Ramakrishnan Kalai Selvan

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.

Eco-friendly synthesis of activated carbon from dead mango leaves for the ultrahigh sensitive detection of toxic heavy metal ions and energy storage applications

A novel spherical carbon nanoparticle decorated activated carbon (SNAC) material with a high surface area of about 1555 m2 g−1 is prepared from the dead mango leaves by an eco-friendly method for the detection of toxic heavy metal ions and energy storage applications. The limits of detection (LODs) for the determination of Cd(II), Pb(II), Cu(II), and Hg(II) ions at the SNAC-modified GCE are 24.4 × 10−9 M, 5.7 × 10−9 M, 23.2 × 10−9 M and 24.6 × 10−9 M, respectively. On the other hand, the obtained maximum specific capacitance for the single electrode from galvanostatic charge discharge is 478 F g−1 at 1 A g−1. The symmetric supercapacitor cell provides a higher specific capacitance (SC) of 55 F g−1 at 1 A g−1, and energy density of 10.75 W h kg−1 at a power density of 300 W kg−1.

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.

The preparation of MnFe2O4 decorated flexible graphene wrapped with PANI and its electrochemical performances for hybrid supercapacitors

A modest, cost effective and eco-friendly method is employed for the preparation of MnFe2O4 nanocube decorated, flexible graphene sheets, followed by polyaniline (PANI) which is wrapped by an in situ chemical oxidative polymerization method. The formation of the hybrid composites and their individual constituents are realized through X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR) and Raman spectroscopy. The MnFe2O4 nanocube decorated flexible graphene and PANI wrapped composite is visualised through transmission electron microscopic (TEM) images. The decorated MnFe2O4 particles have sizes in the range of 75–100 nm. The capacitive properties of the ternary composite is investigated and it has the obtained specific capacitance of 338 F g−1 at 0.5 mA cm−2 in 1 M NaCl aqueous electrolyte, which is 10 times greater than the pristine MnFe2O4 (32 F g−1). Similarly, the fabricated hybrid supercapacitor (MGP‖AC) provides the specific capacitance of about 51.87 F g−1 at 5 mV s−1 and its energy density is 10.25 W h kg−1 at 10 mA cm−2. Thus the obtained significant properties of the ternary composite are due to the distinctive characteristics of the individual constituents which leads to enhanced electrochemical properties like reducing the internal resistance and diffusion path length via the synergistic effect.

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.

An overview of AB2O4- and A2BO4-structured negative electrodes for advanced Li-ion batteries

Energy-storage devices are state-of-the-art devices with many potential technical and domestic applications. Conventionally used batteries do not meet the requirements of electric or plug-in hybrid-electric vehicles due to their insufficient energy and power densities. Graphite is used for the conventional anodes of Li-ion batteries. However, the specific capacity (372 mA h g−1) of a graphite electrode is not sufficient for high-power applications. Therefore, Co-, Ni-, Mn-, and Zn-based simple oxides have been investigated as anode components due to their high specific capacities (500–1000 mA h g−1). Among these, Co-based anodes have demonstrated the best electrochemical performances; however, Cos high cost and toxicity limit its use as an ideal anode component. Recently, mixed-metal oxides with AB2O4 (A = Cu, Co, Ni, Mn, and Zn; B = Co, Mn, and Fe) and A2BO4 (A = Co, Mn, and Fe; B = Sn, Si, Ti, and Ge) structures have received much interest, and their electrochemical performances have been extensively studied. This type of mixed-metal oxide affords the following main advantages: they store charge through conversion as well as alloying–dealloying processes, and they exhibit higher electronic conductivities than that obtained with simple metal oxides. The above points indicate the importance of AB2O4- and A2BO4-structured materials. The present review emphasizes the recent literature on the electrochemical performance of AB2O4- and A2BO4-structured materials and their composites and feasible ways to implement these materials in Li-ion batteries in the near future.

The sonochemical synthesis and characterization of Cu1−xNixWO4 nanoparticles/nanorods and their application in electrocatalytic hydrogen evolution

Cu(1-x)Ni(x)WO(4) (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) nanoparticles/nanorods have been prepared by a novel sonochemical method using cetyltrimethylammonium bromide (CTAB) as the structure directing agent. The prepared materials have been characterized by thermogravimetric analysis (TGA), x-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and BET specific surface area. The electrocatalytic activity towards the hydrogen evolution reaction (HER) has been studied for the Ni(2+)-substituted CuWO(4) nanoparticles by using linear sweep voltammogram measurements in a 1 M H(2)SO(4) solution. Cu(0.4)Ni(0.6)WO(4) (-473 mA cm(-2) at -1 V) shows a better catalytic activity than native CuWO(4) (-300 mA cm(-2) at -1 V).

SnO2 Pinning: An Approach to Enhance the Electrochemical Properties of Nanocrystalline CuFe2O4 for Lithium-Ion Batteries

A first attempt to synthesize and explore SnO2 pinned CuFe2O4 material as an anode for lithium-ion batteries has been made. The study highlights the approach of exploiting SnO2 pinning to enhance the electrochemical properties of nanocrystalline CuFe2O4 anodes. Virgin CuFe2O4 and SnO2 pinned CuFe2O4 powders were synthesized with 10–30 nm via under a one pot solution combustion method with specific calcination conditions. It is further understood that SnO2 pinning has reduced saturation magnetization and bulk resistance and thereby enhanced the charge-discharge characteristics of native CuFe2O4 anodes significantly in rechargeable lithium cells.

Surfactant-free hydrothermal synthesis of hierarchically structured spherical CuBi2O4 as negative electrodes for Li-ion hybrid capacitors

Hierarchically structured spherical CuBi2O4 particles were prepared using a facile hydrothermal method without using a surfactant over various hydrothermal reaction periods. The prepared CuBi2O4 samples were examined via X-ray diffraction (XRD), which confirmed the formation of a tetragonal crystal structure. The morphological features were analyzed using field emission scanning electron microscopy (FESEM), which elucidated the construction of the hierarchical microspherical CuBi2O4 particles. The plausible growth mechanism of the hierarchical structure was explained in terms of a time-dependent synthesis process and its crystal structure. The uniform hierarchical CuBi2O4 microspheres were used to fabricate a Li-ion hybrid capacitor (Li-HC) along with activated carbon (AC), the generated device delivers a stable specific capacitance of 26.5 F g(-1) over 1500 cycles at a high current density of 1000 mA g(-1) and a capacity retention of ∼86%. The AC/CB2 Li-ion hybrid cell exhibits high energy density and power density values of 24 W h kg(-1) and 300 W kg(-1), respectively.