SnO2 Nanocrystals Research Articles

Multifunctional Polymer-Regulated SnO2 Nanocrystals Enhance Interface Contact for Efficient and Stable Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) have rapidly developed and achieved power conversion efficiencies of over 20% with diverse technical routes. Particularly, planar-structured PSCs can be fabricated with low-temperature (≤150 °C) solution-based processes, which is energy efficient and compatible with flexible substrates. Here, the efficiency and stability of planar PSCs are enhanced by improving the interface contact between the SnO2 electron-transport layer (ETL) and the perovskite layer. A biological polymer (heparin potassium, HP) is introduced to regulate the arrangement of SnO2 nanocrystals, and induce vertically aligned crystal growth of perovskites on top. Correspondingly, SnO2 -HP-based devices can demonstrate an average efficiency of 23.03% on rigid substrates with enhanced open-circuit voltage (VOC ) of 1.162 V and high reproducibility. Attributed to the strengthened interface binding, the devices obtain high operational stability, retaining 97% of their initial performance (power conversion efficiency, PCE > 22%) after 1000 h operation at their maximum power point under 1 sun illumination. Besides, the HP-modified SnO2 ETL exhibits promising potential for application in flexible and large-area devices.

Effect of the Eu3+-Sn4+ substitution on the structural and optical properties of SnO2:Eu3+

SnO2 nanocrystals with an average partiaxsxddccle size around 50 nm were prepared by using hydrothermal method. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) data show that the doping of Eu3+ with concentrations ranging from 0 to 2 mol% resulted in a slight decrease of size from 50 to 35 nm. The High Resolution Transmittance Electron Microscopy (HRTEM) results of 1 mol% doping sample provide that the crystals size is around 38 nm and the interplanar spacing is 0.34 nm characterized for (110) planes of SnO2. Moreover, the peak shape and relative intensity of Eu3+ emission upon a direct and indirect excitation indicate the presence of two sites around Eu3+ ions, that are in the D2h sites of SnO2 and on the surface of nanocrystals. The Eu3+ ions located in different sites are selectivity excited. An optimizing of synthesis parameters can promote the incorporation of Eu3+ ions in SnO2 crystal lattice. Specially, the doping leads to the growth of crystallites along (101) preferred plane. The competition between red and orange emission as a function of Eu3+ contents was also considered. Under indirect excitation, the asymmetric ratio between 5D0-7F2 and 5D0-7F1 transitions of Eu3+ ions is unaltered at 0.3 in the range of Eu concentrations from 0.5 to 2 mol% achieved for the first time. PL spectra and decay measurements give evidence about the strong energy transfer between SnO2 and Eu3+ ions.

(Invited) Manipulating Carrier Polarization in Semiconductor Nanocrystals

We investigated the role of the synthesis method and post-synthesis processing on the plasmonic properties of antimony-doped SnO2 nanocrystals. The nanocrystal samples having variable doping concentrations were prepared by coprecipitation and solvothermal methods, and subsequently thermally annealed for different durations. We found that solvothermally-synthesized Sb-doped SnO2 nanocrystals exhibit strong localized surface plasmon resonance in the near-infrared region, which is distinctly absent in the nanocrystals synthesized by the coprecipitation method. Upon thermal annealing, the plasmon absorption emerges in the nanocrystals prepared by the coprecipitation method, and increases in intensity in solvothermally-synthesized nanocrystals. Using X-ray photoelectron spectroscopy, we correlated the plasmon intensity to the oxidation of Sb3+ to Sb5+. These results demonstrate that synthesis methodology and post-synthesis treatment can dramatically influence the plasmonic properties of aliovalently-doped semiconductor nanocrystals via dopant oxidation state, and can be effectively used to design semiconductor nanocrystals with targeted plasmonic properties.

Nanostructuring Pt Electrocatalysts Supported on Nanocrystalline SnO2 for Polymer Electrolyte Fuel Cells

For nanostructuring PEFC electrocatalysts using oxides stable under strongly acidic conditions, freeze drying is applied as an effective fabrication procedure for highly dispersing SnO2 nanoparticles of a few nanometers in diameter, on relatively-stable conductive framework in the electrocatalyst layers. Platinum catalysts are deposited on SnO2 nanocrystals on an atomic level by applying a chemical procedure for preparing oxide-core Pt-shell electrocatalysts. Their high-resolution STEM images and preliminary electrochemical results are reported, and remaining issues are discussed.

Electrochemically exfoliated graphene as high-performance catalyst support to promote electrocatalytic oxidation of methanol on Pt catalysts

Electrochemically exfoliated graphene (EEG) is a kind of high-quality graphene with few oxygen-containing functional groups and defects on the surface, and thereby is more suitable as catalyst support than other carbon materials such as extensively used reduced graphene oxide (rGO). However, it is difficult to grow functional materials on EEG due to its inert surface. In this work, ultra-small Pt nanocrystals (∼2.6 nm) are successfully formed on EEG and show better electrocatalytic activity towards methanol oxidation than Pt catalysts on rGO. The outstanding catalytic properties of Pt catalysts on EEG can be attributed to the fast electron transfer through EEG and high quality of Pt catalysts such as small grain size, high dispersibility and low oxidation ratio. In addition, SnO2 nanocrystals are controllably generated around Pt catalysts on EEG to raise the poison tolerance of Pt catalysts through using glycine as a linker. Owing to its outstanding properties such as high electrical conductivity and mechanical strength, EEG is expected to be widely used as a novel support for catalysts.

HClO4-assisted fabrication of SnO2/C60 bilayer electron-transport materials for all air-processed efficient and stable inverted planar perovskite solar cells

In inverted planar perovskite solar cells (PSCs), fullerene (C60) and its derivatives are widely utilized as electron-transport layer (ETL) materials, however, possess some drawbacks such as low electron mobility, interfacial degradation, and relatively inferior stability. In this work, we develop a facile thermal annealing-free hydrothermal route to synthesize high-crystalline SnO2 nanocrystals through controlling the crystallization process with HClO4. An interlayer of SnO2 nanocrystals is inserted between C60 ETL and Ag electrode. The SnO2 interlayer can not only serve as an ETL to help improve electron extraction and transport but also act as a passivation/barrier layer to prevent oxygen and moisture ingress and ion migration. Based on the p-i-n structure of fluorine-doped tin oxide (FTO)/NiOx/MAPbI3/C60/SnO2/Ag, the power conversion efficiency (PCE) of the champion device is up to 16.36% with almost negligible hysteresis. The unencapsulated inverted PSCs retain more than 80% of its initial PCE value after storage in atmosphere for 90 days (>2100 h), and degrade only about 20% its initial efficiency after 41 h under heating at 85 °C. More important, all the preparation processes are performed under ambient conditions. Our work provides a viable strategy for assembling highly efficient and stable inverted PSCs in the air.

Ultrasmall SnO2 nanocrystals with adjustable density embedded in N-doped hollow mesoporous carbon spheres as anode for Li+/Na+ batteries

SnO2 has been widely studied in lithium-ion batteries (LIBs) because of its high theoretical specific capacity and reversible alloying reaction. Herein, we reported a novel strategy of confinement growth to implant nano-sized SnO2 crystals into N-doped hollow mesoporous carbon spheres (NHMCS) to form SnO2@NHMCS composite with unique nanoscale voids. The nanocrystals (~ 5 nm) decrease the required activation energy for redox reactions, and the carbon shell of NHMCS improves the conductivity and structural stability. It is worth noting that this method can effectively control the filling degree of ultrasmall nanocrystals in NHMCS and adjust the nanosize of voids between nanocrystals and NHMCS. When SnO2@NHMCS is evaluated as an anode material for LIBs, it is proved to exhibit high reversible capacity and stable cycling performance, which is attributted to the appropriate content of active components and the ample buffer space for conversion reaction of SnO2 and alloying reaction of Sn. It also shows excellent electrochemical property as anode material for sodium-ion batteries.

Preparation and photoluminescence of high silica glass containing Eu:SnO2 nanocrystals

Transparent nanocrystalline glass with Eu:SnO2 is synthesized successfully by a modified porous glass sintering technology. As confirmed by High-resolution TEM (HRTEM) analyses, Eu ions are completely concentrated in SnO2 crystal particles rather than uniformly distributed in the amorphous matrix. The differences between Eu single-doped, Eu/SnO2 co-doped, and Eu:SnO2 doped glasses in X-ray diffraction (XRD) patterns, transmission spectra, and photoluminescence spectra are discussed in detail. The local environment that Eu3+ is in, as well as the host-to-activator energy transfer mechanism, is analyzed. Furthermore, the role of SnO2 in inhibiting Eu3+ reduction reaction and enhancing luminescence intensity is proved. This study not only demonstrates a simple way to fabricate pure Eu:SnO2-doped nanocrystalline silica glass but also further extends the applications of semiconductor oxide nanocrystals in the field of gain materials.

Thermal Evaporation Syntheis and Luminescence Properties of SnO2 Nanocrystals using Mg as the Reducing Agent

Thermal Evaporation Syntheis and Luminescence Properties of SnO2 Nanocrystals using Mg as the Reducing Agent

Antimony-Doped Tin Oxide Nanocrystals for Enhanced Photothermal Theragnosis Therapy of Cancers.

The doped semiconductor nanocrystal with free holes in valence band exhibits strong near-infrared (NIR) local surface plasmon resonance effects, which is essential for photothermal agents. Herein, the hydrophilic Sb doped SnO2 nanocrystals were successfully prepared by a simple hydrothermal synthesis method. The doping makes the Sb doped SnO2 nanocrystals possessing defect structures. Compared with the un-doped SnO2 nanocrystals, Sb doped SnO2 nanocrystals exhibit stronger absorption in the NIR region from 500 to 1,100 nm and higher photothermal conversion efficiency (up to 73.6%) which makes the synthesized Sb doped SnO2 nanocrystals be used as excellent photothermal agents. Importantly, Sb doped SnO2 nanocrystals can efficiently kill cancer cells both in vitro and in vivo under the irradiation of a 980 nm laser with a power density of 0.6 W cm–2. In addition, Sb doped SnO2 nanocrystals can also be served as efficient CT imaging agents owing to the large X-ray attenuation coefficient of tin.

Instant Postsynthesis Aqueous Dispersion of Sb-Doped SnO2 Nanocrystals: The Synergy between Small-Molecule Amine and Sb Dopant Ratio.

Direct printing of transparent conducting oxide (TCO) nanocrystal dispersions holds great promise in solution-processed optoelectronics due to its advantages of low material waste and direct patterning on substrates. An essential prerequisite for printable TCO colloidal solutions is the effective stabilization of TCO nanocrystals to prevent their strong aggregation. In situ stabilization uses long-chain ligands to provide interparticle steric repulsion between TCO nanocrystals during the growth of TCO nanocrystals. In sharp contrast, the postsynthesis dispersion of TCO nanocrystals is particularly challenging since the agglomeration already occurs, especially for TCO nanocrystals synthesized without protection by any organic species. Herein, we propose an instant postsynthesis strategy for aqueous colloidal dispersions of Sb-doped SnO2 (ATO) nanocrystals using small-molecule amines of propylamine, ethylenediamine, monoethanolamine, and triethylamine. The average size of ATO secondary particles in aqueous dispersions can be instantly reduced from around 400 to about 25 nm using these amines. The increased Sb dopant ratio also plays a synergistic role in the dispersion effect. The small-molecule amines are found to be preferably adsorbed onto the Sb sites exposed on ATO nanocrystal surface. A higher Sb dopant ratio would facilitate the adsorption of more amines and induce stronger surface charge repulsion that benefits the stable dispersion of ATO nanocrystals. TCO films fabricated with the ATO nanocrystal dispersions have a high transparency of 80.6% and low sheet resistance of 492 Ω/sq, showing promising application in electrochromic devices.

Synthesis of crumpled SnO2/rGO nanocomposites with 2D-in-3D structure and high performance

Tin oxide/reduced graphene oxide (SnO2/rGO) composite was extensively used in the area lithium ion batteries, solar cells, sensors and catalysts. High loading of SnO2 was effective for improving the performance, however, which inevitably led to large clusters of SnO2 and the active sites would decrease accordingly. Herein, crumpled SnO2/rGO with concentrated sites was prepared by spray pyrolysis, the density of SnO2 crystals was increased without agglomeration. The ultrafine SnO2 nanocrystals with the size of 3.5 nm interconnected with each other to form an intensive 2D web, which compounded with rGO nanosheets by Sn–O–C covalent bonds, and the SnO2/rGO nanosheets assembled to form a 3D crumpled ball-like structure. The crumpled 2D-in-3D structure and the Sn–O–C bonds endowed the SnO2/rGO with excellent dispersion, good electrical conductivity and structural stability, increased active sites and multilevel mass transfer channels, therefore, SnO2/rGO demonstrated good electrochemical and catalytic performance. The capacity and coulombic efficiency of Sn-1-550 as anode material of lithium battery were 943 mA h g−1 and 94% after 80 cycles, and methyl blue (MB) was catalytic degraded completely by Sn-1-550 in 15 min at room temperature.

Detection of Ppb-level NO2 using mesoporous ZnSe/SnO2 core-shell microspheres based chemical sensors

Detection of ultralow concentrations of the hazardous gases is the major demand and challenge for the development of biosensors. A novel mesoporous ZnSe-core/SnO2-shell microspheres based chemiresistive-type sensor was fabricated for ppb-level NO2 detection, and the theoretical detection limit is calculated to be 0.87 ppb. The as-fabricated sensor presents an excellent performance for low-concentrations of NO2 up to 2.4 ppm and exhibits significantly higher response approximately 6.94 than those of pristine SnO2 (∼2.86) and ZnSe based sensors (almost no response) to 2.4 ppm NO2 at 160 °C. The response and recovery time of the core-shell microspheres based sensor are 64 s and 52 s, respectively, which are substantially improved compared to those of the pristine SnO2 based sensor (∼149 s and ∼133 s). The sensor demonstrates a superior long-term stability with a deviation in the response of the sensor less than 5 % for one month, and a brilliant selectivity to several possible interferents. The significantly improved sensing performance could be attributed to the obtained mesoporous structures and the formed ZnSe/SnO2 hybrid interfaces. It yields more active sites and promotes the electrons transferred between ZnSe and SnO2 nanocrystals. The density functional theory (DFT) calculations are employed to reveal the potential transducing mechanisms.

Enhancing the selectivity of CO formation for electrochemical reduction of CO2 on tin(IV) oxide-based catalysts

In this work, the relationship between crystal size of SnO2 and CO selectivity (the CO/formate ratio) is investigated and a great enhancement in CO selectivity is achieved by reduction in its crystal size. The crystal size of SnO2 is less than 5 nm by the synthesis of a core-shell-like microstructure of SnO2 on the rutile-phase TiO2 particles (denoted as R-TiO2@SnO2). The faradaic efficiency and CO selectivity are promoted to be over 42% and 1.18, which are two folds of that of pure SnO2 nanocrystals. According to the X-ray photoelectron spectroscopic results, SnO is more active for the CO2ER to generate CO than Sn or SnO2 and the corresponding electrochemical reduction pathway of CO2 on SnOx is proposed. The increase in the electron density on the oxygen atom of SnO may increase the possibility of *COOH formation, favoring the formation of CO.

Engineering of the band gap induced by Ce surface enrichment in Ce-doped SnO2 nanocrystals

Surface modification of oxide semiconductors nanocrystals can promote news effects mainly in nanocrystals up to 10 nm in diameter. In these systems, the ratio surface/core is increased, and the quantum effect can not rule out. A form of tuning the crystallite size is by doping process. Our results showed a monotonic nanoparticle size decrease from ~10 to ~3 nm accompanied by the progressive Ce-enriched surface, with the volume of the unit cell increases as the Ce content is increased, evidencing solid-solution formation between the Sn and Ce ions in the rutile-type structure. The Fourier Transform Infrared spectroscopy measurements show a redshift of the Sn-O stretching vibration peak, which is in good agreement with the solid solution of Ce and Sn ions. The dopant enrichment of the nanocrystal surface, as evidenced by Raman spectroscopy is associated with a monotonic decrease of the PL intensity. The latter is induced by a progressive decreasing of the relative dielectric constant between the core and shell regions, which in turn is related to the narrowing of the optical band gap energy with increasing of Ce content. We attribute this effect to the enhancement of the surface polarization contribution that overtakes the confinement effect contribution.

Solution-phase growth of tin oxide (SnO2) nanostructures: Structural, optical and photocatalytic properties

Tin dioxide (SnO2) nanostructures have been synthesized successfully via solution phase growth technique. Effect of reaction temperature, time and surfactant on morphology, size and bandgap has been studied. The rods, flowers, and spheres like morphologies of SnO2 have been observed using Scanning Electron Microscopy (SEM). Structural analysis of synthesized SnO2 has been carried out by X-Ray Diffraction (XRD). XRD peaks revealed the tetragonal structure of SnO2 nanocrystals. The increase in grain size was observed with an increase in reaction time and reaction temperature of the synthesis process. Fourier Transform Infrared Spectroscopy (FTIR) has been employed to study the vibrational modes. Optical properties of the SnO2 nanostructures have also been studied by UV–vis spectroscopy. The energy bandgap of the as-prepared SnO2 nanocrystals were estimated between 3.76 eV and 4.05 eV. Photocatalytic activities of SnO2 nanostructures were studied on Rhodamine B (Rhd B) dye under solar light illumination. Approximately 91% degradation of Rhd B was observed with as-synthesized SnO2 nanostructures.

A Low Temperature NO2 Sensor Based on SnSe2/SnO2 Heterojunction

Introduction Nitrogen dioxide (NO2) is one of the main air pollutants which is harmful to human health. A Higher concentration of NO2 may cause serious damage to respiratory system and even death. Moreover, the concentration of NO2 in the exhaled breath can be regarded as a diagnostic marker of asthma. Therefore, it is necessary to develop a low-energy consumption gas sensor which can sensitive and accurate analysis of NO2 in the atmosphere and exhaled breath.In this aspect, two dimensional (2D) layered nanostructured materials such as metal dichalcogenides (MX2, M=Mo, W, Sn etc..; X=S, Se, Te etc..) have received widespread attentions in NO2 detection due to their high specific surface area and unique electrical properties[1]. For example, SnS2 demonstrated excellent NO2 sensing properties [2]. Moreover, as reported in literature [3], the formation of SnO2/SnS2 heterostructure is beneficial to the further improvement of sensing performance. However, the gas sensing properties of SnSe are rarely reported. Therefore, the gas sensing properties of SnSe2 and SnSe2/SnO2 heterojunctions have investigated in this work. The SnSe2/SnO2 heterojunctions displays much improved sensitivity and superior selectivity toward NO2 at 120 °C. Experiment The SnSe2 powder was purchased from Chengdu Alfa Metal Material Co. Ltd. After grinding for half an hour, the SnSe2 powder was dispersed in an alcohol solution to obtain suspension by ultrasonic treatment. The paste was deposited onto the alumina substrates with Au interdigital electrodes. Then, the sensors were dried at 70 °C for 12 h. The SnSe2/SnO2 heterojunction based sensor was obtained by in-situ oxidation SnSe2 at 500 °C for 1 h in simulation air which is composed of 84.8 % dry nitrogen and 15.2 % dry oxygen. For comparison, the SnO2 sensor was also prepared by in-situ oxidation SnSe2 at 750 °C. Results and conclusions 1. Structure and MorphologyFig.1a shows the XRD patterns of SnSe2, SnO2 and SnSe2/SnO2, respectively. For the SnSe2/SnO2 sample, the diffraction peaks located at (001), (002), (003), (004), (005) lattice planes are assigned to the hexagonal SnSe2 (JCPDS Card No. 89-2939) [4], and the other diffraction peaks are consistent with tetragonal SnO2 (JCPDS No. 41-1445). No third phase was observed in the SnSe2/SnO2 sample indicating the product with high purity. This is consistent with the HRTEM analysis. As shown in Fig. 1(b), the fringe spacing of 0.296 nm and 0.192 nm are corresponded to the d-spacing of (002) and (003) crystal planes of SnSe2, whereas the fringe spacing of 0.340 nm and 0.265 nm are assigned to the d-spacing of (110) and (101) crystal planes of SnO2. Additionally, the EDX mapping images and EDX spectrum of SnSe2/SnO2 sample are shown in Fig.1c-d. It can be noticed that there only exist Sn, Se, and O elements in the composites material, and Sn (yellow), Se(red), and O (green) elements are uniformly distributed in the material, which confirming that the formation of SnO2 nanocrystals on the surface of SnSe2 and the oxidation of SnSe2 to SnSe2/SnO2 is partial.2. Gas-Sensing PropertiesFig. 2a shows the dynamic response and recovery curve of sensors to 8 ppm NO2 at 120 °C. Compared to pristine SnSe2 and SnO2 based sensor, the SnSe2/SnO2 based sensor exhibits the highest response value (5.6), which is approximately 10 times higher than that of SnSe2 based sensor (0.54). In contrast, since SnO2 didn’t work at the optimum temperature (usually at 200-400 °C), the redox reactions to induce a sensor response were almost inertia at 120 °C. The selectivity of the SnSe2/SnO2 based sensor to several VOCs, including ethanol, ammonia, formaldehyde, acetone and methanol at 8 ppm in Fig. 2b. The response towards 8 ppm NO2 is much higher compared to the other tested gases indicating a possible excellent selectivity towards NO2. The above results fully prove that the formation of SnSe2/SnO2 heterojunctions can enhance the sensing performance of materials.

Two Dimensional Mxene (Ti3C2) Decorated By SnO2 Nanocrystals for Enhanced Chemical Gas Sensors at Room Temperature

Introduction A low-cost chemical sensor for ammonia (NH3) detection is highly demanded nowadays for several important applications. Two-dimensional (2D) nanomaterials such as graphene/reduced graphene oxide (rGO), transitional metal dicharcogenides, black phosphor and transition metal carbonitride (MXene) have found a promising application in the fields of gas sensing electronics at room temperature due to their unique microstructure, electrical properties and excellent gas adsorptions ability. Decoration of the secondary phase such as noble metals and metal oxide nanocrystals to form heterojunctions with two-dimensional materials can effectively improve the inadequacy of two-dimensional materials based gas sensors. It takes advantages of the difference in the Fermi level of each phase to make the electrons transfer from one material to the other and thus enriching the electron concentration on the surface of one material that is dominant in the electrical transport. In this way, more ionized oxygen is chemisorbed, leading to the improvement of the gas sensing properties [1].In this work, 2D MXene heterojunctions incorporated with SnO2 nanoparticles have been synthesized by using hydrothermal method. The as-fabricated MXene/SnO2 heterojunction based chemiresistive-type sensor showed excellent sensitivity to different concentrations of ammonia from 0.5-100 ppm at room temperature. The response has about 20 times higher than those reported in literature to 100 ppm NH3 and an excellent selectivity. Preparation and characterizations The Ti3AlC2 was purchased directly from Beijing Forsman Corp. The concentrated hydrochloric acid (HCl) was diluted to 9M. 2g of lithium fluoride (LiF) was added into 20ml diluted hydrochloric acid and stirred with magnetic mixer. 2g Ti3AlC2 was slowly and evenly dispersed in the solution over a period of several minutes and subsequently stirred at 35℃ for 48h to obtain the MXene. 70 mg of MXene powder was dispersed in 30ml of deionized water after grinding and sonicated for 30min. 73.5mg of stannic chloride pentahydrate (SnCl4·5H2O) was added into the suspension and stirred with magnetic stirrer at room temperature. The suspension was then loaded in a 50ml Teflon-lined autoclave. The autoclave was sealed and heated in an KSL-1200X hydrothermal system at 180℃ for 12h to obtain the MXene-SnO2 hybirds. The samples were then characterized by XRD, SEM, XPS, Raman and TEM-ED. The MXene/SnO2 based chemirestive-type sensor was measured by a static volumetric method. The resistance of the sensor is directly measured by a digital multimeter (Agilent 34410A). The responses of the sensors were defined as the relative change in the resistances of the sensors in the air and those in the tested gas. Results and Conclusions Fig.1a shows the XRD of the prepared samples. Appearance and down-shift of the peak at ~10 oC indicates the successful achievements of MXene and thus the MXene-SnO2 composite heterojunctions [2-3].Fig.1 (b-c) show the micrographs of the surface morphology of the MXene and heterojunctions. The etched MXene material has obvious layered structure with sizes ranging from 2 μm to 4 μm. The thickness of MXene is about 75 nm indicating the sample contains about 100 single layers of MXene. The granular SnO2 nanoparticles are intimately attached to the surface of MXene. Fig.2 (b) shows the Raman spectra of MXene and Mxene/SnO2 heterojunction. The appearance of both D-band and G-band in the MXene/SnO2 heterojunction sample indicated that MXene remained well during the hydrothermal reaction. Fig.2(c) shows the Ti core level (2p) spectra of the MXene and MXene/SnO2. Ti - X corresponds to titanium carbide or titanium oxynitride. Fig.2d indicates that the peaks at 530.1 and 532 eV correspond to oxygen vacancies and O=C-OH, respectively, suggesting that these and surface-adsorbed oxygen tend to form more active sites, thereby enhancing sensing capability.The sensors using MXene/SnO2 heterojuction shows excellent response and selectivity to low-level NH3 from 0.5-9 ppm at RT (Fig.3). Since the work function of MXene (4.465 eV) was slightly lower than that of SnO2 (4.7 eV), Schottky-type junctions were formed across MXene/SnO2 interfaces (Fig.4). Electrons would transfer from SnO2 to MXene, and the depletion layer was deepened on the surface of MXene. MXene could then chemically adsorb more oxygen, and the response of the MXene/SnO2 heterojunction was thus significantly enhanced.

In-situ preparation of LixSn-Li2O–LiF/reduced graphene oxide composite anode material with large capacity and high initial Coulombic efficiency

Anode materials with large capacity have a growing application due to the booming electric vehicle and energy storage market. However, the low initial Coulombic efficiency (ICE) and poor cycle stability hinder their commercial development. Herein, we investigate the effective and convenient method of preparing LixSn-Li2O–LiF/reduced graphene oxide (LixSn-Li2O–LiF/RGO, Li-GFTO) composite anode material with large capacity and high ICE. Firstly, the highly-dispersed fluorine-doped tin oxide and reduced graphene oxide (F–SnO2/RGO, GFTO) composite is in-situ synthesized by one-pot reflux method. The fluorine-doped SnO2 nanocrystals are uniformly anchored on graphene sheets. Secondly, the F–SnO2/RGO was lithiated by reacting with the lithium dissolved in the solution of biphenyl and 1,2-dimethoxyethane to get LixSn-Li2O–LiF/RGO composite. The Li2O and LiF will be formed and prevent the diffusion and coarsening of Sn and LixSn during cycling. Used as the anode material, the ICE of the LixSn-Li2O–LiF/RGO composite is as high as 97%. The composite anode material also shows high cycling stability. The residual capacity is as high as 992 mAhg−1 at 0.1 Ag-1 after 100 cycles, and the charge capacity retention is 99%. Most of all, the mild preparation condition promotes the mass production and practical application of tin-lithium alloy based composite anode materials.

Morphosynthesis of SnO2 nanocrystal networks as high-capacity anodes for lithium ion batteries

Tin dioxide (SnO2) is of interest as an alternative anode material for lithium ion batteries. However, the major concern is the significant volume expansion during lithiation process, resulting in poor capacity retention and rate capability. Here, a facile morphosynthesis route is adapted for the fabrication of hierarchical SnO2 nanocrystal networks with interwoven fibers, by immersing sacrificial eggshell membrane in a Sn-based sol followed by a calcination process in air. With both structural and compositional advantages, the synthesized SnO2 networks electrode manifests superior reversible capacities of 938, 802, 736, 636, and 506 mAh g−1 even at high current densities of 0.2, 0.5, 1, 2, and 5 A g−1, respectively. Besides, its initial Coulombic efficiency (72.6%) is also much enhanced compared with that of bare SnO2 nanoparticles (59.6%) and commercial SnO2 nanopowders (46.8%). The finding highlights the probable potential application of the SnO2 networks for next-generation lithium ion batteries.