Synthesis of carbon-doped SnO2 nanostructures for visible-light-driven photocatalytic hydrogen production from water splitting

Environmental issues: global warming, organic pollution, CO₂ emission, energy shortage, and fossil fuel depletion have become severe threats to the future development of humans. In this context, hydrogen production from water using solar light by photocatalytic/photoelectrochemical technologies, which results in zero CO₂ emission, has received considerable attention due to the abundance of solar radiation and water. Herein, a single-step thermal decomposition procedure to produce carbon-doped SnO₂ nanostructures (C–SnO₂) for photocatalytic applications is proposed. The visible-light-driven photocatalytic performance of the as-prepared materials is evaluated by photocatalytic hydrogen generation experiments. The bandgaps of the photocatalysts are determined by ultraviolet–visible diffused reflectance spectroscopy. The crystallinity, morphological features (size and shape), and chemical composition and elemental oxidation states of the samples are investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The proposed simple thermal decomposition method has significant potential for producing nanostructures for metal-free photocatalysis.     

Facile precipitation synthesis and electrochemical evaluation of Zn2SnO4 nanostructure as a hydrogen storage material

A facile precipitation method with the subsequent thermal treatment has been developed for the synthesis of Zn₂SnO₄ nanostructures in presence of tetraethylenepentamine (TEPA) with long chain as a capping and basic agent. The effects of different parameters such as precursor of Zn, solvent, reaction time and temperature were studied to reach optimum size and morphology conditions. More importantly, through controlling the experimental conditions, three different morphologies of nanoparticle, nanorod and nanoplate Zn₂SnO₄ mesoporous through one reaction were successfully obtained. In this paper, hydrogen storage capacity of Zn₂SnO₄ nanoparticle reported for the first time. Furthermore, the mesoporous of Zn₂SnO₄ nanoparticle showed high electrochemical hydrogen storage capacities at room temperature. After 13 cycles, the discharging capacities of the electrode still remain above 4650 mAh/g. These results indicate that the mesoporous Zn₂SnO₄ nanoparticle may be potentially applied for electrochemical hydrogen storage.     

Synthesis of SnO2 nanorods and hollow spheres and their electrochemical properties as anode materials for lithium ion batteries

Abstract

SnO₂ nanorods and hollow spheres were conducted via a surfactant assisted hydrothermal reaction with the hydrothermal temperature. The crystalline structure and morphologies of the as prepared samples were characterised by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the products are hollow spheres with diameters of approximately 400–800 nm and shell thicknesses of 60–70 nm via hydrothermal treating at 160°C for 42 h and rod-like nanostructures with diameters of ～30 nm and lengths of 100–300 nm via hydrothermal treating at 200°C for 42 h respectively. The as prepared samples were used as anode materials for lithium ion battery, whose charge–discharge properties and cycle performance were examined. The results show that the initial discharge capacities of SnO₂ hollow spheres and SnO₂ nanorods samples are 1303 and 1426 mA h g^?1 at 0·2C rate, and still retain charge capacities of 518 and 578 mA h g^?1 respectively. Its good cycling behaviour and charge capacities make it a promising cathode material for advanced electrochemical devices for lithium ion batteries.     

Hydrothermal synthesis of Co2SnO4 nanocrystals as anode materials for Li-ion batteries

Cubic spinel Co₂SnO₄ nanocrystals are successfully synthesized via a simple hydrothermal reaction in alkaline solution. The effect of alkaline concentration, hydrothermal temperature, and hydrothermal time on the structure and morphology of the resultant products were investigated based on X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is demonstrated that pure Co₂SnO₄ nanocrystals with good crystallinity can be obtained in NaOH solution (2.0 M) at 240 °C for 48 h. The galvanostatic charge/discharge and cyclic voltammetry were conducted to measure the electrochemical performance of the Co₂SnO₄ nanocrystals. It is shown that Co₂SnO₄ nanocrystals exhibit good electrochemical activity with high reversible capacity (charge capacity) of 1088.8 mAh g⁻¹ and good capacity retention as anode materials for Li-ion batteries, much better than that of bulk Co₂SnO₄ prepared by high temperature solid-state reaction.     

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.     

Pt support of multidimensional active sites and radial channels formed by SnO2 flower-like crystals for methanol and ethanol oxidation

SnO₂ nanoflowers and nanorods have been synthesized by the hydrothermal method without using any capping agent. Both types of SnO₂ nanostructures are selected as a support of Pt catalyst for methanol and ethanol electrooxidation. The synthesized SnO₂ nanostructures and SnO₂ supported platinum (Pt/SnO₂) catalysts are characterized by X-ray diffraction, scanning electron microscope and high resolution transmission electron microscope. The electrocatalytic properties of the Pt/SnO₂ and Pt/C catalysts for methanol and ethanol oxidation have been investigated systematically by typical electrochemical methods. The influence of SnO₂ morphology on its electrocatalytic activity is comparatively investigated. The Pt/SnO₂ flower-shaped catalyst shows higher electrocatalytic activity and better long-term cycle stability compared with other electrocatalysts owing to the multidimensional active sites and radial channels of liquid diffusion.     

Free-standing SnO2/MWCNT nanocomposite anodes produced by different rate spin coatings for Li-ion batteries

Free standing SnO₂/multiwalled carbon nanotube (MWCNT) nanocomposite anode materials were prepared for Li-ion batteries by sol–gel technique. Firstly, SnO₂ precursor sols were synthesized after removing chloride ions. Then the sols coated on MWCNT buckypapers, which used as substrates to form nanocomposite electrodes by spin coating method. Sintered nanocomposite structures were then characterized by field emission gun-scanning electron microscopy (FEG-SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) analyses. Electrochemical tests were performed for the produced electrodes, assembled as CR2016 cells. The effect of spin rate on the anode capacity was investigated. Coating on the MWCNT buckypapers was thought to use as mechanical support to prevent electrode failure and prevented the formation of cracks of the sol–gel thin film on the MWCNT surfaces. The results showed beneficial effects to prevent mechanical disintegration and subsequent anode pulverization of SnO₂ anodes because of huge volume increase during lithium intercalation. The results indicated that the nanocrystalline SnO₂/MWCNT composites are suitable for applying as an anode electrode for Li-ion batteries to increase electrochemical energy storage performance.     

Electrochemical deposition of Zn3P2 thin film semiconductors on tin oxide substrates

Zn₃P₂ semiconductor thin films were prepared by electrodeposition technique form aqueous solutions. The deposition mechanism was investigated by cyclic voltammetry technique. Crystal structure, morphology and composition of as deposited and annealed Zn₃P₂ thin films grown on SnO₂/glass substrates were determined by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis. X-ray diffraction data indicated the formation of Zn₃P₂ as the predominant phase for both as-deposited and annealed films. The compositions of the deposited films were controlled by the bath temperature, deposition potential and Zn/P ratio in the solution.The dark current–voltage measurements of SnO₂/Zn₃P₂/C devices indicated a rectifying behavior and a reverse saturation current density of 1.7×10⁻⁷ A/cm², which is in good accordance with that obtained from films prepared using vacuum technique. Also, the capacitance–voltage measurements showed that the number of interface states and the built in potential are in the order of 5×10⁻⁹ cm⁻³ and 0.85 V, respectively. These preliminary results for Zn₃P₂ thin films reveal that, this semiconductor material can be used for solar cell applications.     

Coating of multi-walled carbon nanotube with SnO2 films of controlled thickness and its application for Li-ion battery

Multi-walled carbon nanotubes (MWCNTs) coated with a smooth and uniform tin oxide (SnO₂) layers of different thickness were prepared by a novel thioglycolic acid assisted one-step wet chemical method. The coatings were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thickness of the SnO₂ coatings can be easily controlled by changing the synthesis conditions, such as pH value of the solution and hydrolysis time. The electrochemical properties of the SnO₂/MWCNTs composites as anode materials for lithium batteries were studied by galvanostatic method. The composites showed high charge capacities and good durability against decay. This could be ascribed to the good dispersion, thin layer and small particle size of SnO₂ on MWCNTs.     

Green solid-state fabrication of new nanocomposites based on La–Fe–O nanostructures for electrochemical hydrogen storage application

Nano-sized La–Fe–O (LFO) structures were fabricated via novel free-solvent and green solid-state route using La (acac)₃. H₂O and Fe (acac)₃ complex precursors. Acetylacetonate (acac) in organometallic complex precursors control nucleation and growth of formed crystals with creation spatial barrier around the cations, and prevent nano-product agglomeration. The mechanism of role of acac has been explained in nanostructure formation. Changing of parameters in synthesis reaction consisting La:Fe molar ratio, calcination time and temperature in turn offer a virtuous control over the nanocomposites size and shape which various compositions of La₂O₃/LaFeO₃, LaFeO₃/La₂O₃ and LaFeO₃/Fe₂O₃ obtained. The as-prepared La–Fe–O nano-products were characterized thorough Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), UV–Vis, BET and energy dispersive X-ray (EDX) analysis in terms of crystallinity structure, composition, porosity and morphology. Different formed La–Fe–O nanostructures were evaluated for electrochemical hydrogen storage capacity through chronopotentiometry technique in stable current (1 mA). The achieved La–Fe–O nanoparticles could be applied as a favorable candidate active material for electrochemical hydrogen storage. Optical, magnetic and reducible characteristics of La–Fe–O nanostructures have positive effect on electrochemical hydrogen storage capacity. It was found out that the LaFeO₃/Fe₂O₃ nanocomposites have the best electrochemical hydrogen storage performance due to oxidation-reduction process of Fe²⁺/Fe³⁺ components which can help to charge-discharge process of hydrogen to increase the storage capability to 790 mAhg^?1 after 20 cycles. Also, the mixed metal oxides illustrate advanced discharge capacity than other binary oxides.     

Ultrasonic assisted synthesis of a nano-sized Co2SnO4/graphene: A potential material for electrochemical hydrogen storage application

A facile and rapid sonochemical method has been developed for the synthesis of Co₂SnO₄ nanostructures in presence of glucose as a green capping agent, for the first time. The effect of different parameters such as ultrasonic irradiation, time irradiation, basic agent and solvent were studied to reach optimum size and morphology conditions. The optimized Co₂SnO₄ nanostructures anchored onto graphene sheets and Co₂SnO₄/Graphene nanocomposite synthesized through pre-graphenization, successfully. In this paper, hydrogen storage capacity of optimized Co₂SnO₄ nanostructures and Co₂SnO₄/Graphene nanocomposite compared for the first time. Co₂SnO₄/Graphene nanocomposite show more excellent electrochemical performance than pure Co₂SnO₄ nanoparticles. It was found that the synergistic effect between Co₂SnO₄ nanoparticles and graphene sheets can improve the electrochemical performance of this hybrid composites electrode. After 25 cycles, the discharging capacities of the Co₂SnO₄ nanostructure and Co₂SnO₄/Graphene nanocomposite electrode reach 1190 and 2700 mAh/g, respectively.     

A new sulfur source for the preparation of efficient Cd(1-x)ZnxS photocatalyst for hydrogen evolution reaction

Cd_(1-x)Zn_xS hexagonal crystals were for the first time synthesized via thermal sulfurization of Cd_(1-x)Zn_xO particles by using the elemental sulfur as the sulfur source. A temperature profile in the tube furnace was designed to obtain the proposed particle size, crystal structure, and morphology. Synthesized Cd_(1-x)Zn_xS particles were characterized with scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and diffuse reflectance UV–Vis spectroscopy. It was seen that there was a polynomial relationship between the band gap and Cd: Zn ratio in the Cd_(1-x)Zn_xS. Cd_0.58Zn_0.23S has shapeless particles between 250 and 500 nm particle size. It was observed that particle size decreased as Zn ratio increased in the Cd_(1-x)Zn_xS. Cd_(1-x)Zn_xS hexagonal crystals had nano-step surfaces which were one of the desired factors for achieving high photocatalytic efficiency. Finally, Synthesized Cd_(1-x)Zn_xS particles were used as photocatalysts for the photocatalytic hydrogen evolution reaction (HER). Cd_0.77Zn_0.23S structure behaved the most active one among the different compositions of Cd_(1-x)Zn_xS nanoparticles. Cd_0.77Zn_0.23S showed almost high photocatalytic activity for HER with 1927 μmol g^?1 h^?1 hydrogen evolution rate without using noble co-catalyst such as platinum. This good photocatalytic activity was believed to be due to the nanostep surface structure Cd_0.77Zn_0.23S which led the separation of the reduction and oxidation reaction sites and inhibited the recombination of the generated electrons and holes. Observation of considerably high photocurrent and open circuit potentials and changes in the electrochemical impedance spectroscopy responses supported the photocatalytic activity of the Cd_0.77Zn_0.23S particles.     

Facile microwave-assisted synthesized reduced graphene oxide/tin oxide nanocomposite and using as anode material of microbial fuel cell to improve power generation

A new nanocomposite material was fabricated by a facile and reliable method for microbial fuel cell (MFC) anode. Tin oxide (SnO₂) nanoparticles were anchored on the surface of reduced graphene oxide (RGO/SnO₂) in two steps. The hydrothermal method was used for the modification of GO and then microwave-assisted method was used for coating of SnO₂ on the modified GO. Nanohybrids of RGO/SnO₂ achieved a maximum power density of 1624 mW m⁻², when used as the MFC anode. The obtained power density was 2.8 and 4.8 times larger than that of RGO coated and bare anodes, respectively. The electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The electrochemical characteristics were also studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The high conductivity and large specific surface of the nanocomposite were greatly improved the bacterial biofilm formation and increased the electron transfer. The results demonstrate that the RGO/SnO₂ nanocomposite was advantageous material for the modification of anode and enhanced electricity generation of MFC.     

The studies of performance of the Au electrode modified by Zn as the anode electrocatalyst of direct borohydride fuel cell

The carbon supported Au-base electrocatalysts (Au_(1−x)Zn_x/C, 0 ≤ x < 1) modified by Zn were synthesized by reverse microemulsion method and employed as anode electrocatalysts of direct borohydride fuel cell (DBFC). The physical and electrochemical properties were investigated by energy dispersive X-ray (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), chronopotentiometry and fuel cell test. The results showed that the morphologies of Au_(1−x)Zn_x nanoparticles all were uniformly spherical no matter what Zn content changed, and the average particle size of Au_(1−x)Zn_x bimetallics varied from 3 to 6 nm. The electrochemical measurements revealed that the Au_(1−x)Zn_x/C electrocatalysts showed no activity toward the NaBH₄ hydrolysis reaction and obviously improved the catalytic activity of borohydride oxidation. Compared with Au/C anode electrocatalyst, the stability of DBFC using the Au_0.65Zn_0.35/C as anode electrocatalyst was apparently improved, and the maximum power density of 39.5 mW cm⁻² was obtained at 20 °C.     

Ethanol oxidation on carbon supported (PtSn)alloy/SnO2 and (PtSnPd)alloy/SnO2 catalysts with a fixed Pt/SnO2 atomic ratio: Effect of the alloy phase characteristics

To evaluate the effect of the alloy phase characteristics on the ethanol oxidation activity, carbon supported (PtSnPd)_alloy/SnO₂ catalysts were prepared and their electrocatalytic activity compared with that of carbon supported (PtSn)_alloy/SnO₂. Pt-Sn-Pd/C samples in the atomic ratio (1:1:0.3) and (1:1:1) were characterized by energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD analysis shows the presence of fcc Pt reflexions, shifted to lower angles, and SnO₂ reflexions. By comparison with the XRD patterns of carbon supported Pt-Sn (1:1) and Pt-Pd (3:1) samples, prepared by the same method, the formation of ternary PtSnPd alloys is postulated. The crystallite size of the ternary catalysts is smaller than that of both binary Pt-Sn/C (1:1) and Pt-Pd/C (3:1) catalysts. Chronoamperometry experiments and tests in direct ethanol fuel cells of the as-prepared catalysts shows that the activity for ethanol oxidation of (PtSn)_alloy/SnO₂ is higher than that of (PtSnPd)_alloy/SnO₂. This result, obtained with the same Pt/SnO₂ atomic ratio in all the samples, indicates the critical role of the alloy phase characteristics of these catalysts on their activity for ethanol oxidation.     

In-situ deposition and subsequent growth of Pd on SnO2 as catalysts for formate oxidation with excellent Pd utilization and anti-poisoning performance

To prepare Pd catalysts for formate oxidation with superior anti-poisoning performance and Pd utilization, a facile strategy is employed by combining in-situ deposition and subsequent Pd growth. The high resolution transmission electron microscopy is used to observe the morphologies, confirming the existence of Pd/SnO₂ interfaces and the uniform Pd layer on SnO₂ through in-situ deposition. After subsequent growth, the Pd crystalline structure is better developed and the size of identifiable Pd moieties increased, as evidenced by X-ray diffraction (XRD) patterns and high resolution transmission electron microscopy (HRTEM) images. The electrochemical characterization indicates that Pd/SnO₂ interfaces together with increased size of Pd moieties promotes the Pd anti-poisoning performance. Besides, with subsequent Pd growth, the Pd utilization is also improved, as evidenced by the increase in area of Pd oxide reduction peak. Considering the facile preparation, superior performance and flexibility of combining in-situ Pd deposition and subsequent metals growth, the strategy is believed to be of promising potential for wide range catalysts development and application.     

Synthesis,characterization and investigation of the electrochemical hydrogen storage properties of CuO–CeO2 nanocomposites synthesized by green method

Pure CuO–CeO₂ nanocomposites were synthesized by simple thermal decomposition method in presence of various Cu salts as a copper source and fructose as a green capping agent. In this study, the effect of various parameters such as the type of copper sources, temperature and time of reaction on the morphology and the particles size were studied. The products were characterized via X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), N2 adsorption (BET), vibrating sample magnetometer (VSM), and infrared spectrum (FT-IR). The optical property of the nanocomposite was examined via UV–vis (DRS) spectroscopy and the band gap was calculated to 3 eV. Also, the hydrogen storage capacity of CuO–CeO₂ nanocomposites and CeO₂ nanoparticles were investigated via chronopotentiometry method for the first time. The discharge capacity of CeO₂ nanoparticles and CuO–CeO₂ nanocomposites in 1 mA current and 20 cycles obtained 2150 and 2450 mAh/g, respectively.     

Synthesis and evaluation of ATO as a support for Pt–IrO2 in a unitized regenerative fuel cell

An IrO₂ catalyst was prepared using a colloidal method followed by a thermal treatment. The catalyst was later mixed with Pt-Black and supported on the Sb-doped SnO₂ (ATO), synthesized through the same colloidal method. ATO was investigated as a possible catalyst support in an electrode of a regenerative fuel cell (URFC), where Pt–IrO₂ was used as the catalyst for the oxygen evolution and reduction reactions. The morphology and composition of the ATO support was investigated through transmission electron microscopy, X-ray diffraction (including Rietveld Refinement), BET analysis, and X-ray fluorescence. An ATO support was obtained with a highly homogeneous distribution and crystal sizes, measuring approximately 4–6 nm.     

Synthesis and characterization of hollow metal oxide micro-tubes using a biomaterial template

Various hollow metal oxide micro-tubes (SnO₂, ZrO₂, ZnO, and NiO) were prepared by a simple impregnation method using Ceiba pentandra (L.) Gaertn. (kapok) as a biomaterial template. Calcination heat treatment was successfully used for the removal of the kapok template. Field emission scanning electron microscopy (FE-SEM) was used to study the uniform morphology of the hollow metal oxide micro-tubes, which had an average diameter of 15–20 μm. The hollow metal oxide micro-tubes were further characterized by thermal gravity analysis (TGA), X-ray diffraction (XRD), and X-ray photo-electron spectroscopy (XPS). This synthesis method provides a new facile route for the fabrication of hollow metal oxide micro-tubes.     

Nanosized Zn–Sn metal composite oxide: a new anode material for Li ion battery

Abstract

The morphological evolution of nanosized Zn–Sn composite oxides, synthesised by the decomposition of ZnSn(OH)₆ precursor at temperature ranged from 300 to 800°C was investigated by using XRD and high resolution TEM. The precursor was also studied by thermal analysis. The electrochemical performance of Zn–Sn composite oxides as anode materials for Li ion batteries was measured in the form of Li/Zn–Sn composite oxides cells. The results reveal that the samples calcined at low temperatures (300 and 500°C) were amorphous Zn₂SnO₄ and SnO₂, and the samples calcined at high temperatures (720 and 800°C) were crystal Zn₂SnO₄ and SnO₂. All the samples have a high reversible specific capacity of over 800 mAh g^?1, and the first charge specific capacity is up to 903 mAh g^?1 for the sample calcined at 500°C. The charge capacity and cyclability were sensitive to the structure and composition of the electrode active materials; the samples calcined at phase transition temperature rage exhibited relatively worse electrochemical properties.