Sofiane Boukhalfa

Atomic layer deposition of vanadium oxide on carbon nanotubes for high-power supercapacitor electrodes

Vanadium oxides may offer high pseudocapacitance but limited electrical conductivity and specific surface area. Atomic layer deposition allowed uniform deposition of smooth nanostructured vanadium oxide coatings on the surface of multi-walled carbon nanotube (MWCNT) electrodes, thus offering a novel route for the formation of binder-free flexible composite electrode fabric for supercapacitor applications with large thickness, controlled porosity, greatly improved electrical conductivity and cycle stability. Electrochemical measurements revealed stable performance of the selected MWCNT–vanadium oxide electrodes and remarkable capacitance of up to ∼1550 F g−1 per active mass of the vanadium oxide and up to ∼600 F g−1 per mass of the composite electrode, significantly exceeding specific capacitance of commercially used activated carbons (100–150 F g−1). Electrochemical performance of the oxide layers was found to strongly depend on the coating thickness.

Chemical Vapor Deposition of Aluminum Nanowires on Metal Substrates for Electrical Energy Storage Applications

Metal nanowires show promise in a broad range of applications, but many synthesis techniques require complex methodologies. We have developed a method for depositing patterned aluminum nanowires (Al NWs) onto Cu, Ni, and stainless steel substrates using low-pressure decomposition of trimethylamine alane complex. The NWs exhibited an average diameter in the range from 45 to 85 nm, were crystalline, and did not contain a detectable amount of carbon impurities. Atomic layer deposition of 50 nm of vanadium oxide on the surface of Al NW allows fabrication of supercapacitor electrodes with volumetric capacitance in excess of 1400 F·cc(-3), which exceeds the capacitance of traditional activated carbon supercapacitor electrodes by more than an order of magnitude.

Small‐Angle Neutron Scattering for In Situ Probing of Ion Adsorption Inside Micropores

Confined ions: The high penetrating power and sensitivity of neutron scattering to isotope substitution are harnessed to observe changes in the ion concentration in a porous carbon material as a function of the applied potential and the pore size. Depending on the solvent properties and the solvent-pore-wall interactions, either enhanced or reduced ion electroadsorption may take place.

In situ small angle neutron scattering revealing ion sorption in microporous carbon electrical double layer capacitors.

Experimental studies showed the impact of the electrolyte solvents on both the ion transport and the specific capacitance of microporous carbons. However, the related structure-property relationships remain largely unclear and the reported results are inconsistent. The details of the interactions of the charged carbon pore walls with electrolyte ions and solvent molecules at a subnanometer scale are still largely unknown. Here for the first time we utilize in situ small angle neutron scattering (SANS) to reveal the electroadsorption of organic electrolyte ions in carbon pores of different sizes. A 1 M solution of tetraethylammonium tetrafluoroborate (TEATFB) salt in deuterated acetonitrile (d-AN) was used in an activated carbon with the pore size distribution similar to that of the carbons used in commercial double layer capacitors. In spite of the incomplete wetting of the smallest carbon pores by the d-AN, we observed enhanced ion sorption in subnanometer pores under the applied potential. Such results suggest the visible impact of electrowetting phenomena counterbalancing the high energy of the carbon/electrolyte interface in small pores. This behavior may explain the characteristic butterfly wing shape of the cyclic voltammetry curve that demonstrates higher specific capacitance at higher applied potentials, when the smallest pores become more accessible to electrolyte. Our study outlines a general methodology for studying various organic salts-solvent-carbon combinations.

Kroll-carbons based on silica and alumina templates as high-rate electrode materials in electrochemical double-layer capacitors

Hierarchical Kroll-carbons (KCs) with combined micro- and mesopore systems are prepared from silica and alumina templates by a reductive carbochlorination reaction of fumed silica and alumina nanoparticles inside a dense carbon matrix. The resulting KCs offer specific surface areas close to 2000 m2 g−1 and total pore volumes exceeding 3 cm3 g−1, resulting from their hierarchical pore structure. High micropore volumes of 0.39 cm3 g−1 are achieved in alumina-based KCs due to the enhanced carbon etching reaction being mainly responsible for the evolution of porosity. Mesopore sizes are uniform and precisely controllable over a wide range by the template particle dimensions. The possibility of directly recycling the process exhaust gases for the template synthesis and the use of renewable carbohydrates as the carbon source lead to a scalable and efficient alternative to classical hard- and soft templating approaches for the production of mesoporous and hierarchical carbon materials. Silica- and alumina-based Kroll-carbons are versatile electrode materials in electrochemical double-layer capacitors (EDLCs). Specific capacitances of up to 135 F g−1 in an aqueous electrolyte (1 M sulfuric acid) and 174 F g−1 in ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) are achieved when measured in a symmetric cell configuration up to voltages of 0.6 and 2.5 V, respectively. 90% of the capacitance can be utilized at high current densities (20 A g−1) and room temperature rendering Kroll-carbons as attractive materials for EDLC electrodes resulting in high capacities and high rate performance due to the combined presence of micro- and mesopores.