Porous Thin Films with Large Specific Surface Area on the Basis of Spray-Coated Metal Aerogels

Abstract

The preparation of aerogels in the form of thin films deposited on a substrate (e.g., as an electrode material) is an attractive but challenging task. Such thin films are expected to combine the highly porous gel nanostructure, good mechanical stability, and a remarkably high specific surface area with efficient charge-carrier transport via the interconnected nanoparticle chains. All together, they make them attractive for the fabrication of (electro)catalysts or sensors for microfluidics, flexible electrodes for microelectronics, soft electrodes compatible with a stress-sensitive bioenvironment, etc. In this work, thin aerogel films of colloidal Pd and PtNi building blocks were prepared from the corresponding wet gels using a spray technique. The films were fabricated on substrates of around 1.5 cm2. During the modification of the substrates, the film thickness can be adjusted by controlling the ink content (flow rate, gas pressure, and temperature) and the number of spray cycles. In this way, both the electrical (down to Rs = ∼0.2 kOhm/sq) and optical parameters of the thin porous films can be tuned. Comparative studies of the pore and surface structures of the films have confirmed their integrity and the highly porous structure typical for aerogels. In perspective, spray-coated aerogels can be easily adapted to industrial applications because upscaling is possible and expensive equipment such as supercritical or freeze-dryers is not required. It is important to note that the spray-coating technique is applicable through a mask or can be converted to inkjet printing, which allows for the desired micropatterning of aerogel thin films.