CoNiSe2 Nanostructures for Clean Energy Production.

Comparative investigation of the electrochemical oxygen evolution reaction (OER) activity for clean energy production was performed by fabricating three different electrodes, namely, NiSe2, CoSe2, and CoNiSe2, synthesized by hydrothermal treatment. Cubic, orthorhombic, and hexagonal structures of NiSe2, CoSe2, and CoNiSe2 were confirmed by X-ray diffraction (XRD) and also by other characterization studies. Perfect nanospheres, combination of distorted nanospheres and tiny nanoparticles, and sharp-edge nanostructures of NiSe2, CoSe2, and CoNiSe2 were explored by surface morphological images. Higher OER activity of the binary CoNiSe2 electrode was achieved as 188 mA/g current density with a comparatively low overpotential of 234 mV along with higher conductivity and low charge transfer resistance when compared to its unary NiSe2 and CoSe2 electrodes. A low Tafel slope value of 82 mV/dec was also achieved for the same binary CoNiSe2 electrode in a half-cell configuration. The overall 100% retention achieved for all of the fabricated electrodes in a stability test of OER activity suggested that the excellent optimum condition was obtained during the synthesis. This could definitely be a revelation in the synthesis of novel binary combinations of affordable metal selenides for clean energy production.

Bi2WO6 and FeWO4 Nanocatalysts for the Electrochemical Water Oxidation Process.

Polyvinylpyrrolidone (PVP)-assisted nanocatalyst preparation was succeeded by employing a controlled solvothermal route to produce efficient electrodes for electrochemical water-splitting applications. Bi2WO6 and FeWO4 nanocatalysts have been confirmed through the strong signature of (113) and (111) crystal planes, respectively. The binding natures of Bi-W-O and Fe-W-O have been thoroughly discussed by employing X-ray photoelectron spectroscopy which confirmed the formation of Bi2WO6 and FeWO4. The freestanding nanoplate array morphology of Bi2WO6 and the fine nanosphere particle morphology of FeWO4 nanocatalysts were revealed by scanning electron microscopy images. With these confirmations, the fabrication of durable, long-term electrodes for electrochemical water splitting has been subjected to efficient oxidation of water, confirmed by obtaining 2.79 and 1.96 mA/g for 0.5 g PVP-assisted Bi2WO6 and FeWO4 nanocatalysts, respectively. The water oxidation mechanism of both nanocatalysts has been revealed with the support of 24 h stability test over continuous water oxidation and faster charge transfer achieved by the smaller Tafel slope values of 75 and 78 mV/dec, respectively. Generally, these nanocatalysts are utilized for photocatalytic applications. The present study revealed the PVP-assisted synthesis to produce electrocatalytically active nanocatalysts and their electrochemical water-splitting mechanism which will offer a pathway for research interests with regard to the production of multifunctional nanocatalysts for both electro- and photocatalytic applications in the near future.

Electrochemical Performance of ß-Nis@Ni(OH)2 Nanocomposite for Water Splitting Applications.

Investigation on the formation mechanism of the ß-NiS@Ni(OH)2 nanocomposite electrode for electrochemical water splitting application was attempted with the use of the hydrothermal processing technique. Formation of single-phase ß-NiS, Ni(OH)2 and composite-phase ß-NiS@Ni(OH)2 has been thoroughly analyzed by X-ray diffractometer (XRD) spectra. Three different kinds of morphologies such as rock-like agglomerated nanoparticles, uniformly stacked nanogills, and uniform nanoplates for ß-NiS, Ni(OH)2, and ß-NiS@Ni(OH)2 materials, respectively, were confirmed by SEM images. The characteristic vibration modes of ß-NiS, Ni(OH)2, and ß-NiS@Ni(OH)2 nanocomposites were confirmed from Raman and Fourier transform infrared spectra. Near band edge emission and intrinsic vacancies present in the nanocomposites were retrieved by photoluminescence spectra. The optical band gaps of the synthesized nanocomposites were calculated as 2.1, 2.5, and 2.2 eV for ß-NiS, Ni(OH)2, and ß-NiS@Ni(OH)2 products, respectively. The high-performance electrochemical water splitting was achieved for the ß-NiS@Ni(OH)2 nanocomposite as 240 mA/g at 10 mV/s from a linear sweep voltammogram study. The faster charge mobile mechanism of the same electrode was confirmed by electrochemical impedance spectra and a Tafel slope value of 53 mV/dec. The 18 h of stability was achieved with 95% retention, which was also reported for the NiS@Ni(OH)2 nanocomposite for continuous electrochemical water splitting applications.