Bismuth oxide coated amorphous manganese dioxide for electrochemical capacitors

With MnSO₄, NaOH and K₂S₂O₈ as the raw materials, the amorphous and δ-type manganese dioxide (MnO₂) is separately prepared by using different chemical precipitation-oxidation methods. The results of charge–discharge and electrochemical impedance spectroscopy (EIS) tests show that (i) the specific capacitance of the amorphous MnO₂ reaches to 301.2 F g⁻¹ at a current density of 200 mA g⁻¹ and its capacitance retention rate after 2000 cycles is 97%, which is obviously higher than 250.8 F g⁻¹ and 71% of the δ-type one, respectively; (ii) good electrochemical capacitance properties of the amorphous MnO₂ should be contributed to easy insertion/extraction of ions within the material; (iii) when 5 wt% Bi₂O₃ is coated on the amorphous MnO₂, its specific capacitance increases to 352.8 F g⁻¹ and the capacitance retention rate is 90% after 2000 cycles.     

In situ polymerization and reduction to fabricate gold nanoparticle‐incorporated polyaniline as supercapacitor electrode materials

Nanocomposites of gold nanoparticles and polyaniline are synthesized by using HAuCl₄ and ammonium peroxydisulfate as the co‐oxidant involving in situ polymerization of aniline and in situ reduction of HAuCl₄. Through these in situ methods, the synthesized Au nanoparticles of ca. 20 nm embedded tightly and dispersed uniformly in polyaniline backbone. With the Au content in composite increasing from 4.20 to 24.72 wt.%, the specific capacitance of the materials first increased from 334 to 392 F g⁻¹ and then decreased to 298 F g⁻¹. Based on the real content of PANI in composite material, the highest specific capacitance is calculated to be 485 F g⁻¹ at the Au amount of 19.15 wt.%, which remains 55.6% after 5000 cycles at the current density of 2 A g⁻¹. Finally, the asymmetric supercapacitor of AuNP/PANI||AC and the symmetric supercapacitor of AuNP/PANI||AuNP/PANI are assembled. The asymmetric supercapacitor device shows a better electrochemical performance, which delivers the maximum energy density of 7.71 Wh kg⁻¹ with power density of 125 W kg⁻¹ and maximum power density of 2500 W kg⁻¹ with the energy density of 5.35 Wh kg⁻¹.     

Dynamic Hydrogen-Bond Network as a Modulator of Bismuth–Antimony Complex Anodes for Self-Healable and Wider Temperature Adaptive Potassium Ion Batteries

Antimony (Sb)-based anodes are attractive candidates in potassium-ion batteries (PIBs) due to their superior capacities and rational potassium inserting voltages. However, the sluggish kinetics and poor interface compatibility severely hinder practical application. Herein, Bi_0.67Sb_1.33S₃ nanospheres embedded into in situ formed poly(3,4-ethylenedioxythiophene) crosslinked with polythioctic acid (PET@PTA) (Bi_0.67Sb_1.33S₃/PET@PTA) were elaborately conceptualized with hydrogen bonds exchangeable binding (HBEB) sites. Bi_0.67Sb_1.33S₃/PET@PTA exhibits notable self-healing ability and wider temperature adaptability. Bi_0.67Sb_1.33S₃/PET@PTA displays an impressive capacity of 819 mAh g⁻¹ at 0.05 A g⁻¹, prominent cycle ability with a 73 % capacity conservation after 500 cycles at 2 A g⁻¹, and high capacity retention of 66 % and 84 % at −40 and 70 °C to that case at room temperature, respectively, for potassium storage. This work provides a new perspective for HBEB sites in maximizing the desirable K⁺ storage performance.     

A facile green approach to the synthesis of Bi2WO6@V2O5 heterostructure and their photocatalytic activity evaluation under visible light irradiation for RhB dye removal

Bismuth tungsten oxide and vanadium pentoxide (Bi₂WO₆/V₂O₅) heterostructures are produced by a green synthesis approach using Azadirachta indica extract for photocatalytic performance. The hydrothermal method at temperatures between 120 °C and 140 °C is used to synthesize Bi₂WO₆. Bi₂WO₆ and V₂O₅ phases are formed in pure orthorhombic wells according to the XRD pattern. The SEM displays V₂O₅ nanorods, Bi₂WO₆ hierarchical microspheres that resemble flowers at 120 °C, and particles with a particle-like character at 140 °C. In V₂O₅, the asymmetric stretching vibrations of the triplely coordinated oxygen (chain oxygen) bonds and the vibration of the doubly coordinated oxygen (bridge oxygen) bonds are responsible for a peak at 611 cm^?1. In FTIR spectra between 600 and 1600 cm^?1, the major absorption bands in Bi₂WO₆ are attributed to the W-O stretching, Bi-O stretching, and W-O-W bridging stretching modes. Bi₂WO₆@V₂O₅ at 120 °C has the lowest bandgap energy (2.32 eV) and optical electronegativity (0.62), as well as the highest refractive index (2.57), extinction coefficient (2.21), and dielectric constant (ε_r = 0.72 and ε_i = 11.4) among all samples, making it a suitable material for photocatalysis. Rhodamine blue (RhB) dye degradation is used to measure the photocatalytic activity (PCA) of certain materials. The results showed that heterostructure V₂O₅@Bi₂WO₆ synthesized at 120 °C is more attractive among all samples due to high degradation of RhB dye under sunlight irradiation in 90 min.     

Facile synthesis of polyaniline/TiO2/graphene oxide composite for high performance supercapacitors

The polyaniline/TiO₂/graphene oxide (PANI/TiO₂/GO) composite, as a novel supercapacitor material, is synthesized by in situ hydrolyzation of tetrabutyl titanate and polymerization of aniline monomer in the presence of graphene oxide. The morphology, composition and structure of the composites as-obtained are characterized by SEM, TEM, XRD and TGA. The electrochemical property and impedance of the composites are studied by cyclic voltammetry and Nyquist plot, respectively. The results show that the introduction of the GO and TiO₂ enhanced the electrode conductivity and stability, and then improved the supercapacitive behavior of PANI/TiO₂/GO composite. Significantly, the electrochemical measurement results show that the PANI/TiO₂/GO composite has a high specific capacitance (1020 F g⁻¹ at 2 mV s⁻¹, 430 F g⁻¹ at 1 A g⁻¹) and long cycle life (over 1000 times).     

Coordination polymer template synthesis of hierarchical MnCo2O4.5 and MnNi6O8 nanoparticles for electrochemical capacitors electrode

Two types of ternary metal oxides, MnCo₂O_4.5 and MnNi₆O₈ nanoparticles have been separately synthesized through chemical transformation from the corresponding bimetallic coordination polymer particles precursor under high-heating conditions. Series of electrochemical measurements are performed to examine the MnCo₂O_4.5 and MnNi₆O₈ electrodes, and the result shows that MnCo₂O_4.5 structure, especially for Mn/Co-600, has much higher capacitance than that of MnNi₆O₈ nanoparticles, indicating MnCo₂O_4.5 electrode is more suitable for applying in neutral electrolyte system. The Mn/Co-600 electrode exhibits a specific capacitance of 158 F g⁻¹ at 5 mV s⁻¹, good rate capability of 53.8% with a 20 times current density increase, good cycle performance (92.9% capacitance retention after 1000 cycles) and high power density (a specific power of 5760 W kg⁻¹ at 4.0 A g⁻¹) with low charge transfer resistance value of 1.8 Ω.     

Electrochemical capacitance of nickel oxide nanotubes synthesized in anodic aluminum oxide templates

Nickel oxide (NiO) nanotubes for supercapacitors were synthesized by chemically depositing nickel hydroxide in anodic aluminum oxide templates and thermally annealing at 360 °C. The synthesized nanotubes have been characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The capacitive behavior of the NiO nanotubes was investigated by cyclic voltammetry, galvanostatic charge–discharge experiment, and electrochemical impedance spectroscopy in 6 M KOH. The electrochemical data demonstrate that the NiO nanotubes display good capacitive behavior with a specific capacitance of 266 F g⁻¹ at a current density of 0.1 A g⁻¹ and excellent specific capacitance retention of ca. 93% after 1,000 continuous charge–discharge cycles, indicating that the NiO nanotubes can become promising electroactive materials for supercapacitor.     

A structural influence on the electrical double-layer characteristics of Al4C3-derived carbon

Several carbon materials were produced by reacting aluminum carbide with chlorine gas at different temperatures (400–900 °C). Chlorination temperature and porosity values showed the inversely related trends whereby the graphitization degree rises with the chlorination temperature. Electrochemical measurements performed in three-electrode test cells with 1.0-M Et₃MeNBF₄ electrolyte revealed that the changes in porosity parameters and the degree of graphitization are in good correlation with specific capacitance values. Capacitance depends on the structure of carbon and varies in studied chlorination range from 109 to 60 F g⁻¹ and from 114 to 64 F g⁻¹ for the negatively and positively charged electrode materials, respectively. An exceptionally low capacitance was observed for the material produced at 700 °C that was explained by the multiwall carbon nanobarrels and the highly ordered curved graphitic flakes, which have low specific surface and possess the relatively low specific surface-related capacitance.     

Proton-conducting membranes based on poly(2,5-benzimidazole) (ABPBI) and phosphoric acid prepared by direct acid casting

We report the preparation of phosphoric acid doped poly(2,5-benzimidazole) (ABPBI) membranes for PEMFC by simultaneously doping and casting from a poly(2,5-benzimidazole)/phosphoric acid/methanesulfonic acid (MSA) solution. The evaporation of MSA yields a very homogeneous membrane having a better controlled composition, avoiding the use of solvent-intensive procedures. Membranes have been prepared with contents of up to 3.0H₃PO₄ molecules per ABPBI repeating unit. These membranes achieve a maximum conductivity of 1.5 × 10⁻² S cm⁻¹ at temperatures as high as 180 °C in dry conditions. These ABPBI membranes are more conveniently prepared than those conventionally formed and doped in separate steps while featuring comparable conductivities (ABPBI × 2.7H₃PO₄ prepared by the soaking method showed a conductivity of 2.5 × 10⁻² S cm⁻¹ at 180 °C in dry conditions).     

Photocatalytic properties of CoOx-loaded nano-crystalline perovskite oxynitrides ABO2N (A = Ca,Sr, Ba,La; B = Nb,Ta)

Highly crystalline niobium- and tantalum-based oxynitride perovskite nanoparticles were obtained from hydrothermally synthesized oxide precursors by thermal ammonolysis at different temperatures. The samples were studied with respect to their morphological, optical and thermal properties as well as their photocatalytic activity in the decomposition of methyl orange. Phase pure oxynitrides were obtained at rather low ammonolysis temperatures between 740 °C (CaNbO₂N) and 1000 °C (BaTaO₂N). Particle sizes were found to be in the range 27 nm–146 nm and large specific surface areas up to 37 m² g⁻¹ were observed. High photocatalytic activities were found for CaNbO₂N and SrNbO₂N prepared at low ammonolysis temperatures. CoO_x as co-catalyst was loaded on the oxynitride particles resulting in a strong increase of the photocatalytic activities up to 30% methyl orange degradation within 3 h for SrNbO₂N:CoO_x.     

Synthesis and electrochemical properties of Li3V2(PO4)3/C with one-dimensional (1D) nanorod structure for cathode materials of lithium-ion batteries

A series of Li₃V₂(PO₄)₃/C cathode materials with different morphologies were successfully prepared by controlling temperatures using maleic acid as carbon source via a simple sol–gel reaction method. The Li₃V₂(PO₄)₃/C nanorods synthesized at 700 °C with diameters of about 30–50 nm and lengths of about 800 nm show the highest initial discharge capacity of 179.8 and 154.6 mA h g⁻¹ between 3.0 and 4.8 V at 0.1 and 0.5 C, respectively. Even at a discharge rate of 0.5 C over 50 cycles, the products still can deliver a discharge capacity of 140.2 mA h g⁻¹ in the potential region of 3.0–4.8 V. The excellent electrochemical performance can be attributed to one-dimensional nanorod structure and uniform particle size distribution. All these results indicate that the resulting Li₃V₂(PO₄)₃/C is a very strong candidate to be a cathode in a next-generation Li-ion battery for electric-vehicle applications.     

Impact of titanium precursors on formation and electrochemical properties of Li4Ti5O12 anode materials for lithium-ion batteries

This work describes comparative study on the application of Li₄Ti₅O₁₂ (LTO) as anode materials for lithium-ion batteries which were successfully prepared by sol-gel synthesis with the use of two titanium sources. One of them was anatase-type titanium dioxide (TiO₂), whereas the second was tetrabutyl titanate (TBT). Both obtained LTO materials were very similar in terms of their crystallinity and purity. In turn, the sample synthetized with TBT source revealed better particle dispersibility, and its particles were slightly lower in size. These particular features resulted in higher Li⁺ diffusion coefficient and better kinetic of Li⁺ ions during charge transfer reactions for the LTO synthetized with TBT source. This reflected in specific capacitance values for both electrodes which equalled 150 mAh g⁻¹, 120 mAh g⁻¹, and 63 mAh g⁻¹ for TBT-LTO and 120 mAh g⁻¹, 80 mAh g⁻¹, and 58 mAh g⁻¹ for TiO₂-LTO at C-rates of 1, 5, and 10 C, respectively.

     

Enhanced photoelectrochemical performance of Bi2S3/Ag2S/ZnO novel ternary heterostructure nanorods

The current work investigates the morphology, crystallinity and photoelectrochemical (PEC) performance of bismuth sulfide/silver sulfide/zinc oxide nanorods (Bi₂S₃/Ag₂S/ZnO NRAs) photoelectrodes as prepared at different annealing temperature. ZnO NRAs was initially grown hydrothermally, deposited in sequence with Ag₂S and Bi₂S₃ via successive ionic layer adsorption and reaction (SILAR) method before undergoing the annealing treatment. The optimised photoelectrode (Bi₂S₃/Ag₂S/ZnO NRAs-400 °C) possesses an optical bandgap of 1.60 eV extending the absorption edge of ZnO to visible light spectrum. The current-voltage characterization of Bi₂S₃/Ag₂S/ZnO NRAs photoelectrodes revealed that the photocurrent density and photoconversion efficiency were strongly dependent on the annealing temperature. The PEC study shows that the photoelectrode annealed at 400 °C achieved impressive photocurrent density of 12.95 mA/cm² at +0.5 V (vs Ag/AgCl/saturated KCl) under 100 mW/cm² illumination with superior photoconversion efficiency of 12.63%. This improvement is due to the cascade-designed band structure alignment of Bi₂S₃/Ag₂S/ZnO/ITO and to the brilliant role of Ag₂S as an intermediate layer that reduced random chance of electron-hole (e⁻_-h⁺) pairs recombination and improved the electrons collection efficiency. This work is highly anticipated to give contribution on further utilisation of Bi₂S₃/Ag₂S/ZnO NRAs as a promising semiconductor material in PEC related applications.     

Effect of Bismuth Oxide Particles Size on the Thermal Excitation and Combustion Properties of Thermite Systems

The influence of Bi₂O₃ particles size at the sub-micron scale on the thermal excitation threshold and combustion performance of nano-thermite systems was investigated. Three formulas were designed and prepared, Al(100 nm)/Bi₂O₃(170 nm), Al(100 nm)/Bi₂O₃(370 nm) and Al(100 nm)/Bi₂O₃(740 nm). The samples were characterized and tested by SEM, XRD, and DSC techniques. Electrical ignition and combustion experiments were performed. The results showed that with the increase of the particle size of Bi₂O₃, in the case of slow linear heating, the exothermic heat decreased (1051.2 J g⁻¹, 527.3 J g⁻¹ and 243.6 J g⁻¹) and the thermal excitation threshold temperature increased (564.52 °C, 658.1 °C and 810.9 °C). Simultaneously, the state of the thermite reaction correspondingly changed to solid-solid, liquid-solid and liquid-liquid thermite reaction. In the case of rapid heating , the increase in particle size increased the excitation current (0.561A, 0.710A and 0.837A). During the combustion process, the thermite system with the smallest Bi₂O₃ particle size showed the largest combustion rate, and that with the largest particle size had the longest combustion duration.     

Hydrogen/oxygen polymer electrolyte membrane fuel cells (PEMFCs) based on alkaline-doped polybenzimidazole (PBI)

When complexed with alkaline such as potassium hydroxide, sodium hydroxide or lithium hydroxide, films (40 μm thick) of polybenzimidazole (PBI) show conductivity in the 5 × 10⁻⁵–10⁻¹ S/cm⁻¹ range, depending on the type of alkali, the time of immersion in the corresponding base bath and the temperature of immersion. It has been shown that PBI has a remarkable capacity to concentrate KOH, even in an alkaline bath of concentration 3 M. The highest conductivity of KOH-doped PBI (9×10⁻² S cm⁻¹) at 25°C obtained in this work is higher than the we had obtained previously as optimum values for H₂SO₄-doped PBI (5 × 10⁻² S cm⁻¹ at 25°C) and H₃PO₄-doped PBI ( 2 × 10⁻³ S cm⁻¹ at 25°C). PEMFCs based on an alkali-doped PBI membrane were demonstrated, and their characteristics exhibited the same performance as those of PEMFCs based on Nafion® 117. Their development is currently under active investigation.     

Doping effects of Yb3+ on the crystal structures,nanoparticle properties and electrical behaviors of ZrO2 derived from a facile urea-based hydrothermal route

Weakly-agglomerated nanocrystalline (ZrO₂)_1−x(Yb₂O₃)_x (x=0.02–0.2) powders with high surface area (109–151 m² g⁻¹) were synthesized by a two-step hydrothermal process in the presence of urea: a stock solution of metal nitrates and urea was heated at 80 °C for 24 h and then at 180 °C for 48 h. For x=0.04–0.2, the as-derived powders were an assembly of uniform nanoparticles with well-defined edges in the size between 6.1–8.4 nm. Before and after calcination at 800 °C, the lattice parameters, microstrain and surface area of the (ZrO₂)_1−x(Yb₂O₃)_x samples tended to increase with Yb³⁺ concentration; while, the average crystallite size decreased correspondingly. In the Arrhenius plots over the measurement temperature range of 400–800 °C, the bulk ionic conductivity of the compacts sintered at 1400 °C for 24 h showed a maximum value at the composition of x=0.08 in cubic structure, with an activation energy of 0.89 eV. At 800 °C, σ_b=0.049 S cm⁻¹ for x=0.08.     

Effect of post-deposition annealing temperature on RF-sputtered HfO2 thin film for advanced CMOS technology

Structural and electrical properties of HfO₂ gate-dielectric metal-oxide-semiconductor (MOS) capacitors deposited by sputtering are investigated. The HfO₂ high-k thin films have been deposited on p-type <100> silicon wafer using RF-Magnetron sputtering technique. The Ellipsometric, FTIR and AFM characterizations have been done. The thickness of the as deposited film is measured to be 35.38 nm. Post deposition annealing in N₂ ambient is carried out at 350, 550, 750 °C. The chemical bonding and surface morphology of the film is verified using FTIR and AFM respectively. The structural characterization confirmed that the thin film was free of physical defects and root mean square surface roughness decreased as the annealing temperature increased. The smooth surface HfO₂ thin films were used for Al/HfO₂/p-Si MOS structures fabrication. The fabricated Al/HfO₂/p-Si structure had been used for extracting electrical properties such as dielectric constant, EOT, interface trap density and leakage current density through capacitance voltage and current voltage measurements. The interface state density extracted from the G–V measurement using Hill Coleman method. Sample annealed at 750 °C showed the lowest interface trap density (3.48 × 10¹¹ eV⁻¹ cm⁻²), effective oxide charge (1.33 × 10¹² cm⁻²) and low leakage current density (3.39 × 10⁻⁹ A cm⁻²) at 1.5 V.     

Water splitting as a tool for obtaining insight into metal–support interactions in catalysis

This review is focused on the use of the water splitting reaction for characterizing oxygen vacancies in supported metal catalysts and more generally to get insight into the high-temperature modifications of metal–support interactions. Three supports widely used in catalysis are considered, namely alumina, silica and ceria. The catalysts were reduced at temperatures T_R ranging from 200 to 1000 °C. The reaction with water was carried out at temperatures T_OX ranging from 100 to 1000 °C. In every case, the metal (Rh or Pt) was chosen among those which are not oxidizable by water. Extensive investigations of the reactivity of water with unsupported metals and films confirmed this choice. The reaction is then selective for the titration of O vacancies, generally associated with reduced cations of the support. On alumina-supported catalysts, reduction at T_R > 600 °C leads to the formation of oxygen vacancies strictly confined to the periphery of metal particles. The amount of hydrogen produced Q_H is coherent with the peripheral oxygen density. Reduction of silica-supported catalysts at T_R > 600 °C generates metal silicides that can be selectively destroyed by water with reformation of silica and metal nanoparticles. Oxygen vacancies are formed on ceria catalysts at 200 °C. These oxygen vacancies are confined to the surface up to 600 °C. At higher temperatures, oxygen vacancies are formed in the bulk: about 50% of CeO₂ would be reduced at 900 °C. The amount of H₂ produced by reaction with water is thus very high on metal-ceria catalysts. At T_R > 900 °C, metal cerides start to form. Remarkably, a significant reactivity of H₂O on a Rh/CeO₂ catalyst reduced at 850 °C is recorded as of 100 °C. However, the quantitative titration of oxygen vacancies required temperatures T_OX > 500 °C. As a rule, the technique of water splitting allows the detection of 1 μmol g⁻¹ of oxygen vacancies, i.e. a few 0.1% of the surface in the case of reducible oxides of 10–20 m² g⁻¹.     

In Situ Pyrolysis Tracking and Real-Time Phase Evolution: From a Binary Zinc Cluster to Supercapacitive Porous Carbon

The in situ tracking of the pyrolysis of a binary molecular cluster [Zn₇(μ₃-CH₃O)₆(L)₆][ZnLCl₂]₂ is presented with one brucite disk and two mononuclear fragments (L=mmimp: 2-methoxy-6-((methylimino)-methyl)phenolate) to porous carbon using TG-MS from 30 to 900 °C. Following up the spilled gas product during the decomposed reaction of zinc cluster along the temperature rising, and in conjunction with XRD, SEM, BET and other materials characterization, where three key steps were observed: 1) cleavage of the bulky external ligand; 2) reduction of ZnO and 3) volatilization of Zn. The real-time-dependent phase-sequential evolution of the remaining products and the processing of pore forming template transformation are proposed simultaneously. The porous carbon structure featuring a uniform nano-sized pore distribution synthesized at 900 °C with the highest surface area of 1644 m² g⁻¹ and pore volume of 0.926 cm³ g⁻¹ exhibits the best known capacitance of 662 F g⁻¹ at 0.5 A g⁻¹.     

Ionic electro-active polymer actuator based on cobalt-containing nitrogen-doped carbon/conducting polymer soft electrode

Nanoscale cobalt-containing nitrogen-doped porous carbon (CoNC) materials were prepared by thermolysis of a zeolitic imidazolate framework (ZIF), ZIF-67, at different temperatures and their application for ionic electro-active polymer (EAP) actuator was evaluated. CoNC-700, which was obtained from ZIF-67 pyrolysis at 700 °C, exhibits specific surface area of 753.86 m² g⁻¹, pore volume of 0.5768 cm³ g⁻¹, and specific capacitance of 120.7 F∙g⁻¹. CoNC/conducting polymer soft electrode were fabricated by unitizing effective interaction of CoNC with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). High-performance ionic actuators were developed for the first time using this CoNC/PEDOT:PSS soft electrode. The developed ionic EAP actuator exhibited large peak-to-peak displacement of 20.4 mm and high bending strain of 0.28% (3 V and 0.1 Hz). Therefore, ZIFs or metal organic frameworks (MOFs) can be applied to provide significant improvements in EAP actuators, which can play key roles as technological advances toward bioinspired actuating devices required for next-generation soft and wearable electronics.