Morphology and Nanostructure of Granular Materials Built from Nanoparticles

Abstract

Nanopowders or nanoparticles can be used as building blocks for the preparationof new materials with a prescribed structure. Monte Carlo simulations have shownthat the morphological properties (bulk porosity and surface roughness) of agranular deposit can be tailored by properly adjusting the velocity of theparticles approaching the deposit. Based on these theoretical predictions,experiments have been conducted to prepare nanostructured materials from carbonnanoparticles. By electrohydrodynamic atomization of a liquid suspension (carbonnanoparticles dispersed in ethanol), an electrospray of small droplets isgenerated. The charged droplets are driven by the electric field with theethanol evaporating along the droplet path, leaving dry nanoparticles thatdeposit on the collecting surface. The surface roughness of the resultingmaterial has been characterized as a function of the voltage drop. Moreover,catalytic suspensions of platinum supported on carbon nanoparticles (Pt/C) inNafion®-alcohol solutions have been electrosprayed overcarbon paper to prepare electrodes for proton exchange membrane fuel cells(PEMFC). The fuel cell power density was measured as a function of the platinumloading and the range of parameters leading to optimal platinum utilization wasobtained.

Keywords

• nanopowders
• powder deposits
• granular materials
• deposit morphology
• electrospray
• catalytic materials
• fuel cell electrodes