Versatile chemical transformations of surface functional groups in 2D transition-metal carbides (MXenes) open up a new design space for this broad class of functional materials. We introduce a general strategy to install and remove surface groups by performing substitution and elimination reactions in molten inorganic salts. Successful synthesis of MXenes with O, NH, S, Cl, Se, Br, and Te surface terminations, as well as bare MXenes (no surface termination) was demonstrated. These MXenes show distinctive structural and electronic properties. For example, the surface groups control interatomic distances in the MXene lattice, and Tin+1Cn (n = 1, 2) MXenes terminated with Te2− ligands show a giant, (>18%) in-plane lattice expansion compared to the bulk TiC lattice. Nb2C MXenes exhibited surface-group-dependent superconductivity.

The kinetics of oxygen reduction was studied in acid solutions on Pt monolayers deposited on a Pd(111) surface and on carbon-supported Pd nanoparticles using the rotating disk-ring electrode technique. These electrocatalysts were prepared by a new method for depositing Pt monolayers involving the galvanic displacement by Pt of an underpotentially deposited Cu monolayer on a Pd substrate and characterized by scanning tunneling and transmission electron microscopies. The kinetics of O 2 reduction shows a significant enhancement at Pt monolayers on Pd(111) and Pd nanoparticle surfaces in comparison with the reaction on Pt(111) and Pt nanoparticles. The four-electron reduction, with a first-charge transfer-rate determining step, is operative on both surfaces. The observed increase in the catalytic activity of Pt monolayer surfaces compared with Pt bulk and nanoparticle electrodes may reflect decreased formation of PtOH. An enhanced atomic scale surface roughness and low coordination of some atoms may contribute to the observed activity. The results illustrate that placing a Pt monolayer on a suitable metal nanoparticle substrate is an attractive way of designing better O 2 reduction electrocatalysts. Also, by using this method the Pt content is reduced to very low levels. The Pt mass-specific activity of the Pt/Pd/C electrode is 5-8 times higher than that of the Pt/C electrocatalyst. The noble metal (Pt + Pd) mass-specific activity is two times higher than that of Pt/C.

Conversion of carbon dioxide (CO2) into fuels is an attractive solution to many energy and environmental challenges. However, the chemical inertness of CO2 renders many electrochemical and photochemical conversion processes inefficient. We report a transition metal dichalcogenide nanoarchitecture for catalytic electrochemical CO2 conversion to carbon monoxide (CO) in an ionic liquid. We found that tungsten diselenide nanoflakes show a current density of 18.95 milliamperes per square centimeter, CO faradaic efficiency of 24%, and CO formation turnover frequency of 0.28 per second at a low overpotential of 54 millivolts. We also applied this catalyst in a light-harvesting artificial leaf platform that concurrently oxidized water in the absence of any external potential.

), and examined their performance for BP exfoliation (see Section S1, Supporting Information). Initially, a chunk of black phosphorous crystal (0.02 mg mL −1 ) was immersed into different solvents and was sonicated for 15 h (total input energy -1 MJ). We noticed that aprotic and polar solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) are appropriate solvents for the synthesis of atomically thin BP nanofl akes and can produce uniform and stable dispersions after the sonication (see Section S2, Supporting Information). The solutions were then centrifuged and their supernatants were carefully collected by a pipette. Figure 1 A shows the BP nanofl ake dispersions in DMSO and DMF after sonication for 15 h (left image) and after the centrifugation (right image), having concentrations up to 10 µg mL −1 (see Experimental Section).As suggested by experimental [ 15 ] and theoretical [ 16,17 ] reports, BP atomic layers have a thickness dependent direct bandgap ranging from ≈0.3 eV in bulk to more than 1 eV in monolayer. Typically, optical absorption spectroscopy is a robust and reliable method to determine the bandgap of semiconductors in solution form. We used this technique to characterize our dispersed nanofl akes in DMF and DMSO solutions with a focus on the near-IR (NIR) range (Wavelength of 830-2400 nm) where the peaks associated with the optical band gap of atomically thin BP nanofl akes are likely to occur. Interestingly, in both DMF and DMSO solutions several spectral peaks were observed in the NIR range at ≈1.38, ≈1.23, ≈1.05, ≈0.85, and ≈0.72 eV (labeled as numbers 1-5 in Figure 1 B) which are believed to be associated with the enhanced light absorption by mono-, to fi ve-layers thick BP nanofl akes, respectively. These results are in a good agreement with the position of photoluminescence peaks reported for mono-to fi ve-layers thick BP fl akes obtained by mechanical exfoliation. [ 12,22 ] The smaller peaks at 1.38 and 1.23 eV compared to other peaks implies that the yields of mono-and bilayers are lower than other atomic layers.We also measured the normalized absorption intensity over the characteristic length of the cell ( A / l ) at λ = 1176 nm ( E = 1.05 eV) for DMF and DMSO solutions at different concentrations ( C ). As suggested by the Lambert-Beer law ( A / l = αC , where α is the extinction coeffi cient), a linear trend was observed for A / l versus concentration (Figure 1 C), suggesting well-dispersed nanofl akes in both solutions. The extinction coeffi cients for DMF and DMSO solutions were extracted to be α = 4819 and 5374 mL mg −1 m −1 , respectively. The BP fl ake size distribution was also analyzed by dynamic light scattering (DLS) spectroscopy and the average fl ake sizes were determined to be ≈190 and ≈532 nm for the DMF and DMSO solutions, respectively (Figure 1 D).2D nanomaterials such as graphene and transition metal dichalcogenides (TMDCs) have shown outstanding potential in many fi elds such as fl exible electronics, [ 1 ] sensing, [ 2,3 ] and optics, [ 4 ] due to their...

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Lithium-air batteries are considered to be a potential alternative to lithium-ion batteries for transportation applications, owing to their high theoretical specific energy. So far, however, such systems have been largely restricted to pure oxygen environments (lithium-oxygen batteries) and have a limited cycle life owing to side reactions involving the cathode, anode and electrolyte. In the presence of nitrogen, carbon dioxide and water vapour, these side reactions can become even more complex. Moreover, because of the need to store oxygen, the volumetric energy densities of lithium-oxygen systems may be too small for practical applications. Here we report a system comprising a lithium carbonate-based protected anode, a molybdenum disulfide cathode and an ionic liquid/dimethyl sulfoxide electrolyte that operates as a lithium-air battery in a simulated air atmosphere with a long cycle life of up to 700 cycles. We perform computational studies to provide insight into the operation of the system in this environment. This demonstration of a lithium-oxygen battery with a long cycle life in an air-like atmosphere is an important step towards the development of this field beyond lithium-ion technology, with a possibility to obtain much higher specific energy densities than for conventional lithium-ion batteries.

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We report here the first synthesis of pure boron single-wall nanotubes by reaction of BCl 3 with H 2 over an Mg-MCM-41 catalyst with parallel, uniform diameter (36 ( 1 Å) cylindrical pores. The composition of the tubular structures observed in TEM was confirmed by electron energy loss spectroscopy, and the tubular geometry was confirmed by the presence of the characteristic spectral features in the Raman breathing mode region.