Uniform Bi2S3 nanorods-assembled hollow spheres with excellent electrochemical hydrogen storage abilities

Hierarchical Bi₂S₃ hollow spheres have been synthesized by a facile solvothermal process in the presence of sodium tartrate. The hollow spheres are composed of numerous ultrathin nanorods with the average diameter of 15 nm. Based on the time dependent electron microscope observations, the formation mechanism of such hierarchical structures has been proposed as a sodium tartrate directed self-assembled process and oriented attachement mechanism. The morphology and size of the subunits can be controlled by adjusting the amount of sodium tartrate. The Nitrogen adsorption-desorption measurements suggest that mesopores exist in these hollow spheres. The as-derived Bi₂S₃ hollow spheres exhibit excellent electrochemical hydrogen storage properties.     

Hydrogen photoproduction from hydrogen sulfide on Bi2S3 catalyst

Films of polycrystalline Bi₂S₃ have been prepared onto bismuth and platinum substrates by electrodeposition from an aqueous sulfide bath. The films were thin, uniform and well adhered. Bi₂S₃ is a direct band gap semiconductor with a value of 1.28 eV optimally matched with the solar spectrum. The photoelectrochemical study was undertaken for the generation of hydrogen by using illuminated n-Bi₂S₃ particles; it was found that hydrogen evolution depends highly on the synthesis method of powder. Impregnation of platinum onto Bi₂S₃ shows a production enhancement of about 25%. The most active photocatalyst, prepared by a solvent thermal process and loaded with Pt in 0.1 M S²⁻ alkaline electrolyte, yields 2.13×10⁻² ml mg⁻¹ of H₂ after 4 h of irradiation with the visible output of a 500 W halogen lamp.     

Semiconductor-sensitized solar cells based on nanocrystalline In2S3/In2O3 thin film electrodes

A possibility of semiconductor-sensitized thin film solar cells have been proposed. Nanocrystalline In₂S₃-modified In₂O₃ electrodes were prepared with sulfidation of In₂O₃ thin film electrodes under H₂S atmosphere. The band gap (E_g) of In₂S₃ estimated from the onset of the absorption spectrum was approximately 2.0 eV. The photovoltaic properties of a photoelectrochemical solar cell based on In₂S₃/In₂O₃ thin film electrodes and I⁻/I₃⁻ redox electrolytes were investigated. This photoelectrochemical cell could convert visible light of 400–700 nm to electron. A highly efficient incident photon-to-electron conversion efficiency (IPCE) of 33% was obtained at 410 nm. The solar energy conversion efficiency, η, under AM 1.5 (100 mW cm⁻²) was 0.31% with a short-circuit photocurrent density (J_sc) of 3.10 mA cm⁻², a open-circuit photovoltage (V_oc) of 0.26 V, and a fill factor ( ff ) of 0.38.     

Solvothermal synthesis and growth mechanism of Sb2Se3 nanoplates with electrochemical hydrogen storage ability

Sb₂Se₃ nanoplates have been synthesized by a solvothermal method in mixtures of tetrahydrofuran and diethylenetriamine at 120 °C with the help of sodium tartrate. The as-prepared samples were determined by means of powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). Some experimental parameters influencing the formation of Sb₂Se₃ nanoplates were systematically investigated. Based on the electron microscope observations, a self-assembly process and Ostwald ripening mechanism was proposed for explaining the formation of the Sb₂Se₃ nanoplates. The electrochemical hydrogen storage measurements reveal that the Sb₂Se₃ nanoplates show a high discharging capacity of 237 mA h g⁻¹ at room temperature.     

Inclusion of Bi2S3 nanoparticles in polypyrrole thin films electropolymerized on chemically deposited bismuth sulfide electrodes: synthesis and characterization

The successful electropolymerization of pyrrole and its codeposition with Bi₂S₃ nanoparticles on chemically deposited bismuth sulfide substrates is described. The materials were designed to explore new approaches to improve light-collection efficiency in polymer photovoltaics. We report the effect of bismuth sulfide nanoparticles on the electropolymerization of pyrrole and on the morphology and optoelectronic properties of the composite film. The differences observed on the optical band gaps, photoaction spectra and open-circuit photovoltages, led to the conclusion that polymerization under the presence of nanoparticles produces tighter and thinner polymeric coatings than the ones obtained without nanoparticles. Under illumination, the composite polymeric coating has low absorption and high electronic conductivity, typical of the oxidized form of polypyrrole. This suggests a photoinduced charge transfer reaction compatible with the electron-accepting nature of bismuth sulfide nanoparticles. When subjected to long time illumination, atomic force microscopy, optical characterization and photoelectrochemical studies showed that the presence of Bi₂S₃ nanoparticles in the polymeric film improves the efficiency of the coating against photocorrosion.     

Effect of Mg3MnNi2 on the electrochemical characteristics of Mg2Ni electrode alloy

Mg₂Ni–x mol% Mg₃MnNi₂ (x = 0, 15, 30, 60, 100), the novel composite alloys employed for hydrogen storage electrode, have been successfully synthesized by a method combining electric resistance melting with isothermal evaporation casting process (IECP). X-ray diffraction (XRD) analysis results show that the composite alloys are composed of Mg₂Ni phases and the new Mg₃MnNi₂ phases. It is found on the electrochemical studies that maximum discharge capacities of the composite alloys increase with the increasing content of the Mg₃MnNi₂ phase. The discharge capacity of the electrode alloy is effectively improved from 17 mAh g⁻¹ of the Mg₂Ni alloy to 166 mAh g⁻¹ of the Mg₃MnNi₂ alloy. Among these alloys, the Mg₃MnNi₂ phase possesses a positive effect on the retardation of cycling capacity degradation rate of the electrode materials. Cyclic voltammetry (CV) results confirm that the increasing content of the Mg₃MnNi₂ phase effectively improves the reaction activity of the electrode alloys. Surface analyses indicate that the Mg₃MnNi₂ phase can enhance the anti-corrosive performance of the particle surface of these composite alloys.     

LiBH4 as solid electrolyte for Li-ion batteries with Bi2Te3 nanostructured anode

The present study highlights the first-ever application of fastest lithium (Li) ion conducting complex hydride containing cluster anions, namely lithium borohydride (LiBH₄) into an all-solid-state Li-ion battery having Bi₂Te₃ as anode material. Bi₂Te₃ nanostructures were prepared by the simple wet chemical method and characterized by their crystal structure, morphology and electronic structure using X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). SEM and TEM experiments revealed the dimensions as 20–60 nm for nanoparticles and 30–90 nm for nanosheets. The formation of Bi₂Te₃ nanostructures along with Bi₂O₃ as the residual phase is confirmed by XRD analysis. The crystallite size of nanoparticles and nanosheets are calculated as 19 nm and 39 nm respectively from XRD profile. The XPS study also confirms the formation of nanostructured Bi₂Te₃ along with Bi₂O₃. Finally, the electrochemical performance of these nanostructures is observed using the galvanostatic charge-discharge curve at 0.1C and 0.5C.     

Characterizations of polybenzimidazole based electrochemical hydrogen pumps with various Pt loadings for H2/CO2 gas separation

Carbon capture and storage (CCS) technologies have been intensively researched and developed to cope with climate change, by reducing atmospheric CO₂ concentration. The electrochemical hydrogen pumps with phosphoric acid doped polybenzimidazole (PBI) membrane are evaluated as a process to concentrate CO₂ and produce pure H₂ from anode outlet gases (H₂/CO₂ mixture) of molten carbonate fuel cells (MCFC). The PBI-based hydrogen pump without humidification (160 °C) can provide higher hydrogen separation performances than the cells with perfluorosulfonic-acid membranes at a relative humidity of 43% (80 °C), suggesting that the pre-treatment steps can be decreased for PBI-based systems. With the H₂/CO₂ mixture feed, the current efficiency for the hydrogen separation is very high, but the cell voltage increase, compared to the pure hydrogen operation, mainly due to the larger polarization resistance at electrodes, as confirmed by electrochemical impedance spectroscopy (EIS). The performance evaluation with various Pt loadings indicates that the hydrogen oxidation reaction at anodes is rate determining, and therefore the Pt loading at cathodes can be decreased from 1.1 mg/cm² to 0.2 mg/cm² without significant performance decay. The EIS analysis also confirms that the polarization resistances are largely dependent on the Pt loading in anodes.     

The preparation of Co9S8 and CoS2 nanoparticles by a high energy ball-milling method and their electrochemical hydrogen storage properties

Two different Co–S compounds with enhanced hydrogen storage properties, Co₉S₈ and CoS₂, were prepared by ball-milling mixtures of Co metal and S powder. X-ray diffractometry, scanning electron microscopy and transmission electron microscopy were used to show that specific molar ratios of Co:S and ball-milling speeds and times result in pure Co₉S₈ and CoS₂, thus overcoming a long-standing inability to obtain pure Co–S compounds via ball-milling. A galvanostatic charge–discharge process and cyclic voltammetry measurements showed that the as-obtained Co₉S₈ and CoS₂ nanoparticles have enhanced electrochemical hydrogen storage capacities of 1.79 and 1.57 wt% hydrogen, respectively, which are higher than those previously reported. In addition, based on the corresponding X-ray photoelectron spectroscopy and cyclic voltammetry measurements, a new electrochemical hydrogen storage mechanism for the two Co–S compounds was proposed and discussed.     

Photocurrent enhancement of wide bandgap Bi2O3 by Bi2S3 over layers

Sintered Bi₂O₃ pellets exhibited insulating properties at room temperature. Partial reduction of sintered Bi₂O₃ pellets increased the conductivity. Reduced Bi₂O₃ pellets exhibited n-type semiconductor properties. Microcrystals of Bi₂S₃ were formed on sintered Bi₂O₃ pellets by sulfurizing them in H₂S atmosphere. The direct band-gap and indirect band-gap of Bi₂S₃ were evaluated as 1.2 and 0.4 eV, respectively. A high incident photon to current conversion efficiency in the near IR region was observed on Bi₂S₃|Bi₂O₃ electrodes. Photocurrent generation of Bi₂S₃|Bi₂O₃ electrodes was explained from the viewpoint of semiconductor sensitization. The flat band potential of Bi₂S₃ was evaluated as −1.1 V vs. Ag|AgCl in aqueous polysulfide redox electrolyte (1 M OH⁻, 1 M S²⁻, 10⁻² M S).     

Physical and electrochemical characterization of Bi2O3-doped scandia stabilized zirconia

Electrolytes based on Sc₂O₃–ZrO₂ exhibit the highest ionic conductivity of zirconia based systems, however, stabilization of the electrochemical properties at operational temperatures, 600–1000 °C, are needed before implementation into SOFCs. Trace additions of Bi₂O₃ are a known sintering aid for zirconia systems. Crystal structures, electrical properties and long-term stability of Bi₂O₃-doped 10ScSZ systems were investigated. The addition of more than 1.0 mol% Bi₂O₃ resulted in suppression of the rhombohedral to cubic phase transformation at 600 °C and cubic phase stabilization at room temperature. The ionic conductivity of 10ScSZ was also improved by Bi₂O₃ additions. A maximum conductivity of 0.034 S cm⁻¹ at 700 °C was observed in 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C. No phase change was observed in 10ScSZ after annealing at 1000 °C. A certain amount of monoclinic phase, and dramatic conductivity decrease, were observed in Bi₂O₃-doped samples sintered below 1200 °C after annealing. However, 10ScSZ and 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C show no significant conductivity degradation with annealing. Samples with more than 1 mol% Bi₂O₃ and sintered above 1300 °C resulted in good ionic conductivity and stability.     

Sonochemistry synthesis of Bi2S3/CdS heterostructure with enhanced performance for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution from water splitting is an efficient, eco-friendly method for the conversion of solar energy to chemical energy. A great number of photocatalysts have been reported but only a few of them can respond to visible-light. Metal sulfides, a class of visible-light response semiconductor photocatalysts for hydrogen evolution and organic pollutant degradation, receive a lot of attention due to their narrow band gaps. Herein, we report the sonochemical synthesis of Bi₂S₃/CdS nanocrystal composites with microsphere structure at mild temperature. The phases of Bi₂S₃ and CdS can be observed obviously in HRTEM image. The heterostructure consisting of the two species of nanocrystals plays a key role in separating photo-generated charge carriers. Photocatalytic activities for water splitting are investigated under visible-light irradiation (λ > 400 nm) and an enhanced photocatalytic activity is achieved. The initial rate of H₂ evolution is up to 5.5 mmol h⁻¹ g⁻¹ without resorting to any cocatalysts.     

Effects of ageing on defect structure in the Bi3NbO7–Bi3YO6 system

Ageing effects in the defect fluorite structure of Bi₃Nb_1−xY_xO_7−x have been studied using powder neutron diffraction. Two compositions at x = 0.4 and x = 0.6 were studied after annealing for prolonged times (400–500 h) at 410 and 550 °C. The results show that significant changes in oxide ion distribution occur at 550 °C, but that at 410 °C only the lower x-value composition exhibited such a change. A comparison of lattice parameter variation with temperature for annealed and unannealed samples suggests that at higher temperatures the oxide ion distribution is independent of thermal history.     

Effect of Bi2O3 content on characteristics of Bi2O3–GDC systems for direct methane oxidation

Ceramic systems of Bi₂O₃ and gadolinia-doped ceria (GDC) solid mixture were prepared as catalysts for direct methane oxidation. These systems were characterized by temperature-programmed reduction using hydrogen and carbon monoxide, temperature-programmed reaction of methane, fixed-temperature direct methane oxidation, and X-ray diffraction analysis. Adding Bi₂O₃ to GDC promotes both hydrogen and CO oxidation activities, because of the presence of surface Bi₂O₃ and the high content of mobile oxygen in Bi₂O₃. The reactivity of CO with surface lattice oxygen is enhanced to a higher extent than that of H₂, and this enhanced extent shows a maximum in Bi₂O₃ content. Such a maximum also exists for the catalytic activity of direct methane oxidation. A synergistic effect occurs due to a combination of the high methane reactivity of GDC and the high content of mobile oxygen in Bi₂O₃. The CO₂ selectivity of direct methane oxidation can be modulated by varying the Bi₂O₃ content. The mixing of Bi₂O₃ with GDC also increases the self-de-coking capability of the catalyst during direct methane oxidation, which stabilizes the activity.     

Direct methane oxidation over a Bi2O3–GDC system

A novel ceramic system was prepared by adding Bi₂O₃ to gadolinia-doped ceria (GDC). This Bi₂O₃–GDC system was characterized by temperature-programmed and fixed-temperature reaction of methane in the absence of gas-phase oxygen. It was found that adding Bi₂O₃ to GDC can promote the catalytic activity for direct methane oxidation. A Bi₂O₃ loading of 25 wt% in the Bi₂O₃–GDC system maximized the activity of direct methane oxidation. Possible carbon deposition after the reaction can be negligible. In the temperature range of an intermediate-temperature solid oxide fuel cell (SOFC), pre-reduction promotes methane oxidation activity. At temperatures of about 600 °C or lower, only CO₂ and H₂O are produced. However, CO and H₂ can be produced only at a temperature of about 700 °C or higher. This Bi₂O₃–GDC system can be applied to design SOFC anode materials for complete methane oxidation and thus full electricity generation, without syngas cogeneration, at low temperature.     

Enhanced electrochemical lithium storage performance of Mg2FeH6 anode with TiO2 coating

Light-weight metal hydrides are potential high-capacity conversion anode materials for lithium-ion batteries, but the poor reaction reversibility and cyclic stability of hydride anodes need to be improved. In this work, the ternary hydride Mg₂FeH₆ was composited with the graphite (G) by ball-milling, and the Mg₂FeH₆-G composite electrode was further coated with amorphous TiO₂ film by magnetron sputtering. The resultant Mg₂FeH₆-G/TiO₂ electrode exhibited a stable charge capacity of 412 mAh g^?1 over 100 cycles, which is much higher than 46 mAh g^?1 at 20th cycle for the pure Mg₂FeH₆ electrode, or 185 mAh g^?1 at 100th cycle for the Mg₂FeH₆-G electrode. There is only little capacity degradation after 20 cycles for the Mg₂FeH₆-G/TiO₂ electrode and the charge capacity retention is 84.7% after 100 cycles. The remarkable improvement in the cyclic stability of Mg₂FeH₆-G/TiO₂ electrode is mainly attributed to the dense TiO₂ coating that maintains the structural integrity of electrode during cycling. The TiO₂ coating also prevents the direct contact of high active LiH/MgH₂ with the liquid electrolyte, and thus ensures the high reversibility of conversion reaction of MgH₂ during cycling.     

Selective growth of vertically aligned two-dimensional MoS2/WS2 nanosheets with decoration of Bi2S3 nanorods by microwave-assisted hydrothermal synthesis: Enhanced photo-and electrochemical performance for hydrogen evolution reaction

In this work, we fabricated MoS₂/WS₂ heterostrucutures with decoration of Bi₂S₃ nanorods through different stacking sequences (MoS₂/WS₂ (bottom layer) +Bi₂S₃ (top layer) and Bi₂S₃ (bottom layer) + MoS₂/WS₂ (top layer), respectively). The morphology and structure were studied by scanning electron microscope (SEM), transmission electron microscope (TEM) and the X-ray powder diffraction (XRD). It was found that the hybrid structure with different stacking sequences was composed of Bi₂S₃ nanorods and MoS₂/WS₂ nanosheets. By UV–visible absorption spectra (UV–vis) and photoluminescence (PL) experiments, we found that the composite catalysts of both stacking sequences can promote visible-light utilization and accelerate the electron transportation. Electrochemical measurements (such as cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscope (EIS) under light illumination or in dark) indicated that the MoS₂/WS₂+Bi₂S₃ possessed higher photoelectrocatalytic activity towards hydrogen evolution reaction (HER) than that of Bi₂S₃+MoS₂/WS₂ due to its proper energy band alignment that facilitates the effective carrier separation, the lower charge transfer resistance, higher electrochemically active surface area as well as the fast electron transfer kinetics. Inspired by these observations, we believe that MoS₂/WS₂+Bi₂S₃ catalyst is a potential candidate for photoelectrocatalytic production of H₂.     

One step synthesis of rGO-Ni3S2 nano-cubes composite for high-performance supercapacitor electrodes

In the last decade, supercapacitors possessing high power density and cyclic stability have attracted great interests in various applications. Graphene-based composite electrodes are known as a promising candidate for supercapacitors due to synergistic effects. For the first time, in this work, we develop a simple one-step hydrothermal synthesis of graphene wrapped Ni₃S₂ nanocubes (rGO-Ni₃S₂) composite for high-performance and low-cost supercapacitor electrodes. The rGO-Ni₃S₂ electrode exhibits an ultrahigh specific capacity of 616 C g^?1 at the current density of 1 A g^?1 with excellent cycling durability of 92.7% after 5000 cycles, which is much better when compared with the counterpart without graphene (pure Ni₃S₂). We attribute the remarkable performance of the rGO-Ni₃S₂ electrode to the synergistic effects of the graphene as the conductive support and Ni₃S₂ cubics as the pseudocapacitive material. This work constitutes a step forward towards the development of low-cost and high-performance supercapacitors for the next generation of portable electronics.     

Enhanced electrochemical hydrogen storage capacity of multi-walled carbon nanotubes by TiO2 decoration

Electrochemical hydrogen storage of multi-walled carbon nanotubes (MWCNTs) decorated by TiO₂ nanoparticles (NPs) has been studied by the galvanostatic charge and discharge method. The TiO₂ NPs are deposited on the surface of MWCNTs by sol-gel method. Structural and morphological characterizations have been carried out using XRD, SEM and TEM, respectively. TiO₂ NPs can significantly enhance the discharge capacity of MWCNTs. The cyclic voltammograms analysis indicates that the electrical double layer contributes little to the discharge capacity of TiO₂-decorated MWCNTs. The MWCNTs modified with a certain amount of TiO₂ NPs have a discharge capacity of 540 mAh/g, corresponding to an electrochemical hydrogen storage capacity of about 2.02 wt%, which is quite interesting for the battery applications. The enhancement effect of TiO₂ NPs on the discharge capacity of MWCNTs could be related to the increased effective area for the adsorption of hydrogen atoms in the presence of TiO₂ NPs on MWCNTs and the preferable redox ability of TiO₂ NPs.