By employing a simple hydrothermal process, a new class of ternary alkali metal-based chalcogenide (NaFeS2 (NFS)) has been produced and anchored on to reduced graphene oxide (rGO) sheets for the first time. Transition metal-based chalcogenides (TMC) exhibit limited conductivity because of their semiconducting nature and hence, engineering TMCs with 2D carbonaceous materials yields better catalytic performance. Alkali metal-based chalcogenides and their composites appear to be promising alternatives, whose electrochemical properties haven't been explored much. This work presents a detailed insight into the structure and morphology of the prepared NFS-rGO composite, along with its electrochemical properties. The cyclic voltammetry (CV) response at the NFS-rGO composite electrode for the redox probe K4Fe(CN)6 is better with low peak to peak separation potentials (ΔEp = 99 mV) compared to the individual components NFS (ΔEp = 190 mV) and GO (∆Ep = 130 mV), indicating a better electron transfer kinetics. The NFS-rGO composite electrode displays an enhanced electrocatalytic activity as evidenced by the high electrochemically active surface area (6.09 × 10−2 cm2) and the heterogeneous electron transfer rate constant (k0 = 5.4 × 10−2 cms−1). In general, the NFS-rGO composite exhibits excellent material as well electrocatalytic properties due to the synergistic effect between NFS and rGO and can further be explored for electrochemical sensing applications as well.
Many metal ions have been found to exert electrophilic effects on the dissociation of complexes and it has been proposed that a ternary intermediate is formed involving the complex and metal ion through the severing of one of the metal ligand bonds. To investigate this aspect, the dissociation of Fe (phen)32+ and effects of metal ion like Cu2+ in the presence of SDS micelles providing anionic micellar surface. These results confirm that the formation of such a ternary intermediate and marked micellar catalysis of the reaction.
A Li-rich layered oxide (LLO) cathode with morphology-dependent electrochemical performance with the composition Li1.23Mn0.538Ni0.117Co0.114O2 in three different microstructural forms, namely, randomly shaped particles, platelets, and nanofibers, is synthesized through the solid-state reaction (SSR-LLO), hydrothermal method (HT-LLO), and electrospinning process (ES-LLO), respectively. Even though the cathodes possess different morphologies, structurally they are identical. The elemental dispersion studies using energy-dispersive X-ray spectroscopy mapping in scanning transmission electron microscopy show uniform distribution of elements. However, SSR-LLO and ES-LLO nanofibers show slight Co-rich regions. The electrochemical studies of LLO cathodes are evaluated in terms of charging/discharging, C-rate capability, and cyclic stability performances. A high reversible capacity of 275 mA h g-1 is achieved in the fibrous LLO cathode which also demonstrates good high-rate capability (80 mA h g-1 at 10 C-rate). These capacities and rate capabilities are superior to those of SSR-LLO [210.5 mA h g-1 (0.1 C-rate) and 4 mA h g-1 (3 C-rate)] and HT-LLO [242 mA h g-1 (0.1 C-rate) and 22 mA h g-1 (10 C-rate)] cathodes. The ES-LLO cathode exhibits 88% capacity retention after 100 cycles at 1 C-rate. A decrease in voltage on cycling is found to be common in all three cathodes; however, minimal voltage decay and capacity loss are observed in ES-LLO upon cycling. Well-connected small LLO particles constituting fibrous microstructural forms in ES-LLO provide an enhanced electrolyte/cathode interfacial area and reduced diffusion path length for Li+. This, in turn, facilitates superior electrochemical performance of the electrospun Co-low LLO cathode suitable for quick charge battery applications.
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