Additive‐free cryoaerogel coatings from noble metal nanoparticles are prepared and electrochemically investigated. By using liquid nitrogen or isopentane as cooling medium, two different superstructures are created for each type of noble metal nanoparticle. These materials (made from the same amount of particles) have superior morphological and catalytic properties as compared to simply immobilized, densely packed nanoparticles. The morphology of all materials is investigated with scanning electron microscopy (SEM). Electrochemically active surface areas (ECSAs) are calculated from cyclic voltammetry measurements. The catalytic activity is studied for the ethanol oxidation reaction (EOR). Both are found to be increased for superstructured materials prepared by cryoaerogelation. Furthermore, cryoaerogels with cellular to dendritic structure that arise from freezing with isopentane show the best catalytic performance and highest ECSA. Moreover, as a new class of materials, cryohydrogels are created for the first time by thawing flash‐frozen nanoparticle solutions. Structure and morphology of these materials match with the corresponding types of cryoaerogels and are confirmed via SEM. Even the catalytic activity in EOR is in accordance with the results from cryoaerogel coatings. As a proof of concept, this approach offers a novel platform towards the easier and faster production of cryogelated materials for wet‐chemical applications.
Different techniques
that enable the selective microstructure design
of aerogels without the use of additives are presented. For this,
aerogels were prepared from platinum nanoparticle solutions using
the cryoaerogelation method, and respective impacts of different freezing
times, freezing media, and freezing temperatures were investigated
with electron microscopy as well as inductively coupled plasma optical
emission spectroscopy. The use of lower freezing temperatures, freezing
media with higher heat conductivities, and longer freezing periods
led to extremely different network structures with enhanced stability.
In detail, materials were created in the shape of lamellar, cellular,
and dendritic networks. So far, without changing the building blocks,
it was not possible to create the selective morphologies of resulting
aerogels in cryoaerogelation. Now, these additive-free approaches
enable targeted structuring and will open up new opportunities in
the future cryoaerogel design.
This paper analyzes the electrochemical and physicochemical properties of activated carbons developed from coffee husk through different activation routes.
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