3 GPa and 1500 K for 15 min, on diamond synthesized with powder catalysts by high pressure and high temperature (HPHT) were investigated. Our results indicated that the nucleation of diamond was disturbed and the graphite/diamond conversion could be completely prevented by high concentrations of nitrogen and hydrogen. These results could be explained by changes in characteristics of catalysts due to different chemical reactions between the elements in Ni–Mn–Co catalyst and nitrogen and hydrogen. [Copyright &y& Elsevier]

Hydrogen-terminated diamond films are capable of displaying p-type character in the near-surface region. This effect can be used to fabricate surface unipolar electronic devices such as diodes and field effect transistors. However, the presence of contaminants within the diamond surface can reduce the carrier concentration and mobility values achieved within this layer to the point where devices can no longer be made. This paper reports on the formation of thin over-layers on relatively inexpensive contaminated ‘black’ polycrystalline diamond grown by hot-filament chemical vapour deposition. It has been found that such a layer is sufficient to enable sheet carrier concentrations approaching 1014 cm−2 to be generated, with mobility values greater than 20 cm2 V−1 s−1, comparable with values obtained on high-quality single crystals at these carrier concentrations. Effective Schottky diodes have been produced. [Copyright &y& Elsevier]

This study covers hydrogen-rich fancy color diamonds that exhibit complex spectra from the UV all the way to the mid-IR. The diamonds with such spectra that are included here show a large range of colors from brownish yellow to brown, yellow-green to olive and gray to violet. The color origin of such diamonds has always been stated as "hydrogen-related", without much evidence pointing towards hydrogen actually causing absorptions in the visible spectral range, but only based on their unusually high IR active hydrogen content determined via their FTIR spectra. The diamonds analyzed during this work always showed a series of absorptions in the near-infrared at 7495, 7850, 8255, and 8615 cm−1. For the first time, this here presented study shows the results of low temperature near-infrared spectroscopy performed for a series of differently colored diamonds that all showed these NIR absorptions. When measured at 77 K, it became clear that these NIR bands are actually part of an electronic optical center with ZPLs at 1329.8 to 1330.2 nm (7520–7518 cm−1)/1331.8 to 1332.2 nm (7508–7506 cm−1) and 1341 to 1341.2 nm (7457–7456 cm−1). In this paper we will refer to this defect as the "1330 nm center" (which corresponds to 7519 cm−1) for the sake of brevity. The detailed analysis of the spectra has demonstrated that the colors of diamonds that exhibit the 1330 nm center spectra are caused partially by this same center, and by complex absorption bands associated to two series of ZPLs represented by a number of sharp bands between 965 and 1001 nm, referred to as the 990 nm series in this study. Of these, the 990 nm series was found only in diamonds with significant IR active hydrogen concentrations, while the 1330 nm center was determined to be independent from the concentration of IR active hydrogen. The 1330 nm center was found in spectra lacking the 990 nm series of ZPLs, but the 990 nm series has never been found in spectra without the 1330 nm center. We are suggesting that the defects involved in these absorptions are all nickel‑nitrogen-related, with the 1330 nm center lacking hydrogen while it seems reasonable to assume that the 990 nm series includes hydrogen in its structure. Unlabelled Image • This is the first time the low temperature spectrum of the 1330 nm defect with all its components is presented. • The spectra of low H 1330 nm center diamonds can exclusively show the 1330 nm center absorptions in the 1340 to 650 nm range. • The 828/836/843 nm absorptions are proposed to be the ZPLs of transitions to a higher excited state of the 1330 nm center. • H-rich 1330 nm diamonds exhibit ZPLs named the "990 nm series" which correlate with most of the broad bands in their spectra. • Nickel and nitrogen are proposed to be involved in the 1330 nm center and - possibly with hydrogen - in the 990 nm series. [ABSTRACT FROM AUTHOR]