Supercapacitors are generally viewed as promising energy storage alternatives for future mobile applications, due to their immense energy and power density. Researchers from the Jiangsu University (China) have now been able to greatly improve electrochemical characteristics of graphene/polyaniline aerogels, which are considered a promising material for super capacitor electrodes, by doping them with nitrogen.

The resulting 3D nitrogen-graphene/polyaniline (N-GE/PANI) foams exhibited a rough and wrinkled surface area on which the PANI spheres were incorporated (see Figure).

SEM images of (a, b) N-GE and (c, d) N-GE/PANI electrode composites. The insets in (c) and (d) are a photo of the 3D N-GE/PANI monolith and an SEM image of PANI nanospheres, respectively

Furthermore, it was found that the combination of N-GE and PANI resulted in superior specific capacitance, when compared to the individual materials. This finding was ascribed to the synergetic effect of combining a conductive polymer ensuring a large pseudocapacitance of the electrode and a highly porous nitrogen-doped carbon matrix which provides a high conductivity and rigidity. Another line of experiment, analyzing the cycling stability of the novel electrode material found that after 5000 cycles the specific capacitance of the electrode was largely retained  (95.9 %), indicating the suitability of the foam composite for long-term operation.

Given these promising results, the authors conclude that the extraordinary characteristics of the synthesized electrode make it an auspicious candidate for applications in supercapacitors.

More details: Jun Zhu, Lirong Kong, Xiaoping Shen, Quanrun Chen, Zhenyuan Ji, Jiheng Wang, Keqiang Xu, Guoxing Zhu; Three-dimensional N-doped graphene/polyaniline composite foam for high performance supercapacitors, Applied Surface Science Volume 428, 15 January 2018, Pages 348-355. https://doi.org/10.1016/j.apsusc.2017.09.148

Researchers from the Swiss Federal Laboratories for Materials Science and Technology (Empa) have discovered that the insulating properties of state-of-the-art insulating bricks can be significantly enhanced by replacing the filling material with silica aerogel granules.

Commercially available insulating bricks (shown in the figure below), which unite structural and insulating functions in one component, are composed of a rigid clay or concrete shell in which the cavities are filled with an insulating material (e.g. mineral wool, PU foam). While their simplicity makes these monoliths, in theory, an ideal building material, their inferior insulating performance compared to a layered approach (i.e. layering different materials for structural and insulating purposes on top of each other), has limited the application of insulating bricks in the building sector.

Image of “Aerobrick” — Insulating brick with silica aerogel granule filling.

However, simulations and measurements showed that by replacing the filling material with silica aerogel the thermal conductivity of the insulating brick can be significantly reduced (> 30 %), yielding a higher insulating performance for a given brick thickness. Accordingly, this facilitates the construction of thinner insulating walls, which is crucial in locations where space-saving architecture is required (e.g. dense urban locations).

Due to the cost of aerogels, the “Aerobrick” is not an economically viable solution today. Nonetheless, the authors conclude that the projected future drop in aerogel prices will potentially transform aerogel-filled insulating bricks into a strong alternative to layered insulating techniques in the near future.

More details: Jannis Wernery, Avner Ben-Ishai, Bruno Binder, Samuel Brunner; Aerobrick – An aerogel-filled insulating brick, Energy Procedia Volume 134, October 2017, Pages 490–498 https://doi.org/10.1016/j.egypro.2017.09.607

Researchers from the SASTRA University (India) have successfully produced biodiesel from crude Hevea brasiliensis oil (CHBO) using an enzymatic transesterification process. 

Figure: Hevea brasiliensis seeds.

The major advantage of this process over the commonly deployed chemical transesterification process is that both the energy and post-treatment requirements are reduced significantly. This is because enzymatic transesterification neither requires high reaction temperatures nor basic or acid catalysts. Instead, an enzyme (here: lipase) active at temperatures slightly above ambient temperature, immobilized on a support material (here: silica aerogel), catalyzes the transesterfication reaction.

The researchers obtained fatty acid methyl ester (FAME) yields comparable to those reported for chemical transesterification (>90 %) at 30 °C when using lipase immobilized on silica aerogels. Furthermore, it was found that the enzymes largely retained their activity even after ten cycles. A characterization of the fuel synthesized from the rubber seeds showed that the fuel properties were compatible with ASTM Biodiesel (D 6751a) and European Biodiesel Standards (EN 14214).

Hence, the authors concluded that the enzymatic transesterfication of CHBO offers a more environmental compatible and economical approach to biodiesel synthesis when compared to the state of the art chemical transesterfication processes.

More details: A.Arumugam, D.Thulasidharan & Gautham B.Jegadeesan; Process optimization of biodiesel production from Hevea brasiliensis oil using lipase immobilized on spherical silica aerogel, Renewable Energy Volume 116, Part A, February 2018, Pages 755-761 https://doi.org/10.1016/j.renene.2017.10.021

A team of researchers from the Fuzhou University (China) has accomplished to synthesized self-supporting carbon nitride (CN) aerogels through an aqueous sol-gel process followed by freeze drying (see Figure).

a) Fabrication strategy of CN aerogel. b) Images of colloidal solutions of CN nanoparticles, CN hydrogel and CN aerogel.

The resulting aerogels, which were manufactured without the need for strong acids or cross-linking agents, exhibit electrical conductivity and high specific surface areas. In theory, these reported material characteristics are ideal preconditions for the utilization of the novel aerogels as photocatalysts.

To demonstrate the aerogels’ photocatalytic activity, the authors measured hydrogen evolution rates of several CN-based materials immersed in an irradiated water/triethanolamine (TEOA) solution and found that for the analyzed settings, the water splitting reaction was accelerated by almost one order of magnitude in the presence of the CN aerogel, when compared to bulk CN. Moreover, it was found that the aerogel catalysts exhibit good cycling stability, ensuring a good long-term reactivity of the material.

Apart from their application in solar-to-chemical energy conversion, the authors also see great potential for the CN aerogels in fields such as separation and sensing.

More details: Honghui Ou et al. Carbon Nitride Aerogels for the Photoredox Conversion of Water, Angewandte Chemie (2017). DOI: 10.1002/ange.201705926. http://onlinelibrary.wiley.com/doi/10.1002/anie.201705926/abstract

Read more at: https://www.analytik-news.de/Presse/2017/480.html

SEM image of (a) pure silica aerogel,
(b) resin without AAm monomer & 5 wt % aerogel)
and (c) resin with AAm monomer & 5 wt % aerogel).

Researchers of the University of Tehran (Iran) have attempted to boost the insulating behavior of two different acrylic resins by incorporating silica aerogels. Both resins were produced using methyl methacrylate, 2-ethylhexyl acrylate and acrylic acid monomers, but one resin additionally contained named acrylamide (AAm).

Unsurprisingly, the thermal properties of the resins were improved by the addition of silica aerogel. However, the mechanical properties (e.g. hardness and pull-off strength), which are a key factor for the application of resins as coating films, were shown to deteriorate in the presence of silica aerogels for the resin without AAm. In contrast to that, the resin containing AAm exhibited outstanding mechanical features, which was related to the formation of hydrogen bonds between the aerogel and the acrylamide monomers, ensuring a more homogeneous dispersion of aerogel particles in the resin (see SEM image on the right). The authors therefore concluded that the acrylic resin modified with acrylamide and silica aerogel particles can be used as an insulating roof coating to reduce the thermal losses in buildings.

It will be interesting to witness whether further developments in this field will transform aerogel containing paints to an integral part of energy efficient infrastructure.

More details: Karami et al. Improvement of thermal properties of pigmented acrylic resin using silica aerogel, Journal of Applied Polymer Science (2017). DOI: 10.1002/app.45640 http://onlinelibrary.wiley.com/doi/10.1002/app.45640/full

Read more at: http://www.farbeundlack.de/Wissenschaft-Technik/Rohstoffe/Lackbindemittel/Verbessert-Silica-Aerogel-die-thermischen-Eigenschaften-von-Acrylharz

Silver nanowire aerogel on flower.

Researchers from the Lawrence Livermore National Laboratory (California, USA) have recently manufactured monolithic aerogels consisting of silver nanowires (AgNW). The newly devised production technique, consisting of freeze-casting and sintering, facilitates tunable aerogel properties (e.g. bulk densities, pore structure, and conductivity). Due to its electrical conductivity, applications for the new material range from fuel cells to medical devices.

Although the discovered aerogel structures are of an outstanding quality, the researchers are already aiming at enhancing the material features.The researchers hope to further increase the electrical conductivity by reducing the average pore size and nanowire diameter, while at the same time increasing the length of the nanowires. Of course this prospect only boosts the likelihood of finding silver nanowire aerogels in future applications.

More details: Fang Qian et al. Ultralight Conductive Silver Nanowire Aerogels, Nano Letters (2017). DOI: 10.1021/acs.nanolett.7b02790

Read more at: https://phys.org/news/2017-10-ultralight-silver-nanowire-aerogel-boon.html