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Designing and preparing highly active and stable nanostructured Pt-based catalysts with ultralow Pt loading are still challenging for electrochemical applications such as water electrolysis and fuel cells. Here we report for the first time an in situ electrochemical process to synthesize Pt-MoO3−x nanoflakes (NFs) overgrown on commercial bulk MoS2 by employing a facile and simple electrochemical method without using any expensive precious metal salts. The overgrowth of Pt-MoO3−x NFs on the bulk MoS2 surface is conducted by applying electrical energy to the bulk MoS2 and using Pt counter electrode dissolution in an acidic solution. In spite of their 10 times lower Pt loadings compared to commercial Pt black (Alfa Aesar), the synthesized Pt-MoO3−x NFs demonstrate excellent catalytic performance with a Pt mass activity of 2.83 A/mgPt at the overpotential of 100 mV for electrochemical hydrogen evolution reaction (HER), an approximately 4 times higher value than the value of 0.76 A/mgPt at the overpotential of 100 mV for commercial Pt black. We hypothesize that the outstanding HER characteristics of Pt-MoO3−x NFs are related to the existence and increase of Pt-MoO3 interfacial sites and oxygen vacancy sites such as Mo5+ in the Pt-MoO3−x NF structures. In addition, our density functional theory (DFT) calculations demonstrate that Pt and O sites at Pt and MoO3 interfaces and O sites at defective MoO3−x in the Pt-MoO3−x NFs contribute to accelerate the HER.

To construct an efficient electrocatalyst for HER, the high binding energy of MXene must be mitigated through electronic modulation of active sites. Here, we propose atomic Pt substitution in V2CTx MXene to modulate the electronic structure and promote catalytic activity toward HER. Pt–V2CTx exhibits high HER performance with a low overpotential of 27 mV at –10 mA cm-2 in acidic media, comparable to the commercial Pt/C catalyst. X-ray absorption spectroscopy and DFT calculations indicate that the Pt atoms are efficiently confined to the V vacancy sites of V2CTx, accompanied by a unique electronic structure. The atomic substitution of Pt with higher occupied d states at the Fermi energy of Pt and surface oxygen sites can significantly indicate an optimum hydrogen-binding free energy (∆GH*), promoting HER performance. This work introduces further prospects for developing efficient electrocatalysts by feasible electronic regulation and highly improved catalytic activity through rational atomic engineering.

Decorating graphene with nanoparticles is an effective method for improving gas selectivity and sensitivity of graphene-based chemical sensors. We report herein the enhancement of the gas selectivity and improved response of a graphene-based chemical sensor by decorating the graphene with synthesized Ag2S nanoparticles. To synthesize uniformly sized Ag2S nanoparticles, we used the ultrasonic irradiation method, and then the synthesized Ag2S nanoparticles were decorated onto graphene uniformly, by using a simple spin coating method. Gas responses of the resulting chemical sensor were tested for volatile organic compounds (VOCs) such as acetone, ethanol, and hexane. While no noticeable gas response changes were obtained for ethanol and hexane vapors, a dramatic increase of ~660% resulted from exposure of the sensor to acetone vapor. In order to determine the mechanism behind the excellent acetone response of graphene decorated with Ag2S nanoparticles, density functional theory (DFT) calculations were performed, and showed higher binding energies and electron transfer between Ag2S and acetone than between Ag2S and the other VOCs. This result indicated that decorating graphene with nanoparticles displaying a high binding energy for the target gas is an efficient way to improve the gas selectivity and response levels of graphene-based chemical sensors.

As a consequence of their unique electronic band structures, low-dimensional materials such as one-dimensional (1D) single-wall carbon nanotubes (SWCNTs), 2D graphene and various 2D transition-metal dichalcogenides have exhibited intriguing electrical transport properties when incorporated into field-effect transistors. Meanwhile, the van-der-Waals (vdW) interfaces between top-contacted metals and low-dimensional materials have become a challenging issue for future high-performance electronics. Here, we report a new aspect of vdW interface that offers vdW-gap tunneling spectroscopy by adopting indium (In) as a top-contacted metal on SWCNTs without an artificial insulating tunnel barrier. We show that multiple differential conductance peaks for varying bias voltages correspond to the van Hove singularities existing in the electronic density of states of SWCNTs. Our first-principles calculations reveal that In forms a physisorption interface with a considerable vdW gap, which causes little disruption to the density of states of the SWCNTs near the metal interface and which thus allows vdW-gap tunneling spectroscopy.

Atomically controlled thin TiO2 layers were coated onto a carbon-supported Pt nanoparticle (Pt/C) surface using an atomic layer deposition (ALD) technique. Then, the resulting TiO2 coated Pt/C (ALD(TiO2)-Pt/C) was heat-treated at 150 °C under N2 atmosphere. The heat-treated ALD(TiO2)-Pt/C (ALD(TiO2)-Pt/C(150 H T)) catalyst demonstrated improved electrocatalytic glycerol oxidation reaction (GOR) activity with a turnover frequency (TOF) 3-times higher than for uncoated Pt/C catalyst. Interestingly, the ALD(TiO2)-Pt/C(150 H T) catalyst maintained its catalytic GOR performance after a cyclic voltammetry (CV) stability test of 1200 cycles, preventing Pt sintering due to strong Pt-TiO2 interaction. The reaction chemistry for GOR on the ALD(TiO2)-Pt/C(150 H T) catalyst also changed due to the newly created Pt-TiO2 interfaces, producing more oxidized chemicals such as glyceric acid and glycolic acid. The enhanced GOR performance is related to the formation of new Pt-O-Ti bonds and to change in the physicochemical properties of the Pt by interaction between the Pt nanoparticles and ALD-coated TiO2.

We have employed computer-aided furnace design and process simulation to optimize the conditions under which single-walled carbon nanotubes (SWCNTs) may be grown in high yields on 4 in. wafers for electronic device applications. Hydrokinetic simulations were performed to obtain optimized furnace structures and process conditions in terms of gas flow, temperature, and gas speed. Shower head structures and a flow isolation barrier were installed in an experimental 6 in. furnace, as suggested by the hydrokinetic simulations. To ensure clean surfaces and uniform catalyst islands, catalyst patterns were lifted off using Au films or polydimethylsiloxane. Photolithography was used to fabricate field-effect transistors with SWCNTs grown on 4 in. wafer substrates. The total yield of the nanotube devices increased from 30.5% to 96.4% after optimization.

K. Kong and H. Chang acknowledge the support from Korea Research Council of Industrial Science & Technology for this study. In addition, K. Kong, H. Chang and S. Im appreciate the support from the National R&D Project for Nano Science and Technology (Grant No. M1-0213-04-0003) for this research. S. Im thanks the Center for Nanoscale Mechatronics & Manufacturing, one of the 21st Century Frontier Research Programs, for the Grant (No. 08k1401-00611), and the National Research Foundation of Korea (NRF) for the Grant (No. R0A-2007-000-20115-0).

We report here the synthesis of self-assembled aligned hexagonal prismatic Cu doped ZnO nanoparticles in aqueous and organic medium. The average particle size was found to be in the range of 40–85 nm. Structural study revealed the existence of ZnO phase with wurtzite structure. The copper was present as oxide, situated at the core of prismatic form of wurtzite ZnO nanoparticle with clear edges and faces. The maximum hydrogen production rate achieved was 1932 μmol h −1 over the as synthesized Cu doped ZnO suggesting as an active photocatalyst for hydrogen sulfide decomposition under visible light irradiation. The effect of copper concentration as a dopant on the photocatalytic activity of Cu-ZnO was studied. The photocatalytic activity of Cu-ZnO synthesized in organic media was observed to be higher as compared to aqueous medium.

The potential of carbon-related materials, such as carbon nanotubes (CNTs) and graphite nanofibers (GNFs), supported metal catalysts as an electrode for fuel cell application was investigated using the first-principle electronic structure calculations. The stable binding geometries and energies of metal catalysts are determined on the CNT surface and the GNF edge. The catalyst metal is more tightly bound to the GNF edge than to the CNT surface because of the existence of active dangling bonds of edge carbon atoms. The diffusion barrier of metal atoms on the surface and edge is also obtained. From our calculation results, we have found that high dispersity is achievable for GNF due to high barrier against the diffusion of metal atoms, while CNT appears less suitable. The GNF with a large edge-to-wall ratio is more suitable for the high-performance electrode than perfect crystalline graphite or CNT.

We have calculated electronic structure of InTaO4 using first-principle method, in order to investigate the relationship between its electronic structures and visible light absorption. We have calculated densities of states (DOS) for various states of InTaO4, such as pristine, oxygen vacancy, Ni-doped, and A-doped (A = C, N, and S) states. We have found that oxygen vacancy can induce the gap states and Ni-doping can narrow the band gap by generating additional states on the top of the valence band as well as on the top of the gap states. For A-doped states, it was found that N-doping and S-doping could narrow the pristine band gap inducing the additional states above the pristine valence band, while C-doping can generate the gap states in the middle of the pristine band gap. To cite this article: H. Chang et al., C. R. Chimie 9 (2006).

The synthesis of highly concentrated silver nanosol assisted by polyelectrolytes for inkjet method was studied. The role of polyelectrolytes on the synthesis of silver nanosol was studied by varying molecular weights and the molar ratios (R = [COO−]/[Ag+]) of them. The concentrated silver nanosol was synthesized by reducing the cation (Ag+) and anionic polyelectrolytes (COO−) complex including the step of initial nucleation and growth of silver nanoparticles to achieve dispersion stability and controlling the size of silver nanoparticles. The maximum concentration of batch-synthesized silver nanosol was possible to 40 wt%. At the same time, the particle size of silver nanoparticles was below 10–20 nm. The synthesized silver nanosol was tested for the possibility of micropatterning of electrode on ITO glass substrate. The connectivity and width of fine line depended largely on the wettability of silver nanosol on ITO glass. These relationships will be understood by wetting angle. The fine line of silver electrode as fine as 50–100 μm was successfully formed on ITO glass substrate.

We have carried out the first-principle electronic structure calculations based on density functional theory on InTaO4 in various states, such as pristine, oxygen vacancy, and Ni-doped states. We have found that oxygen vacancy can induce the gap states and Ni-doping can narrow the band gap by generating additional states on the top of the valence band as well as on the top of the gap states. From our calculated results, we have shown that oxygen vacancy can do a crucial role to generate gap states which let InTaO4 absorb the visible light.

The atomic structure of amorphous Al 2 O 3 has been determined using a molecular dynamics simulation. The local electronic structures of the simulated amorphous structure and of the crystalline structure of Al 2 O 3 were investigated using first principle cluster calculations. The calculated partial densities of states for the two structures are compared with their photoelectron spectra. We find that there is a local oxygen deficiency around Al atoms in amorphous Al 2 O 3 , which results in a different local electronic structure in amorphous Al 2 O 3 . We also show with our calculations and photoelectron spectroscopy that Al 2 O 3 thin films have both crystalline and amorphous properties.

The luminescence properties of fergusonite phosphors, YNbO4 and YNbO4:Bi, were investigated with photoluminescence (PL) measurements and first-principles calculations. The various absorption spectra of these phosphors have been interpreted using the calculated partial density of states in the framework of density functional theory. We were able to determine the charge-transfer gap of YNbO4, 4.3 eV, that agrees well with our experimental measurement. From our analysis of PL spectra and calculations, we have investigated the Bi effect in YNbO4:Bi, which shows an excitation peak at a longer wavelength than YNbO4. We have found that the charge transfer from oxygen to bismuth is the main reason for the peak position shift in the excitation spectra.