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In order to explore the effect of vacancy defects on the structural, electronic, magnetic and optical properties of CoS2 and FeS2, first-principles calculation method was used to investigate the alloys. The calculated results of materials without vacancy are consistent with those reported in the literatures, while the results of materials with vacancy defect were different from those of literatures due to the difference vacancy concentration. The Co vacancy defect hardly changes the half-metallic characteristic of CoS2. The Fe vacancy defect changes FeS2 from semiconductor to half-metal, and the bottom of the spin-down conduction band changes from the p orbital state of S to the d(t2g) orbital state of Fe, while the top of the valence band remains the d orbital d(eg) state of Fe. The half-metallic Co vacancy defects of CoS2 and Fe vacancy defects of FeS2 are expected to be used in spintronic devices. S vacancy defects make both CoS2 and FeS2 metallic. Both the Co and S vacancy defects lead to the decrease of the magnetic moment of CoS2, while both the Fe and S vacancy defects lead to the obvious magnetic property of FeS2. Vacancy defects enhance the absorption coefficient of infrared band and long band of visible light obviously, and produce obvious red shift phenomenon, which is expected to be used in photoelectric devices. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of CoS 2 /PPy nanocomposites as electrode materials for supercapacitors. We performed a simple and effective one-step hydrothermal fabrication of these nanostructures on nickel foam as substrate. After accurate characterization, electrochemical studies were performed using various techniques, such as cyclic voltammetry (CV), galvanostatic discharge (GCD), and electrochemical impedance spectroscopy (EIS). The result shows excellent electrochemical behaviour of the synthesized electrode with a specific capacitance of 605.2 C g−1 at a current density of 1 A g−1. Moreover, considerable capacitance retention (∼90.9% after 5000 cycles) was obtained. Next, an asymmetric supercapacitor was developed using a prepared electrode and activated carbon (AC /Ni foam) as cathode and anode, respectively. The device showed a high specific energy of 88.07 Wh kg−1 with a significant power of 4.95 kW kg−1 at an operating voltage of These unexpected results indicate that the CoS 2 /PPy nanostructure has the potential to become a promising electrode for energy storage systems. • The demand to enhance energy production and storage technologies has increased as natural energy supplies become scarcer. • Due to their many benefits, supercapacitors have been the subject of studies and papers in the realm of energy production and storage. • The new electrode material for use in electrochemical supercapacitors, which was made using a very straightforward and effective process, has been introduced and studied in the current research. • The major goal of this research is to create an effective electrode material for an electrochemical supercapacitor by utilizing the synergistic effects of a transition metal sulfide and the redox reactions of a conductive polymer to maximize the benefits. • The suggested modified electrode may be a competitive electrode material for usage in renewable energy suppliers and provide greater chances for a variety of future applications in power augmentation systems. [ABSTRACT FROM AUTHOR]

Acid-catalyzed hydrolysis and metal-catalyzed hydrogenolysis are two important methods for conversion of cellulose into high value-added chemicals, which preferentially use homogeneous acids and precious metals as catalysts, respectively. This paper reports that cobalt disulfide (CoS 2) can be competent in both acid hydrolysis and hydrogenolysis reactions as an inexpensive heterogeneous catalyst by controlling its morphology. Two kinds of CoS 2 with imperfect spherical (A-CoS 2) and regular octahedral (Syn-CoS 2) morphologies were tested in the conversion of 5-hydroxymethylfurfural (HMF) under a hydrogen atmosphere. Interestingly, A-CoS 2 showed high activity in the hydrogenolysis of HMF to 2,5-hexanedione (2,5-HD) with a yield of 81.5 wt%, while Syn-CoS 2 was responsible for the acid hydrolysis of HMF to methyl levulinate (ML) in high yield of 90.8 wt%. Characterization of the two catalysts suggested that Syn-CoS 2 had higher Co2+/Co3+ ratio in comparison to A-CoS 2 , leading to a proportional difference in their acid site numbers. The unique activity of these two catalysts was also reflected in the conversion of cellulose. In particular, Syn-CoS 2 exhibited high selectivity to ML formation from cellulose and good recyclability. CoS 2 can be competent in both acid hydrolysis and hydrogenolysis of cellulose as a heterogeneous catalyst by controlling its morphology. [Display omitted] • The morphology of CoS 2 plays an important role in its catalytic performance. • Spherical CoS 2 favors the production of 2,5-HF from HMF. • Regular octahedral CoS 2 favors the production of ML from HMF. • Regular octahedral CoS 2 has a higher Co2+/Co3+ ratio than spherical CoS 2. [ABSTRACT FROM AUTHOR]