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Polyvinylpyrrolidone (PVP)-assisted nanocatalyst preparation was succeeded by employing a controlled solvothermal route to produce efficient electrodes for electrochemical water-splitting applications. Bi 2 WO 6 and FeWO 4 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 Bi 2 WO 6 and FeWO 4 . The freestanding nanoplate array morphology of Bi 2 WO 6 and the fine nanosphere particle morphology of FeWO 4 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 Bi 2 WO 6 and FeWO 4 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.

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Investigation on the formation mechanism of the β-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 β-NiS, Ni(OH) 2 and composite-phase β-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 β-NiS, Ni(OH) 2 , and β-NiS@Ni(OH) 2 materials, respectively, were confirmed by SEM images. The characteristic vibration modes of β-NiS, Ni(OH) 2 , and β-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 β-NiS, Ni(OH) 2 , and β-NiS@Ni(OH) 2 products, respectively. The high-performance electrochemical water splitting was achieved for the β-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.

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