Prem Kumar Srivastava

Electrochemical performance of Ni/TiO2 hollow sphere in proton exchange membrane water electrolyzers system

This work presents the electrocatalytic evaluation of Ni/TiO2 hollow sphere materials in PEM water electrolysis cell. All the electrocatalysts have shown remarkably enhanced electrocatalytic properties in comparison with their performance in aqueous electrolysis cell. According to cyclic voltammetric results, 0.36 A cm−2 peak current density has been exhibited in hydrogen evolution reaction (HER) from 30 wt% Ni/TiO2 electrocatalyst. 15 wt% Ni-doped titania sample has shown the best result in oxygen evolution reaction (OER) with the anodic peak current density of 0.3 A cm−2. In the anodic polarization curves, the performance of 15 wt% Ni/TiO2 hollow sphere electrocatalyst was evaluated up to 140 mA cm−2 at comparatively lower over-potential value. 20 wt% Ni/TiO2 hollow sphere electrocatalyst has also shown electrochemical stability in PEM water electrolyzer for 48 h long analysis. The comparative electrocatalytic behavior of hollow spherical materials with non-sphericals is also presented, which clearly shows the influence of hollow spherical structure in greater electrocatalytic activity of the materials. The physical characterization of all the hollow spherical materials is presented in this work, which has confirmed their better electrochemical behavior in PEM water electrolyzer.

Nanostructured diffusion-limited-aggregation crystal pattern formation in a reactive microemulsion system

Nanostructured diffusion-limited-aggregation (DLA) crystal pattern formation in microemulsion consisting of water, styrene, cetyltrimethylammonium chloride (CTACl), potassium persulphate and an oscillating Belousov–Zhabotinsky (BZ) reactant is reported. A variety of spatiotemporal patterns like concentric wave, spatial (stripe) and chaotic patterns appear. A colloidal phase composed of numerous nano-sized particles has been observed. The solid phase nucleation has been found to occur in the colloidal phase and has been found to grow in a symmetric crystal pattern with the progress of the reaction finally exhibiting DLA structures. We show that the formation of a nanostructured DLA crystal pattern is governed by spatial structures emerging in the BZ microemulsion system. Without any spatial structure in the microemulsion system only hydrogel of high viscosity is formed. A nano-sized branched crystal pattern was formed with a particle diameter in the range of 60–100 nm, as evident by transmission electron microscope, powder x-ray diffraction and particle size analyser studies.

Morphological orders of spherulitic crystal textures in Belousov-Zhabotinsky-type oscillatory reaction system

The morphological orders of spherulitic crystal patterns in a Belousov-Zhabotinsky-type oscillatory reaction system were studied. The experiments showed that the morphology of crystal patterns were highly dependent on the reaction temperature. The reaction was initially carried out at 30 °C, leading to the growth of multi-centred spherulitic patterns. The single-centred spherulitic patterns with fairly large crystal fibrils were obtained at 35°C. A number of undersized crystal assemblies with fractal geometry were also investigated at 25°C. The gross morphology of the crystal patterns was examined using optical microscopy and a scanning electron microscope which revealed the fibrous organisations. A particle-mediated self-assembly scheme was proposed for the growth of the spherulitic patterns. The insight into the nucleation mechanism, growth behaviour, and morphological orders of the growing patterns is discussed in detail. The crystal phases, ordering of textures, and composition of the crystals were characterised by thermal and X-ray diffraction techniques.

Mechanism of Trees / Bushes Like Pattern in Chemical System

Trees / bushes like pattern have been investigated in succinic acid + ethylacetoacetate + Br O 3 − + Fe (phen)3+2 + Ce+4 + H2SO4 system at 30 °C in a petridish after 6 hours. These patterns are dependent on initial concentration of reactants and temperature. The system first shows fast appearing / disappearing blue and red pattern then bifurcate into concentric waves and finally shows a tree / bushes type pattern which grows in length and breadth against time. Microphotographs of trees / bushes pattern, succinic acid and ceric ammonium sulphate shows that a new compound has been formed which is responsible for this pattern. It is further confirmed by X-ray powder spectrum of trees / bushes pattern material and succinic acid. IR spectra of pattern material show that presence of cyclic compound in which Ce+4 ion coordinated by hydroxyethylacetoacetate. A tentative mechanism of pattern formation is proposed.