Ambient pressure dried resorcinol–formaldehyde (RF) organic aerogels are usually hard and brittle with Young's moduli in the range of 1–2 MPa, strengths of about 100 kPa and densities in the range of 0.2 to 0.4 g cm⁻³. Modifications of the classical sol–gel synthesis route transform these brittle materials into rubber- or cork-like flexible aerogels. We observed that in a small window of process parameters, the aerogel density decreases by an order of magnitude as well as the Young's moduli and the compression strengths. These new types of RF aerogels are elastically deformable by more than 40% in an almost reversible manner. In this paper we describe the effects of various sol–gel parameters on the flexibility, such as resorcinol to water and catalyst molar ratio and the pH of the initial solution. The aerogels are characterized with respect to the envelope density, stress–strain behavior and microstructure as observed from SEM fractographs. The chemical structure and structural differences arising between brittle and flexible RF aerogels were studied by recording ¹³C-NMR spectra.

Highly porous carbon materials employed in sulfur cathodes are of utmost importance to the charge transport, conductivity and stability of the cathode in metal–sulfur batteries. Herein, ultramicroporous carbon aerogels as conductive matrices embedding sulfur for cathode application in lithium–sulfur batteries are synthesized and investigated. Resulting from organic resorcinol–formaldehyde aerogels, the synthesized carbon aerogels feature a highly porous structure with a surface area of 500–2000 m² g⁻¹ and large micropore volume up to 0.6 cm³ g⁻¹. The effective gas-phase sulfur infiltration of the carbon aerogels and the resulting confinement of sulfur in the micropores are demonstrated. It is indicated that sulfur-infiltrated microporous carbon aerogel cathodes are able to suppress the polysulfide shuttle effect, maintaining 80% (≥1000 mA h g_(S) ⁻¹) and 70% (≥800 mA h g_(S) ⁻¹) of the initial discharge capacity after 200 cycles at a rate of 0.3C in carbonate and ether-based electrolytes, respectively. Remarkably, the herein prepared composite cathode can still deliver a discharge capacity of at least 700 mA h g_(S) ⁻¹ at a faster rate of 2C in both electrolyte systems. The cyclability and compatibility of the ether and carbonate-based electrolytes with such a composite cathode are discussed elaborately.

The solvent exchange as one of the most important steps during the manufacturing process of organic aerogels was investigated. This step is crucial as a preparatory step for the supercritical drying, since the pore solvent must be soluble in supercritical carbon dioxide to enable solvent extraction. The development and subsequent optimization of a suitable system with a peristaltic pump for automatic solvent exchange proved to be a suitable approach. In addition, the influence of zeolites on the acceleration of the process was found to be beneficial. To investigate the process, the water content in acetone was determined at different times using Karl Fischer titration. The shrinkage, densities, as well as the surface areas of the aerogels were analyzed. Based on these, the influence of various process parameters on the final structure of the obtained aerogels was investigated and evaluated. Modeling on diffusion in porous materials completes this study.

The production of a new composite material embedding aramid honeycomb materials into nano-porous silica aerogels is studied. Our aim is to improve the poor mechanical strength of silica aerogels by aramid honeycombs without losing the amazing properties of the aerogels like little density and low thermal conductivity. The composite materials were prepared using two formulations of silica aerogels in combination with aramid honeycomb materials of different cell sizes. The silica aerogels are prepared using silicon alkoxides methyltrimethoxysilane and tetraethylorthosilicate as precursors in a two-step acid–base sol–gel process. Shortly in advance of the gelation point, the aramid honeycombs were fluted by the sol, gelation occurred and, after the aging process, the gel bodies were supercritically dried. The properties of the received composite materials are satisfying. Even the thermal conductivities and the densities are a bit higher than for pure aerogels. Most importantly, the mechanical strength is improved by a factor of 2.3 compared to aramid honeycomb materials and by a factor of 10 compared to the two silica aerogels themselves. The composite materials have a good prospective to be used as an impressive insulation material.

This study presents the correlation between the morphological, structural and electrical properties of four different carbon aerogels, as well as the influence of thermal activation on their properties. The role of conductive additives is discussed.