Pradip Kar

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.

Isomeric Effects on Structures and Properties of Polyaminophenols Synthesized in Basic Medium

The oxidative chemical polymerizations of three isomers of aminophenol, ortho, meta, and para (PoAP, PmAP, PpAP) were performed in aqueous NaOH using ammonium persulfate (APS) as oxidant. Solubility tests for the synthesized polymers were performed in various solvents and it was found that all three polymers are soluble in DMSO and DMF. PpAP is soluble in aqueous strong acid, as well as in base, but PoAP is soluble in acid, whereas PmAP is soluble in base. The difference in their solubility is due to their structural difference, which can be supported by the proposed mechanisms of polymerizations. The film casting from the DMF or DMSO solution of PoAP and PpAP is difficult due to the presence of quinone impurity while casting of PmAP film from DMSO solution is possible. The intrinsic viscosities of the polymers were determined from the DMSO solution. The polymers were characterized by UV-VIS, FTIR and1H-NMR spectroscopy and elemental analyses. From structural analysis, it is found that PoAP and PpAP do not contain π -electron conjugation due to ether linkage in the backbone chain. So, PoAP and PpAP do not show any conductivity like sulfuric acid doped PmAP.

Optimization for the Chemical Synthesis of Conducting Poly (m-aminophenol) in HCl using Ammonium Persulfate

Poly (m-aminophenol) (PmAP) was synthesized from m-aminophenol (mAP) by ammonium persulfate (APS) as an oxidizing agent in aqueous HCl. Polymerization conditions were optimized by varying HCl concentration, amount of mAP and APS, temperature and time. The synthesized polymers were insoluble in organic solvents even after dedoping. The polymers were characterized by UV-VIS and Fourier transform infrared spectroscopy, thermogravimetric and elemental (CHNS) analyses. Four-probe DC electrical conductivity of the pelletized polymer was measured. The spectral results clearly indicated that the ladder structure was formed during the chemical polymerization of mAP in aqueous HCl. This structure was supported by elemental analysis. Thermal stability of the undoped and in-situ HCl doped polymers was measured. The highest conductivity of the synthesized polymer pellet was 1.0 × 10-7 S cm -1. A polymerization mechanism was proposed.

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.

Doping of the Processable Conducting Poly(m-Aminophenol) with Inorganic Acids

Poly(m-aminophenol) (PmAP) was synthesized from m-aminophenol (mAP) in aqueous sodium hydroxide (NaOH) using ammonium persulfate (APS) as an oxidative initiator. Free standing PmAP films were cast from dimethyl sulfoxide (DMSO) solution of the polymer. Then the film was doped with various inorganic acids using a solution doping technique. Various inorganic acid doped PmAP films were characterized by ultraviolet-visible (UV-Vis), Fourier transform infrared (FTIR), and energy dispersive X-ray (EDS) spectroscopies, X-ray diffraction (XRD) analysis and elemental (C, H, N, S, O) analysis. All the results were explained on a comparative basis and the doping scheme was proposed. The DC-conductivity of the inorganic acid doped films was measured using a standard four-probe method. From the DC-conductivity measurements it was found that sulfuric acid had a better doping effect in terms of conductivity than that of the other inorganic acids used, perchloric acid and phosphoric acid. An explanation of the reason for the better doping effect of sulfuric acid than that of the other inorganic acids is given.

Effect on Structure, Processability, and Conductivity of Poly(m-aminophenol) of the Initial Acidity/Basicity of the Polymerization Medium

Poly(m-aminophenol) was synthesized chemically from aqueous solutions of the monomer meta-aminophenol (mAP) in the initially acidic or basic medium by using ammonium persulfate as an oxidant. The polymer (PmAPA) synthesized in initially aqueous HCl medium was insoluble in organic solvents even after dedoping, while the polymer (PmAPB) synthesized in initially aqueous NaOH solution was found to be soluble in high pH water, dimethyl sulfoxide (DMSO), and dimethylformamide. It was possible to obtain a stable, free-standing film from the DMSO solution of PmAPB but, due to insolubility and infusibility, film casting was not possible for PmAPA. The synthesized polymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analyses, X-ray diffraction spectroscopy, and four-probe DC electrical conductivity. A ladder-type structure was formed during the chemical polymerization of mAP in aqueous HCl, while a hydroxyl derivative of polyaniline was obtained in aqueous NaOH. The conductivity of sulfuric acid-doped PmAPB was 104 times higher than that of in situ HCl-doped PmAPA. An explanation of the difference in properties of both polymers is given based on molecular modeling.

Synthesis of processable conducting poly(m-aminophenol) having structure like keto derivative of polyaniline

Poly(m-aminophenol) was synthesized chemically from m-aminophenol in aqueous hydrochloric acid using ammonium persulfate as an oxidizing agent. To get processable poly(m-aminophenol) the polymerization condition was optimized by varying HCl concentration and temperature. The synthesized polymers at lower HCl concentration were insoluble in organic solvents, but synthesized polymers at higher acid concentration were found to be soluble in aqueous sodium hydroxide, dimethyl formamide, dimethyl sulfoxide. The polymers were characterized by ultraviolet visible, proton magnetic resonance and Fourier transform infrared spectroscopy. X-ray diffraction analysis and elemental analysis of the synthesized polymers were also performed. DC electrical conductivity of the acid doped polymers was measured by Four-probe method. The spectral evidences clearly indicated that the ladder structure was formed in lower aqueous HCl concentration while open ring keto derivative of polyaniline was formed at higher HCl concentration. The polymer with open ring structure was better processabe and higher conductive in doped state than that of the other one. Difference of their properties like solubility, conductivity of the polymers synthesized at different condition was due to their structural difference.

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.