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Synthesis and characterization of aluminum doped zinc oxide nanostructures via hydrothermal route
(2014)
Stable crystalline aluminum doped zinc oxide (AZO) nanopowders were synthesized using hydrothermal treatment processing. Three different aluminum precursors have been used. The Al-precursors were found to affect the morphology of the obtained nanopowders. AZO nanoparticles based on zinc acetate and aluminum nitrate have been prepared with different Al/Zn molar ratios. XRD investigations revealed that all the obtained powders have single phase zincite structure with purity of about 99%. The effect of aluminum doping ratio in AZO nanoparticles (based on Al-nitrate precursor) on structure, phase composition, and particle size has been investigated. The incorporation of Al in ZnO was confirmed by UV-Vis spectroscopy revealing a blue shift due to Burstein-Moss effect.
Atomic layer deposition has proven to be a particularly attractive approach for decorating mesoporous carbon substrates with redox active metal oxides for electrochemical energy storage. This study, for the first time, capitalizes on the cyclic character of atomic layer deposition to obtain a highly conformal and atomically controlled decoration of carbon onions with alternating stacks of vanadia and titania. The addition of 25 mass% TiO2 leads to an expansion of the VO2 unit cell, thus greatly enhancing lithium intercalation capacity and kinetics. Electrochemical characterization revealed ultrahigh discharge capacity of up to 382 mAh[middle dot]g-1 of the composite electrode (554 mAh[middle dot]g-1 per metal oxide) with an impressive capacity retention of 82 mAh[middle dot]g-1 (120 mAh[middle dot]g-1 per metal oxide) at a high discharge rate of 20 A[middle dot]g-1 or 52 C. Rigorous stability benchmarking showed superior stability over 3,000 cycles when discharging to a reduced potential of -1.8 V vs. carbon. These capacity values are among the highest reported for any metal oxide system, while in addition, supercapacitor-like power performance and longevity are achieved. On a device level, high specific energy and power of up to 110 Wh[middle dot]kg-1 and 6 kW[middle dot]kg-1, respectively, were achieved when employing the hybrid material as anode versus activated carbon cathode.
This study presents electrospun niobium carbide/carbon (NbC/C) hybrid nanofibers, with an average diameter of 69 +/- 30 nm, as a facile precursor to derive either highly nanoporous niobium carbide-derived carbon (NbC-CDC) fibers for supercapacitor applications or niobium pentoxide/carbon (Nb2O5/C) hybrid fibers for battery-like energy storage. In all cases, the electrodes consist of binder-free and free-standing nanofiber mats that can be used without further conductive additives. Chlorine gas treatment conformally transforms NbC nanofiber mats into NbC-CDC fibers with a specific surface area of 1508 m2 g-1. These nanofibers show a maximum specific energy of 19.5 W h kg-1 at low power and 7.6 W h kg-1 at a high specific power of 30 kW kg-1 in an organic electrolyte. CO2 treatment transforms NbC into T-Nb2O5/C hybrid nanofiber mats that provide a maximum capacity of 156 mA h g-1. The presence of graphitic carbon in the hybrid nanofibers enabled high power handling, maintaining 50% of the initial energy storage capacity at a high rate of 10 A g-1 (64 C-rate). When benchmarked for an asymmetric full-cell, a maximum specific energy of 86 W h kg-1 was obtained. The high specific power for both systems, NbC-CDC and T-Nb2O5/C, resulted from the excellent charge propagation in the continuous nanofiber network and the high graphitization of the carbon structure.
