SnO2 Surface Research Articles

First-Principles Study of Epoxy Resin Adhesion to Tin Oxide Surface

A density functional theory (DFT) is used to investigate the energetics of an epoxy resin adhere on a tin oxide and a hydroxylated-alumina surface within a supercell approach. Self—consistent geometry optimization is performed for models of adhesion interface, which is comprised of a fragment of epoxy resin and hydroxylated-Al2O3 (001), and SnO2(001) and (110) surface. The epoxy resin studied was simplified fragment based on diglycidyl ether of bisphenol A (DGEBA). It is found that the distance between the resin and the surface where the adhesion force is maximized is substantially the same for all models. Analysis of the energy-distance plot reveals that the fragment of DGEBA molecule adhere most strongly to the SnO2(001) surface, suggesting that the adhesion force is induced by van der Waals (vdW) interaction.

CO2 reduction on metal-doped SnO2(110) surface catalysts: Manipulating the product by changing the ratio of Sn:O

The electrocatalytic carbon dioxide reduction reaction (CO2RR) producing HCOOH and CO is one of the most promising approaches for storing renewable electricity as chemical energy in fuels. SnO2 is a good catalyst for CO2-to-HCOOH or CO2-to-CO conversion, with different crystal planes participating the catalytic process. Among them, (110) surface SnO2 is very stable and easy to synthesisze. By changing the ratio of Sn:O for SnO2(110), we have two typical SnO2 thin films: fully oxidized (stoichiometric) and partially reduced. In this work, we are concerned with different metals (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au)-doped SnO2(110) with different activity and selectivity for CO2RR. All these changes are manipulated by adjusting the ratio of Sn:O in (110) surface. The results show that stochiometric and reduced Cu/Ag doped SnO2(110) have different selectivity for CO2RR. More specifically, stochiometric Cu/Ag-doped SnO2(110) tends to generate CO(g). Meanwhile, the reduced surface tends to generate HCOOH(g). Moreover, we also considered the competitive hydrogen evolution reaction (HER). The catalysts SnO2(110) doped by Ru, Rh, Pd, Os, Ir, and Pt have high activity for HER, and others are good catalysts for CO2RR.

Bi-Directional functionalization of urea-complexed SnO2 for efficient planar perovskite solar cells

SnO2 is regarded as the most promising electron transporting layer (ETL) material for perovskite solar cells (PSCs). Various functional groups are introduced onto the SnO2 surface by interface modification with the purpose of improving the performance of the PSCs. However, most of the modifications are achieved in two-step approach, which are complicated and not easily realized. Here, we employ a facile one-step, low-temperature, and effective method to synthesis urea-complexed SnO2 ETL (referred as Urea-SnO2). The –NH2 groups on Urea-SnO2 attributes to facilitate the charge transfer within the SnO2 ETL and reduce trap state density in the perovskite film through the chemical interactions. Therefore, The PSCs based on the Urea-SnO2 ETL exhibit a champion power conversion efficiency (PCE) of 20.25%, which is more excellent than the devices based on the pristine SnO2 ETL (17.60%). Functionalization of SnO2 in situ by the precursor solution method offers an efficient method for high performance planar PSCs.

In Ukrainian

The prevalence of tin compounds, economic affordability and non-toxicity determine its wide range of applications. Modern scientific literature on the properties, methods of preparation and application of tin nanooxide is analyzes in review. Its main characteristics and structural features are described. The ability of tin cations to be in two oxidation states, the ease of reduction of Sn+4 to Sn+2 and reverse oxidation, determines the redox properties of the SnO2 surface. In addition to stable oxides Sn4+ and Sn2,+ the existence of a homologous series of Snn+1O2n metastable compounds is assumed. It is proved that four-coordinated Sn+2 cations on the SnO2 surface can coexist only with oxygen vacancies in the immediate environment. Such cationic sites have the properties of strong Lewis acids and are highly reactive. Computer simulation of the SnO2 crystal surface allows us to propose a number of catalytic activity of SnO2 surfaces: (110) < (001) < (100) < (101). Preparation methods and synthesis parameters (nature and type of precursor, stabilizing agent and solvent, duration and temperature of the reaction, pH of the reaction mixture, etc.) determine the physicochemical properties of nanoparticles (shape, size, morphology and degree of crystallinity). The main (sol-gel, precipitation and coprecipitation, CVD, spray pyrolysis, hydrothermal, “green”) and less common (detonation, electric discharge) methods of nano-SnO2 obtaining are analyzed in the work. A variety of methods of synthesis and conditions makes it possible to obtain SnO2 nanoparticles with desired properties, which determine the activity of tin oxide in redox reactions, namely: nanosize and morphology of particles with prevalence of the most reactive faces - (100) і (101). Among the methods that do not require complex hardware design, one can dwell on the methods of sol-gel, "green" and coprecipitation. Tin oxide is traditionally used as an abrasive for polishing metal, glass and ceramic products. The transition to nanosized particles allows this material to reversibly absorb and release oxygen, which has determined its use in the design of gas-sensitive and biosensors, the creation of solar cells, fuel cells, lithium-ion batteries, oxidation catalysts, transparent and photoconductors. The multivalence and the presence of oxygen vacancies on the surface of tin oxide nanoparticles, the ease and speed of penetration into the cell membrane give nano-SnO2 properties of medicinal preparations, which makes it possible to use it in biomedical technologies for the treatment of diseases associated with oxidative stress lesions. The size, concentration of nanoparticles and modification of their surface are the key factors of influence, which usually intensify the antimicrobial, antibacterial, antitumor and antioxidant activity of the material.

Improving Lithium-Ion Half-/Full-Cell Performance of WO3 -Protected SnO2 Core-Shell Nanoarchitectures.

Anodes derived from SnO2 offer a greater specific capacity comparative to graphitic carbon in lithium-ion batteries (LIBs); hence, it is imperative to find a simple but effective approach for the fabrication of SnO2 . The intelligent surfacing of transition metal oxides is one of the favorite strategies to dramatically boost cycling efficiency, and currently most work is primarily aimed at coating and/or compositing with carbon-based materials. Such coating materials, however, face major challenges, including tedious processing and low capacity. This study successfully reports a new and simple WO3 coating to produce a core-shell structure on the surface of SnO2 . The empty space permitted natural expansion for the SnO2 nanostructures, retaining a higher specific capacity for over 100 cycles that did not appear in the pristine SnO2 without WO3 shell. Using WO3 -protected SnO2 nanoparticles as anode, a coin half-cell battery was designed with Li-foil as counter-electrode. Furthermore, the anode was paired with commercial LiFePO4 as cathode for a coin-type full cell and tested for lithium storage performance. The WO3 shell proved to be an effective and strong enhancer for both current rate and specific capacity of SnO2 nanoarchitectures; additionally, an enhancement of cyclic stability was achieved. The findings demonstrate that the WO3 can be used for the improvement of cyclic characteristics of other metal oxide materials as a new coating material.

Enhanced efficiency and stability of planar perovskite solar cells using SnO2:InCl3 electron transport layer through synergetic doping and passivation approaches

There are many defect states at the interface between SnO2 and perovskite due to the preparation process and the lattice mismatch. These defects will trap photo-generated carriers, resulting in low carrier extraction efficiency and loss of device stability. Many researches are underway to further improve the performance of perovskite solar cells (PSCs) based on SnO2 electron transport layer (ETL), including doping of ETL and effective passivation of interface defects. Here, the SnO2:InCl3 ETL is used in planar perovskite solar cells to simultaneously dope ETL and passivate the defects at the ETL/perovskite interface. First, Cl ions can passivate the defects on the SnO2 surface, and part of the chloride ions can also diffuse into the perovskite to passivate the grain boundaries. Additionally, In ions themselves are suitable dopants and can provide better doping performance for SnO2. The result shows that the simultaneous ETL doping and interface passivation result in a significant increase of PCE from 19.1% to 20.8% due to the enhancement of short-circuit current density. This method expands the ETL/perovskite interface optimization work by using anions and cations for passivation and doping, respectively, and has some inspiration for the delivery of high efficiency and stable planar structure PSCs based on SnO2 ETL.

Atomic Structure and Properties of SnO2 (100) and (101) Surfaces and (301) Steps in the (100) Surface

The atomic and electronic structures of SnO2 surfaces are closely related to their catalysis and gas detection properties. In this study, the atomic structure of SnO2 (100) and (101) surfaces has b...

Effects of Hexamethyldisilazane Modification on Gas-Sensing Properties of Semiconductor Gas Sensors

Introduction Metal-oxide based semiconductor-type gas sensors have been used as gas leak detectors, but their sensing performances are easily influenced by the adsorption of organosilicon compounds containing in spray cans and air refreshers. In this study, the surface of SnO2-based gas sensors was thermally modified by hexamethyldisilazane (HMDS, ((CH3)3Si)2NH)), one of representative organosilicon compounds, and their sensing properties to CH4 and H2 were examined. Based on the obtained results, effects of the adsorption of HMDS on the gas sensing properties were discussed. Experimental A SnO2 powder was prepared according to the following procedure. An appropriate amount of NH4HCO3 aqueous solution was added into SnCl4 aqueous solution. The obtained white precipitate was repeatedly centrifuged and washed with pure water, and then dried at 100°C for overnight. The resultant powder was calcined at 600°C for 3 h in air. In some cases, Pd or Pt nanoparticles were loaded onto the surface of SnO2 powders by using a conventional impregnation method. The resultant solids were heat-treated at 200°C for 2 h in H2, to obtain metallic nanoparticles on the oxide surface. The prepared SnO2-based powders were mixed with α-terpineol, and the obtained paste was screen-printed onto an alumina substrate equipped with a pair of interdigitated Pt electrodes (gap size: ca. 200 μm), followed by drying at 100°C. Then, they were calcined at 500°C for 3 h in air.The obtained gas sensors were mounted in the tubular furnace, and the surface of some sensors was modified with HMDS at 400°C, in dry air saturated with HMDS at 80°C. The obtained SnO2 sensors loaded with and without noble metal (N: Pd or Pt) were denoted as nN/SnO2(t) and SnO2(t) [n: amount of noble metal, 0.5, 1.0 (wt%); t: exposure time to HMDS-saturated air, 0, 15 or 30 (min)], respectively. Gas responses of the obtained sensors to CH4 and H2 (2000 ppm) diluted with dry air were measured at a flow rate of 100 cm3 min−1 at 300–400°C. The magnitude of response was defined as the ratio (R a/R g) of resistance in air (R a) to that in CH4 and H2 balanced with air (R g). Results and Discussion The resistance of the SnO2(0) sensor in air decreased with an increase in the operating temperature, and the thermally HMDS-modified SnO2(t) sensors (t: 15, 30) showed smaller resistance in air than the SnO2(0) sensor over all the temperature range studied. The resistance of the SnO2(t) sensors decreased upon exposure to CH4, and the magnitude of response to CH4 increased with an increase in the operating temperature.Figure 1 shows the variations in response of the SnO2(t) and nN/SnO2(t) sensors to CH4 and H2 at 400°C. The CH4 and H2 responses of the SnO2(0) sensor were increased by the loading of Pt and Pd, except for those of the 1.0Pd/SnO2(0) sensor, and the 1.0Pt/SnO2(0) sensor showed the largest responses to CH4 and H2 among the examined sensors. In addition, the CH4 response of all the sensors decreased with an increase in the HMDS exposure time, while their H2 response increased with an increase in the HMDS exposure time. The response time of the 1.0Pt/SnO2(t) sensor to CH4 increased with an increase in the amount of HMDS exposure time, although its response time to H2 was almost independent of the exposure time.These results can be explained by a decrease in the amount of negatively charged oxygen adsorbates on the SnO2 surface and a restriction of the gas diffusion to the SnO2 surface (especially CH4 and O2, due to their larger molecular size than that of H2), and they were caused by the adsorption of Si-based compounds on the SnO2 surface by the thermal decomposition of the HMDS. The details will be discussed in the presentation. Figure 1

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

Introduction Conventional Pt/C electrocatalysts for PEFCs have a difficulty in durability against start-stop potential cycling, mainly due to degradation of carbon black through electrochemical oxidation especially on the cathode side. SnO2 is known to be stable at a high potential under the PEFC cathode conditions, so that SnO2 is considered as an alternative support material for PEFC cathodes [1-4]. In particular, we have prepared the oxide-core Pt-shell electrocatalyst that can reduce materials cost of PEFCs while developing electrocatalysts with both higher durability and ORR mass activity [3]. In our previous study [5], freeze drying has been successfully applied as an effective procedure for highly dispersing SnO2 nanoparticles on relatively-stable conductive framework, for nanostructuring PEFC electrocatalysts as shown in Fig. 1. Here, the objective of this study is to directly deposit Pt on SnO2 on an atomic level by applying a chemical procedure towards the oxide-core Pt-shell electrocatalyst preparation. Experimental Graphitized carbon black (GCB200, Cabot) was used as the conductive filler of the electrocatalysts acting as the conductive framework. SnO2 was prepared on the conductive filler via the microwave homogeneous precipitation. In order to deposit Pt on the surface of the SnO2, Pt(acac)2 and acetone were added to the Sn-containing solution. Pt/SnO2/GCB was prepared via the freeze drying, and heat treatment was performed to obtain a Pt-based catalyst powder. Nanostructure of the electrocatalysts obtained was observed by FE-SEM and STEM. ICP analysis was also made to quantify Pt loading. Electrochemical characterization of these electrocatalysts was carried out by half-cell measurements. Electrochemical surface area (ESCA) was measured by cyclic voltammetry (CV). Oxygen reduction reaction (ORR) activity was derived from kinetically controlled current density (ik) after the rotating disk electrode (RDE) measurement. Results and discussion We have succeeded to prepare SnO2 nanoparticles with a diameter of about 3 nm on the conductive filler in higher dispersion by applying the microwave homogeneous precipitation and the freeze drying. In addition, it was revealed that Pt nanoparticles were selectively deposited on nanocrystalline SnO2. Furthermore, high-resolution STEM observation revealed that a part of Pt was deposited near an atomic level on the SnO2 surface which could be a Pt-shell of the electrocatalysts, as shown in Fig. 2. Especially in Fig. 2(b), Pt atoms could be distinguished on the nanocrystalline SnO2 particles acting as a core of the electrocatalyst, with a minimized electron-conductive pathway between the Pt catalyst and the GCB conductive framework. Electrochemical properties of such nanostructured electrocatalysts will be reported and discussed. References Y. Nakazato, D. Kawachino, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi and K. Sasaki, J. Electrochem. Soc., 165 (14), F1154 (2018).S. Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 165 (14). F1165 (2018).M. Nagamine, Z. Noda, H. Manabe, J. Matsuda, A. Hayashi, and K. Sasaki, ECS Trans., 86 (13), 531 (2018).K. Kakinuma, R. Kobayashi, A. Iiyama, M. Uchida, J. Electrochem. Soc., 165 (15), J3083 (2018).T. Yoshizumi, M. Nagamine, Z. Noda, J. Matsuda, A. Hayashi, and K. Sasaki, ECS Trans., 92 (8), 479 (2019). Figure 1

Influence of the Quality of SnO2 Electron Transport Layer on the Stability of FA1-XCsxpb(I1-yBry)3 perovskite Layer

Organic-inorganic lead halide perovskites have attracted great attention as light absorbers of hybrid perovskite solar cells (PSCs). Among the organic-inorganic hybrid perovskites (OIHP), CH3NH3PbI3 (MAPbI3) and CH(NH2)2PbI3 (FAPbI3) have been extensively studied as light absorbers of PSCs. PSCs are expected to be next-generation solar cells due to their high conversion efficiency and low fabrication cost. However, power conversion efficiency of PSCs declines shortly after being fabricated, because of degradation of hybrid perovskite layers. OIHP such as FAPbI3 decomposes easily into PbI2 and transforms to d-phase from a-phase, which is suitable for the application to the solar cells, under ambient condition [1]. It was reported that partial substitution of inorganic monovalent ions such as Cs and Rb ions at FA site is effective to improve the phase stability of a-phase [2]. This can be easily explained by the Goldschmidt tolerance factor [3], which is an indicator for the stability of perovskite structure. Ionic radius of FA is too large, but the partial substitution of Cs or Rb can make the average ionic radius smaller than that of FA, which stabilizes the a-phase. For example, d-phase is the stable phase in FAPbI3 at ambient condition, which transforms to a-phase above 165 ℃ [4]. However, the partially substituted FAxCsyPbI3 is stable even at room temperature. The perovskite layers are grown on electron transport layers (ETL) such as TiO2, SnO2, and ZnO by spin-coating method. Although TiO2 has been widely used for ETL of PSCs, SnO2 has been also applied to ETL because of its excellent band energy level alignment with that of the perovskite layers and its higher electron mobility [5]. In addition, devices using SnO2 as ETL decrease their photoconversion efficiency more slowly than using TiO2 under ambient condition, which suggests that decomposition processes of the perovskites on TiO2 and SnO2 is different [6]. In the fabrication process of ETL, SnO2 is annealed after spin-coating. If the annealing temperature is high above 450 degrees Celsius, rutile structured crystalline SnO2 thin film grows, while only amorphous structured SnO2 thin film appear by the low temperature annealing, such as between 150 and 200 degrees Celsius. Some studies have shown that amorphous SnO2 fabricated by low temperature process increases performances of devices compared with crystalline SnO2 [7, 8].In this study, FA1-xCsxPb(I1-yBry)3 was synthesized by spin-coating method on the SnO2 layers and annealed at various temperature to evaluate the dependence of SnO2 substrate structure on the stability of perovskite layers. Stability of all the samples here synthesized were monitored with the X-ray diffraction technique at 0, 1, 2, 3, 4, 24, 96 and 168 hours kept in air after fabrications. Fig.1 shows the intensity of diffraction peaks of d-FAPbI3 (100) as a function of time. Although the intensity of d-FAPbI3 peaks increased in FA0.85Cs0.15PbI3 and FA0.85Cs0.15Pb(I0.85Br0.15)3 formed on SnO2 annealed at 450 ℃ , it unchanged in FA0.85Cs0.15PbI3 and FA0.85Cs0.15Pb(I0.85Br0.15)3 on SnO2 annealed at 180 degree Celsius. These results sugessts that the stability of a-FAPbI3 grown on SnO2 annealed at 180 degree Celsius is better than that annealed at 450 degree Celsius. The crystal structures of SnO2 annealed at 200, 300 and 400 degree Celsius were characterized with the Glazing Incident X-ray diffraction technique. The surface morphology of SnO2 were obsereved with the scannning electron microscope, which suggest SnO2 surface became rougher as annealing temperature increased. The chemical composition of the surface of SnO2 layers were investigated by Auger electron spectroscopy, from which Cl peaks were obsererved in SnO2 annealed at 200 ℃ and 300 ℃, while Cl were not detected in SnO2 annealed at 400 degree Celsius.[1] T. Leijtens et al., J. Mater. Chem. A.5, 11483-11500 (2017)[2] M. Saliba et al., Science 354, 206-209 (2016)[3] C. C. Stoumpos et al., Acc. Chem. Res. 48, 2791-2802 (2015)[4] Z. Li et al., Chem. Mater. 28, 284-292 (2016)[5] L. B. Xiong et al., J. Mater. Chem. A.4, 8374-8383 (2016)[6] Q. Dong et al., Nano Energy 40, 336-344 (2017)[7] W. J. Ke et al., J. Mater. Chem. A.3, 24163-24168 (2015)[8] K.-H Jung et al., J. Mater. Chem. A.5, 24790-24803 (2017) Figure 1

Scalable Fabrication of Scratch-Proof Transparent Al/F-SnO2 Hybrid Electrodes with Unusual Thermal and Environmental Stability.

Fabrication protocols of transparent conducting electrodes (TCEs), including those which produce TCEs of high values of figure of merit, often fail to address issues of scalability, stability, and cost. When it comes to working with high-temperature stable electrodes, one is left with only one and that too, an expensive choice, namely, fluorine-doped SnO2 (FTO). It is rather difficult to replace FTO with a low-cost TCE due to stability issues. In the present work, we have shown that an Al nanomesh fabricated employing the crack template method exhibits extreme thermal stability in air even at 500 °C, compared with that of FTO. In order to fill in the non-conducting island regions present in between the mesh wires, a moderately conducting material SnO2 layer was found adequate. The innovative step employed in the present work relates to the SnO2 deposition without damaging the underneath Al, which is a challenge in itself, as the commonly used precursor, SnCl2 solution, is quite corrosive toward Al. Optimization of spray coating of the precursor while the Al mesh on a glass substrate held at an appropriate temperature was the key to form a stable hybrid electrode. The resulting Al/SnO2 electrode exhibited an excellent transparency of ∼83% at 550 nm and a low sheet resistance of 5.5 Ω/□. SnO2 coating additionally made the TCE scratch-proof and mechanically stable, as the adhesion tape test showed only 8% change in sheet resistance after 1000 cycles. Further, to give FTO-like surface finish, the SnO2 surface was fluorinated by treating with a Selectfluor solution. As a result, the Al/F-SnO2 hybrid film exhibited one order higher surface conductivity with negligible sensitivity toward humidity and volatile organics, while becoming robust toward neutral electrochemical environments. Finally, a custom-designed projection lithography technique was used to pixelate the Al/SnO2 hybrid film for optoelectronic device applications.

Experimental Evidence of CO2 Photoreduction Activity of SnO2 Nanoparticles.

Tin dioxide (SnO2 ) has intrinsic characteristics that do not favor its photocatalytic activity. However, we evidenced that surface modification can positively influence its performance for CO2 photoreduction in the gas phase. The hydroxylation of the SnO2 surface played a role in the CO2 affinity decreasing its reduction potential. The results showed that a certain selectivity for methane (CH4 ), carbon monoxide (CO), and ethylene (C2 H4 ) is related to different SnO2 hydrothermal annealing. The best performance was seen for SnO2 annealed at 150 °C, with a production of 20.4 μmol g-1 for CH4 and 16.45 μmol g-1 for CO, while for SnO2 at 200 °C the system produced more C2 H4 , probably due to a decrease of surface -OH groups.

SnO-SnO2 modified two-dimensional MXene Ti3C2Tx for acetone gas sensor working at room temperature

Acetone, as widely used reagents in industry and laboratories, are extremely harmful to the human. So the detection of acetone gas concentrations and leaks in special environments at room temperature is essential. Herein, the nanocomposite combining SnO-SnO2 (p-n junction) and Ti3C2Tx MXene was successfully synthesized by a one-step hydrothermal method. Because of the existence of a small amount of oxygen during the hydrothermal conditions, part of the p-type SnO was oxidized to n-type SnO2, forming in-situ p-n junctions on the surface of SnO. The hamburger-like SnO-SnO2/Ti3C2Tx sensor exhibited improved acetone gas sensing response of 12.1 (Rg/Ra) at room temperature, which were nearly 11 and 4 times higher than those of pristine Ti3C2Tx and pristine SnO-SnO2, respectively. Moreover, it expressed a short recovery time (9 s) and outstanding reproducibility. Because of the different work functions, the Schottky barrier was formed between the SnO and the Ti3C2Tx nanosheets, acting as a hole accumulation layer (HALs) between Ti3C2Tx and tin oxides. Herein, the sensing mechanism based on the formation of hetero-junctions and high conductivity of the metallic phase of Ti3C2Tx MXene in SnO-SnO2/Ti3C2Tx sensors was discussed in detail.

Double-Step Modulation of the Pulse-Driven Mode for a High-Performance SnO2 Micro Gas Sensor: Designing the Particle Surface via a Rapid Preheating Process.

To improve the sensing properties toward volatile organic compound gases, a preheating process was introduced in a miniature pulse-driven semiconductor gas sensor, using SnO2 nanoparticles. The miniature sensor went through a short preheating span at a high temperature before being cooled and then experienced a measurement span under heating; this is the double-pulse-driven mode. This operating profile resulted in the modification of the surface conditions of naked SnO2 nanoparticles to facilitate the adsorption of O2- and ethanol-based adsorbates. Temperature-programmed reaction measurement results show that ethanol gas was adsorbed onto the SnO2 surface at 30 °C, and the adsorption amount of ethanol and its byproducts was increased after ethanol exposure at high temperatures followed by cooling. The electrical resistance of the sensor in synthetic air increased as the preheating temperature increased. The sensor responses, Si and Se, to 1 ppm ethanol at 250 °C were enhanced by introducing the preheating process; Si values at 250 °C with and without preheating at 300 °C are 40 and 15, respectively. The obtained improvements were attributed to an increase in O2- adsorption onto the SnO2 surface during the preheating phase. During the cooling phases, the adsorption of ethanol-based molecules onto the SnO2 surface and their condensation in the sensing layer contributed to the enhanced performance. In addition, the double-pulse-driven mode improves the recovery speed in the electrical resistance after gas detection. These improvements made in the sensing properties of the double-pulse-driven semiconductor gas sensors provide desirable advantages for healthcare and medical devices.

Investigations on the Temperature-Dependent Interaction of Water Vapor with Tin Dioxide and Its Implications on Gas Sensing.

This work presents an operando infrared spectroscopic study of the temperature-dependent water adsorption on pristine SnO2 surfaces and discusses the possible implications on the oxygen ionosorption and gas-sensing mechanism. The impact of water on the sensor resistance, CO-sensing performance, and CO conversion was studied, and the obtained phenomenological results provide the basis for discussing the operando spectroscopic investigation findings. The provided information allows identification of three different water adsorption regimes ranging from physisorption and dominant associative adsorption to mainly dissociative water adsorption. In these regions, water has different impacts on the surface composition, sensor resistance, and gas-sensing performance.

Effects of Hexamethyldisilazane Modification on Gas-Sensing Properties of Semiconductor Gas Sensors

SnO2-based sensors were modified with hexamethyldisilazane (HMDS), and their sensing properties to CH4 and H2 were examined. The HMDS modification decreased the CH4 response and increased the H2 response of all the sensors tested. In addition, the response time of all the sensors to H2 remained unchanged by the HMDS modification, even though their response time to CH4 and their recovery times to both CH4 and H2 tended to become long with an increase in the amount of HMDS modified. The XPS analyses suggested that the formation of a SiO2 thin layer on the surface of SnO2 by the HMDS modification. The existence of the SiO2 thin layer moderately decreased the amount of negatively charged oxygen adsorbates on the SnO2 surface, and drastically restricted the diffusion of large-sized gases, CH4 and O2, to the SnO2 surface. They are possible reasons why the HMDS modification enhanced the H2 response of the sensors.

Regulation of electro-optical activities of nanostructured SnO2:Al powders by using a micro drop fluidized reactor

Nanostructured SnO2:Al powders were prepared and their electro-optical activities were regulated by using a micro drop fluidized reactor (MDFR), which were conducted continuously in a simple one-step process without additional calcination, annealing, and drying steps. The crystallite size and BET surface area (up to a 2.6 times) increased but bandgap energy of SnO2:Al powders decreased, respectively, by providing the unique pyro-hydraulic reaction conditions during the formation of powders. The micro shear force and strain generated due to the fluidization of micro drops could enhance the doping effects and surface activities of SnO2:Al powders. The analyzes of room-temperature photoluminescence (PL) spectra, UV–vis photospectroscope and X-ray photoelectron spectra (XPS) exhibited that the surface activities of SnO2:Al powders were enhanced considerably by regulating the excitation and separation of electrons and holes and increasing the oxygen vacancies at the surface of SnO2:Al powders by means of UMB control. The optimum amount of dopant of Al3+ ions (CAl) and flow rate of micro bubbles (UMB) for effective surface activities were 2.0at% and 1.0 L/min, respectively. The scheme of photocatalytic mechanism of SnO2:Al powders to degrade the methylene blue (MB) was discussed by means of surface charge transfer and morphology of the powders.

Sodiophilic Zn/SnO2 porous scaffold to stabilize sodium deposition for sodium metal batteries

Sodium is regarded as a promising electrode material in the post lithium ion battery era due to its high theoretical specific capacity of 1166 mAh g−1, low electrochemical potential (−2.71 V vs standard hydrogen electrode), low cost and high natural abundance. However, similar to lithium metal anode, sodium metal anode also shares the problems of uncontrollable dendrites growth, formation of unstable solid electrolyte interface and large volume change during repeated plating/stripping. Herein, a porous sodiophilic zinc metal framework modified with SnO2 surface layer is introduced on copper substrate and used as 3D current collector for sodium metal batteries in order to realize even deposition of Na, moderate the volume change and construct a stable solid electrolyte interface layer simultaneously. Theoretical calculations based on density functional theory are used to interpret the deposition behavior of the metallic Na on different current collectors. The electrochemical performance results show that the Cu/Zn/SnO2@Na symmetric cell can deliver an extremely low nucleation overpotential (0 mV), outstanding long-term rate performance over 1000 h and also can be cycled for around 700 h even at a high current density of 5 mA cm−2 for total capacity of 5 mAh cm−2. Cu/Zn/SnO2@Na//Na3V2(PO4)3 full cell is also constructed to display the feasible application of the designed Cu/Zn/SnO2 porous current collector in advanced sodium metal anode.

Regulating SnO2 surface by metal oxides possessing redox or acidic properties: The importance of active O2−/O22− and acid sites for toluene deep oxidation

To explore the surface doping effects of metal oxides possessing redox (Cr, Co, Mn) or acidic (In, Bi) properties on SnO2, SnO2 doped by different metal oxides has been designed. All the doping metal oxides disperse finely on the SnO2 support surface, which can improves the reaction activity, obeying the order of 1%Mn/SnO2 > 1%Co/SnO2 > 1%Cr/SnO2 > 1%Bi/SnO2 > 1%In/SnO2 > SnO2. By modifying SnO2 surface with Cr, Co and Mn oxides, both the active surface oxygen (O2− and O22−) and acid sites quantities have been significantly improved, thus resulting in remarkable activity increment. Whereas, by modifying SnO2 surface with In and Bi oxides, only the surface acid sites amount has been improved, hence having limited activity improvement effect. 1%Mn/SnO2 catalyst possesses considerable amount of both types of active sites, thus showing the optimal toluene deep oxidation activity in all the catalysts.

Self-Assembled SnO2/SnSe2 Heterostructures: A Suitable Platform for Ultrasensitive NO2 and H2 Sensing

By means of experiments and theory, the gas-sensing properties of tin diselenide (SnSe2) were elucidated. We discover that, while the stoichiometric single crystal is chemically inert even in air, the nonstoichiometric sample assumes a subnanometric SnO2 surface oxide layer once exposed to ambient atmosphere. The presence of Se vacancies induces the formation of a metastable SeO2-like layer, which is finally transformed into a SnO2 skin. Remarkably, the self-assembled SnO2/SnSe2-x heterostructure is particularly efficient in gas sensing, whereas the stoichiometric SnSe2 sample does not show sensing properties. Congruently with the theoretical model, direct sensing tests carried out on SnO2/SnSe2-x at an operational temperature of 150 °C provided sensitivities of (1.06 ± 0.03) and (0.43 ± 0.02) [ppm]-1 for NO2 and H2, respectively, in dry air. The corresponding calculated limits of detection are (0.36 ± 0.01) and (3.6 ± 0.1) ppm for NO2 and H2, respectively. No detectable changes in gas-sensing performances are observed in a time period extended above six months. Our results pave the way for a novel generation of ambient-stable gas sensor based on self-assembled heterostructures formed taking advantage on the natural interaction of substoichiometric van der Waals semiconductors with air.