L. Qiao

Well-dispersed palladium nanoparticles on graphene oxide as a non-enzymatic glucose sensor

Palladium nanoparticles with excellent uniform size and even distribution were prepared on graphene oxide (Pd NPs/GO) by using a simple and environmentally-friendly ultrasonic method in an ice bath. Ultrasonication time and composition ratios of GO and Pd influenced the morphology of the palladium nanoparticles and their electrocatalytic performance. Transmission electron microscopy (TEM) and electrochemical characterization demonstrated that GO acted as a good supportive substrate for controlling the size and activity of palladium nanoparticles. The optimized nanocomposite exhibited high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium. The Pd NPs/GO nanocomposite was developed as a non-enzymatic biosensor for the determination of glucose with a linear range of 0.2–10 mM, which is nearly insusceptible to common electroactive interfering species. This simple and effective composite platform could potentially be extended to other metal/graphene nanomaterials, and have broad applications in biosensing, fuel cells, and other fields.

First-principles density-functional investigation of the effect of water on the field emission of carbon nanotubes

The geometrical structures and the field-emission properties of capped (5, 5) single-walled carbon nanotubes with water adsorbed on the tip with and without an applied electric field have been investigated using first-principles density-functional theory. It is found that the structures of carbon nanotubes with water molecules are stable under field-emission conditions. The dipole moments induced by the adsorption of water molecules point from the water molecules to the CNT tips. The Mulliken charges are redistributed and accumulated on the carbon nanotube tips. Under an applied electric field, the number of Mulliken charges that transfer from the carbon nanotube body to both its tip and water molecules increases with the increase of the number of water molecules. The local density of states at the Fermi level increases with the adsorption of water molecules. These results elucidate that the field-emission properties of carbon nanotubes can be enhanced by the adsorption of water molecules, and are consistent with the experimental results.

Electronic and Field Emission Properties of Carbon Nanocones: A Density Functional Theory Investigation

Using density functional theory calculations, we investigate the electronic structures and field emission properties of carbon nanocones (CNCs). We find that the cohesive and formation energies for various types of CNCs are dependent on the cone angles, while the work function, local density of states, redistribution of the charge, and field emission pattern are sensitive to the morphologies of CNCs that are governed by the position of pentagonal rings in the cone apex. Most importantly, the nanocone with three pentagons in the cone apex exhibits the best field emission property.

First-principles investigations on the adsorption and diffusion of carbon atoms on the surface and in the subsurface of Co (111) related to the growth of graphene

The adsorption and diffusion of carbon atoms on the surface of a catalyst are key steps in the chemical vapor deposition of carbon nanomaterials. Using first-principles density functional theory, the adsorption and diffusion of carbon atoms on the surface and in the subsurface of Co (111) have been systematically investigated to identify the catalyzed growth of graphene on Co (111). In view of the maximization of the adsorption energy, the hexagonal close-packed site and the octahedral site are the most stable sites for carbon atoms on the surface and in the subsurface of Co (111), respectively. Furthermore, to reveal the rate-determining step of the growth of graphene, the energy barriers for the diffusion of carbon atoms on the surface of Co (111) and from the subsurface to the surface have been obtained. The Co (111) surface has the highest mobility for carbon atoms due to the lower diffusion energy barrier, and the vertical diffusion of carbon atoms from the subsurface to the surface is relatively difficult due to the higher diffusion energy barrier. The results may be related to the growth of graphene on Co (111) and we come to the conclusion that the direct surface growth should be the predominant way for the synthesis of graphene on Co (111).

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt(1ML)) supported on an M surface, Pt(1ML)/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt(1ML) shell depending on the conditions. In vacuum conditions, the Pt1ML shell can be stabilized on the most of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt(ML) shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt(1ML)/M(1ML)/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt(1ML) shell were also discussed.