10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Electrospray Atomization and Deposition of Nanoparticle Suspensions Leading to Nanostructured Porous Coatings
JOSE L CASTILLO, Santiago Martin, Daniel Rodriguez-Perez, Francisco J Higuera, Pedro L Garcia-Ybarra, Universidad Nacional de Educacion a Distancia - UNED
Abstract Number: 93 Working Group: Materials Synthesis
Abstract The controlled deposition of aerosols is a valuable tool to prepare thin nanostructured porous coatings as required in many applications. Thus, aerosol nanoparticles can be used as building blocks for materials synthesis leading to thin porous layers with a prescribed morphological structure and still retaining a large surface/volume ratio as distinctive feature. Coatings formed by the accumulation and adhesion of incoming aerosol nanoparticles acquire a morphological structure controlled by the form of the constitutive particles and by the way in which these particles arrive and attach to the forming material. A proper control of the aerosol particle dynamics may lead to granular deposits with a well-prescribed bulk morphology and surface structure.
Experiments have been conducted to prepare nanostructured materials from the steady electrohydrodynamic atomization of liquid suspensions. The electrospray is kept in the cone-jet mode with a Taylor cone at the needle exit and a very thin jet emerging from the cone tip. At some distance away from the cone tip, the jet breaks up into a spray with droplets much smaller that the needle radius, forming a cloud with a narrow distribution of tiny charged droplets. The droplets are driven by the electric field and evaporate along their path leaving a solid residue of charged nanoparticles which are collected on a substrate. The range of parameters leading to a stable cone-jet was studied for two different suspensions; carbon nanoparticles in ethanol and catalytic inks formed by Pt supported on carbon nanoparticles and Nafion® in ethanol.
The morphology of the deposits has been examined by means of digital scanning electron microscope (SEM) images. Upper views of the deposit show a layer structure based on clusters of nanoparticle agglomerates formed by the attachment at the deposit of nanoparticles coming from several electrospray droplets, with the cluster size (of the order of 10 microns) increasing with the flow rate. Lateral SEM images of the deposits cross-sections were processed to calculate the deposit mean density and porosity. The porosity is rather high (always larger than 90%) decreasing as the electrospray flow rate increases.
Coatings prepared from catalytic inks were tested as electrodes in a fuel cell. The performance of the electrodes synthesized using different values of the electrospray flow rate was studied. The electrodes have shown extremely large specific power (reaching a power of 21 kW per gram of Pt in the cell) due to the outstanding properties of the electrosprayed catalytic layer: large porosity, uniform distribution of the catalyst and high density of (Pt) active sites.
These results for fuel cell electrodes show the advantages of the electrospray method in a particular case. But the same methodology could also be used for other applications. The structure of the synthesized material can be tailored according to the application needs to have a given porosity and surface composition. Moreover, layered or composed materials (with a different porosity or different composition on each layer) can be prepared by adequate changes in the control parameters (liquid flow rate and applied voltages in the electrospraying technique) which determine the dynamics of the particles approaching the deposit.