B. Senthilkumar

Nano α-NiMoO4 as a new electrode for electrochemical supercapacitors

Nickel molybdate (α-NiMoO4) nanoparticles were prepared by a solution combustion synthesis (SCS) technique and, for the first time, were studied as a potential electrode material for supercapacitors. High specific capacitance (1517 F g−1) and energy density (52.7 W h Kg−1) were delivered by nano-α-NiMoO4 at a current density of 1.2 A g−1, due to the pseudocapacitive nature of the material.

Synthesis and improved electrochemical performances of nano β-NiMoO4–CoMoO4·xH2O composites for asymmetric supercapacitors

Nano-sized β-NiMoO4–CoMoO4·xH2O composites were synthesized by a solution combustion synthesis (SCS) technique. The effect of weight ratio of transition metal on the electrochemical capacitive performance of the nanocomposites was investigated by cyclic voltammetry and galvanostatic charge–discharge methods. The NiMoO4–CoMoO4·xH2O nanocomposite with weight ratio of 3:1 (Ni:Co) exhibits enhanced capacitive behaviour relative to other composites and delivered a maximum specific capacitance of 1472 Fg−1 at a current density of 5 mAcm−2. The enhancement in specific capacitance is due to the small particle size, uniform size distribution, high surface area and high weight fraction of Ni. The synergistic effect of nickel and cobalt improves the electrochemical behaviour relative to pure nickel and cobalt molybdates. A full cell was fabricated using the β-NiMoO4–CoMoO4·xH2O nanocomposite (3:1) and activated carbon (AC) as a positive and negative electrode, respectively. The cell delivered high capacitance (80 Fg−1) and energy density (28 Wh kg−1) and good cycling stability up to 1000 cycles.

Synthesis and electrochemical performances of maricite-NaMPO4 (M = Ni, Co, Mn) electrodes for hybrid supercapacitors

Sodium metal phosphates, NaMPO4 (M = Mn, Co and Ni) were successfully synthesized by a solution combustion synthesis (SCS) method using glycine-nitrate as a precursor. An XRD Rietveld refinement method revealed the crystal structure and lattice parameters of NaMPO4 (M = Mn, Co and Ni). For the first time, the crystal structure parameters of the orthorhombic NaNiPO4 maricite-type phase were evaluated. Similarly, it was identified that the NaCoPO4 and NaMnPO4 have high temperature hexagonal and maricite phases, respectively. The calculated BET specific surface areas (SBET) of NaMnPO4, NaCoPO4 and NaNiPO4 were 17.7, 22.6 and 18.7 m2 g−1, respectively. The NaMPO4 (M = Mn, Co and Ni) electrode exhibits good specific capacitance in 1 M NaOH electrolyte, when compared with 1 M Na2SO4, 1 M NaNO3 and 1 M NaCl. This difference in specific capacitance was analysed based on the influence of electrolyte anions (Cl−, SO42−, OH− and NO3−) and pH conditions of the electrolyte solution. Overall, maricite-NaNiPO4 nanoparticles provided a high specific capacitance of 368 F g−1 compared to NaMnPO4 (163 F g−1) and NaCoPO4 (249 F g−1) in 1 M NaOH electrolyte. Subsequently, a hybrid supercapacitor (AC‖NaNiPO4) was fabricated and it delivered a good specific capacitance and cyclic stability compared to the commercially available device.

Hydrothermal synthesis and electrochemical performances of 1.7 V NiMoO4⋅xH2O||FeMoO4 aqueous hybrid supercapacitor

One-dimensional (1D) NiMoO4⋅xH2O nanorods and β-FeMoO4 microrods are successfully synthesized by simple hydrothermal method without using any organic solvents. X-ray diffraction (XRD) patterns reveal the single phase formation of nickel molybdate (NiMoO4⋅xH2O) and pure monoclinic phase of β-FeMoO4. The growth of one dimensional morphology of both the molybdates are identified from scanning and transmission electron microscopes (SEM and TEM). The cyclic voltammogram envisage the pseudocapacitance behavior of NiMoO4⋅xH2O and β-FeMoO4 through the reversible redox reactions of Ni(3+)/Ni(2+) and Fe(3+)/Fe(2+) ions. An asymmetric supercapacitor is fabricated using NiMoO4⋅xH2O nanorods and β-FeMoO4 as a positive and negative electrode, respectively. The β-FeMoO4||NiMoO4⋅xH2O asymmetric supercapacitor delivers a capacitance of 81 F g(-1) at a current density of 1 mA cm(-2). The cell exhibits a high energy density of 29 W h kg(-1) and good cycling stability even after 1000 cycles.

Iron environment non-equivalence in both octahedral and tetrahedral sites in NiFe2O4 nanoparticles: Study using Mössbauer spectroscopy with a high velocity resolution

Mossbauer spectrum of NiFe2O4 nanoparticles was measured at room temperature in 4096 channels. This spectrum was fitted using various models, consisting of different numbers of magnetic sextets from two to twelve. Non-equivalence of the 57Fe microenvironments due to various probabilities of different Ni2+ numbers surrounding the octahedral and tetrahedral sites was evaluated and at least 5 different microenvironments were shown for both sites. The fit of the Mossbauer spectrum of NiFe2O4 nanoparticles using ten sextets showed some similarities in the histograms of relative areas of sextets and calculated probabilities of different Ni2+ numbers in local microenvironments.

Molten‐Salt Synthesis and Characterization of Li4Ti5O12

The submicron sized Li4Ti5O12 has been prepared by molten‐salt method at 800° C. The structural and morphological properties of synthesized Li4Ti5O12 were investigated by XRD, FTIR and SEM techniques. X‐ray diffraction pattern enumerates the formation of cubic structure with the lattice constant of 8.3019 A°. SEM image shows the uniform distribution of the particles with octahedral shape. The d.c. electrical conductivity is increased with increase in temperature and maximum conductivity is observed as 8.96×10−6 S.cm−1 at 200° C.