Hierarchical nanocomposites of polyaniline scales coated on graphene oxide sheets for enhanced supercapacitors

The homogeneous polyaniline–graphene oxide (PANI-GO) nanocomposites were facilely assembled with a redox system in which cumene hydroperoxide (CHP) and iron dichloride (FeCl₂) acted as oxidant and reductant, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that PANI scales coated uniformly on the surface of GO sheets owing to the synergistic effect between the PANI and GO. The obtained PANI-GO nanocomposites exhibited improved electrochemical performance as an electrode material for supercapacitors compared with the pure PANI. The specific capacitance of the PANI-GO nanocomposites was high up to 308.3 F g^?1, much higher than that of the pure PANI with specific capacitance of 150 F g^?1 at a current density of 1 A g^?1 in 2 M H₂SO₄ electrolyte. The Raman and XPS results illustrated that enhanced electrochemical performance might be attributed to the π-π conjugation between the PANI and GO sheets.     

One-step preparation of sulfonated carbon and subsequent preparation of hybrid material with polyaniline salt: a promising supercapacitor electrode material

The present trend to increase the energy density of electrochemical supercapacitor is to hybrid the electrochemical double layer capacitance electrode materials of carbon with loading or encapsulation of transition metal oxide or conductive polymeric pseudocapacitor materials as the binary or ternary hybrid electrochemical active materials. In this work, we selected polyaniline salt-sulfonated carbon hybrid (PANI-SA?C _SA ) as a cheaper electrode material for supercapacitor electrode. Sulfonated carbon (C _SA ) was prepared from hydrothermal carbonization of furaldehyde and p-toluenesulfonic acid. Polyaniline-sulfate salt containing sulfonated carbon was prepared by chemical oxidative polymerization of aniline using ammonium persulfate in presence of sulfuric acid and sulfonated carbon via aqueous, emulsion and interfacial polymerization pathways. Formation of hybrid material was confirmed from scanning electron microscopy. Among the hybrid prepared with three different polymerization pathways, hybrid prepared by aqueous polymerization pathway showed better electrochemical performance. The specific capacitance of the hybrid prepared via aqueous polymerization was 600 F g^?1, which is higher than that of the pristine PANI-SA (350 F g^?1) and C _SA (30 F g^?1). Hybrid material was subjected for 8000 charge-discharge cycles and at 8000 cycles; it showed 88% retention of its original specific capacitance value of 485 F g^?1 with coulombic efficiency (97–100%). These results showed that C _SA micro spheres prevent the degradation of PANI-SA chains during charge/discharge cycles. Specific capacitance, cycle life, low solution resistance, low charge transfer resistance and high phase angle value of PANI-SA?C _SA supercapacitor cell indicates a higher performance supercapacitor system.

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Graphical abstract Synthesis of hybrid of sulfonated carbon with polyaniline sulfate salt and its supercapacitor performance Ravi Bolagam, Palaniappan Srinivasan,^* Rajender Boddula

     

Electrochemical exfoliation and in situ carboxylic functionalization of graphite in non-fluoro ionic liquid for supercapacitor application

Simultaneous electrochemical generation and functionalization of nano-sized graphite from graphite had been carried out in a non-fluoroanion-based ionic liquid, namely, triethylmethylammonium methylsulfate (TEMAMS) containing water and acetonitrile (AN) in different weight ratios. The oxygen-based functional groups attached with the exfoliated material had been identified using Fourier transform infrared spectroscopy (FTIR), and morphological changes were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A symmetrical supercapacitor was fabricated using the exfoliated nano-sized graphite, and the influence of surface functionalities on its performance was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge–discharge cycles (CC). The highest specific capacitance (C _sp) value of 140 F g^?1 at 0.25 A g^?1 was obtained in 1.0 M H₂SO₄, followed by aqueous TEMAMS (125 F g^?1), TEMAMS/acetonitrile (115 F g^?1), and TEMAMS (106 F g^?1) at 0.10 A g^?1.     

Pyridine-containing metal-organic frameworks as precursor for nitrogen-doped porous carbons with high-performance capacitive behavior

A novel pyridine-containing metal-organic framework (MOF, [Zn(bpdc)DMA]·DMF, bpdc = 2,2′-bipyridine-5,5′-dicarboxylate) was directly carbonized at different temperature to produce nitrogen-doped porous carbons (NPCs). The as-prepared porous carbons, NPC800 (obtained at 800 °C) and NPC1000 (obtained at 1000 °C), were characterized by scanning electron microscopy, X-ray powder diffraction, N₂ sorption isotherms, and X-ray photoelectron spectroscopy (XPS). The results from elemental analysis and XPS confirmed that the pyridine groups in MOF served as nitrogen sources to produce NPCs, and NPC800 possessed the higher nitrogen content than NPC1000. N₂ sorption data demonstrated that NPC800 exhibited the larger specific surface area and pore volume than NPC1000. The capacitive properties of NPC800 and NPC1000 were investigated in KOH aqueous electrolyte by cyclic voltammetry and galvanostatic charge–discharge curves. NPC800 showed the higher specific capacitance (226.6 F g^?1 at 1 A g^?1) than NPC1000 and retained 178.0 F g^?1 even at a high current density up to 10 A g^?1. It was found that the donation of N species to capacitance was more than the role of porosity in view of their synergetic effect.     

Pomegranate rind-derived activated carbon as electrode material for high-performance supercapacitors

In this paper, activated carbon materials were synthesized from pomegranate rind through carbonization and alkaline activation processes. The effects of pyrolytic temperature on the textual properties and electrochemical performance were investigated. The surface area of the activated carbon can reach at least 2200 m² g^?1 at different pyrolytic temperatures. It was found that, at the range of 600–900 °C, decreasing the carbonization temperature leads to the increase of t-plot micropore area, t-plot micropore volume, and capacitance. Further decreasing the carbonization temperature to 500 °C also leads to the increase of t-plot micropore area and t-plot micropore volume, but the capacitance is slightly poorer. The activated carbon carbonized at 600 °C and activated at 800 °C possesses very high specific area (2931 m² g^?1) and exhibits very high capacitance (～268 F g^?1 at 0.1 A g^?1 and ～242 F g^?1 at 1 A g^?1). There is no capacitance fading after 2000th cycle.     

Effects of sodium dodecyl sulfate on the electrochemical behavior of supercapacitor electrode MnO2

Supercapacitor electrode material MnO₂ was prepared by liquid co-precipitation with different concentration of anionic surfactant sodium dodecyl sulfate (SDS). As evidenced by X-ray diffraction, the obtained MnO₂ are all typical amorphous α-MnO₂ with poor crystallinity. Scanning electron microscopy reveals that the dispersity of MnO₂ initially get better and then worse with the increase of SDS, and the particle sizes first become smaller then larger as well. It is worthwhile noting that the morphology of MnO₂ tested by transmission electron microscopy undergoes a changeable process: fibrous, pine needle like, cotton like, round bubble like, flocculent, and nervous tissue like as SDS increases. Through cyclic voltammetry and galvanostatic charge/discharge tests, SDS addition amount 0.2 g (0.017 mol L^?1) is found to be the optimal effect value, and the as-prepared Mn-0.2 obtains the highest specific capacitance (C _sp) of 154.5 F g^?1 at a current density of 500 mA g^?1. Compared with the sample Mn-0 synthesized without SDS, the C _sp increases by about 50 % (±5 %), which can be attributed to its largest Brunauer–Emmett–Teller–specific surface area of 255.9 m² g^?1, best particle dispersity, and smallest particle size of approximately 50–80 nm. Meanwhile, the rate capability and cycle stability of Mn-0.2 also improves obviously, and the equivalent series resistance decreases a lot, only 0.120 Ω.     

The preparation of LaSr<Subscript>3</Subscript>Fe<Subscript>3</Subscript>O<Subscript>10 − <Emphasis Type="Italic">δ</Emphasis></Subscript> and its electrochemical performance

LaSr₃Fe₃O_10 ? δ powders were synthesized by hydrothermal method and characterized by XRD and SEM. The XRD patterns showed that the sample calcined at 1000 °C was single phase and the sample calcined at 900 °C had tiny amount of LaSrFeO₄ phase. The single-phase LaSr₃Fe₃O_10 ? δ powders were used to prepare test electrode. The capacitive behaviors of LaSr₃Fe₃O_10 ? δ electrode were analyzed by cyclic voltammetry, galvanostatic charge-discharge techniques, and electrochemical impedance spectroscopy. The electrochemical results showed a capacity as high as 470 F g^?1 at a scan rate of 1 mV s^?1 and 380 F g^?1 at a charge-discharge current density of 0.1 A g^?1 in 6 M KOH solution. The electrode showed good cyclic stability since its capacitive retention is 87.1% after 1000 charge-discharge cycles. The electrochemical performances suggest that LaSr₃Fe₃O_10 ? δ could be a potential candidate as a capacitive electrode material.     

Source molarity affected surface morphological and electrochemical transitions in binder-free FeO(OH) flexible electrodes and fabrication of symmetric supercapacitive device

Binderless chemical synthesis of flexible electrodes (FEs) of FeO(OH) has been carried out by simple and cost-effective successive ionic layer adsorption and reaction (SILAR) technique. In aqueous route synthesis, FeCl₃ and NaOH solutions were used as cationic and anionic sources, respectively. Molar concentration of NaOH was kept constant while the molar concentration of FeCl₃ was varied from 0.2 to 0.8 M with step increments of 0.2 M to study its effect on physical and electrochemical characteristics of prepared FEs. X-ray diffraction (XRD) patterns of the FEs exhibit existence of tetragonal FeO(OH). SEM images show the rice grain-like morphologies. Cyclic voltammetric analyses indicate the decrease in specific capacitance value with the increase in molar concentration of cationic precursor. For the electrode prepared with 0.2 M FeCl₃ as precursor, the observed maximum specific capacitance (SC) was 444.44 F g^?1 at 5 mV s^?1 in 1 M NaOH, hence these electrodes were used to fabricate the symmetric solid state supercapacitors. Prepared symmetric supercapacitive devices (SSD) were electrochemically analyzed. The maximum SC for the symmetric supercapacitor was found to be 320.50 F g^?1 at 5 mV s^?1 which was nearly same as that given by GCD analysis which is 313.27 F g^?1 at 0.5 mA. Nyquist plot of the device shows minute semicircle in the high frequency region and the mid-low frequency region shows straight line with inclination of nearly \( 40^\circ \) with X-axis. The equivalent series resistance (ESR), charge transfer resistance (R_ct) and Warburg impedance (R_w) are found to be 2.58, 2.56 and 0.8 Ω, respectively. The prepared SSD shows high cycling stability with 88% of capacitive retention even after 2000 cycles.     

Hybrid system of nickel<Emphasis Type="Bold">–</Emphasis>cobalt hydroxide on carbonised natural cellulose materials for supercapacitors

Advanced carbon materials formed from abundant biomass are an exciting and promising class for energy devices due to the clear advantages of low cost, sustainability and good physical and electrochemical properties. However, these materials typically do not compete well with their metal functionalised counterparts. In this work, we demonstrate that xCo(OH)₂–(1?x)Ni(OH)₂ with various Ni:Co ratios can be deposited onto biomass-derived carbon to make a hybrid inorganic-carbon electrode with tuneable physical features and electrochemical performance. These features were tuned by adjusting the Ni:Co ratio within precursor solutions. The electrodes had shown a capacitance ranging from 780.7 to 2041 F g^?1, which is very close to the theoretical value for Ni(OH)₂ (2365 F g^?1). A hypothesis is presented to help explain this performance for a modified, biomass-derived carbon electrode.     

The sol–gel chromium-modified V<Subscript>6</Subscript>O<Subscript>13</Subscript> as a cathodic material for lithium batteries

A new V₆O₁₃-based material has been synthesized via the sol–gel route. This sol–gel mixed oxide has been obtained from an appropriate heat treatment of the chromium-exchanged V₂O₅ xerogel performed under reducing atmosphere. This new compound, with the chemical formula Cr_0.36V₆O_13.50, exhibits a monoclinic structure (C2/m) with the following unit cell parameters, a=11.89 Å, b=3.68 Å, c=10.14 Å, β=101.18°. The electrochemical characterization of this compound has been performed using galvanostatic discharge–charge experiments in the potential range 4–1.5 V and completed by ac impedance spectroscopy measurements. It exhibits a specific capacity of about 370 mAh g^?1, which makes the compound Cr_0.36V₆O_13.50 the best one in the V₆O₁₃-based system: 85% of the initial capacity (315 mAh g^?1) after the 35th cycle is still available at C/25 without any polarization. From impedance spectroscopy, a high kinetics of Li transport (D _Li=1.8×10^?9 cm² s^?1) is found at mid-discharge.     

Electrochemical polymerization of polyaniline doped with Zn2+ as the electrode material for electrochemical supercapacitors

Polyaniline doped with Zn²⁺ (PANI/Zn²⁺) films was synthesized by cyclic voltammetric method on stainless steel mesh substrates in 0.2 mol L^?1 aniline and 0.5 mol L^?1 sulfuric acid electrolyte with various concentrations of zinc sulfate (ZnSO₄·7H₂O). The structure and morphology of PANI and PANI/Zn²⁺ films were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques, respectively. The electrochemical properties of PANI and PANI/Zn²⁺ films were investigated by cyclic voltammetry, galvanostatic charge–discharge test, and electrochemical impedance spectroscopy in 0.5 mol L^?1 H₂SO₄ electrolyte in a three-electrode system. The results show that the surface morphology of PANI/Zn²⁺ is more rough than that of pure PANI. The specific capacitance of the PANI/Zn²⁺ film displays a larger specific capacitance of 738 F g^?1, lower resistance, and better stability as compared with the pure PANI film. Thus, good capacitive performance demonstrates its potential superiority for supercapacitors.     

Fabrication of vesicular polyaniline using hard templates and composites with graphene for supercapacitor

Vesicular polyaniline (VPANI) has been fabricated for the first time via a facile two-step method, which uses high-quality multilamellar vesicular SiO₂ as hard templates. The graphene-wrapped VPANI (VPANI@RGO) composites were prepared by self-assembling graphene oxide onto VPANI and subsequently conducting the hydrothermal reduction process. The morphological characterization of the composites confirms the uniform wrapping of the graphene sheets on the VPANI. The structural characterization of the composites reveals a strong π–π electron and hydrogen bond interaction in the composites. The VPANI@RGO composites exhibit an excellent supercapacitor performance with an enhanced specific capacitance (573 F g^?1) and a good cycling stability, which maintains its capacity of up to 85.7 % over 1000 cycles at 1 A g^?1.     

Enhanced lithium-ion intercalation and conduction of transparent tantalum oxide films by lithium addition with an atmospheric pressure plasma jet

An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO _y C _z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC₂H₅)₅] and lithium tert-butoxide [(CH₃)₃COLi] precursors. Transparent organo-lithiated tantalum oxide (Li _x TaO _y C _z ) films expose noteworthy Li⁺ ion intercalation and conduction performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li⁺ ionic diffusion coefficient and conductivity of 6.2?×?10^?10 cm²/s and 6.0?×?10^?11 S/cm for TaO _y C _z films are greatly progressed of up to 9.6?×?10^?10 cm²/s and 7.8?×?10^?9 S/cm for Li _x TaO _y C _z films by co-synthesis with an APPJ.     

Effect of carbonaceous support between graphite oxide and reduced graphene oxide with anchored Co<Subscript>3</Subscript>O<Subscript>4</Subscript> microspheres as electrode-active materials in a solid-state electrochemical capacitor

Hydrothermally synthesized Co₃O₄ microspheres were anchored to graphite oxide (GO) and thermally reduced graphene oxide (rGO) composites at different cobalt weight percentages (1, 10, and 100 wt%). The composite materials served as the active materials in bulk electrodes for two-electrode cell electrochemical capacitors (ECCs). GO/Co₃O₄–1 exhibited a high energy density of 35 W kg^?1 with a specific capacitance (C _sp) of 196 F g^?1 at a maximum charge density of 1 A g^?1. rGO/Co₃O₄-100 presented high specific power output values of up to 23.41 kW h kg^?1 with linear energy density behavior for the charge densities applied between 0.03 and 1 A g^?1. The composite materials showed Coulombic efficiencies of 96 and 93 % for GO/Co₃O₄–1 and rGO/Co₃O₄–100 respectively. The enhancement of capacitive performance is attributed to the oxygenated groups in the GO ECC and the specific area in the rGO ECC. These results offer an interesting insight into the type of carbonaceous support used for graphene derivative electrode materials in ECCs together with Co₃O₄ loading to improve capacitance performance in terms of specific energy density and specific power.

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Graphical abstract ?

     

Efficient Biotransformation of Phytosterols to Dehydroepiandrosterone by <Emphasis Type="Italic">Mycobacterium</Emphasis> sp.

In this study, a method for the efficient production of dehydroepiandrosterone (DHEA) from phytosterols in a vegetable oil/aqueous two-phase system by Mycobacterium sp. was developed. After the 3-hydroxyl group of phytosterols was protected, they could be converted into DHEA with high yield and productivity by Mycobacterium sp. NRRL B-3683. In a shake flask biotransformation, 15.05 g l^?1 of DHEA and a DHEA yield of 85.39% (mol mol^?1) were attained after 7 days with an initial substrate concentration of 25 g l^?1. When biotransformation was carried out in a 30-l stirred bioreactor with 25 g l^?1 substrate, the DHEA concentration and yield was 16.33 g l^?1 and 92.65% (mol mol^?1) after 7 days, respectively. The results of this study suggest that inexpensive phytosterols could be utilized for the efficient production of DHEA.     

Enzymatic Hydrolysis of Black Liquor Xylan by a Novel Xylose-Tolerant,Thermostable β-Xylosidase from a Tropical Strain of <Emphasis Type="Italic">Aureobasidium pullulans</Emphasis> CBS 135684

From three cell-associated β-xylosidases produced by Aureobasidium pullulans CBS 135684, the principal enzyme was enriched to apparent homogeneity and found to be active at high temperatures (60–70 °C) over a pH range of 5–9 with a specific activity of 163.3 units (U) mg^?1. The enzyme was thermostable, retaining over 80% of its initial activity after a 12-h incubation at 60 °C, with half-lives of 38, 22, and 10 h at 60, 65, and 70 °C, respectively. Moreover, it was tolerant to xylose inhibition with a K _i value of 18 mM. The K _m and V _max values against p-nitrophenyl-β-d-xylopyranoside were 5.57 ± 0.27 mM and 137.0 ± 4.8 μmol min^?1 mg^?1 protein, respectively. When combining this β-xylosidase with xylanase from the same A. pullulans strain, the rate of black liquor xylan hydrolysis was significantly improved by up to 1.6-fold. The maximum xylose yield (0.812 ± 0.015 g g^?1 dry weight) was obtained from a reaction mixture containing 10% (w/v) black liquor xylan, 6 U g^?1 β-xylosidase and 16 U g^?1 xylanase after incubation for 4 h at 70 °C and pH 6.0.     

Binding interaction and conformational changes of human serum albumin with ranitidine studied by spectroscopic and time-resolved fluorescence methods

This study was designed to examine the interaction of histamine H₂-receptor antagonist drug ranitidine (RTN) with human serum albumin by multi-spectroscopic methods. The experimental results showed the involvement of dynamic quenching mechanism which was further confirmed by lifetime spectral studies. The binding constants (K _a) at three temperatures (288, 298, and 308 K) were 2.058 ± 0.020, 4.160 ± 0.010 and 6.801 ± 0.011 × 10⁴ dm³ mol^?1, respectively, and the number of binding sites (m) were 1.169, respectively; thermodynamic parameters ΔH ⁰ (44.152 ± 0.047 kJ mol^?1), ΔG ⁰ (?26.214 ± 0.040 kJ mol^?1), and ΔS ⁰ (236.130 ± 0.025 J K^?1 mol^?1) were calculated. The distance r between donor and acceptor was obtained (r = 3.40 nm) according to the Förster theory of non-radiative energy transfer. Synchronous fluorescence, CD, AFM and 3D fluorescence spectral results revealed the changes in secondary structure of the protein upon interaction with RTN. A molecular modeling study further confirmed the binding mode obtained by the experimental studies.     

Activated hierarchical porous carbon@π-conjugated polymer composite as cathode for high-performance lithium storage

Organic compounds become promising candidates for cathodes of rechargeable lithium battery (RLB) due to the high theoretical capacity and improved safety. However, they exhibit low conductivity and easy dissolution in electrolyte, which leads to the low utilization of active materials and poor cycling stability of RLBs. Here, we synthesize a novel composite of activated hierarchical porous carbon supporting poly(1,5-diamino-anthraquinone) (aHPC@PDAA), using Ce(SO₄)₂ as oxidant and naphthalenesulfonic acid (NSA) as soft template for PDAA. The as-synthesized composite exhibits uniformly nanoporous structure with nano-sized PDAA particles distributed homogenously inside and outside of pores. The aHPC@PDAA cathode for RLBs achieves high electrochemical performance with a discharge capacity as much as 250 mAh g^?1 at the current density of 100 mA g^?1, which still maintains 176 mAh g^?1 after 2000 charging-discharging cycles.     

In situ synthesis of crosslinked-polyaniline nano-pillar arrays/reduced graphene oxide nanocomposites for supercapacitors

Crosslinked-polyaniline (CPA) nano-pillar arrays adsorbed on the surface of reduced graphene oxide (RGO) sheets were synthesized by in situ solution polymerization through two steps of reduction. The electrochemical analyses demonstrated that the befittingly reduced CPA/RGO composite exhibited high performance as electrode materials for supercapacitors. The CPA/RGO composite showed very high specific capacitance of 1532 F g^?1 at a scan rate of 10 mV s^?1 or 694 F g^?1 at a current density of 2 A g^?1 in 1 M H₂SO₄ electrolyte, as well as great energy density of 61.4 W h kg^?1 at a current density of 2 A g^?1. The electrode material also had decent power density of 4 kW kg^?1 at a current density of 10 A g^?1, and good cycling stability of 92.5 % capacitance retained after 500 cycles of cyclic voltammetry at 500 mV s^?1. The neat microstructures and super electrochemical properties suggest the potential use of the composites in supercapacitors.     

Enhanced electrochemical performance of straw-based porous carbon fibers for supercapacitor

The efficient utilization of natural biomass as renewable raw materials is of importance. We herein prepared porous carbon fibers (PCFs) by activation of the extracted cellulose microfibers from the agriculture byproduct of corn straw. Different from the porous carbons (PCs) by directly activating straw, the obtained PCFs had typical one-dimensional morphology with high surface area (2013 m² g^?1) and large pore volume (1.27 cm³ g^?1). The influence of the ZnCl₂/cellulose mass ratio on the electrochemical performance was studied, and the optimized PCF(1:1) possessed a much higher specific capacitance than the PC(1:1) sample, which was attributed to the improved specific surface area as well as the fiber-like morphology where it had short ion diffusion route and small interfacial resistance in comparison to PCs. PCFs have a high specific capacitance of 230 F g^?1 at 0.5 A g^?1, and 183 F g^?1 was retained at 20 A g^?1 (79.6%), revealing an excellent rate capability. The assembled symmetrical supercapacitor exhibited a wide potential window of 1.8 V, small electrochemical impedance, and superior cycle performance. Moreover, a high energy density of 16.0 Wh kg^?1 was obtained at a power density of 450.4 W kg^?1, which was preserved of 6.9 Wh kg^?1 at a high power density of 14,194.3 W kg^?1.