Ternary alkali metal chalcogenide engineered reduced graphene oxide (rGO) as a new class of composite (NaFeS2-rGO) and its electrochemical performance

Elucidating an efficient super-capacitive response of a Sr2Ni2O5/rGO composite as an electrode material in supercapacitors

Mixed transition metal oxides have emerged as efficient electrode materials because of their significant cycling stability, and superior capacitance values, resulting in remarkable electrochemical outputs. In this regard, Sr2Ni2O5/rGO composites were synthesized using a facile solvothermal method to achieve efficient electrochemical pursuits. X-ray diffraction confirmed the formation of finely crystallized samples with the phase evolution from orthorhombic to hexagonal. Morphological studies using field emission scanning electron microscopy depicted the desired porosity in samples with well-defined shapes and sizes of homogeneously distributed grains. Elemental analysis verified the pictorial depiction of sample compositions in terms of their stoichiometric ratios. The composite sample with composition Sr2Ni2O5@15%rGO exhibited superior electrochemical performance compared to other samples, depicting the highest specific capacitance of 148.09 F g-1 at a lower scan rate of 0.005 V s-1 observed via cyclic voltammetry. In addition, the cyclability performance of Sr2Ni2O5@15%rGO exhibits 68.5% capacitive retention after 10 000 cycles. The energy density as determined using a two-electrode system remained 4.375 W h kg-1 for the first cycle which reduced to 1.875 W h kg-1 for the 10 000th cycle, with a maximum power density of 1.25 W kg-1. The Nyquist plot represented less barrier to charge transfer. The electrode with particular composition Sr2Ni2O5@15%rGO emerged as significant, exhibiting a superior surface capacitive charge storage, that makes it a potential candidate as an electrode material.

Valorization of waste Fe-rich sludge as erdite/KFeS2 rods under atmosphere condition and evaluation of their mutual transformation

Pilot scale production of one-dimensional (FeS₂)_n^n- rods was performed by using an automatic 20 L vessel at 80 °C under atmosphere condition with the resource utilization of Fe-rich sludge. The sludge was simulated at lab-scale with chemical pure of ferric trichloride. After the sludge treatment, the corresponding rods were not formed at room temperature. But by heating at 80 °C, erdite rod was well-crystallized after 0.5 h by only adding Na halite, and KFeS₂ rod was crystallized weakly after 2 h and highly at 10 h with the addition of K halite. After 48 h heating, the rods grow radially to 300 nm for erdite, but to 5 μm for KFeS₂. However, at room temperature, erdite rod was converted to high crystallized KFeS₂ in KOH water or ethanol solution, whilst the conversion of KFeS₂ rod to erdite also occurred in NaOH water solution, but terminated in NaOH ethanol solution, without any morphology change. It is also noted that with the presence of both Na and K halite, the rod was an intermediate of erdite to KFeS₂ with 1 μm length after heating at 100 °C but converted to 10-μm-length KFeS₂ crystal at the temperature of > 120 °C. The thermodynamic results confirmed that during the rod polymerization, the Fe(OH)₃HS^- formation was the sole rate-limiting step and showed a positive Gibbs value of 6.45 kJ/mol at room temperature and negative values at the temperature of > 48 °C. In summary, this method not only enabled the vaporization of waste Fe-rich sludge as value-added rods without generating any secondary waste but also showed a new route for the in situ conversion of erdite/KFeS₂ rods at room temperature.