The influence of substrate temperature on growth of para-sexiphenyl thin films on Ir{111} supported graphene studied by LEEM

The growth of para-sexiphenyl (6P) thin films as a function of substrate temperature on Ir{111} supported graphene flakes has been studied in real-time with Low Energy Electron Microscopy (LEEM). Micro Low Energy Electron Diffraction (\mu LEED) has been used to determine the structure of the different 6P features formed on the surface. We observe the nucleation and growth of a wetting layer consisting of lying molecules in the initial stages of growth. Graphene defects -- wrinkles -- are found to be preferential sites for the nucleation of the wetting layer and of the 6P needles that grow on top of the wetting layer in the later stages of deposition. The molecular structure of the wetting layer and needles is found to be similar. As a result, only a limited number of growth directions are observed for the needles. In contrast, on the bare Ir{111} surface 6P molecules assume an upright orientation. The formation of ramified islands is observed on the bare Ir{111} surface at 320 K and 352 K, whereas at 405 K the formation of a continuous layer of upright standing molecules growing in a step flow like manner is observed.Comment: 9 pages, 7 figures, Revised Version as accepted for publication in Surface Scienc

Composite Electrodes for Electrochemical Supercapacitors

Manganese dioxide nanofibers with length ranged from 0.1 to 1 μm and a diameter of about 4–6 nm were prepared by a chemical precipitation method. Composite electrodes for electrochemical supercapacitors were fabricated by impregnation of the manganese dioxide nanofibers and multiwalled carbon nanotubes (MWCNT) into porous Ni plaque current collectors. Obtained composite electrodes, containing 85% of manganese dioxide and 15 mass% of MWCNT, as a conductive additive, with total mass loading of 7–15 mg cm−2, showed a capacitive behavior in 0.5-M Na2SO4 solutions. The decrease in stirring time during precipitation of the nanofibers resulted in reduced agglomeration and higher specific capacitance (SC). The highest SC of 185 F g−1 was obtained at a scan rate of 2 mV s−1 for mass loading of 7 mg cm−2. The SC decreased with increasing scan rate and increasing electrode mass

Effet de l’hydrogène sur les propriétés électriques et optiques de films de polyparaphénylène et de parasexiphényle implantés

Nous présentons les effets de divers traitements par l'hydrogène sur le polyparaphénylène ou le parasexiphényle implantés. Ce dernier matériau semble particulièrement fragile alors que le PPP paraît légèrement amélioré par ces procédés

Modeling pseudo capacitance of manganese dioxide

International audienceIn order to better analyze and to explain the electrochemical and physical behavior during both charge and discharge of a manganese dioxide based ECs, an original electrochemical model is developed in this paper. The 1D model is an adaptation of the transmission line model (TLM), taking into account the cation diffusion in the solid oxide. A linear relation between redox potential and oxidation state is used and leads to a physical relation between its slope and the pseudo capacitance of the material, confirmed by an experimental investigation of cyclic voltammograms. The model can be applied for any metal oxide pseudo-capacitive material

Theoretical and experimental investigation of the optical properties of poly(paraphenylene):evidence of chain length distribution

The optical properties of PPP have been investigated as function of the model based on distribution of conjugated segmentsof the polymer

Electrochemical Performance of Carbon/MnO2 Nanocomposites Prepared via Molecular Bridging as Supercapacitor Electrode Materials

International audienceThe chemical binding of amorphous manganese oxide and carbon particles was achieved with the diazonium chemistry. The synthesis was performed in two steps, with a first step consisting in the surface functionnalization of carbon particles with aminophenyl groups and the subsequent attachment of amorphous manganese oxide particles through generated phenyl groups. The bond between carbon and MnO2 particles is believed to occur between the carbon from the phenyl groups attached to carbon particles, and the oxygen atoms from the manganese oxide lattice. The capacitance of the carbon/MnO2 grafted nanocomposite electrode is doubled compared to a simple mixture of its two components. The capacitance of the nanocomposite electrode is also retained for faster cycling rates, thus highlighting the role of intimate coupling of carbon and MnO2

Electrochemical Performance of Carbon/MnO2 Nanocomposites Prepared via Molecular Bridging as Supercapacitor Electrode Materials

International audienc

Polycationic oxides as potential electrode materials for aqueous-based electrochemical capacitors

International audienc

Prototyping Aqueous Electrochemical Capacitors

International audienceAn ever increasing number of electrode materials are nowadays presented as potential candidates for electrochemical capacitor. This includes different forms of carbons (carbon nanotubes, graphene, activated carbon, ...), conducting polymers (PEDOT, PANI, PPy, ...), metal oxides (RuO2, MnO2, FeWO4, ...), or other inorganic materials such as metal nitrides, phosphates, etc... However, most of the reported performance of related electrodes are based on only few mg of active material and/or few mm2 surface area. Such low values definitely do not enable to upscale the performance using simple multiplying factor. Indeed, several studies have shown that experimental up-scaling of electrodes and devices often leads to quite different values, usually much lower than those reported for small scale electrodes.[1-3]In this manuscript, we will illustrate such discrepancy between small cell and larger cell performance by using commercially available activated carbon in different configurations, including coin-type cells (< 1F) and pouch cells (up to 25 F). The different parameters influencing the electrode preparation (binder, additives, porosity, ...) as well as those related with cell assembly (current collectors, separators, ...) will be detailed as well as their influence on the cell performance. Finally, a practical illustration of symmetrical carbon based EDLC in neutral aqueous electrolyte will be given, namely the internal hybridization of such cell in a PEMFC. Its influence on power capability will be reported and compared with external hybridization using a commercial cylindrical EDLC.[1] True performance metrics in electrochemical energy storage, Y. Gogotsi and P. Simon, Science, 334, 917 (2011).[2] Improving the volumetric energy density of supercapacitors, N. Goubard-Bretesché, O. Crosnier, F. Favier, T. Brousse, Electrochimica Acta 206 (2016) 458–463.[3] A Guideline for Reporting Performance Metrics with Electrochemical Capacitors: From Electrode Materials to Full Devices, A. Balducci, D. Belanger, T. Brousse, J.W. Long, W. Sugimoto, Journal of The Electrochemical Society (2017) 164 (7), A1487-A148