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Al-doped LiMn2O4 nanostructures are prepared by a single-step solution combustion method. The phase and vibrational mode of the prepared nanostructures are confirmed by XRD and Raman analyses. The SEM showed nanorod and nanosphere morphologies of the prepared samples. The nanostructures have a high specific surface area of 29.75 m2g−1 and a high specific capacitance of 361 Fg−1, in addition to better cyclic stability and high rate capability of oleic acid-based Al-doped LiMn2O4 electrodes. The nanostructures have a better performance in a stable electrolyte solution, a desirable electrolyte for supercapacitor applications under ambient conditions. [ABSTRACT FROM AUTHOR]

This work investigates the improved electrochemical performance of CoS 2 on composites CoS 2 /AC and CoS 2 /AC/g-C 3 N 4 that are prepared via hydrothermal method and the production of activated carbon is of bio-derived configuration. The structural, vibrational modes, and functional groups of the as synthesized nanostructures are confirmed through X-ray Diffraction (XRD), Raman, and FTIR analyses. The specific surface area of CoS 2 /AC and CoS 2 /AC/g-C 3 N 4 is 54.3 m2g−1, and 41.3 m2g−1, respectively. X-ray Photoelectron Spectroscopy (XPS) reveals the charge state of Co2+ and high charge transfer between Co and C in CoS 2 /AC/g-C 3 N 4 compared to CoS 2 /AC. Nanoprobe Projection X-ray microscopy (PXM) discloses distorted octahedral coordination of Co2+ and site-dependent charge transfer by Co in CoS 2 /AC in comparison with CoS 2 /AC/g-C 3 N 4. Further, the CoS 2 /AC electrode demonstrates a high specific capacity of 984 Fg−1 in the three-electrode system. The high-performance CoS 2 /AC electrode produced a high-power density of 2042.21 W Kg−1 and an energy density of 28.36 Whkg−1 in an aqueous electrolyte. The integration of CoS 2 nanoparticles into the CoS 2 /AC and CoS 2 /AC/g-C 3 N 4 composite framework significantly contributes to the improvement of specific capacity and excellent cycle stability up to 5000 cycles. This improvement could be influenced by several factors, such as reduced ion transport distances, strengthened interfacial interactions, high surface area, distortion of octahedral coordination of Co2+, and spatial-dependent charge transfer by Co in CoS 2 /AC. The distinct characteristics in specific capacity and cycling stability is attributed to the incorporation of CoS 2 nanoparticles within the CoS 2 /AC and CoS 2 /AC/g-C 3 N 4 composites that cause the short transport distance of the ions, enhanced interfacial interaction, and further provide better structural stability of the CoS 2 /AC and CoS 2 /AC/g-C 3 N 4 composite network. • CoS 2 /AC and CoS 2 /AC/g-C 3 N 4 Nanostructures are synthesized via hydrothermal method • Nanoprobe Projection X-ray Microscopy was performed to study the structural characteristics • Enhanced power density and energy density was obtained for the nanostructure • Excellent cyclic stability was obtained [ABSTRACT FROM AUTHOR]

• First report on strong hybridization of Fe-O in FeHAp for supercapacitor application. • High unoccupied density of states of Fe at 0.01FH compared with the other samples. • Reduction of coordination of Fe-O and its interatomic distance at 0.01FH. • The specific capacitance of asymmetric supercapacitor cell is 90 F/g at 30 mAg−1. Hydroxyapatite (HAp) is an interesting phosphate candidate with a weak electrical conductivity that can be tuned by doping metal ions to enhance the active sites for electrochemical charge storage. HAp and Fe-doped HAp were prepared by a wet chemical method. On doping, the crystallite size reduces to 9.56 nm. The surface area of 0.01FH (0.01% Fe) is 152.17 m2/g which is ∼3 times higher compared to PH. The 0.01FH sample shows the highest specific capacitance of 351.3 F/g at 30 mA/g. While X-ray photoemission spectroscopy shows the oxidation states of Fe in 2+ and 3+, X-ray absorption indicates (i) the enhancement of unoccupied density of states of Fe, and (ii) reduced interatomic distance of Fe-O in 0.01FH. These results show that the augmentation of surface properties and hybridization of Fe-O and the modification of its local atomic structures are responsible for high electrochemical charge storage in 0.01FH. [Display omitted] [ABSTRACT FROM AUTHOR]