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Energy

Super & ultra capacitors

Supercapacitors fill the power and energy gap between electrolytic capacitors and batteries.Enhancing the energy and power density of supercapacitors is of greatinterest as it would open up a much wider application range.Thin film supercapacitors made of random networks of single-walled carbon nanotubes (SWNTs) were enhanced by the use of carbon nanohorns providing enhanced surface area and maintaining high permeability and porosity.

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Image of a typical SWNH/SWNT composite electrode bent to show its self-supporting capability (left). Schematic depicting the role of SWNTs as scaffolding for SWNH particles (left-high). Higher magnification SEM micrograph of SWNH/SWNT composite showing the SWNTs connecting the SWNH particles (right)

        

This combination results in an enhanced specific capacitance and a reduced equivalent series resistance (ESR) compared to a capacitor made of either individual component.the  a supercapacitor electrode based on this novel composite exhibited a very high power rating (990 kW/kg  396 kW/l). Moreover, these new hybrid electrodes allow the fabrication of supercapacitors with novel properties, e.g., a semitransparent supercapacitor. Likewise, polyaniline (PANI) nanobrushes/carbon nanohorn electrodes were synthesized by SWCNH solution containing aniline monomers and these materials were applied in supercapacitors observing an improvement of capacitive current.

Hydrogen & methane storage

Hydrogen is the energy vector which could help to replace fossil fuels. Apart the traditional storage methods, storing hydrogen by adsorption in porous materials seems the most efficient and potentially cheap way.Because of their low mass and high adsorption capacity, carbon-based nanostructures (nanotubes or nanohorns) turn out to be excellent candidates as porous materials.First results show that the interaction between hydrogen and nanohorns is far stronger than between carbon nanotubes and hydrogen. The findings suggest that carbon nanohorns are promising materials for the storage of hydrogen. Moreover, preliminary results suggest that addition of metal catalysts (transition metal, Ca or Mg) to nanoporous carbons with controlled nanoscale structure and porosity results in enhanced H2 adsorption. Theoretical calculations have demonstrated that this adsorption may be significantly increased if sufficient control of the structure can be attained.

Methane stands out among various alternative fuels when its profusion and availability are considered. However, the lack of an effective, economic and safe on-board storage system is one of the major technical barriers preventing methane-driven automobiles. The adsorption of methane inside single-wall carbon nanohorns was analysed and it was observed that the adsorption in the internal spaces of SWNH tubes is enhanced as the concentration of methane increases in the interstitial spaces.

Fuel cells

SWCNH were successfully used as Pt and Pt/Ru supports in polymer electrolyte membrane fuel cells (PEMFC).In particular, SWNH were used as electrocatalyst supports and tested in H2-fed PEMFC and direct methanol fuel cells (DMFC) showing catalytic activities 60% higher than using carbon black as the electrocatalyst support in both types of fuel cells.

Other

Notable electronic transfer within zinc phthalocyanine and oxidized single-walled nanohorn was revealed in both the ground and excited states is revealed by steady-state absorption and fluorescence spectroscopy measurements. This kind of electron transfer may broaden the use of SWNH nanoensembles in photochemistry and photobiology. Also a water-soluble nanoensemble of SWCNH and anionic porphiryne/pyrene was studied to evidence the importance of CNHs as electron acceptors towards the preparation of some novel donor-acceptor nanosystems.

The feasibility of a miniature biofuel cell (BFC) with single-walled carbon nanohorn (SWNH)-modified carbon fiber microelectrodes (CFMEs) as the substrate was demonstrated. The bioanode was constructed by using glucose dehydrogenase (GDH) as the biocatalyst on SWNH-modified CFMEs and  an electrically contacted bilirubin oxidase (BOD)-SWNHs/CFME was prepared as the cathode.The maximum power output of the miniature cell was 140 µW cm-2 at 0.51 V

References & Examples

Enhanced supercapacitors from hierarchical carbon nanotube and nanohorn architectures - J. Mater. Chem., 2011, 21, pp 7810-17815

High-Power Supercapacitor Electrodes from Single-Walled Carbon Nanohorn/Nanotube Composite - ACS Nano, 2011, 5 (2), pp 811–819

US Patent 7209341 - Carbon nanohorn supercapacitor

Template-free electrochemical nanofabrication of polyaniline nanobrush and hybrid polyaniline with carbon nanohorns for supercapacitors - Nanotechnology 21 (2010) 435702

Tailoring of single walled carbon nanohorns for hydrogen storage and catalyst supports - Carbon 2007 Conference Proceedings

Changes in hydrogen storage properties of carbon nano-horns submitted to thermal oxidation - International Journal of Hydrogen Energy Volume 35, Issue 17, September 2010, Pages 9070–9081

High-density of methane confined in internal nanospace of single-wall carbon nanohorns - Carbon, Volume 43, Issue 13, November 2005, Pages 2826-2830

US Patent application 20060165992 - Single walled carbon nanohorn adsorptive material and method for production thereof

Use of single wall carbon nanohorns in polymeric electrolyte fuel cells - Journal of Materials Science, Volume 46, Issue 22, November 2011, Pages 7198-7205

Patent WO2004/030128 Catalytic electrode for fuel cell, fuel cell, catalyst bearing particle for fuel cell and process for producing the catalytic electrode for fuel cell

Aqueous carbon nanohorn-pyrene-porphyrin nanoensembles: Controlling charge-transfer interactions - Diamond and Related Materials Volume 16, Issue 4-7 SPEC. ISS., April 2007, Pages 1150-1153

Photoinduced Electron Transfer in Zinc Phthalocyanine Loaded on Single-Walled Carbon Nanohorns in Aqueous Solution - Advanced Materials Volume 21, Issue 43, pages 4366–4371, November 20, 2009

A single-walled carbon nanohorn-based miniature glucose/air biofuel cell for harvesting energy from soft drinks - Energy and Environmental Science Volume 4, Issue 4, April 2011, Pages 1358-1363

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