Supercritically exfoliated Bi2Se3 nanosheets for enhanced photocatalytic hydrogen production by topological surface states over TiO2

Owing to the unique electronic properties of layered materials, topological insulators have interestingly grabbed much attention in the field of photocatalytic water splitting. Nowadays, 2D layered materials were composited with semiconductor photocatalysts, encourage much as it provides enormous active sites and also significantly prevent photogenerated charge recombination. Especially, Bi2Se3 possesses exceptional properties like topologically preserved conducting surface states with bulk insulating behavior and high surface area, which provides unconventional electron dynamics, resulting in facile electron transport and effective charge separation to photocatalyst. So far, several methods have been attempted to synthesize few-layered Bi2Se3 nanosheets from its bulk crystals. Here, a unique attempt is made and succeeded to exfoliate bulk Bi2Se3 to few layered nanosheets via surfactant free supercritical fluid processing using N-Methyl-2-pyrrolidone (NMP) as an exfoliating agent, with a short reaction time of 15 min. The exfoliation of Bi2Se3 crystal was confirmed by several characterization techniques, such as XRD, SEM, Raman, and HR-TEM. Furthermore, different weight percentages of exfoliated Bi2Se3 sheets/anatase TiO2 nanoparticles were prepared and examined the photocatalytic activity using glycerol as a hole scavenger. Among them, 15 wt.% Bi2Se3 coupled TiO2 nanocomposite showed enormous hydrogen evolution rate of 84.9 mmol h-1g-1cat, which is 80 times higher than that of TiO2 nanoparticles. In addition, the photostability of the nanocomposite was also verified, where it retains 94% of activity even after 4 cycles of continuous experiments. The improved rate of H2 production was understood by theoretical calculations that topologically preserved conducting surface states of co-catalyst, Bi2Se3 nanosheets is supported to high mobile and scatter free electrons. It mediates the transport of electrons with TiO2 nanoparticles that helped the effective charge separation. Thus, it proves a promising candidate for photocatalytic hydrogen production

Experimental and theoretical study on optimizing caxBa1-xSnO3 perovskite materials as photoanode of dye-sensitized solar cells

The various compositions of CaxBa1−xSnO3 perovskite materials were synthesized by hydrothermal method and they were fabricated as the photoanode of dye-sensitized solar cells (DSSC). Among them, Ca0.1Ba0.9SnO3 composition shows better efficiency with the JSC of 4.64 mA cm−2 and VOC of 0.726 V. The conduction band minimum (CBM) of Ca0.1Ba0.9SnO3 material is slightly lower than excited-state potential of N719 dye molecules. This provides high electron transfer from dye to this perovskite material after shining the light. The structural stability and electronic properties of these materials were studied by first principles density functional theory (DFT) calculations. Our study revealed that CBM is mainly distributed by Sn 5s states, which provides high electronic mobility. This mobility is not altered much even for substitution of small amount of Ca atoms into BaSnO3

Effect of orange peel derived activated carbon as a negative additive for lead-acid battery under high rate discharge condition.

In the present study, the effect of orange peel derived activated carbon (OPAC) as an additive to the negative active material in lead acid battery cell was investigated and compared with control cell containing carbon black (CB). The electrochemical performance of negative electrodes is measured by cyclic voltammetry, impedance spectroscopy, galvanostatic charge-discharge. The surface area, crystal structure and morphology are characterized by Brunauer–Emmett–Teller, X-ray diffraction, Raman spectroscopy, transmission electron microscopy and scanning electron microscopy, respectively. OPAC carbon with high surface area (2160 m2/g) and meso/microporous structure exhibits significant influence on the electrochemical kinetics of the negative electrode. The lead acid cells containing OPAC show enhanced discharge performance under high rate discharge conditions, and charge acceptance, when compared to CB containing control cell. The optimum composition for the best electrochemical performance is determined at 0.1 wt% for OPAC. Cell with 0.1 wt.% OPAC show better discharge characteristics (with ~ 20% increase in average discharge capacity) than cell with 0.25 wt.% CB at C2 discharge rate. Oxygen and hydrogen gassing potential delayed by 31 and 37 minutes, respectively, in a cell comprising 0.1 wt.% OPAC, indicating the efficient charging process (PbSO4 to Pb conversion) at C2 rate. Lead acid cell infused with 0.1 wt.% OPAC showed ~ 89% increase in charge acceptance, over control cell containing CB. The inclusion of high specific surface area OPAC linearly increases the redox activity (Pb/PbSO4) especially at high discharge rates, and suppress the sulfation of negative active material

Electrodeposited partially oxidized Bi & NiCo alloy based thin films for aqueous hybrid high energy microcapacitor

Electrochemical energy storage (EES) devices play an important role in meeting the demand for the electrical energy. Particularly, electrochemical hybrid capacitors (HCs) are considered as one of the potential candidates for fulfilling the energy requirement. In this work, aqueous electrolyte-based high voltage HC is fabricated and its electrochemical characteristics are analyzed. Here, electrochemically prepared NiCo and Bi thin films on stainless steel substrate were used as positive and negative electrodes, respectively. The phase structure and crystalline size of the electrodeposited films are confirmed from XRD and AFM. It is observed that the as prepared NiCo film showed an excellent specific capacitance value of 83.33 mF cm−2 at 0.5 mA cm−2; on the other side, Bi film also showed a good storage capacity of 32.2 μA h cm−2 at 1 mA cm−2; To realize the high energy density, Bi||NiCo combination of the thin film HC is fabricated and the HC devices showed excellent performance at a tested potential window of 1.5 V. The cell plateau voltage is observed at 0.8 V. The maximum specific energy density of 7.3 μW h was achieved at a specific power density is 0.3 mW cm−2. Maximum specific power of 7.5 mW cm−2 at an energy density of 1.875 μW h was obtained from HSC. This indicates the excellent performance of the HC at various conditions. Thus, the binder-free, electrodeposited active electrode materials of the present work will play a significant role in the various electronic applications by supplying the energy demand

Molecularly engineered oxygen deficient magnetite decorated carbon as electrocatalysts for oxygen reduction reaction

Herein, we report the in situ synthesis of poly (ferrocene-urea) (PFUA) by reacting ferrocene diacylazide and tris (4-aminophenyl) amine. The formation of urea linkages between the precursors was confirmed by Fourier transform Infrared (FTIR) spectroscopy. The synthesized PFUA was pyrolyzed at different temperatures under Argon atmosphere to obtain hematite at 600 °C and magnetite embedded N-doped carbons at 800 and 1000 °C. Both hematite and magnetite was found to have particulate morphology embedded on porous N-doped carbon. The N-doping into the carbon matrix was confirmed by X-ray photoelectron spectroscopy (XPS). Further, their electrocatalytic activity towards oxygen reduction reaction (ORR) was carried out under standard conditions. PFUA pyrolyzed at 800 °C was found to exhibit better ORR activity than the other samples. The improved electrocatalytic activity toward ORR can be ascribed to the reductive environment generated during the thermal treatment of the urea linkages (formed between FDA and TAPA) which controls the structural transformation of the hematite phase to magnetite phase of iron oxide with creation of oxygen vacancies with improved Fe2+ to Fe3+ ratio

Metal organic framework laden poly(ethylene oxide) based composite electrolytes for all-solid-state Li-S and Li-metal polymer batteries

In this work, the possibility of employing aluminium terephthalic acid metal organic framework (Al-TPAMOF)- laden composite polymer membranes as electrolyte for all-solid-state lithium-sulfur (Li-S) and lithium-metal (Li-metal) polymer batteries is explored. The prepared composite polymer electrolytes (CPEs) based on a poly(ethylene oxide) (PEO) network with lithium bis(trifluoromethane)sulfonimide (LiTFSI) and Al-TPA-MOF are mechanically robust and thermally stable up to 270 �C, and provide appreciable ionic conductivity in the order of 0.1mS cm�1 at 60 �C. The enhanced compatibility of CPEs with the lithium metal anode is attributed to the scavenging effect of Al-TPA-MOF. Laboratory scale allsolid- state Li-S and Li-metal polymer cells are assembled, which deliver specific capacities exceeding 800 and 130mAh g�1, respectively, and a stable performance upon prolonged cycling even at 60 �C, which is superior to earlier reports on similar systems

Advancement of technology towards developing Na-ion batteries

The Na-ion-batteries are considered much attention for the next-generation power-sources due to the high abundance of Na resources that lower the cost and become the alternative for the state of the art Li-ion batteries in future. In this review, the recently reported potential cathode and anode candidates for Na-ion-batteries are identified in-light-of-their high-performance for the development of Na-ion-full-cells. Further, the recent-progress on the Na-ion full-cells including the strategies used to improve the high cycling-performance (stable even up-to 50000 cycles), operating voltage (even ≥ 3.7 V), capacity (> 350 mAhg−1 even at 1000 mAg−1 (basedon-mass-of-the-anode)), and energy density (even up-to 400 Whkg−1 ) are reviewed. In addition, Na-ion-batteries with the electrodes containing reduced graphene oxide, and the recent developments on symmetric Na-ionbatteries are discussed. Further, this paper identifies the promising Na-ion-batteries including the strategies used to assemble full-cell using hard-carbon-anodes, Na3V2(PO4)3 cathodes, and other-electrode-materials. Then, comparison between aqueous and non-aqueous Na-ion-batteries in terms of voltage and energy density has been given. Later, various types of electrolytes used for Na-ion-batteries including aqueous, non-aqueous, ionic-liquids and solid-state electrolytes are discussed. Finally, commercial and technological-developments on Na-ion-batteries are provided. The scientific and engineering knowledge gained on Na-ion-batteries afford conceivable development for practical application in near futur

Silica template assisted synthesis of ordered mesoporous be MnO2 nanostructures and their performance evaluation as negative electrode in Li-ion batteries

In the pursuit of high capacity anode materials transition metal oxides have paid great deal of attention. However poor electronic conductivity, high discharge potential and volume change during electrochemical cycling hinders their practical applications. In this report, we synthesize the well-ordered mesoporous b-MnO2 phases (pyrolusite structure) using SBA-15 and MCM-48 templates. The product derived from SBA-15, designated as SBA-MnO2 has interconnected nanorod like morphology, whereas the product derived from MCM-48, designated as MCM-MnO2 exhibits open cage/bowl like morphology. The products are characterized by XRD, FTIR, FESEM, TEM, XPS, BET surface area measurements. Further, electrochemical studies are carried out to investigate their application as anode material for Li-ion batteries. Galvanostatic cycling shows initial discharge capacity of ~1500 mAhg�1 and 1750 mAhg�1 respectively for SBA-MnO2 and MCM-MnO2. After 100 charge-discharge cycles, MCM-MnO2 electrode exhibits capacity 345 mAhg�1 and SBA-MnO2 shows a capacity of 245 mAhg�1 . Though both the materials show capacity fading upon long cycling, their performance is better compared to other MnO2 nanostructures reported in the literature. They also exhibit good rate capability indicating that mesoporous MnO2 materials reported here can be potential candidate for Li-ion storag

Symmetric supercapacitor performances of CaCu3Ti4O12 decorated polyaniline nanocomposite

To explore the possibility of developing an electrode material with better supercapacitor performances, a composite of polyaniline (PANI) and varying amount of CaCu3Ti4O12 (CCTO) was synthesized using a simple technique involving in-situ polymerization of aniline using ammonium persulphate as oxidant. The pristine PANI and the composite were characterized using X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis (EDAX) and transmission electron microscope (TEM). The electrochemical activities of the PANI/CCTO nanocomposites were examined in 1M H2SO4 in a three electrode assembly. It turned out that the specific capacity of the PANI can be largely tuned by making composite with the inorganic filler, CCTO. The composite consisting of just 5 wt % CCTO in PANI (PC5) exhibited the highest electrochemical activity with excellent stability compared to other compositions as well as the pristine PANI. A symmetric supercapacitor device consisting of the PC5 composite as both positive and negative electrodes that were fabricated have exhibited energy density of 30 W h kg�1 with an excellent power density of 20 kW kg�1 . Glowing of an LED using the proto-type solid-state symmetric device was demonstrate

Methanol electro-oxidation by nanostructured Pt/Cu bimetallic on poly 3,4 ethylenedioxythiophene (PEDOT)

Herein, we report the preparation, characterisation and electrocatalysis of Pt/Cu bimetallic nanostructure formed on Poly 3,4 ethylenedioxythiophene (PEDOT) modified glassy carbon electrode, Pt-Cu-PEDOT/GC. A three-step procedure was adopted for the fabrication of the catalyst. Initially the glassy carbon electrode (GC) was modified by a uniform coating of PEDOT by potential cycling. Copper NPs were then deposited on the PEDOT film by deposition from a 2 mM solution of CuSO4 in 0.1 M NaClO4 at a constant potential of �0.477 V vs. SCE. Pt/Cu-PEDOT/GC catalyst was prepared by substitution of copper by galvanic displacement with various concentrations of H2PtCl6. The electrode thus prepared displayed very good electrocatalytic effect for methanol oxidation characterized by cyclic voltammetry. It was found that the catalyst prepared with 2 mM H2PtCl6 exhibited the highest catalytic activity, with If/Ib values of 1.80 and 1.38 for methanol concentrations of 1 M and 5 M, respectively. At a relatively low Pt loading of 5.48 10�6 /cm2 , the Pt/Cu-PEDOT/GC should be a cost-effective alternative anode catalyst for DMFC