Tuning the porous texture and specific surface area of nanoporous carbons for supercapacitor electrodes by adjusting the hydrothermal synthesis temperature

10.1039/c3ta12649hJournal of Materials Chemistry A14112962-1297

Flexible, Free-Standing and Holey Graphene Paper for High-Power Supercapacitors

Flexible supercapacitors based on bendable electrodes have aroused much interest for integration in clothing materials and portable electronic devices. However, simultaneous achievement of high areal energy and high power densities still presents a great challenge. Herein we report the fabrication of free-standing, flexible graphene papers suitable for high-performance flexible supercapacitors. The binder-free graphene paper is made up of two types of holey graphene units (i.e., wrinkled graphene sheets and graphene nanoscrolls) that produce closely interconnected, porous 3D graphene architectures. The graphene papers reported here can be fabricated with a variety of thicknesses and areal densities, in the 10–70 μm and 1–5 mg cm−2 ranges, respectively. They exhibit a remarkable electrochemical performance in aqueous electrolytes: a) a high cell areal capacitance (230–190 mF cm−2 in H2SO4 and 180–170 mF cm−2 in Li2SO4), b) an outstanding capacitance retention of 60 % at ultra-large current densities of 1200 mA cm−2, c) an excellent long-term cycling stability and d) high areal power (≈280 mW cm−2) and energy densities (≈32 and ≈60 μWh cm−2 in H2SO4 and Li2SO4, respectively). These highly flexible graphene papers show a great improvement, in terms of areal energy-power densities, in relation to the state-of-the-art graphene-based film electrodes.This research work was supported by the FICYT Regional Project (GRUPIN14- 102), Spanish MINECO (CTQ2015-63552-R) and Fondo Europeo de Desarrollo Regional (FEDER). G. A. F. thanks the MINECO for his predoctoral contract.Peer reviewe

Enhanced adsorption capacity and selectivity towards strontium ions in aqueous systems by sulfonation of CO2 derived porous carbon

Oxygen-enriched carbon materials derived from carbon dioxide were functionalized using sulfonic acid to remove Sr2+ ions from aqueous solutions. Synthesized sulfonated porous carbon materials (PC-SO3H) showed higher adsorption capacity and selectivity towards Sr2+ than non-functionalized porous carbons (PC). The formation of the C-SO3H functional group in PC-SO3H and its ability to proton exchange with Sr2+ was the main contributor to the enhanced performance. The maximum uptake capacity of Sr2+ by PC-SO3H was 18.97 mg g−1, which was 1.74 times greater than PC. PC-SO3H removed 99.9% and 97.6% of Sr2+ from aqueous solutions with initial Sr2+ concentrations of 5 mg L−1 and 10 mg L−1, respectively. Sr2+ adsorption showed rapid kinetics, reaching the adsorption equilibrium within 1 h with high adsorption capacity at equilibrium which is 3.52 times greater than that of PC. Additionally, PC-SO3H selectively adsorbed Sr2+ even in the presence of excess amounts of competing ions. Sulfonation of oxygen-enriched carbon had a significant effect on enhancing the affinity towards Sr2+ and suppressing adsorption towards other competing ions

Iron and Copper Containing Oxygen Reduction Catalysts From Templated Glucose-Histidine

International audienceNitrogen doped carbons loaded with non-precious transition metals are currently investigated as substitutes of Pt-based catalysts for oxygen reduction in Polymer Electrolyte Fuel Cells (PEMFC's). This paper reports the preparation of one kind of such catalysts using glucose/histidine mixtures added with Fe and Cu salts in the presence of silica gels as hard templating agent to increase carbon surface area. The resulting carbons contain nitrogen in amounts that depend on heating temperature (T=600 and T=900°C) on the glucose/histidine molar ratio and, more weakly, on the relative Fe/Cu amount. Surface areas are a function of reactant concentration and heating temperature, whereas pore size and pore size distribution only depend on glucose-histidine molar ratio. Cyclic voltammetry results on oxygen reduction depend on Fe/Cu ratio, the best result both in terms of incipient oxygen reduction potentials and currents being observed on samples only containing Fe, with no Cu added