RESUMEN
A new catalyst, prepared by a simple physical mixing of ruthenium (Ru) and tungsten (W) powders, has been discovered to interact synergistically to enhance the electrochemical hydrogen evolution reaction (HER). In an aqueous 0.5 M H2SO4 electrolyte, this catalyst, which contained a miniscule loading of 2-5 nm sized Ru nanoparticles (5.6 µg Ru per cm2 of geometric surface area of the working electrode), required an overpotential of only 85 mV to drive 10 mA/cm2 of H2 evolution. Interestingly, our catalyst also exhibited good immunity against deactivation during HER from ionic contaminants, such as Cu2+ (over 24 h). We unravel the mechanism of synergy between W and Ru for catalyzing H2 evolution using Cu underpotential deposition, photoelectron spectroscopy, and density functional theory (DFT) calculations. We found a decrease in the d-band and an increase in the electron work function of Ru in the mixed composite, which made it bind to H more weakly (more Pt-like). The H-adsorption energy on Ru deposited on W was found, by DFT, to be very close to that of Pt(111), explaining the improved HER activity.
RESUMEN
An investigation of the catalysis of the electrochemical hydrogen evolution reaction (HER, 2H+ + 2e- â H2) in aqueous 0.5 M H2SO4 electrolyte using composites consisting of gold nanoparticles (AuNP), carbon (Black Pearl 2000) and group 4, 5, and 6 metals is presented. This study is a continuation of our earlier work (Phys. Chem. Chem. Phys., 2016, 18, 21548-21553) on molybdenum and AuNP, which we found to interact synergistically to enhance the HER. We demonstrate here that tungsten not only also showed synergy with AuNP, but the extent of synergy is even larger than that of the Mo-AuNP composite. The average overpotential needed by the tungsten-based composite catalyst to drive a H2 current density (jH2) of 10 mA cm-2 was 300 mV. In contrast, other metals such as Ti, Zr, V, Nb and Ta did not have any observable synergy with AuNP. Our experimental results indicate that the absence of synergy with these non-performing composites could be related to the absorption of hydrogen into the bulk lattice of the metals to give hydrides. The strong binding of H to these metals could have also prevented their further reaction. We also propose that the aforementioned metal hydrides suppressed HER because they are ineffective for the initial proton discharge step.
RESUMEN
Molybdenum nitride has been recently reported to interact synergistically with gold to show an enhanced activity for the electrochemical hydrogen evolution reaction (2H(+) + 2e(-)â H2, HER). In this work, we elucidated the roles of nitrogen, carbon, molybdenum and gold on this observed phenomenon. Composites of Mo-based compounds, carbon black (black pearl 2000) and/or Au nanoparticles (AuNP) were prepared, and their activities for the HER in a 0.5 M H2SO4 electrolyte were measured using linear sweep voltammetry. We show and discuss here for the first time that, while the presence of carbon is necessary for the synergy phenomenon, the nitrogen atoms present in the compounds play no apparent role in this synergy. In fact, all the compounds containing Mo, namely Mo2N, MoB and metallic Mo(0), exhibited extensive synergy with Au for the HER. A hypothesis for the enhanced catalysis of H2 evolution by the mixed metal composites is proposed and discussed.
RESUMEN
A method for the extraction and analysis of ink samples was developed using microscopy with direct analyte probe nanoextraction coupled to nanospray ionization mass spectrometry (DAPNe-NSI-MS) for localized chemical analysis of document inks. Nanomanipulation can be effectively coupled to nanospray ionization mass spectrometry providing picomolar sensitivity, and the capability to analyze ultra-trace amounts of material and reduce the required sample volume to as low as 300 nL. This new and innovative technique does not leave destructive footprints on the surface of a document. To demonstrate the breadth of this technique, analysis of inks from various eras were tested, iron gall ink and modern inks, as well as the capability to detect the oxidative products of polyethylene glycol (PEG), a common binding agent. The experimental results showed that DAPNe-NSI-MS was able to chelate iron(II) and manganese(II) ions of iron gall ink and organic components of modern and carbon-based inks. Regardless of whether the ink composition is modern or ancient, organic or inorganic, this new instrumental approach is able to identify and characterize the ingredients by modifying the extraction solvent, illustrating the potential diversity of the DAPNe technique.
RESUMEN
RATIONALE: While electrospray ionization is a popular technique for mass analysis, without a charged species it is ineffective. This coupled with solvent restrictions hinders the analysis of organometallic complexes. Detecting neutral species whose solubility is limited to nonconventional solvents is a problem that can be overcome with the right charge carrier, which is described in this study. METHODS: Ionic liquids were synthesized and analyzed by electrospray ionization quadrupole ion trap mass spectrometry. The neutral palladium complex was also analyzed using different imidazolium salts as the charge carrier with the same method and instrumentation. Theoretical complements were also performed using Gaussian 09 at the density functional theory levels, using B3LYP functionals and the 6-31 g (d,p) basis set for geometry optimizations. RESULTS: Low concentration imidazolium salts in methanol showed aggregation behavior of the ionic liquid, where the cation peak and [cation](n+1)[anion]n peaks were observed in positive mode, while the [cation]n[anion](n+1) peaks were seen in negative mode. The unbound anion was observed in all the negative mode spectra except for the salt with the SCN anion when in THF. Solutions of PdCl2(PPh3)2 and a small amount of ionic liquid in THF showed the palladium complex adducted with the imidazolium cation for each of the ionic liquids studied. CONCLUSIONS: A charge carrier for a neutral organometallic complex was found in imidazolium salts, where the cation was observed as the ionizing agent. Differing ion intensities of the complex-adduct peak resulted from the anions ability to dissociate from the cation.
RESUMEN
RATIONALE: Developments in instrumentation aimed at microscopic sampling have led to an emphasis on applications analyzing small volumes and molecular concentrations within biological, chemical, and industrial samples. Simultaneous improvements in the sensitivity and versatility of nanospray mass spectrometers have made it possible to directly couple these sampling and analysis processes. METHODS: We developed a versatile liquid-phase lipid microextraction (LPME) technique for nanoliter to microliter volumes that is amenable to direct nanospray mass spectrometry (NMS). Lipophilic analytes within several types of biological samples were extracted and analyzed by partitioning and concentrating the analytes based on their solubility within two immiscible or partially miscible liquid phases. RESULTS: The utility of LPME-NMS is demonstrated by extracting and analyzing molecules in four different types of applications: (1) visualization of an extracted neutral lipid-specific fluorescent dye from an aqueous solvent; (2) identification of controlled acid-catalyzed hydrolysis of triacylglycerols within nanospray capillaries; (3) reproducible sampling of a fatty acid emulsion; and (4) profiling of diverse lipids in a complex biological matrix of rabbit serum. CONCLUSIONS: The modified instrumentation of a multi-port, on-stage bioworkstation shows considerable versatility by combining nanomanipulation, microextraction and direct NMS for a variety of chemical, biological, industrial, and clinical applications.