Perumal Elumalai

Tunable supercapacitor performance of potentiodynamically deposited urea-doped cobalt hydroxide

Cobalt hydroxide with or without adding urea was potentiodynamically synthesized from a nitrate bath, and the resultant hydroxides were examined as electrode material for supercapacitor applications. The deposited hydroxides were characterized by X-ray diffraction, field-emission scanning electron microscopy and Fourier transformed infra-red spectroscopy. With urea in the nitrate bath, the specific capacitance of Co(OH)2 could be tuned from 700 F g−1 to 1200 F g−1 at a current of 0.5 mA. It was shown that the addition of just 2 wt% urea in the nitrate bath had a strong influence on the supercapacitor performance, exhibiting the highest specific capacitance of 1200 F g−1. The high-performance of the urea-doped Co(OH)2 was attributed to the better access of electrolyte due to well-stabilized basal length.

Performance of Solid-state Hybrid Energy-storage Device using Reduced Graphene-oxide Anchored Sol-gel Derived Ni/NiO Nanocomposite

The influence of (nickel nitrate/citric acid) mole ratio on the formation of sol-gel end products was examined. The formed Ni/NiO nanoparticle was anchored on to reduced graphene-oxide (rGO) by means of probe sonication. It was found that the sample obtained from the (1:1) nickel ion: citric acid (Ni2+: CA) mole ratio resulted in a high specific capacity of 158 C/g among all (Ni2+: CA) ratios examined. By anchoring Ni/NiO on to the rGO resulted in enhanced specific capacity of as high as 335 C/g along with improved cycling stability, high rate capability and Coulombic efficiency. The high conductivity and increased surface area seemed responsible for enhanced electrochemical performances of the Ni/NiO@rGO nanocomposite. A solid-state hybrid energy-storage device consisting of the Ni/NiO@rGO (NR2) as a positive electrode and the rGO as negative electrode exhibited enhanced energy and power densities. Lighting of LED was demonstrated by using three proto-type (NR2(+)|| rGO(−)) hybrid devices connected in series.

Highly selective zirconia-based propene sensor attached with sol–gel derived NiO nanospheres

Nanospheres of nickel oxide (NiO) were synthesized by a simple modified sol–gel route using nickel nitrate as a precursor and citric acid as a gelling agent. An yttria-stabilized zirconia (YSZ)-based sensor was fabricated using the sol–gel derived NiO nanospheres as the sensing electrode (SE) and Pt as the reference electrode (RE), and its sensing characteristics were examined in the temperature range of 650–800 °C under various O2 concentrations (5, 10, 15 and 21 vol%). The fabricated NiO-SE was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It turned out that the sensor attached with the sol–gel derived NiO-SE exhibited a selective and sensitive response to propene (C3H6) at 700 °C in all measured O2 concentrations. The sensor showed the highest sensitivity and selectivity to propene in 21 vol% O2. In addition, the sensor exhibited a stable response to C3H6 for about two months. The sensing mechanism was confirmed to be mixed-potential-type. It is believed that the nanofeatures associated with the sol–gel derived NiO seemed to be responsible for the high sensitivity and selectivity to C3H6.

Supercapacitor and photocatalytic performances of hydrothermally-derived Co3O4/CoO@carbon nanocomposite

Cobalt oxide (Co3O4/CoO) nanoparticle-embedded carbon matrix (Co3O4/CoO@carbon) was synthesized by pyrolysis of cobalt-salen complex ([Co(salen)]) followed by hydrothermal treatment. The X-ray diffraction, Raman and Fourier transform infra-red spectroscopies confirmed the presence of Co3O4/CoO in the carbon matrix. The scanning electron microscopy observation showed highly agglomerated spike-like grains. The TEM observation confirmed that the Co3O4/CoO grains were embedded in the carbon matrix. The supercapacitor studies conducted on the Co3O4/CoO@carbon matrix revealed a specific capacity of 324 C g−1 at 1 A g−1 in 1 M KOH. The Co3O4/CoO@carbon electrode also exhibited long-term life cycle with a high Coulombic efficiency of 96%. It is believed that the carbon present in Co3O4/CoO acted as a conductive nano-network, leading to such a high supercapacitor performance. The Co3O4/CoO@carbon material was also tested for its catalytic property, and it was found that the prepared material exhibited excellent photocatalytic degradation of azure A dye.

Effect of citric acid on formation of oxides of Cu and Zn in modified sol-gel process: A comparative study

AbstractWe report here the influence of citric acid concentration on the formation of sol-gel products in each of Cu and Zn systems by using respective metal nitrate as precursor and citric acid as gelling agent. The synthesized sol-gel products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), Fourier transform infra-red (FT-IR) spectroscopy and UV-Visible diffused reflectance spectroscopy (UV-Vis DRS). The influence of citric acid concentration on the formation of metal/metal oxide in each case was primarily investigated by varying the molar ratio of each metal nitrate (N) and citric (C) acid (N:C = 1:1, 1:2, 1:4, 1:6 and 1:8). It was observed that at low N:C molar ratios (1:1) and (1:2), the Cu system had only CuO and at high N:C molar ratio, lower oxidation state of copper (Cu2O and Cu) has resulted. Distinctly, irrespective of the N:C molar ratio, the sol-gel product of Zn system was only single phase of ZnO. The SEM observations confirmed that the grains of these two metal systems were spherical in nature. In each metal system, at high N:C molar ratio, small grain size has resulted. At high N:C ratio, lower oxidation state of metal ion is resulted where the metal system is susceptible for reduction. The susceptibility of metal ions to undergo reduction controlled the formation of end products in the sol-gel process. Graphical AbstractInfluence of citric acid concentration on the formation of sol-gel products in Cu and Zn systems was investigated. The end products in sol-gel process is controlled by the ability of metal ion to undergo reduction.

Tunable compositions of Pd100−xCux catalysts towards the electrooxidation of ethanol and ethylene glycol

We present here an extensive study on the electrocatalytic activity of varying compositions of Pd100−xCux (100 ≤ x ≤ 0) catalysts towards the electrooxidation of ethanol and ethylene glycol (EG). The Pd100−xCux catalysts were electrochemically synthesized and characterized by field-emission scanning electron microscopy, energy-dispersive X-ray analysis, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Electrochemical investigations were carried out by means of cyclic voltammetry, linear sweep voltammetry and chronoamperometry studies in 1 M KOH and the respective alcohols. The electrocatalytic activity of the Pd100−xCux catalysts was quantified by their mass activity (mA mg−1) and onset potential (V vs. RHE). It turned out that the catalysts Pd90Cu10, Pd80Cu20 and Pd70Cu30 exhibited enhanced activity compared to pristine Pd for both the alcohols. On the other hand, the Pd60Cu40 and Pd samples exhibited a similar performance towards ethanol oxidation implying possible attractive substitution of 40% Pd with Cu, which will remarkably reduce the cost of the Pd electrocatalyst for direct alcohol alkaline fuel cell applications. For EG oxidation, the Pd80Cu20 and Pd70Cu30 catalysts exhibited stable performance accompanied by high mass activity. The combined effects of electronic coupling between Pd and Cu and the preferential oxophilicity of copper in the PdCu alloy are ascribed to be responsible for such an enhanced electrocatalytic activity.