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- Different alkyl xanthate complexes of cobalt (alkyl = Ethyl, Hexyl, Octyl) were synthesized and used for the synthesis of nanoparticles by a solvent-less route. The p-XRD of the nanoparticles showed the formation of the CoS phase only from all precursors. The effect of size and surface capping on energy generation and energy storage applications was investigated. The electrocatalytic performance of the synthesized samples for hydrogen (HER) and oxygen evolution reaction (OER), indicates that CoS synthesized from the octyl xanthate complex (CoS-Oct) showed higher electrocatalytic performance. A lower over potential of 325 mV and 200 mV was observed for CoS-Oct, at a current density of 10 mA/cm2, for OER and HER, respectively. The charge storage performance was also investigated, where an inverse trend was observed i.e. the highest specific capacitance (1500 F/g, at scan rate 2 mV/s) was observed for the CoS sample synthesized from ethyl xanthate (CoS-ET). Similarly, the discharge time for CoS-ET was longer as compared to the other samples, suggesting better performance for the charge storage applications. The use of cobalt xanthate complexes for the preparation of CoS by melt method, and the effect of self-capped and uncapped surface of CoS on supercapacitance and OER/HER performance, has never been investigated before.
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- The photocatalytic performance of graphitic carbon nitride can be enhanced multifold by introducing suitable dopants. Here we report incorporating a cost-effective, non-toxic and abundant element, i.e., tin, in elongated semiconducting carbon nitride (g-C3N4). A novel procedure was used to introduce varying amounts of tin to the g-C3N4 framework. The new photocatalysts (Sn–CN) were characterized by X-Ray Diffraction (XRD) and FT-IR measurements, confirming the absence of tin oxide and incorporation of tin in the g-C3N4 backbone. The SEM, EDX, TEM and XPS measurements demonstrated the elongated morphology and the presence of tin in the composite materials. BET measurements showed a relative increase in the specific surface area for the composites. The optical measurements showed enhanced solar light absorption and promoted the charge carrier's separation after the insertion of Sn to g-C3N4. Photoelectrochemical water dissociation measurements showed that 10% tin doping increased the activity of g-C3N4 to water photo-oxidation about four times. This improvement was analyzed by electrochemical impedance spectroscopy measurements.
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- The production of molecular hydrogen by photoelectrochemical dissociation (PEC) of water is a promising technique, which allows the direct transformation of solar energy into hydrogen, an energy vector acclaimed by the scientific community and policymakers. Hydrogen stores solar energy and will help overcome the energy crisis and associated environmental problems. Currently, the design and development of innovative photocatalysts with strong photoelectrochemical activity remain a major challenge, and the subject of intense research activity within the international scientific community. Here we describe the synthesis and photoelectrochemical properties of one-dimensional nanostructures of graphitic carbon nitride (1D-gC3N4) doped with phosphorus or sulfur (1D-P-gC3N4 &1D-S-gC3N4, respectively). A new synthesis method using supramolecular melamine, ammonium dihydrogen phosphate, and tri-thiocyanuric acid as precursors has been developed. The samples were characterized by powder-X Ray diffraction (p-XRD), X-Ray spectroscopy (EDS), transmission electron microscopy (TEM), Ultraviolet–visible (UV–Vis) spectroscopy, Fourier transform infrared spectra (FT-IR) and photoluminescence (PL) analysis. The activity towards the photo-oxidation of water was studied by linear scanning voltammetry (LSV). Compared to 3D material, the activity was found to be significantly improved, thanks in particular to the 1D morphology of gC3N4. It was further strengthened by doping with phosphorus and sulfur. The photo-oxidation mechanism of water was analyzed by photoelectrochemical impedance spectroscopy (PEIS). The measurements show that the resistance to charge transfer at the electrode/electrolyte interface can be greatly reduced by controlling the morphology of gC3N4, and that doping with phosphorus and sulfur also plays a positive role. The PEIS analysis makes it possible to demonstrate that the lifetime of the photo-generated electrons in 1D-gC3N4 is increased compared to 3D-gC3N4, and that doping with phosphorus or sulfur further improves it. The width of the forbidden bands and the position of the valence and conduction bands of the different materials were determined by Mott - Schottky type measurements.
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- Increasing demand for sustainable energy has boosted the exploration of inexpensive and efficient catalysts. Transition metal sulfides have been proven as efficient electrocatalysts for energy storage or energy generation applications. Herein, cubic phase α-MnS and transition metal (Cu2+, Fe3+, and Ni2+) doped MnS nanoparticles were synthesized via the hot injection method from their piperazinyl dithiocarbamate complexes, respectively. The morphology of pristine and TM-doped MnS nanoparticles was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis, while optical and structural properties were studied using UV–visible spectroscopy and powder X-ray diffraction (p-XRD), respectively. p-XRD analysis confirmed the successful incorporation of dopants into MnS lattice structure and suitability of heterocyclic dithiocarbamate complexes for phase/composition controlled synthesis of nanomaterials. The effect of doping on electrocatalytic properties was also investigated. The MnS-based electrodes doped with Ni and Fe presented satisfactory specific capacitances of 840 and 900 F/g at 2 mV/s scan rate. In addition, the testing for electrocatalysis for the water-splitting process demonstrated that Ni–MnS had a superior performance for HER with a η of 132 mV at 10 mA/cm2 and Tafel slope of 44 mV/dec. On the other hand, Fe–MnS showed better performance towards OER with a η of 280 mV at 10 mA/cm2 and a Tafel slope of 60 mV/dec.
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