Poulomi Roy

Nanostructured anode materials for lithium ion batteries

High-energy consumption in our day-to-day life can be balanced not only by harvesting pollution-free renewable energy sources, but also requires proper storage and distribution of energy. In this regard, lithium ion batteries are currently considered as effective energy storage devices and involve the most active research. There exist several review articles dealing with various sections of LIBs, such as the anode, the cathode, electrolytes, electrode–electrolyte interface etc. However, the anode is considered to be a crucial component affecting the performance of LIBs as evident from the tremendous amount of current research work carried out in this area. In the last few years, advancements have been focused more on the fabrication of the nanostructured anode owing to its special properties, such as high surface area, short Li+ ion diffusion path length, high electron transportation rate etc. As the work in this area is growing very fast, the present review paper deliberates the recent developments of anode materials on the nanoscale. Different types of anode materials, such as carbon-based materials, alloys, Si-based materials, transition metal oxides, and transition metal chalcogenides, with their unique physical and electrochemical properties, are discussed. Various approaches to designing materials in the form of 0, 1 and 2D nanostructures and their effect of size and morphology on their performance as anode materials in LIBs are reviewed. Moreover, the article emphasizes smart approaches for making core–shell particles, nanoheterostructures, nanocomposites or nanohybrids with the combination of electrochemically active materials and conductive carbonaceous or electrochemically inactive materials to achieve LIBs with high capacity, high rate capability, and excellent cycling stability. We believe the review paper will provide an update for the reader regarding recent progress on nanostructured anode materials for LIBs.

In situ deposition of Sn-doped CdS thin films by chemical bath deposition and their characterization

In-situ Sn-doped CdS thin films have been deposited successfully by the chemical bath deposition method using tartaric acid as a complexing agent. The films have been characterized by x-ray diffraction for structure determination, and microstructural parameters like crystallite size, rms strain and dislocation density have been calculated using x-ray line profile analysis. The composition of the films has been determined by x-ray photoelectron spectroscopy and energy dispersive x-ray analysis. Optical studies show that the band gap decreases significantly for pure CdS (2.39?eV) to 3.8?mol% of Sn-doped CdS (1.84?eV). A detailed PL study of CdS when doped with varying Sn concentrations has also been discussed. Temperature variation of the electrical resistivity of Sn-doped CdS thin films confirmed their semiconducting behaviour similar to the pure CdS. It also shows that doping of Sn in CdS makes a pronounced drop in the room temperature resistivity value from 1010?103???cm for pure CdS to 3.8?mol% of Sn-doped CdS, respectively.

Nanostructured copper sulfides: synthesis, properties and applications

Among different metal chalcogenides, copper sulfides have been extensively studied in the past few years due to their semiconducting and non-toxic nature, making them useful in a wide range of applications from the energy to the biomedical fields. A series of stoichiometric compositions of copper sulfides from Cu-rich, Cu2S to Cu-deficient, CuS2 exist with different crystal structures as well as phases, resulting in different unique properties. The suitable band gap values in the range of 1.2–1.5 eV and unique optoelectronic properties indicate that the material is photocatalytically active and exhibits excellent plasmonic behavior. The material is also known for promising thermoelectric properties, converting waste heat into electricity through the Seebeck effect. The nanodimensional form of copper sulfides promotes their use to a more advanced level, tuning their properties with the size of the materials. In view of this, the present review article is focused on the compositions, phases and crystal structures, and different synthetic methodologies involved in the fabrication of 0D, 1D and 2D nanostructured copper sulfides. Moreover, recent advancements on their use in various applications will also be briefly discussed.

Three-dimensional NiCo2O4/NiCo2S4 hybrid nanostructure on Ni-foam as a high-performance supercapacitor electrode

The spinel structured ternary mixed metal oxide NiCo2O4 and sulphide NiCo2S4 are considered as promising pseudocapacitive materials. In view of this, the present work involves the fabrication of NiCo2O4 nanosheets and a NiCo2O4/NiCo2S4 hybrid nanostructure on Ni-foam as a conductive substrate by a facile ammonia evaporation technique. The NiCo2O4/NiCo2S4 hybrid nanostructure exhibits remarkable supercapacitive performance compared to bare NiCo2O4 nanosheets due to its three dimensional open structure and synergistic effect of NiCo2O4 and NiCo2S4. The hybrid nanostructure exhibits a specific capacitance as high as 3671 F g−1 at a current density of 1.8 A g−1 and 2767 F g−1 at 9 A g−1 with a capacity retention value of 84% at 10 A g−1 after 2000 cycles. Furthermore, the electrode composed of the NiCo2O4/NiCo2S4 hybrid nanostructure displays a noticeably high energy density as well as power density (8820 W kg−1 at 41.65 W h kg−1) compared to the NiCo2O4 nanosheets (5374.28 W kg−1 at 20.90 W h kg−1) with great flexibility. It is anticipated that the combination of materials and the special structural design lead to fast electrochemical redox reactions, fast electron/ionic transportation and mechanical integrity, which promote the NiCo2O4/NiCo2S4 hybrid nanostructure as a superior electrode in high performing flexible supercapacitors.

Structure and properties of conducting poly( o -phenylenediamine) synthesized in different inorganic acid medium

Poly(o-phenylenediamine) was chemically synthesized from the monomer o-phenylenediamine in various inorganic acid medium, viz., hydrochloric (HCl), sulphuric (H2SO4) and phosphoric acid (H3PO4) to investigate the differences in structures and properties of the synthesized polymers. From the various characterizations, it was confirmed that the ladder type polymer with some open ring structure was formed in HCl medium while open ring type amine derivative of polyaniline structure was obtained in H2SO4 medium and the ladder type dimer was formed in H3PO4 medium. The structural differences of the polymers were correlated with the polymerization mechanism in different acid medium. Thus, the polymer synthesized in H2SO4 was well soluble in polar organic solvent like dimethyl sulfoxide (DMSO), N,N-dimethyl formamide, tetrahydrofuran etc. and casting of freestanding film was possible from DMSO solution. The highest average DC conductivity of H2SO4 doped polymer synthesized in H2SO4 medium was observed as 7.14×10−4 S/cm. The conductivity and doping properties of the polymer were explained here from the proper characterizations.

Deposition of Tin Oxide Thin Films by Successive Ionic Layer Adsorption Reaction Method and Its Characterization

Tin oxide thin films were uniformly deposited by successive ionic layer adsorption reaction (SILAR) method on glass substrates using ethylene diamine as a complexing agent. The proper annealing treatment in air converts as-deposited amorphous films into crystalline and removes defects, reducing strain in the crystal lattice. The films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FTIR) spectroscopy. The film shows good optical transparency in the range of 200-1000 nm wavelength and electrical resistivity decreases upon annealing.