Mesoporous Tin Oxide Research Articles

Oxide-supported IrNiO(x) core-shell particles as efficient, cost-effective, and stable catalysts for electrochemical water splitting.

Active and highly stable oxide-supported IrNiO(x) core-shell catalysts for electrochemical water splitting are presented. IrNi(x)@IrO(x) nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiO(x)/Meso-ATO) were synthesized from bimetallic IrNi(x) precursor alloys (PA-IrNi(x) /Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNi(x)/Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core-shell particles. The core-shell IrNiO(x)/Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.

Catalytic Activity of Spherical Meso-Porous Pt Films-Deposited Fluorine-Doped Tin Oxide Substrate Covered By Multi-Walled Carbon Nanotube for Iodine Reduction

Platinum (Pt) is known to be one of the best catalysts for various electrochemical reactions although it is an expensive rare metal. Therefore, a investigation on reducing consumption of Pt is of great interest by many researchers. For this purpose, we recently focus our attention on a mesoporous Pt film which posses not only a large surface area but also extremely high catalytic activity for methanol oxidation [1].To make most of the mesoporous Pt film effectively, we focus our attention to moderately small spherical configuration. Spherical configuration increase the active surface area for electrochemical reactions. However, the interface between Pt particles and the substrate is considered to yield high interfacial resistance because of the limited point contacts. Therefore, in this study, Multi-Walled Carbon Nanotube (MWCNT), which is superior in mechanical strength and electric conductivity, a specific thermal conductivity, and the large surface area, was deposited to bypass the spherical mesoporous Pt film and the substrate as depicted in Fig.1. In this presentation, the redox reaction of the iodide ions will be mainly discussed for the application to dye-senstized solar cell. MWCNT/mesoporous Pt composite film was prepared by two steps. At first, the mesoporous Pt was deposited on TiO2/ Fluorine-doped Tin Oxide (FTO) substrates, and then the surface was wholly covered by MWCNT. The electrodeposition was performed in a three-electrode cell by chronoamperometry: various FTO substrates are used for working electrode, platinum wire for counter electrode, and an Ag/AgCl electrode for reference electrode. For the electrolyte, 20 mM K2PtCl4aqueous solution resolving 1.0 wt % Brij58 (Aldrich) was utilized. 10 mg/mL of CNT solution resolving sodium dodecylbenzenesulfonate was dropped on the mesoporous Pt film and dried at room temperature. The spherical mesoporous Pt film was demonstrated to deposit at the potential of -0.1 V when a TiO2/FTO is used as substrate. Cyclic voltamograms of the bare TiO2/FTO substrate, and the TiO2/FTO substrates modified with the composite film, the spherical mesoporous Pt film, and the MWCNT film, respectively were measured in an acetonitrile solution consisting of 0.1M TBAP, 1 mM I2, and 0.1 M LiClO4. As shown in Fig.2, the reduction peak current corresponding to iodine reduction for the composite film showed approximately three times larger than that for the both substrates modified only with the spherical mesoporous Pt film and the MWCNT film. These results revealed that the composite film can be the best catalyst for iodine reduction.[1] H. Wang et al., Chem. Mater., 2012, 24, 1591-1598.

Multifunctional organized mesoporous tin oxide films templated by graft copolymers for dye-sensitized solar cells.

AbstractInvited for this month′s cover is the group of Jong Hak Kim at Yonsei University in South Korea. The image shows how organized mesoporous SnO2 film plays a role in controlling light harvesting, electron transport and interfacial/internal resistance of dye‐sensitized solar cells (DSSCs). The Full Paper itself is available at 10.1002/cssc.201301215

Cover Picture: Multifunctional Organized Mesoporous Tin Oxide Films Templated by Graft Copolymers for Dye-Sensitized Solar Cells (ChemSusChem 7/2014)

The Front Cover image illustrates the importance of organized mesoporous SnO2 film with high porosity, larger pores, and good interconnectivity in dye-sensitized solar-cells (DSSC) applications. Although SnO2 films have been studied to increase electron transport, a multifunctional SnO2 film with high porosity and an organized mesoporous structure has not yet been reported. The group of Prof. Jong Hak Kim prepared multi-functional organized mesoporous SnO2 (om-SnO2) film through a facile sol–gel process using a cheap graft copolymer as a structure-directing agent. The use of om-SnO2 film resulted in enhanced light harvesting, increased electron transport, reduced charge recombination, and decreased interfacial/internal resistance. More details can be found in the Full Paper on page 2037 (DOI: 10.1002/cssc.201301215), while more information about the research group is available in the Cover Profile (DOI: 10.1002/cssc.201400102).

Limits of ZnO Electrodeposition in Mesoporous Tin Doped Indium Oxide Films in View of Application in Dye-Sensitized Solar Cells.

Well-ordered 3D mesoporous indium tin oxide (ITO) films obtained by a templated sol-gel route are discussed as conductive porous current collectors. This paper explores the use of such films modified by electrochemical deposition of zinc oxide (ZnO) on the pore walls to improve the electron transport in dye-sensitized solar cells (DSSCs). Mesoporous ITO film were dip-coated with pore sizes of 20–25 nm and 40–45 nm employing novel poly(isobutylene)-b-poly(ethylene oxide) block copolymers as structure-directors. After electrochemical deposition of ZnO and sensitization with the indoline dye D149 the films were tested as photoanodes in DSSCs. Short ZnO deposition times led to strong back reaction of photogenerated electrons from non-covered ITO to the electrolyte. ITO films with larger pores enabled longer ZnO deposition times before pore blocking occurred, resulting in higher efficiencies, which could be further increased by using thicker ITO films consisting of five layers, but were still lower compared to nanoporous ZnO films electrodeposited on flat ITO. The major factors that currently limit the application are the still low thickness of the mesoporous ITO films, too small pore sizes and non-ideal geometries that do not allow obtaining full coverage of the ITO surface with ZnO before pore blocking occurs.

Multifunctional Organized Mesoporous Tin Oxide Films Templated by Graft Copolymers for Dye‐Sensitized Solar Cells

The synthesis of organized mesoporous SnO2 films with high porosity, larger pores, and good interconnectivity, obtained by sol-gel templating with an amphiphilic graft copolymer, poly(vinyl chloride)-graft-poly(oxyethylene methacrylate), is reported. An improved performance of dye-sensitized solar cells (DSSCs) is demonstrated by the introduction of a 400 nm thick organized mesoporous SnO2 interfacial (om-SnO2 IF) layer between nanocrystalline TiO2 (nc-TiO2 ) and a fluorine-doped tin oxide substrate. To elucidate the improved efficiency, the structural, optical, and electrochemical properties of the devices were characterized by SEM, UV/Vis spectroscopy, noncontact 3D surface profilometry, intensity-modulated photocurrent/voltage spectroscopy, incident photon-to-electron conversion efficiency, and electrochemical impedance spectroscopy measurements. The energy-conversion efficiency of the solid polymerized ionic liquid based DSSC fabricated with the om-SnO2 IF/nc-TiO2 photoanode reached 5.9% at 100 mW cm(-2) ; this is higher than those of neat nc-TiO2 (3.5%) and organized mesoporous TiO2 interfacial/nc-TiO2 layer (5.4%) photoanodes. The improved efficiency is attributed to the antireflective property, cascadal energy band gap, good interconnectivity, and high electrical conductivity of the om-SnO2 IF layer, which results in enhanced light harvesting, increased electron transport, reduced charge recombination, and decreased interfacial/internal resistance.

Comparison of photoelectrochemical water oxidation activity of a synthetic photocatalyst system with photosystem II.

This discussion describes a direct comparison of photoelectrochemical (PEC) water oxidation activity between a photosystem II (PSII)-functionalised photoanode and a synthetic nanocomposite photoanode. The semi-biological photoanode is composed of PSII from the thermophilic cyanobacterium Thermosynechococcus elongatus on a mesoporous indium tin oxide electrode (mesoITO|PSII). PSII embeds all of the required functionalities for light absorption, charge separation and water oxidation and ITO serves solely as the electron collector. The synthetic photoanode consists of a TiO(2) and NiO(x) coated nanosheet-structured WO(3) electrode (nanoWO(3)|TiO(2)|NiO(x)). The composite structure of the synthetic electrode allows mimicry of the functional key features in PSII: visible light is absorbed by WO(3), TiO(2) serves as a protection and charge separation layer and NiO(x) serves as the water oxidation electrocatalyst. MesoITO|PSII uses low energy red light, whereas nanoWO(3)|TiO(2)|NiO(x) requires high energy photons of blue-end visible and UV regions to oxidise water. The electrodes have a comparable onset potential at approximately 0.6 V vs. reversible hydrogen electrode (RHE). MesoITO|PSII reaches its saturation photocurrent at 0.84 V vs. RHE, whereas nanoWO(3)|TiO(2)NiO(x) requires more than 1.34 V vs. RHE. This suggests that mesoITO|PSII suffers from fewer limitations from charge recombination and slow water oxidation catalysis than the synthetic electrode. MesoITO|PSII displays a higher 'per active' site activity, but is less photostable and displays a much lower photocurrent per geometrical surface area and incident photon to current conversion efficiency (IPCE) than nanoWO(3)|TiO(2)|NiO(x_.

Bioelectrocatalysis at mesoporous antimony doped tin oxide electrodes—Electrochemical characterization and direct enzyme communication

In this paper we report immobilization and bioelectrocatalysis of human sulfite oxidase (hSO) on nanostructured antimony doped tin oxide (ATO) thin film electrodes. Two types of ATO thin film electrodes were prepared via evaporation induced self-assembly of ATO nanoparticle sols. The use of a porogen results in different porosity and film thickness. Nevertheless both electrode types reveal similar quasi reversible electrochemical behavior for positive and negatively charged small mediators. Facile and durable immobilization of catalytically active enzyme in a direct electron transfer configuration was achieved without further chemical modification of the ATO surfaces. Interestingly, the binding of hSO onto the ATO surface seems to be not only of electrostatic nature, but also originates from a strong interaction between the histidine-tag of the enzyme and the supporting material. This is suggested from stable sulfite dependent bioelectrocatalytic signals at high ionic strength and imidazole desorption experiments. As such, ATO appears as a promising conductive platform for the immobilization of complex enzymes and their application in bioelectrocatalysis.

Synthesis of mesoporous antimony-doped tin oxide (ATO) thin films and investigation of their electrical conductivity

Mesoporous antimony-doped tin oxide (ATO) thin films with crystallized frameworks are synthesized by using a laboratory-made thermally-stable triblock copolymer (named as ‘sulfonated HmSEBmS’) as the template at optimized conditions. The porous structure is strongly affected by the amount of copolymer, which causes variation in the electrical conductivity of the synthesized ATO films.

Enhanced electronic contacts in SnO2–dye–P3HT based solid state dye sensitized solar cells

We present an investigation on the optimisation of solid-state dye sensitized solar cells (SDSCs) comprising mesoporous tin oxide photoanodes infiltrated with poly(3-hexylthiophene-2,5-diyl) (P3HT) hole conductor and sensitized with an organic dye. We chose both the SnO(2) and P3HT for their high charge carrier mobilities and conductivities, but as a result preclude conventional device configurations because of high leakage current and low shunt-resistance. To minimize the "hole leakage current" through the FTO anode, we employed a double compact layer structure, and to minimize "electron leakage current" at the silver cathode, we developed a protocol for depositing an optimal P3HT "capping layer". After optimisation of cell fabrication, the electron lifetime is increased considerably and the solar cells exhibited simulated AM1.5 full sun solar power conversion efficiencies in excess of 1%.

The influence of preparation conditions and doping on the physicochemical and sensor properties of mesoporous tin oxide

Abstract The influence of conditions used for preparation of mesoporous materials and thin layers based on tin oxide on physicochemical and sensor properties of these materials were studied. Thermal stability, acidic, sorption and electric properties were studied. The advantage of thin (≈1 μm) thermostable nanocomposite layers with relatively high parameters of the porous structure ( V = 0.460 cm 3 /g, S ВЕТ = 440 m 2 /g) was shown. Obtained materials can be used for selective gas/vapor sensing.

Surface functionalization of mesoporous antimony doped tin oxide by metalorganic reaction

Electrically conducting mesoporous antimony doped tin oxide was functionalized by the metalorganic reaction with several Grignard reagents. This fast and efficient grafting approach enables a direct connection of the metal atoms with the organic functionalities avoiding the formation of insulating Si–O linkers, which is of special interest for the interfacial charge transfer processes. Using this approach we introduced vinyl, allyl and phenyl groups into the pores of mesoporous ATO, which was confirmed by IR spectroscopy, TGA and nitrogen sorption measurements. We obtained a high loading of organic groups corresponding to about 50–60% of the monolayer surface coverage. The obtained mesoporous inorganic–organic hybrids can serve as a platform for incorporation of electrochemically active species.

Facile Synthesis of Mesoporous Tin Oxide Spheres and Their Applications in Dye-Sensitized Solar Cells

Mesoporous tin oxide spheres (MS-SnO2) with a main size ranging from 100 to 800 nm are synthesized via a simple solution route. These spheres consist of packed nanocrystals and possess a specific surface area of 29.4 m2·g–1 and a main pore size of about 4 nm. Due to large particle size, high specific surface area, and good intercrystalline connections, a dye-sensitized solar cell (DSSC) based on the MS-SnO2 film photoanode shows an energy conversion efficiency of 4.97%, which is higher than that of a DSSC based on current SnO2 nanoparticle film photoanodes. On the other hand, the photovoltaic performance of the DSSC can be improved by modifying the photoanode with a TiO2 blocking layer and TiCl4 post-treatment.

Nanocasting synthesis of ordered mesoporous indium tin oxide (ITO) materials with controllable particle size and high thermal stability

Ordered mesoporous indium tin oxide (ITO) materials were successfully synthesized by doping tin element into the nanocast-synthesized mesoporous In2O3 intermediate via a post-treatment process. The particle size can be systematically controlled by utilizing the “container effect” during the synthesis of mesoporous In2O3 intermediate. With the increase of Sn doping concentration, the electrical resistivity first decreases and then increases. The minimum resistivity value is 0.34Ωcm for mesoporous ITO sample with 10mol% of Sn doping concentration. We also discussed the effect of calcinations atmosphere and temperature on the crystallinity, mesoporous regularity and conducting properties in detail. The mesoporous ITO products prepared in this work possess high thermal stability up to 700°C and may be used as excellent optoelectronic materials at elevated temperature without any detectable collapse in porosity.

Strong metal–support interaction as activity requirement of palladium-supported tin oxide sol–gel catalyst for water denitration

Two nanocrystalline palladium-supported tin oxide catalysts for water denitration were synthesized by a modified sol–gel technique using appropriate chloride precursors for both support and active phases, and citric acid to tune the rate of hydrolysis and condensation. The difference among sample preparation procedures refers to the moment of the noble metal loading to the support, as well as to the calcination temperature altitude followed. Thus, mesoporous tin oxide was synthesized by a sol–gel method following calcination at 700°C. The palladium active phase was introduced afterwards by means of palladium chloride solution impregnation, followed by calcination at 400°C (sample 1). Alternatively, simultaneous complexation of both metal and support precursors followed by single calcination at 700°C was applied for preparation of sample 2. The former sample showed higher activity and selectivity in hydro-denitration of water model system initially containing 100 ppm of nitrates. This was explained by preferential textural, morphological and structural properties accomplished by early contact of metal and support nanoparticles, while achieved by calcination at high single temperature forcing diffusion of palladium ions into the tin oxide matrix. The outcome is very well distribution of palladium and strong metal–support interaction leading to multivalent tin. This indicates partly reduced tin oxide formation in the course of its reduction in hydrogen, which may act as active site in denitration reaction.

Assembly of mesoporous indium tin oxide electrodes from nano-hydroxide building blocks

We describe the elaboration of nanostructured transparent conducting indium tin oxide (ITO) materials that is based on controlled self-assembly of ultra-small indium tin hydroxide nanoparticles. We developed a strategy for preparing nanosized, nearly spherical and highly dispersible nanoparticles of indium tin hydroxide (“nano-hydroxides”), which can be assembled into regular mesoporous architectures directed by a commercially available Pluronic polymer. The assembled structures are easily transformed into conducting crystalline mesoporous ITO films by a mild heat treatment at 300 °C. The resulting ITO layers feature a regular mesoporosity with a mesostructure periodicity of about 13 ± 2 nm, high surface area of 190 m2 cm−3, porosity of 44% and electrical conductivity up to 9.5 S cm−1. The ITO films can accommodate large amounts of redox-active molecules and serve as efficient conducting electrodes with a very high surface area. The perfect dispersibility of nano-hydroxides without any stabilizing agents, their preferential interaction with the hydrophilic part of amphiphilic molecules leading to their self-assembly, and a facile transformation of the assembled nano-hydroxides into crystalline ITO with similar morphology make the nano-hydroxides very attractive building blocks for the elaboration of nanostructured ITO materials. We believe that the nano-hydroxides can become universal building blocks for the fabrication of crystalline ITO materials with arbitrary nano-morphologies.

In this issue

AbstractProcess analytical sensors for single‐use bioreactorsBluma et al., Eng. Life Sci. 2011, 11, 550–553.Online measurement of process parameters within bioreactors is still a challenge. Most analytical sensor systems used in the conventional stirred‐tank reactors cannot be transferred to single‐use bioreactors. This is because most conventional sensor systems are invasive and must be sterilized, calibrated, and validated before use. In addition, regulations of the US Food and Drug Administration concerning process documentation, imposed by the Process and Analytical Technology (PAT) Initiative, have increased the demand for sensors that are able to very accurately monitor and document the production process. In this issue, Sascha Beutel et al. (Hanover, Germany) compare sensor systems that are currently on the market for single‐use bioreactors and discuss the use of image‐based biosensors.……………550.http://dx.doi.org/10.1002/elsc.201000191magnified imageProtein‐based optical device with reset functionFrasca et al., Eng. Life Sci. 2011, 11, 554–558.Analytical single‐use test strips evaluated by a color change have been used in industry/academia for almost half a century. In this issue, Ulla Wollenberger and co‐workers (Golm and Gießen, Germany) present the development of a reusable sensing system coupled to optical detection. In their model, cytochrome c was immobilized in a mesoporous indium tin oxide film. The cytochrome c‐catalyzed oxidation of a redox‐sensitive dye is then measured spectroscopically. When the dye is co‐immobilized with the protein, its redox state can be easily controlled by application of an electrical potential at the supporting material. This electrochemical reset function enables repetitive signal generation and direct calibration of small test devices. The described principle can be extended to other color‐forming redox reactions and enzyme systems.……………554http://dx.doi.org/10.1002/elsc.201100079magnified imageAptasensor platform based on surface plasmon resonanceHenseleit et al., Eng. Life Sci. 2011, 11, 573–579.Aptamers are synthetic single‐stranded oligonucleotides exhibiting several advantages for their use as biosensors compared with antibodies: target molecules include toxic or pathological substances, production is quicker and cheaper, they are easy to modify without loss of activity and show high stability under a width range of conditions. In this issue, researchers from the Technical University and Fraunhofer Institutes in Dresden, Germany present a novel aptasensor platform based on a surface plasmon resonance (SPR)‐system using a thrombin–aptamer interaction as a model system. The platform is intended to be used as a low‐cost biosensor, which is robust, easy to transport, and demonstrates sensitive and label‐free detection of target molecules, such as peptides, proteins, nucleotides, and whole virus particles.……………573http://dx.doi.org/10.1002/elsc.201100036magnified image

Electrochemical switchable protein‐based optical device

AbstractThe present work contributes to the development of reusable sensing systems with a visual evaluation of the detection process related to an analyte. An electrochemical switchable protein‐based optical device was designed with the core part composed of cytochrome c immobilized in a mesoporous indium tin oxide film. A color‐developing redox‐sensitive dye was used as switchable component of the system. The cytochrome c‐catalyzed oxidation of the dye by hydrogen peroxide is spectroscopically investigated. When the dye is co‐immobilized with the protein, its redox state is easily controlled by application of an electrical potential at the supporting material. This enables to electrochemically reset the system to the initial state and repetitive signal generation. The implemented reset function of the color forming reaction will make calibration of small test devices possible. The principle can be extended to other color forming redox reactions and to coupled enzyme systems, such as rapid food testing and indication of critical concentrations of metabolites for health care.

Ordered mesoporous carbon/SnO2 composites as the electrode material for supercapacitors

A series of composites as electrode materials for supercapacitors were prepared via incipient wetness impregnation method utilizing ordered mesoporous carbon (OMC) and tin (IV) oxide (SnO2) with different ratio. The structure and electrochemical properties of the OMC/SnO2 composites were characterized by XRD, TEM and cyclic voltammetry (CV). Pore characteristics were measured by nitrogen adsorption and desorption isotherms. The results show that the structure and electrochemical properties of the composites depend mainly on the loading amount of SnO2 in the ordered mesoporous carbon. The optimum amount of SnCl4 added is found to be 40 % (1.54 g ethanol-based SnCl4·5H2O added to 1 g OMC) of the saturated solution. The specific capacitance of the composite of optimum amount of SnCl4 (200 F g−1) is nearly three times of that of the pristine SnO2 (72 F g−1) at the scan rate of 5 mV s−1, and its specific capacitance is almost equal to that of the ordered mesoporous carbon (126 F g−1) at the scan rate of 200 mV s−1. Meanwhile, it has better specific volumetric energy density than OMC due to its higher density. Besides, in the potential range of 0–0.9 V the composite electrode material exhibits a stable cycle life after 500 cycles.

A Molecular Precursor Approach to Tunable Porous Tin-Rich Indium Tin Oxide with Durable High Electrical Conductivity for Bioelectronic Devices

The preparation of porous, i.e., high surface area electrodes from transparent conducting oxides, is a valuable goal in materials chemistry as such electrodes can enable further development of optoelectronic, electrocatalytic, or bioelectronic devices. In this work the first tin-rich mesoporous indium tin oxide is prepared using the molecular heterobimetallic single-source precursor, indium tin tris-tert-butoxide, together with an appropriate structure-directing template, yielding materials with high surface areas and tailorable pore size. The resulting mesoporous tin-rich ITO films show a high and durable electrical conductivity and transparency, making them interesting materials for hosting electroactive biomolecules such as proteins. In fact, its unique performance in bioelectronic applications has been demonstrated by immobilization of high amounts of cytochrome c into the mesoporous film which undergo redox processes directly with the conductive electrode material.