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Abstract: Composites made from RuO2·xH2O particles supported on carbon nanofibres (CNF) have been prepared for supercapacitor electrodes. CNF, produced by Grupo Antolin Ing. SA. using a floating catalyst procedure was treated either in HCl or in HNO3. Then the composites were obtained by impregnation of CNF with an aqueous RuCl3·0.5H2O solution followed by filtering and alkali solution treatment. Heat treatment at 150°C for 2h was done. Specific capacitance of the composites has been measured and discussed on the basis of their RuO2·xH2O content and RuO2·xH2O particle size. The composites having RuO2·xH2O contents below 11wt% show RuO2·xH2O particles, which grow from 2 to 4nm as the RuO2·xH2O content increases. The specific capacitance of supported RuO2·xH2O, which can be very high (up to 840Fg−1), decreases as the RuO2·xH2O content increases and RuO2·xH2O particles grow. The composites having RuO2·xH2O contents above 11wt% show RuO2·xH2O particles of nearly constant size (4nm); the effect of increasing the RuO2·xH2O content is to increase the amount of particles but not the size of the particles. In these composites the specific capacitance of supported RuO2·xH2O is nearly constant (440Fg−1) and close to bare RuO2·xH2O (460Fg−1). [Copyright &y& Elsevier]

Abstract: Spinels of composition LiM Y Mn2−Y O4, M=Cr3+, Co3+, or Ni2+, Y =0.1 and 1 for the Cr and Co dopants, Y =0.05 and 0.5 for the Ni sample, have been synthesized by a sucrose-aided combustion method. The samples as prepared require of an additional thermal treatment at 700°C, 1h to get stoichiometric single-phase spinels. The samples consist of aggregated particles of small size (45–50nm) as deduced from transmission electron microscopy and X-ray powder diffraction. The electrochemical behaviour of the six spinels as cathodes in lithium cells has been analysed at 5 and 4V under high current, 1C rate. At 5V the discharge capacity of LiNi0.5Mn1.5O4 is higher than the one shown by LiCrMnO4 and LiCoMnO4, and it shows an elevated cyclability, i.e. capacity retention of 85.3% after 100 cycles. At 4V the discharge capacity is similar for LiNi0.05Mn1.95O4, LiCr0.1Mn1.9O4 and LiCo0.1Mn1.9O4, and all the three spinels show similar and very high cyclability, i.e. capacity retention >90% after 100 cycles. The spinels preserve their starting capacity up to currents as high as 2C rate. The nanometric size of the samples explains the high rate capability of the synthesized spinels. [Copyright &y& Elsevier]