Nanostructured Bi2Te3 as anode material as well as a destabilizing agent for LiBH4

Lithium borohydride, a well known complex hydride with its high hydrogen capacity, has shown its application as a solid electrolyte for Li-ion battery. It has been employed as a solid electrolyte with Bi₂Te₃ nanosheets as anode material for lithium-ion batteries (LIBs). The Bi₂Te₃ nanosheets were synthesized by the solvothermal method with an average crystallite size of 55 nm as calculated by Debye Scherrer formula. The scanning electron microscopy (SEM), and transmission electron microscopy (TEM) experiments reveal the morphology of the prepared sample as hexagonal nanosheets with the thickness in the range of 20–40 nm. Initial discharge and charge capacity of the negative electrode is found to be 555 mAhg⁻¹ & 1290 mAhg⁻¹ using galvanostatic charge-discharge analyzer at a rate of 0.1C. During the electrochemical charging-discharging experiment, strange but interesting gas evolution was observed, which resulted in the opening of the cell. The careful investigation of this reaction using TG/MS suggest the destabilization of LiBH₄. The thermal dehydrogenation analysis depicts that the LiBH₄–Bi₂Te₃ nanosheets composite starts to desorb hydrogen at 61 °C with a total of 9% weight loss. The above destabilization is investigated using XRD and XPS experiments and the detailed mechanism is proposed herein.     

Facile fabrication of Bi2O3/TiO2-xNx nanocomposites for excellent visible light driven photocatalytic hydrogen evolution

Mesoporous Bi₂O₃/TiO_2−xN_x nanocomposites (BiNT) were synthesized by soft chemical template free homogeneous co-precipitation technique. XRD, XPS, TEM, UV-Vis DRS and photoluminescence studies were adapted to determine the structural, electronic and optical properties. The photocatalytic activities of the catalysts were evaluated for water splitting to generate clean hydrogen fuel under visible light irradiation (λ ≥ 400 nm). BiNT-400 catalyst showed highest results towards hydrogen production (198.4 μmol/h) with an apparent quantum efficiency of 4.3%. The pronounced activity of BiNT-400 sample towards hydrogen production was well consistent with high crystallinity, large surface area, proper excitation by N doping and Bi₂O₃ sensitization.     

Enhanced photocatalytic hydrogen evolution using a novel in situ heterojunction yttrium-doped Bi4NbO8Cl@Nb2O5

The novel in situ Z-scheme heterostructure materials Y-doped Bi₄NbO₈Cl@Nb₂O₅ (Bi_4-xY_xNbO₈Cl, x = 0, 1, 1.33, 2, 2.67, 3) have been synthesized successfully via a solid-state method. The as-prepared samples were characterized by XRD, Raman spectrum, SEM, EDS, element mapping, HRTEM, XPS and UV–vis spectrum to explore the structures, morphologies and optical properties. Photocatalytic activities were evaluated for hydrogen generation using the Pt as the co-catalysts. HRTEM results indicated the Pt particles were deposited on the surface of the Bi₄NbO₈Cl. Photocatalytic activities were evaluated by hydrogen generation. While photocatalytic results showed that BiY₃NbO₈Cl composites exhibited the best performance of hydrogen production under the full-range irradiation (λ > 300 nm) while the Y-doped Bi₄NbO₈Cl@Nb₂O₅ with Y:Bi molar ratio 1:1 obtained the highest efficiency with ultraviolet light eliminated. The H₂ production was 1.35 mmol and 0.9 mmol in 8 h, respectively. Furthermore, a direct Z-scheme mechanism with enhanced hydrogen evolution competent for accelerating the separation of photogenerated carries has been presented and proved by electrochemical impedance spectroscopy (EIS). Finally, considering the conclusions of the electron spin-resonance spectroscopy (EPR), ·OH radicals served as an active species played an important role in the hydrogen production. Mechanisms about the action of the ·OH radicals were also proposed.     

Hydrogenation of CO2 over Co supported on carbon nanotube,carbon nanotube-Nb2O5, carbon nanofiber,low-layered graphite fragments and Nb2O5

CO₂ hydrogenation was studied with catalysts containing 1.5–35 wt% Co supported on carbon nanotubes, nanofibers, low-layered graphite fragments and composites of carbon nanotube-Nb₂O₅. All catalytic processes with Co/supported catalysts were investigated using XRF, DSC, TGA, H₂-TPR, TEM, SEM and XPS. Based on obtained results, it is indicated that the products from CO₂ hydrogenation were CH₄ and/or CO under reaction conditions pressure of 1.5 MPa and temperature of 200–500 °C, as well as the size of the particles of Co and their phase state directly affected on the catalysts activity. 3 wt% Co catalyst supported on carbon nanotubes has shown catalytic inactivity due to amorphous state of metal. It is possible to activate them during Co crystallization after thermal treatment. It is shown, that the size of Co particles supported on carbon nanotubes is 4–6 nm. The methods of fictionalization the surface of carbon nanomaterials ensuring an additional stability of metal nanoparticles is recommended.     

Electrochemical performance of In2O3 thin film electrode in lithium cell

Indium oxide (In₂O₃) coating on Pt, as an electrode of thin film lithium battery was carried out by using cathodic electrochemical synthesis in In₂(SO₄)₃ aqueous solution and subsequently annealing at 400 °C. The coated specimens were characterized by X-ray photoelectron spectroscopy (XPS) for chemical bonding, X-ray diffraction (XRD) for crystal structure, scanning electron microscopy (SEM) for surface morphology, cyclic voltammetry (CV) for electrochemical properties, and charging/discharging test for capacity variations. The In₂O₃ coating film composed of nano-sized particles about 40 nm revealing porous structure was used as the anode of a lithium battery. During discharging, six lithium ions were firstly reacted with In₂O₃ to form Li₂O and In, and finally the Li_4.33In phase was formed between 0.7 and 0.2 V, revealing the finer particles size about 15 nm. The reverse reaction was a removal of Li⁺ from Li_4.33In phase at different oxidative potentials, and the rates of which were controlled by the thermodynamics state initially and diffusion rate finally. Therefore, the total capacity was increased with decreasing current density. However, the cell delivering a stable and reversible capacity of 195 mAh g⁻¹ between 1.2 and 0.2 V at 50 μA cm⁻² may provide a choice of negative electrode applied in thin film lithium batteries.     

One-step synthesis of the 3D flower-like heterostructure MoS2/CuS nanohybrid for electrocatalytic hydrogen evolution

In this work, a facile one-step hydrothermal method was developed to fabricate three types different of nanomaterials: the two-dimension (2D) of MoS₂ nanosheets; 3D spherical CuS nanoparticles; and 3D flower-like heterostructure of MoS₂/CuS nanohybrid, respectively. The as-synthesized MoS₂, CuS and MoS₂/CuS were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (SEM) and X-ray diffraction (XRD) etc. The morphology of the MoS₂/CuS nanohybrid is different from the MoS₂ nanosheets and CuS nanoparticles. The hydrogen evolution reaction (HER) activity of MoS₂ nanosheets, CuS nanoparticles and MoS₂/CuS nanohybrid, were investigated by the Linear Sweep Voltammetry (LSV) and Tafel slope. The HER activity of MoS₂/CuS nanohybrid is better than those of MoS₂ nanosheets and CuS nanoparticles, which can be attributed to the good electron-transport ability of CuS and the strong reduction ability of hydrogen ions by MoS₂. Thus, MoS₂/CuS nanohybrid exhibited excellent activity for HER with a small onset potential of 0.15 V, a low Tafel slope of 63 mV dec^?1, and relatively good stability. However, the MoS₂ nanosheets and CuS nanoparticles respectively shows a bigger onset potential of 0.25 V and 0.35 V, a higher Tafel slope of 165 and 185 mV dec^?1. This 3D flower-like heterostructure of MoS₂/CuS nanohybrid catalyst exhibits great potential for renewable energy applications.     

Photocatalytic hydrogen evolution over the isostructural titanates: Ba3Li2Ti8O20 and Na2Ti6O13 modified with metal oxide nanoparticles

Isostructural titanates exhibiting rectangular tunnel structure with the general formula Na₂Ti₆O₁₃ and Ba₃Li₂Ti₈O₂₀, were synthesized by solid state and sol-gel methods. The structural, morphological, optical, textural and electrical properties of the materials were characterized by XRD, SEM, UV-vis, BET and EIS. The photocatalytic activity for hydrogen evolution of the materials was evaluated under UV light. Na₂Ti₆O₁₃ exhibited higher activity (120 μmol/gh) than Ba₃Li₂Ti₈O₂₀ (30 μmol/gh), and it was attributed to the distortion of the octahedrons in Ba₃Li₂Ti₈O₂₀, which increases the recombination of charges in the material. Additionally, the 1D dimension obtained in Na₂Ti₆O₁₃ promotes a better charge separation, transport and utilization in this phase. The activity of the materials was enhanced with the incorporation of metal oxide nanoparticles MO (M = Cu, Ni) as cocatalysts. The activity of Ba₃Li₂Ti₈O₂₀ increased 10 times with the addition of CuO (240 μmol/gh), while the activity of Na₂Ti₆O₁₃ increased 3.5 times (416 μmol/gh). This improvement in the photocatalytic activity of the isostructural titanates was attributed to the formation of a p-n heterostructure between n-type titanates and p-type CuO, which promoted an enhanced charge separation, transference and utilization.     

Li3V2(PO4)3 cathode material synthesized by chemical reduction and lithiation method

The monoclinic-type Li₃V₂(PO₄)₃ cathode material was synthesized via calcining amorphous Li₃V₂(PO₄)₃ obtained by chemical reduction and lithiation of V₂O₅ using oxalic acid as reducer and lithium carbonate as lithium source in alcohol solution. The amorphous Li₃V₂(PO₄)₃ precursor was characterized by using TG–DSC and XPS. The results showed that the V⁵⁺ was reduced to V³⁺ by oxalic acid at ambient temperature and pressure. The prepared Li₃V₂(PO₄)₃ was characterized by XRD and SEM. The results indicated the Li₃V₂(PO₄)₃ powder had good crystallinity and mesoporous morphology with an average diameter of about 30 nm. The pure Li₃V₂(PO₄)₃ exhibits a stable discharge capacity of 130.08 mAh g⁻¹ at 0.1 C (14 mA g⁻¹).     

Hierarchical chlorophytum-like Bi2S3 architectures with high electrochemical performance

Hierarchical chlorophytum-like Bi₂S₃ nanostructures are produced successfully on the large scale by a solvothermal method in the mixture of water and tetrahydrofuran. The crystal structure and morphology of the product are determined by X-ray diffraction (XRD) pattern, field emission scanning electron microscope (FESEM), and transmission electron microscopy (TEM). Time-dependent SEM observations indicate that the structure evolution of Bi₂S₃ contains self-assembly process and anisotropic growth mechanism. Furthermore, the electrochemical measurements present that the hierarchical Bi₂S₃ architectures display high electrochemical hydrogen storage and electrochemical Li intercalation performance.     

Decoration of Bi2Se3 nanosheets with a thin Bi2SeO2 layer for visible-light-driven overall water splitting

Exploring and developing novel semiconductor photo-catalysts for visible-light-driven water splitting are of great scientific significance to solve energy and environmental problems. Herein, Bismuth Selenide (Bi₂Se₃) nanosheets decorated with a thin layer of Bi₂SeO₂ to form Bi₂Se₃/Bi₂SeO₂ nanocomposites were successfully prepared using a conventional reflux and heating method. Fabricated Bi₂Se₃/Bi₂SeO₂ heterojunctions were characterized via X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. It has revealed that, the thickness of outer Bi₂SeO₂ layer can be tuned upon the annealing temperatures, which strongly influenced the performance of catalyst towards water splitting performances. Annealed at 200 °C, the Bi₂Se₃/Bi₂SeO₂ heterojunction with ～5 nm of Bi₂SeO₂ layer yielded the highest hydrogen production rate of 136 μmol g^?1 h^?1. This enhanced photo-catalytic activity was ascribed to the synergy effect between the Bi₂Se₃/Bi₂SeO₂ layer, increased the visible light absorbance capacity, adjustment of the band gap and accelerate the electron-hole separation efficiency. The results represent a simply solution-based method towards a material with high photo-catalytic performance through the appropriate regulation of the oxidation degree of Bi₂Se₃ nanosheets, promising their industrial applications.     

rGO supported PdNi-CeO2 nanocomposite as an efficient catalyst for hydrogen evolution from the hydrolysis of NH3BH3

The hydrogen economy is a proposed system that utilizes hydrogen to deliver energy. For the realization of this concept, how to safely, controllably and reversibly store and release hydrogen are critical problems which must be resolved. Metal alloys combined with suitable support materials are widely applied to various catalytic reactions. Here palladium nickel bimetallic nanoparticles doped with cerium oxide on a reduced graphene oxide (rGO) support were prepared by combining metal ion precursors and graphene oxide in a one-pot co-reduction approach. The as-received catalysts were characterized by XRD, TEM, SEM, XPS and ICP-OES, and the results revealed that PdNi-CeO₂ nanoparticles were uniform dispersal on rGO. The as-synthesized PdNi-CeO₂/rGO had been adopted as a heterogeneous catalyst for the hydrogen evolution from the hydrolysis of ammonia borane (NH₃BH₃, AB) at room temperature. Kinetically, the hydrogen-release rate was first-order with the increased concentration of catalysts. The optimized catalyst of Pd_0.8Ni_0.2-CeO₂/rGO with the CeO₂ content of 13.9 mol% exhibited an excellent activity with a turnover frequency value of 30.5 mol H₂ (mol catalyst)^?1 min^?1 at 298 K, and a low apparent activation energy (E_a) of 37.78 kJ mol^?1. The robust catalytic performance of the Pd_0.8Ni_0.2-CeO₂/rGO is attributed to the uniform controlled nanoparticle size, the synergic effect between the nanoparticles bimetallic properties, and the effective charge transfer interactions between the metal and support.     

A Li-doped Co3O4 oxygen evolution catalyst for non-precious metal alkaline anion exchange membrane water electrolysers

Li-doped Co₃O₄ (Li_xCo_3−xO₄, x = 0, 0.07, 0.21, 0.35, 0.49) spinel powders were prepared with a thermal decomposition method and characterized by XRD, SEM, TEM, and XPS. The Li_xCo_3−xO₄ samples were formed as tetragonal powders with a simple spinel structure and with particle sizes about 30–40 nm. All Li_xCo_3−xO₄ samples exhibited a 50 mV more negative onset potential for oxygen evolution reaction (OER) than Co₃O₄. The influence of Li-doping is discussed regarding cation distribution, electronic conductivity and oxygen binding energy. Li_0.21Co_2.79O₄ exhibited the highest OER activity amongst the five samples. A single cell, non-precious metal alkaline anion exchange membrane water electrolysers (AAEMWE) with Li_0.21Co_2.79O₄ anode exhibited a current density of 300 mA cm⁻² at a voltage 2.2 to 2.05 V at temperatures of 20–45 °C and the stability was examined with a continuous operation for 10 h at 300 mA cm⁻² and at 30 °C.     

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.     

Ionothermal synthesis of TiO2 nanoparticles for enhanced photocatalytic H2 generation

Photocatalytic hydrogen generation is one of the most promising solutions to convert light energy into green chemical energy. In the present work, methoxy ethyl methyl imidazolium methyl sulphonate ionic liquid is used for the synthesis of i-TiO₂ nanoparticles via ionothermal method at 120 °C. The obtained products were characterized by various spectroscopic techniques like XRD, FTIR, Raman, UV–visible, DRS, TEM and TG-DSC analysis. XRD pattern confirmed the anatase phase with minor rutile phase having average crystallite size of 5 nm. From the FTIR spectrum, the band appeared at ～547 cm^?1 confirmed the Ti–O–Ti stretching and also few bands of ionic liquid. UV–vis spectrum clearly reveals the blue shift due to size effect of TiO₂. The spherical surface structure and particle size (15–30 nm) have been studied in detail using TEM images. Finally, the practical applicability of the as synthesized i-TiO₂ nanoparticles is shown by using it as a photocatalyst towards the generation of H₂ through water splitting reaction and it is found to be 462 μmol h^?1g^?1.     

ACo2O4 (A=Ni,Zn, Mn) nanostructure arrays grown on nickel foam as efficient electrocatalysts for oxygen evolution reaction

Developing highly efficient, low-cost and superior stable electrocatalysts for the oxygen evolution reaction (OER) is essential for coping with global energy shortage and environmental crisis. In this article, ACo₂O₄/NF (A = Mn, Zn, Ni) composites were synthesized via a facilely hydrothermal and calcination method and used as electrocatalytic water oxidation catalysts. The hybrid structure, chemical composition, oxidation state and surface morphology of ACo₂O₄/NF (A = Mn, Zn, Ni) has been confirmed by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX), X-ray photoelectron (XPS), scanning electron microscopy (SEM), transmission Electron Microscope (TEM) and Brunaure-Emmett-Teller (BET) analysis. Such self-supported NiCo₂O₄/NF hybrid shows a smaller overpotential of 271 mV at current density of 10 mA cm^?2 in 1 M KOH, which is comparable to most reported NiCo₂O₄ materials (monomer or composite) for OER. Influence on catalytic activity of doping different metal ions in ACo₂O₄/NF was investigated systematically for the first time. Improved electrocatalytic activity of NiCo₂O₄/NF is attributed to the special homogeneous urchin-like structure and porous property.     

Micron-sized, carbon-coated Li4Ti5O12 as high power anode material for advanced lithium batteries

Spherical, high tap density, carbon-coated Li₄Ti₅O₁₂ powders are synthesized by a spray-drying process followed by a facile pitch coating. XRD, SEM, TEM analyses show that the carbon layer uniformly coats the Li₄Ti₅O₁₂ particles without producing any crystalline changes. We demonstrate that the carbon coating significantly increases the electrical conductivity of Li₄Ti₅O₁₂ making it an efficient, high rate electrode for lithium cells. The electrochemical tests in fact confirm that the 3.25 wt% carbon-coated Li₄Ti₅O₁₂ electrode operates with ultra high rate capacity levels, i.e., 100 C and has excellent capacity retention and charge-discharge efficiency for a life extending over 100 cycles.     

Core/shell Fe3O4@Fe encapsulated in N-doped three-dimensional carbon architecture as anode material for lithium-ion batteries

Core-shell Fe₃O₄@Fe nanoparticles embedded into porous N-doped carbon nanosheets was prepared by a facile method with NaCl as hard-template. The three-dimensional carbon architecture built by carbon nanosheets enhance the conductivity of the encapsulated Fe₃O₄@Fe nanoparticles and strengthen the structure stability suffering from volume expansion during extraction and insertion of lithium ions. Rich Pores enhance the surface between electrode and electrolyte, which short the transmission path of ions and electrons. The core-shell structure with Fe as core further improves charge transferring inside particles thus lead to high capacity. The as-prepared Fe₃O₄@Fe/NC composite displays an irreversible discharge capacity of 839 mAh g^?1 at 1 A g^?1, long cycling life (722.2 mAh g^?1 after 500th cycle at 2 A g^?1) and excellent rate performance (1164.2 and 649.2 mAh g^?1 at 1 and 20 A g^?1, respectively). The outstanding electrochemical performance of the Fe₃O₄@Fe/NC composite indicates its application potential as anode material for LIBs.     

Effect of CO2 on layered Li1+zNi1−x−yCoxMyO2 (M = Al,Mn) cathode materials for lithium ion batteries

We investigated the effect of CO₂ on layered Li_1+zNi_1−x−yCo_xM_yO₂ (M = Al, Mn) cathode materials for lithium ion batteries which were prepared by solid-state reactions. Li_1+zNi_(1−x)/2Co_xMn_(1−x)/2O₂ (Ni/Mn mole ratio = 1) singularly exhibited high storage stability. On the other hand, Li_1+zNi_0.80Co_0.15Al_0.05O₂ samples were very unstable due to CO₂ absorption. XPS and XRD measurements showed the reduction of Ni³⁺ to Ni²⁺ and the formation of Li₂CO₃ for Li_1+zNi_0.80Co_0.15Al_0.05O₂ samples after CO₂ exposure. SEM images also indicated that the surfaces of CO₂-treated samples were covered with passivation films, which may contain Li₂CO₃. The relationship between CO₂-exposure time and CO₃²⁻ content suggests that there are two steps in the carbonation reactions; the first step occurs with the excess Li components, Li₂O for example, and the second with LiNi_0.80Co_0.15Al_0.05O₂ itself. It is well consistent with the fact that the discharge capacity was not decreased and the capacity retention was improved until the excess lithium is consumed and then fast deterioration occurred.     

Selective substitution of Ni by Ti in LaNiO3 perovskites: A parameter governing the oxy-carbon dioxide reforming of methane

A series of LaNi_1?xTi_xO₃ perovskite catalysts varying titanium (x = 0.0, 0.2, 0.4, 0.5, 0.6 and 1.0) are synthesized and investigated using BET, XRD, TPR, TEM, FT-IR and XPS. The catalysts were evaluated for oxy-carbon dioxide reforming of methane at 800 °C under atmospheric pressure maintaining CO₂/CH₄/O₂ ratio 0.8/1.0/0.2. LaNi_0.5Ti_0.5O₃ is showing typical stability with gradual H₂ consumption in TPR. The stability of these catalysts is supported by O 1s binding energies wherein it is clearly evident that incorporation of Ti stabilized LaNiO₃ generating suitable catalysts in the range of x = 0.4–0.6 with high performance.     

Synthesis, characterization and application of Li3Fe2(PO4)3 nanoparticles as cathode of lithium-ion rechargeable batteries

This work introduces a new method to synthesize Li₃Fe₂(PO₄)₃ nanoparticles in the nanopowder form and study its electrochemical performance by cyclic voltammetry and battery tests. Li₃Fe₂(PO₄)₃ is synthesized by the gel combustion method based on polyvinyl alcohol (PVA) as gel making agent. The optimum conditions of the synthesis include 8 wt% PVA, 0.34 wt% lithium slat, 1 wt% iron salt, 0.57 wt% ammonium dihydrogen phosphate, ethanol-water 50:50 as solvent, 675 °C combustion temperature and 4 h combustion time. Characterization of the samples is performed by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), EDX analysis, XRD patterns, BET specific surface area and DSL size distribution. In the optimum conditions, a nanopowder is obtained that consisting of uniform nanoparticles with an average diameter of 70 nm. The optimized sample shows 12.5 m² g⁻¹ specific surface areas. Cyclic voltammetry (CV) studies show that the synthesized compound has good reversibility and high cyclic stability. The CV results are confirmed by the battery tests. The obtained results show that the synthesized cathodic material has high practical discharge capacity (average 125.5 mAh g⁻¹ approximately same with its theoretical capacity 128.2 mA h⁻¹) and long cycle life.