High density and super ultra-microporous-activated carbon macrospheres with high volumetric capacity for CO2 capture

Activated carbon (AC) spheres with a diameter of 1.0–2.0 mm are synthesized from coal tar pitch for postcombustion carbon capture. The as-prepared AC macrospheres after KOH activation are found to possess extraordinarily developed microporosity of which 87% is ultra-microporosity with pore diameters less than 0.8 nm. Despite the relatively low surface area of just 714 m2 g−1 with a pore volume of 0.285 cm3 g−1, the macrospherical carbon adsorbents achieve exceedingly high CO2 uptake capacities of 3.15 and 1.86 mmol g−1 at 0 and 25 °C, respectively, with a CO2 partial pressure of 0.15 bar. Cyclic lifetime performance testing demonstrates that the CO2 uptake is fully reversible with fast adsorption and desorption kinetics. More importantly, due to their high bulk density of ≈1.0 g cm−3, the AC macrospheres exhibit extremely high volumetric CO2 uptakes of up to 81.8 g L−1 at 25 °C at 0.15 bar CO2, which represents the highest value ever reported for ACs. The high ultra-microporosity coupled with the potassium-modified physiochemical surface properties is found to be responsible for the outstanding CO2 adsorption performance of the pitch-based AC macrospheres

Supercapacitance from cellulose and carbon nanotube nanocomposite fibers

Copyright © 2013 American Chemical SocietyACS AuthorChoice open access articleMultiwalled carbon nanotube (MWNT)/cellulose composite nanofibers have been prepared by electrospinning a MWNT/cellulose acetate blend solution followed by deacetylation. These composite nanofibers were then used as precursors for carbon nanofibers (CNFs). The effect of nanotubes on the stabilization of the precursor and microstructure of the resultant CNFs were investigated using thermogravimetric analysis, transmission electron microscopy and Raman spectroscopy. It is demonstrated that the incorporated MWNTs reduce the activation energy of the oxidative stabilization of cellulose nanofibers from 230 to 180 kJ mol–1. They also increase the crystallite size, structural order, and electrical conductivity of the activated CNFs (ACNFs). The surface area of the ACNFs increased upon addition of nanotubes which protrude from the fiber leading to a rougher surface. The ACNFs were used as the electrodes of a supercapacitor. The electrochemical capacitance of the ACNF derived from pure cellulose nanofibers is demonstrated to be 105 F g–1 at a current density of 10 A g–1, which increases to 145 F g–1 upon the addition of 6% of MWNTs.The authors would like to thank the [Engineering and Physical Sciences Research Council] EPSRC (EP/F036914/1 and EP/I023879/1), Guangdong and Shenzhen Innovative Research Team Program (No. 2011D052,KYPT20121228160843692), National Natural Science Foundation of China (Grant No. 21201175), R&D Funds for basic Research Program of Shenzhen (Grant No. JCYJ20120615140007998), and the Universities of Exeter and Manchester for funding this research

Computational chemistry for graphene-based energy applications: progress and challenges

YesResearch in graphene-based energy materials is a rapidly growing area. Many graphene-based energy applications involve interfacial processes. To enable advances in the design of these energy materials, such that their operation, economy, efficiency and durability is at least comparable with fossil-fuel based alternatives, connections between the molecular-scale structure and function of these interfaces are needed. While it is experimentally challenging to resolve this interfacial structure, molecular simulation and computational chemistry can help bridge these gaps. In this Review, we summarise recent progress in the application of computational chemistry to graphene-based materials for fuel cells, batteries, photovoltaics and supercapacitors. We also outline both the bright prospects and emerging challenges these techniques face for application to graphene-based energy materials in future.vesk

A self-standing hydrogel neutral electrolyte for high voltage and safe flexible supercapacitors

International audienceThe development of safe flexible supercapacitors implies the use of new non-liquid electrolytes for avoiding device leakage which combine mechanical properties and electrochemical performance. In this sense, hydrogel electrolytes composed of a solid non-conductive matrix holding an aqueous electrolytic phase are a reliable solution. In this work, we propose a green physical route for producing self-standing hydrogel films from a PVA polymer based on the freezing/thawing method without using chemical cross-linking agents. Moreover, a neutral electrolytic phase as Na2SO4 is used for reaching higher cell voltages than in an acidic or basic electrolyte. Such new PVA-Na2SO4 hydrogel electrolyte, which also acts as separator, allows reaching voltages windows as high as 1.8 V in a symmetric carbon/carbon supercapacitor with optimal capacitance retention through thousands of cycles. Additionally, in reason of the fast mobility of the ions inside of the polymeric matrix, the hydrogel electrolyte based supercapacitor keeps the power density of the liquid electrolyte device

Vanadium nitride/carbon nanotube nanocomposites as electrodes for supercapacitors

International audienceNanostructured vanadium nitride/multiwalled carbon nanotubes (VN/CNTs) composites for pseudo-capacitor applications were obtained via the sol–gel synthesis of organic or inorganic vanadium oxide precursors followed by temperature programmed ammonia reduction. Nitrogen adsorption and impedance spectroscopy measurements showed that the incorporation of CNTs during VN synthesis allows VN/CNTs nanocomposites to be obtained with higher porosity, narrower pore size distribution, better conductivity and improved electrochemical properties compared to VN without CNTs. In particular, cyclic voltammetry using three-electrode cells in KOH shows that the contribution of the redox peaks is increased when VN is associated with the carbon nanotubes. As a consequence, a capacitance increase was measured in the two-electrode system. Another important advantage of using VN/CNTs composites is their high capacitance retention (58%) at high current density (30 A g−1) compared with VN (7%), resulting in an enhancement of the energy density at high power. All these positive aspects were significantly more marked when CNTs were incorporated during VN synthesis compared to a material resulting from the physical mixture of VN with CNTs. TEM, XPS and Raman analyses point out that the enhanced electrochemical performance observed with the VN/CNTs composite could be related to an intimate contact between VN and the CNT network, a homogeneous distribution of VN on CNTs and the presence of an open mesoporous texture favouring the access of the electrolyte to the active material surface

Solvent-free ionic liquids as in situ probes for assessing the effect of ion size on the performance of electrical double layer capacitors

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The Large Electrochemical Capacitance of Microporous Doped Carbon Obtained by Using a Zeolite Template

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