Cong Feng

Diffusion mechanism of platinum nanoclusters on well-aligned carbon nanotubes

Carbon supported platinum (Pt/C) remains among the preferred catalyst materials for use in proton exchange membrane fuel cells; however, its durability must be improved. In this work, we considered well-aligned carbon nanotubes (WACNTs) as a carbon support material and investigated the diffusion mechanism of Pt nanoparticles by using molecular dynamic (MD) simulations, including calculation of the binding energy, aggregation probability, and the diffusion coefficient. Moreover, the use of graphene as a support material is also examined. The trenches in well-aligned carbon nanotubes were found to not only increase the binding energy between the Pt particles and the substrates but also decrease the aggregation probability of Pt particles compared with the graphene substrates. Furthermore, we estimated the Pt mass per substrate area (Pt loading) when there is no occurrence or a reduced occurrence of Pt agglomeration: a value of 0.167 μg cm−2 for WACNTs (24, 24), and a Pt particle diameter of 2.4 nm are suggested.

PREDICTED MECHANICAL PROPERTIES OF CARBON NANOTUBE-BASED STRUCTURES

Carbon nanoring (CNR) with heptagon–pentagon defects is formed by single-walled carbon nanotubes (SWCNTs) (5, 5) and (9, 0) and each junction is constructed by connecting a heptagonal and a pentagonal carbon-atom ring. Then cutting the ring into two pieces along the junction, one pitch of carbon nanocoil will be obtained by constraining one end and stretching the other end along the helical axis. Molecular mechanics (MM) simulations are employed to investigate the mechanical characteristics of CNRs and nanocoils with and without defects. The Youngs modulus of the nanoring with defects is about 282 GPa, which is larger than that of perfect nanorings with the similar ring radii, such as (5, 5) and (9, 0). The spring stiffness of the carbon nanocoil is calculated with a maximum value of 2.08 N/m, and it is found to be nonlinear and decreases with the increase in the relative elongation.

Moisture and thermal expansion properties and mechanism of interaction between ions of a Nafion-based membrane electrode assembly

A membrane electrode assembly (MEA) is a multi-layer composite material. The different water and thermal expansion properties in MEA layers easily lead to delamination and electrode cracks, greatly decreasing the cell performance. Based on commonly used materials, we establish molecular models, investigate the coefficients of moisture and thermal expansion, and explore the diffusion mechanism and interaction behaviors of various particles. The effects of system size, oligomer chain length, and catalyst size and content are discussed. The moisture expansion properties of the membrane are verified by experimental results obtained with Nafion® 117. The differences in moisture and thermal expansion between layers can be reduced by decreasing the chain length of the oligomer and the size and content of Pt in the catalyst layer; increasing the chain length of the oligomer in the membrane; and controlling the working temperature at approximately 320 or 358 K. The introduction of Pt and graphene is also found to prevent the diffusion of water molecules and decrease water connectivity.