Abstract
Electrocatalytic water splitting is a promising solution to resolve the global energy crisis. Tuning the morphology and particle size is a crucial aspect in designing a highly efficient nanomaterials-based electrocatalyst for water splitting. Herein, green synthesis of nickel oxide nanoparticles using phytochemicals from three different sources was employed to synthesize nickel oxide nanoparticles (NiOx NPs). Nickel (II) acetate tetrahydrate was reacted in presence of aloe vera leaves extract, papaya peel extract and dragon fruit peel extract, respectively, and the physicochemical properties of the biosynthesized NPs were compared to sodium hydroxide (NaOH)-mediated NiOx. Based on the average particle size calculation from Scherrer’s equation, using X-ray diffractograms and field-emission scanning electron microscope analysis revealed that all three biosynthesized NiOx NPs have smaller particle size than that synthesized using the base. Aloe-vera-mediated NiOx NPs exhibited the best electrocatalytic performance with an overpotential of 413 mV at 10 mA cm−2 and a Tafel slope of 95 mV dec−1. Electrochemical surface area (ECSA) measurement and electrochemical impedance spectroscopic analysis verified that the high surface area, efficient charge-transfer kinetics and higher conductivity of aloe-vera-mediated NiOx NPs contribute to its low overpotential values.
Highlights
One of the greatest challenges of the technological era is the inflating global energy demand as electricity becomes a necessity in every facet of life
FESEM results show that NiOx NPs synthesized without extract had a particle size between 40 and 60 nm, whereas plant-extract-mediated NiOx were between 20 and 30 nm
The reduction in particle size upon introducing plant extracts was further supported by the shifting of the band gap to a higher value based on optical characterization
Summary
One of the greatest challenges of the technological era is the inflating global energy demand as electricity becomes a necessity in every facet of life. One of the major advantages of chemical capping agents is the tunability of the species to yield nanoparticles with different particle size and morphology. In this study we have explored three different plant extracts, namely, aloe vera leaves extract, papaya fruit peel extract and dragon fruit peel extract, as capping agents for NiOx NPs. Aloe vera gel contains mostly water and polysaccharides, such as pectins, cellulose, hemicellulose, glucomannan and acemannan [7,8]. Dragon fruit peel is reported to contain wide compositions of antioxidants such as betasianin, flavonoids, phenols, terpenoids, thiamine, niacin, pyridoxine and cobalamin [10] The effect of these different phytochemical compositions of extracts on the structural and morphological properties of the NiOx NPs and, their electrocatalytic activities for OER were studied and reported in detail
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