Advances in Photocatalytic Materials for Energy and Environmental Sustainability
Session FE-1 - Tailored Synthesis of Nanostructured Materials for Photofunctional Properties
FE-1:IL01 Development of Nanostructured Materials for Environmental and Energy Applications
A. ORLOV, SHEN ZHAO, Stony Brook University, NY, USA
Development of novel nanostructured materials can offer outstanding opportunities to control reaction rate, light absorbance and diffusion of reactants within the porous matrix. This work has focused on application of new generation of mesoporous materials with large pore diameter and short pore channels template with photocatalysts. The samples were characterized by TEM, SAXS, and BET and tested for photocatalytic reactions. This work also included the novel use of sub-1 nm Au nanoparticles for catalysts modification which substantially increased the reaction rate. In addition we have also explored application of photonic crystals to couple photonic bandgap with electronic bandgap of semiconductors.
FE-1:IL02 Polymeric Materials as Substrates for Photocatalytic Degradation: Plasma and Selective Stabilization
M.C. CANELA, M.S. CURCIO, W.R. WALDMAN, E.C. RANGEL, B.C. SANCHEZ, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, Brazil
Technological solutions to enable products based on catalytic photodegradation can only be ensured by broadening the possibility of different substrates. The polymeric substrates have a number of advantages such as low cost of raw materials and processing, flexibility and easy conformation, which ensures greater design options to generate fluid turbulence, ensuring more efficient processes. However, due its organic nature, polymeric substrates have sensitivity to free radicals generated in the photocatalyst. Two solutions are specially addressed for this situation: the plasma surface treatment and specific stabilization for catalytic photodegradation. In this work, the deposition of SiO2-like thin film on the surface of polypropylene (PP) and non-woven polypropylene (NWPP) by plasma exposure is intended to provide a layer of protection against the photodegradation. The deposition occurred in an atmosphere of O2:HMDSO 50:50, at 80 W in 1800, 2700 and 3600 s of deposition time. TiO2 sol gel was deposited on SiO2-like thin film by dip-coating. The thin film depositions, by plasma of organ silicones, allow the formation of a homogeneous and flexible film which increases the efficiency of photocatalysts deposition and stabilization, reducing its rate of degradation.
FE-1:L04 Photocatalytic Films by Molecular Layer Deposition
R. YERUSHALMI, Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem, Israel
A significant challenge to-date is the formation of highly controlled photocatalytic films on high aspect ratio nanometric scaffolds and templates. Such materials and architectures are desirable for the formation high surface area structures with controlled surface properties and functionality at the nanometric scale leading to highly favorable catalytic activity.
Recently we demonstrated the first application of Molecular Layer Deposition (MLD) for preparation of highly photoactive thin films. As a proof-of-concept we focused on titnaucone, a titanium oxide-organic hybrid film. The MLD films exhibit crystalline as well as amorphous regions for a wide temperature range, which is valuable feature for designing highly active photocatalytic films by combining high affinity towards molecules and crystalline regions. The amorphous and crystalline regions are in close interaction embedded within the same thin film. Our results demonstrate the feasibility and high potential of using MLD process to form nanometric hybrid structures for photocatalysis. I will present results for the degradation of benzoic acids in aqueous solutions as well as the formation of H2O2 without the need for sacrificial compounds or externally applied potential.
FE-1:IL05 Engineering Design and Analysis to Determine the Kinetics of Contaminant Removal from Photocatalytic Self-Cleaning Surfaces
D.F. OLLIS, North Carolina State University, Raleigh, NC, USA
We make the case that a kinetic understanding of photocatalytic self-cleaning surfaces requires answers to the following five questions. In each case, the observed apparent kinetic order depends upon the answer, that is, the interplay among the distributions of photocatalyst, reactant, and irradiance determines the apparent reaction order.
1.Is the photocatalyst porous or non-porous ?
Example: stearic acid on/within non-porous/porous photocatalyst layer.
2 Is the photocatalytically active layer optically thin or thick ?
Examples: Dye conversion in TiO2 layers vs. TiO2/SiO2 layers.
3. Is the probe reactant deposit a submonolayer or multilayer?
Examples: Dye sub/multilayers with TiO2
4. Is the probe reactant distributed as a continuous film or as discrete islands ? If distributed, what is breadth of distribution ?
Examples: long chain carboxylic acids on TiO2
5. Is probe reactant light absorption negligible or important ?
Example: Stearic acid vs. soot
We demonstrate apparent reaction orders for contaminant removal of 0, ½, 1, and 2 ! Engineering design and analysis for the multiple configurations listed above is used to explain these different apparent reaction orders.
FE-1:L07 Photoelectrochemical Properties of Doped Lanthanum Orthoferrites
I. NATALI SORA, F. FONTANA, INSTM R.U. Bergamo and Dipartimento di Ingegneria, University of Bergamo, Dalmine, Italy; R. PASSALACQUA, C. AMPELLI, S. PERATHONER, G. CENTI, INSTM/CASPE R.U. and Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale (DIECII), University of Messina, Messina, Italy; F. PARRINO, L. PALMISANO, "Schiavello-Grillone" Photocatalysis Group, Dipartimento di Energia, Ingegneria dell'Informazione e Modelli Matematici (DEIM), University of Palermo, Palermo, Italy
LaFeO3 powders doped with Sr (20 mol%) and Cu (0-10-20 mol%) were prepared by citrate auto-combustion synthesis and investigated in terms of crystal structure, morphology, surface area and optical properties. All powders showed photocurrent response in the form of a pasted and annealed electrode and as slurry electrode; the highest value was obtained for undoped orthoferrite calcined at 600°C. The position of the quasi-Fermi level of electrons for all the photocatalysts calcined in the range 600-980°C is about the same within experimental error (between −0.62 and −0.67 V with respect to Ag/AgCl reference electrode, at pH 7). Doping with 20 mol% of strontium did not influence the flat band potential of the powders, while doping with copper caused an important and reproducible change in the potentiometric titration curve, indicating the presence of intermediate energy states in the samples calcined at 600°C, but not in those calcined at 980°C. Based on these photoelectro-chemical characteristics, the proposed perovskite-type lanthanum powders could be considered not only as traditional electrodes for high temperature solid oxide fuel cells (SOFC) but also as functional inorganic materials in photocatalytic applications operating at low temperature.
FE-1:L11 Overall Water-splitting Photocatalyst under Visible Light; Conduction-Band-Controlled Silver Tantalate
H. IRIE, Clean Energy Research Center, University of Yamanashi, Kofu, Yamanashi, Japan
The photo-induced water splitting to convert photon energy into H2 energy using photoelectrodes and powdered photocatalysts has been extensively investigated. Due to its simplicity, water splitting using a powdered photocatalyst is currently a subject of interest, with most research focusing on the visible light sensitization of catalysts. However, the number of visible-light-sensitive photocatalysts that are able to split water into H2 and O2 in stoichiometric amounts (overall water splitting) is limited. Domen et al. have reported overall water splitting in the presence of GaN-ZnO powdered photocatalyst . In the present study, based on the knowledge of AgTaO3 that absorbs only UV light , we tried to control the conduction band of AgTaO3 by introducing Nb at Ta site to be sensitive to visible light. Then, we prepared NiO-grafted AgTa0.7Nb0.3O3. We examined water-splitting over the photocatalyst under irradiation with visible light (420 nm-LED lamp). The H2 and O2 evolved almost linearly with increasing the irradiation time with ratio of 2 to 1. Also, the turnover number exceeded 1. Thus, overall water-splitting in the presence of the photocatalyst was achieved.
 K. Domen et al., Nature, 440, 295 (2006).  A. Kudo et al., J. Phys. Chem. B, 106, 5029 (2002).
FE-1:L12 Photoelectrochemical Study of Anodized TiO2 Nanotubes and Electrospun TiO2 Fibres
D. REGONINI1, A.C. TELOEKEN2, A.P. GARCIA2, A.K. ALVES2, A. BRAUN1, F. CLEMENS1, 1Laboratory for High Performance Ceramics, EMPA-Swiss Federal Laboratories for Materials Science & Technology, Dübendorf, Switzerland; 2Laboratory of Ceramic Materials, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil
This work focuses on the evaluation of the photoelectrochemical properties of anodized TiO2 Nanotubes (NTs) obtained from the anodization of Ti and Ti-Nb, Ti-W alloys. Their ability to sustain transport of electrons during the solar water splitting process is considered in comparison with electrospun Fibres composite photoelectrodes obtained by embedding
the fibres in a sol-gel matrix (SG-fibres). The Incident Photon to Current Efficiency (IPCE) values of SG-fibre composites (in 1M KOH at 0.23V vs Ag/AgCl) is in the range 20-45% at 360-320nm. Similarly, the IPCE of TiO2 NTs, especially of those doped with Nb or alloyed with W, is above 45% below 400nm. The good connectivity of the particles making up the fibres allow for an efficient electron transport during water splitting. The poor packing density of the pristine fibres (i.e. microporosity between fibres limiting the photoactive surface area available) is overcome by embedding the fibres in a sol-gel matrix, as shown by the good IPCE values (up to 45%). Higher IPCE are difficult to achieve because of recombination at the fibre/sol-gel interface. Such issue can be bypassed by using anodized NTs, which are also offering good electron transport and good packing density (i.e. only nanoporosity between each single NT).
FE-1:L14 Solar Light Water Splitting at Nanostructured Metal Oxide Photoelectrodes
J. AUGUSTYNSKI, R. SOLARSKA, University of Warsaw, Center of New Technologies, Warsaw, Poland
Overview of the literature dealing with photoelectrochemical (PEC) water splitting might suggest using nanostructured semiconductors to form the photoelectrodes as being a kind of panacea to enhance their energy conversion efficiency. In fact, the actual situation is largely contrasted going from a substantial improvement to a spectacular drop of the PEC performance. The latter situation is illustrated by the behaviour of nanoparticulate (NP) TiO2 films dominated by the surface e-/h+ recombination mediated by the peroxo intermediates of the photo-oxidation of water. Although the NP TiO2 film photoanodes exhibit quite generally poor efficiencies for water splitting, the situation is totally different for another n-type semiconducting oxide - WO3 having a band gap of 2.5 eV. The use of relatively thick mesoporous WO3 films composed of a network of stacked NPs with sizes in the range of tens of nanometers allows excellent photocurrent-voltage characteristics. Ongoing efforts devoted to minimize the bias voltage required to perform visible light-driven photo-oxidation of water at NP WO3 photoanodes will be discussed. These include the use of dopants and incorporation of plasmonic metal nanostructures allowing to enhance the light capture by the WO3 films.
FE-1:L15 Development of High Surface Area Titania on Glass Fibre Supports for Photocatalysis
P. YILMAZ, A.M. LACERDA, I. LARROSA, S. DUNN, School of Engineering and Materials Science, Queen Mary University of London, London, UK
We have developed a hydrothermal process that produces a surface area TiO2 on glass fibre supports. The as produced titania shows good photocatalytic activity against standard commercial dyes - Rhodamine B and Methyl Red - giving full decolourisation within 5 hours under UV irradiation. The samples are mechanically robust and act as a photocatalytic filter for waste streams and pollutants. In addition to testing standard titania we have also photochemically deposited nanostructures of Pd. These hybrid catalysts show enhanced decolourisation by an order of magnitude over the native titania systems. We show that this enhanced performance is due to the increased energy harvesting of the hybrid system through a visible light plasmon interaction and the direct injection of electrons from the noble metal into the adsorbed dye molecules. There is a clear relationship between the absorbed light and photochemical reactivity of the system which is further explained in terms of electron hole generation and separation and plasmonic interaction.
In summary we have generated a high performance catalyst that is produced on a bulk commodity substrate with enhanced activity due to control of the surface plasmon and direct band gap transition of electron hole pairs in the semi-conductor.
FE-1:L16 Low Temperature Deposition of Photocatalytic TiO2 Coatings by Ink-jet Printing
P. LOMMENS, J. WATTÉ, I. VAN DRIESSCHE, SCRiPTs, Department of Inorganic and Physical Chemistry, Ghent University, Ghent, Belgium
TiO2 coatings can be used to create transparent, photocatalytic, self-cleaning surfaces and therefore have a high industrial relevance. Functional TiO2 layers are only obtained after crystallization of the material at temperatures above 400 °C. This means that chemical deposition approaches do not allow deposition on heat-sensitive substrates such as polymers. Therefore, it is important to investigate innovative deposition processes that can significantly reduce the minimal temperature required for crystallization and full processing. In this work, we studied the synthesis of crystalline titania nanoparticles by microwave-assisted solvothermal methods. The use of microwaves allows to optimize the production and energy efficiency of the synthetic process. Once stable suspensions of anatase nanoparticles are obtained, these are optimized for use in ink-jet printing devices. The fact that the crystalline building blocks for the layer are now already present in the precursor inks, allows efficient deposition of transparent titania coatings at reduced temperatures. Weathering/durability tests and extensive characterization of the photocatalytic activity and hydrophilic behaviour of these layers was performed to analyze the performance and processing limits for these TiO2 coatings.
FE-1:L17 Highly Efficient Metal Supported Photocatalyst due to the Excitation of Localised Surface Plasmon Resonance
A.M. LACERDA, I. LARROSA, S. DUNN, Queen Mary, University of London, London, UK
Research in the field of photocatalysis over the years has sought to improve the absorption and efficiency of these materials in waste water purification, hydrogen generation and microbial disinfection. This work reports the synthesis and effect of loading TiO2 (Degussa P25) with transition metal nanoparticles (TMNPs) to produce a highly efficient photocatalyst, which was determined to be an order of magnitude more active than TiO2 powder in dye degradation experiments under simulated solar conditions. The increased activity of the photocatalyst is the result of a combination of contributions from two mechanisms. These are the absorption of super band gap UV light from the semiconductor support and also the absorption of UV and visible light from the SPR of the supported metal. While the SPR effects of some noble metals such as gold and silver are known, and the mechanisms are well reported, the mechanism of this complex phenomenon for other transition metal nanoparticles, such as the type that is investigated in this work, is yet to be as extensively researched. In this study TMNPs were photo-chemically reduced onto the surface of TiO2 and the photocatalytic activity of the metal-TiO2 catalyst was determined by measuring the decolourisation of the textile dye rhodamine B (RhB).
FE-1:L18 Photocatalytic Reduction of CO2 into Solar Fuel Using Oxide-based Catalysts
TAO HE, National Center for Nanoscience and Technology, Beijing, China
Carbon dioxide (CO2) is one of the major greenhouse gases. Managing CO2 emission is one of the major technological as well as political challenges. The photocatlytic reduction of CO2 to value-added solar fuels (such as methanol, methane and CO) is an attractive option for capturing greenhouse gas and meanwhile to solve the problem of shortage of sustainable energy. Here we have studied the oxide-based photocatalysts for the photoreduction of CO2. Those oxides mainly include Cu2O, TiO2, zirconate, titanate, and the related composites. Different products have been obtained. The heterojunction fabrication has also been utilized to change/improve the yield of different photoreduction products. The mechanism has been studied as well. We envision this would afford a viable approach for the photoreduction of CO2 and a better understanding of the related mechanism, which would facilitate the R&D of the high-efficient photocatalysts for the photoreduction of CO2.
FE-1:L20 Tuning the Visible Light Activity of Plasmonic Photocatalysts to the Solar Spectrum
S.W. VERBRUGGEN, M. KEULEMANS, S. LENAERTS, University of Antwerp, Antwerp, Belgium; J.A. MARTENS, KU Leuven, Heverlee, Belgium
TiO2 based photocatalysis has become state-of-the-art technology in various application fields such as water and air purification, water splitting and self-cleaning surfaces. The large band gap of the TiO2 semiconductor (ca. 3.2 eV) remains a large drawback, limiting the use of TiO2 photocatalysis to UV-light driven applications. Adapting of the photoresponse of anatase TiO2 to match the solar spectrum is therefore an important scientific challenge. Generating surface plasmon resonance (SPR) effects under visible light illumination through modification of TiO2 with noble metal nanoparticles is a very promising approach. Composition-dependent SPR of Au-Ag alloy nanoparticles can be used to create plasmonic TiO2-based photocatalysts with SPR at desired visible light wavelengths in a predictable and reliable way. Visible light activity of a plasmonic photocatalyst with a photoresponse tuned to the maximum solar light intensity wavelength (490 nm) is demonstrated.
FE-1:L22 Preparation, Characterization and Photocatalytic Properties of Periodically Organized Mesoporous Titania Thin Film: Influence of Doping for Visible Light Activity
S. SEMLALI1, 2, T. PIGOT1, S. LACOMBE1, D. FLAHAUT1, L. NICOLE2, 1IPREM-UMR CNRS 5254, Pau, France; 2LCMCP, UMR CNRS 7574, College de France, France
This study was devoted to the preparation of Periodically Organized Mesoporous Titania Thin Films (POMTFS) by a coupled sol-gel/Evaporation Induced Self-Assembly (EISA) process. It was shown that multilayers films with well-defined cristallinity and mesoporosity could be obtained and characterized. The addition of Pt, V or W as dopants in various ratios did not modify the characteristics of the film.
The optimal number of layers for maximum photocatalytic efficiency was determined with three different experiments: stearic acid decomposition (solid-solid), methylene blue degradation (solid-liquid) and acetone mineralization (solid-gas).
The influence of the nature and ratio of the dopant on the photocatalytic efficiency was then analyzed under UV and Visible irradiation with the previously described tests. Various trends were observed, depending on the nature of the dopant, on the test used and on the irradiation range. The correlation of the photocatalytic activity with hydroxyl radicals production (HO.) under UV light was attempted, as well as singlet oxygen determination under visible light.
The general trends emerging from this whole set of results will be presented.
FE-1:L23 New UV and Visible Photocatalysts Prepared by a Microwave Assisted Approaches: from Better Knowledge to Better Efficiency
O. DURUPTHY, F. DUFOUR, M.-A. LAVERGNE, S. PIGEOT-REMY, S. CASSAIGNON, C. CHANÉAC, LCMCP-UPMC, Paris, France; C. COLBEAU-JUSTIN, LCP-UPSud, France
In addition to their intrinsic physical properties due to their electronic band structure, photocatalytic materials must display a relatively high specific surface and a good crystalline structure to display high activity. Indeed, defects may act as recombination center between photogenerated electrons and holes and decrease photocatalyst efficiency. With a solid background in oxide nanoparticles tailoring from metallic salts in aqueous solution, our research group succesfully transferred conventionnal syntheses of titanium dioxide and bismuth based oxides to microwave assisted thermohydrolyses.
In the case of TiO2, pure anatase could be obtained through microwave heating. The use of organic additive was thus avoided and good photocatalyst with clean surface were consequently obtained. As regards Bi2WO6 and BiOBr nanomaterials, significant improvements were obtained in term of synthesis time and particles size and shape.5 Photocatalysts obtained by microwave synthesis displayed significant improvement in Rhodamine B degradation. Additionnaly time resolved microwave condutivity was used to probe the crystalline improvement of the materials.
Session FE-2 - Advances in Fundamental Mechanism Understanding
FE-2:IL01 Fundamental Studies on Photocatalysis
B. OHTANI, Hokkaido University, Sapporo, Japan
In the history of photocatalysis studies, titania has been recognized as the best ultraviolet-light sensitive photocatalyst. However, there have been still no answers for the question why titania shows excellent photocatalytic activities. In this talk, the author would like to discuss fundamental aspects in photocatalysis to explain what are titania photocatalysts and to design and develop active photocatalysts. As a thermodynamic requirement, it is often claimed that conduction bottom and valence band top positions should be more negative (cathodic) and more positive (anodic) than the standard electrode potentials of substances to be reduced by photoexcited electrons and oxidized by positive holes, respectively. This thermodynamic interpretation, electron and hole reactions proceed depending on negative partial Gibbs energy change for each step, seems true and consistent with experimental results. However, it should be noted that this interpretation is not a sole necessary condition for heterogeneous photocatalysis and there is, at least, a significant necessary condition, electron and hole reactions should proceed separately. One of the possible solutions to satisfy this condition is to use facetted particles which may separate electrons and holes to induce reactions.
FE-2:L03 Isotope Labeled Titania: Raman spectra, Photocatalysis and Electrochemistry
L. KAVAN, J. Heyrovsky Institute of Physical Chemistry, Prague, Czech Republic
Six isotopologues of titanium dioxide were synthesized (16-O,17-O, 18-O), each in anatase and rutile forms. The Raman spectra were analyzed with the aid of DFT simulation. The interaction of TiO2 with carbon dioxide was investigated using high-resolution FTIR spectroscopy, in dark and upon UV-excitation. The mechanism for the 18-O/16-O exchange process was discussed at the molecular level. The UV photocatalytic formation of methane, acetylene and CO was studied at the 18-O titania modified by adsorbed H2O and HCl. Compatible data were acquired for photocatalytic and catalytic processes of formic acid at this surface. Electrochemistry of titania is highlighted by the effects of Li-insertion. Specifically, the electrochemical Li-insertion into anatase was followed by in-situ Raman spectroscopy using 18/16-O and 6/7-Li labeling.
Acknowledgement: This work was supported by by the Grant Agency of the Czech Republic (contract No. 13-07724S) by the COST Action CM1104.
FE-2:L04 Effect of Ferroelectricity on Solar-Light-Driven Photocatalytic Activity of BaTiO3 -Influence on the Carrier Separation and Stern Layer Formation
YONGFEI CUI, J. BRISCOE, S. DUNN, Materials Research Institute, School of Engineering and Materials Science, Queen Mary University of London, London, UK
There has been a growing interest in the field of photochemistry in ferroelectric materials and their photocatalytic properties. It has been demonstrated that the internal dipole of ferroelectrics can drive electron-hole separation and then spatially selective REDOX reactions on the surface. This research makes ferroelectrics a new promising candidate for photocatalysis in water treatment and artificial photosynthesis.
BaTiO3 was selected as catalysts to investigate the effect of ferroelectricity on its photocatalytic performance in decolourisation of an organic dye, Rhodamine B. A thermal treatment was employed to increase the ferroelectric tetragonal phase content of BaTiO3. It was found that the dye adsorption in the dark increased 5 times after anneal. The catalysts with higher ferroelectric content also demonstrated enhanced dye decolourisation rate, which should stem from the stronger dye adsorption leading to a strong Stern layer formation and effective charge carrier and therefore REDOX separation due to the internal electric field. Photodeposition of Ag on these catalysts was performed which improved the photocatalytic activity further. These findings provide a further understanding of ferroelectric materials as catalysts and demonstrate their promising future.
FE-2:L05 Hydrogen-doping of Mesoporous TiO2: Characterization of Electronic States and Impact on Photocatalytic Performance
T. BERGER1, 2, J. IDÍGORAS2, J.A. ANTA2, 1Department of Materials Science and Physics, University of Salzburg, Salzburg, Austria; 2Área de Química Física, Universidad Pablo de Olavide, Sevilla, Spain
Semiconductor oxides are highly relevant for different technological applications due to their suitable intrinsic properties and their susceptibility to bulk or surface modification. Some material properties, such as the doping degree, depend not only on material history (e.g. synthesis procedure, post-synthesis treatments). Furthermore, they may significantly change in situ (i.e. in the course of a physical or chemical process). It will be shown that such a dynamic change may have important implications for material performance.
In this contribution photoinduced hydrogen-doping of mesoporous anatase TiO2 films in different environments (gas phase, aqueous media) will be highlighted. The process is connected to the accumulation of photogenerated electrons in the semiconductor compensated by hydrogen uptake from the ambient. The transient charge accumulation improves the activity of the TiO2 films in the water photooxidation reaction. A spectroscopic approach was used to characterize the electronic states generated upon doping. The build-up of a broad signal in the MIR was observed upon electron accumulation and attributed to shallow (e-)(H+) traps [1,2].
 J. Idígoras et al., J. Phys. Chem. C, 2013, 117, 1561.
 D. A. Panayotov et al., J. Phys. Chem. C, 2011, 115, 22400.
FE-2:IL06 On the Mechanism of the Photoactivity under Visible Light of N-doped Titanium Dioxide and Analogous Systems (third generation photoactive systems)
E. GIAMELLO, Dipartimento di Chimica, Università di Torino, Torino, Italy
The generation of surface charge carriers in N-doped TiO2 has been investigated by electron paramagnetic resonance (EPR) by scavenging surface migrated carriers using oxygen and hydrogen as scavengers for electrons and holes respectively. N-doped TiO2, which is moderately active in photocatalytic processes under visible light, forms surface electrons and, at lower extent, surface holes due to the synergistic effect of visible components (around 400 nm) and near-infrared ones. The visible radiation excites electrons from intra band gap NOx− states to the conduction band, while NIR frequencies excite electrons from the valence band to the NOx− centers.The limited concentration of such centers explains the moderate efficiency of the whole process and, consequently, of the photocatalytic activity of N-TiO2 in visible light with respect to the case of UV light irradiation. In the second part of the talk preliminary results showing the photoactivation in visible light of a wide band gap oxide (zirconium dioxide, band gap of about 5 eV) will be illustrated indicating that it is possible to go beyond the classic TiO2 and modified TiO2 systems in the search of new efficient (third generation) photoactive oxide systems.
FE-2:IL07 Bimetallic PdxPt1-x/TiO2 Photocatalysts for Enhanced Simultaneous Removal of CO and VOC in the Presence of Humidity: Structural and Electronic Effects
O. ROSSELER1, A. LOUVET2, V. KELLER1, N. KELLER1, 1Institut de Chimie et Procédés pour l’Energie, l’Environnement et la Santé (ICPEES), CNRS, University of Strasbourg, France; 2Direction Générale de L’Armement (DGA), DGA CBRN Expertise, Vert-le-Petit, France
Compared to works on the removal of VOCs, few articles deal with room temperature CO photo-oxidation, although this topic gained increasing interest for applications such as indoor air treatment. It is thus of interest to develop photocatalysts able to oxidize CO efficiently in presence of other atmospheric pollutants. Unfortunately, bare TiO2 as well as Metal/TiO2 photocatalysts cannot maintain a high efficiency in both CO and VOC removal in humid conditions (20-80%) in multi-pollutant applications.
Here we point out that the negative effect of humidity on CO photooxidation is overcome by tuning the composition of Pd–Pt bimetallic particles supported on TiO2. By contrast to single metal/TiO2 and bare TiO2 that showed poor efficiencies, optimized statistically mixed bimetallic Pd0.5Pt0.5/TiO2 is a very efficient photocatalytic material for CO photooxidation in presence of humidity. It is also efficient for simultaneously removing CO and acetone – taken as model VOC – in presence of humidity, so that it is a promising photocatalyst for real indoor air treatment.
Complementary XPS, H2-TPR, CO-TPD, CO-FTIR, HRTEM and HAADF-STEM analyses coupled to HAADF-STEM PdxPt1-x/TiO2 simulated image computations are presented for 0
FE-2:IL08 Resonant Light Trapping in Iron Oxide (Fe2O3) Ultrathin Film Photoanodes for Solar Powered Water Photoelectrolysis
H. DOTAN, A. ROTHSCHILD, Department of Materials Science and Engineering Technion - Israel Institute of Technology, Haifa, Israel
Iron oxide (Fe2O3) is one of few materials meeting the requirements for stable photoanodes for solar powered water photoelectrolysis, but its poor transport properties present challenges for efficient charge-carrier generation, separation, collection and injection. We explore an innovative solution to these challenges by means of resonant light trapping in ultrathin films designed as optical cavities. Resonant interference between forward- and backward-propagating waves enhances the light absorption in quarter-wave or, in some cases, deeper subwavelength films, amplifying the intensity close to the surface wherein photogenerated minority charge carriers (holes) can reach the surface and oxidize water before recombination takes place. Combining this effect with photon retrapping using V-shaped structures provides efficient light harvesting in ultrathin films of high internal quantum efficiency, overcoming the intrinsic trade-off between light absorption and charge collection. Water photooxidation current density of 4 mA cm-2 was achieved using a V-shaped cell comprising 26-nm-thick Ti-doped Fe2O3 films on back-reflector substrates coated with silver-gold alloy (Nature Mater. 2013. This is an important step towards potentially affordable large scale production of solar hydrogen.
FE-2:L10 Photocatalytic Degradation Diesel of Soot: Unravelling the Reaction Mechanism
M. SMITS, S. LENAERTS, Laboratory for Sustainable Energy and Air Purification, Department of Bioscience-engineering, University of Antwerp, Antwerp, Belgium; YUN LING, S. VAN DOORSLAER, Department of Physics, University of Antwerp, Antwerp, Belgium
In this 'Year of Air' the detrimental effect of soot on human health and environment is highlighted. Chronic exposure to soot has detrimental effects on cardiovascular and respiratory diseases and increases the risk of lung cancer. Photocatalytic soot oxidation processes also contribute to slowing global warming in the immediate future.
Illuminated titanium dioxide is able to oxidise diesel soot if the contact time is sufficiently high. The photogeneration of oxidising OH radicals that are both surface mobile and capable of air-borne diffusion mediates the solid-phase photocatalytic oxidation of carbon soot. Nevertheless, the evidence that the oxidising species is an OH radical and the possible role of oxygen in this reaction is not straightforward.
The present study sheds light on the reaction mechanism of the photocatalytic soot oxidation on titanium dioxide. Electron paramagnetic resonance (EPR) spectroscopy allows distinguishing the different radicals and paramagnetic defects that play a role in the soot oxidation. The data unravel the role of oxygen and Ti3+ centres. The presence of oxygen is vital to initiate the photocatalytic process. In addition, the complete oxidation of soot to CO2 is proven by in-situ FTIR spectroscopy to unravel photocatalytic soot oxidation.
Session FE-3 - Design Approaches for Advanced Applications
FE-3:IL01 Nanocrystal Self-assembly as a Route to Atomically Coherent 2-D Semiconductor Superlattices with Dirac-type Charge Carriers
W.H. EVERS4, D. MITORAJ1, M. DIJKSTRA1, C. MORAIS-SMITH2, C. DELERUE3, E. KALESAKI3, D. VANMAEKELBERGH1, 1Debye Institute for Nanomaterials Science, University of Utrecht, The Netherlands; 2Institute for Theoretical Physics, Utrecht, The Netherlands; 3IEMN-ISEN and University of Lille, France; 4Kavli-Institute for Nanoscience, Delft University of Technology, The Netherlands
In this lecture, I will detail the self-assembly of PbSe nanocrystals (monodisperse truncated cubes) at the liquid air interface, and the remarkable structures that are the result of this.
Nanocrystal self-assembly is the only known route to prepare honeycomb lattices with a period far below 10 nm. In a recent collaboration, the electronic band structure of these systems was calculated with atomistic tight-binding. It is predicted that the band structure of CdSe (CdTe) zinc blende honeycomb structures show S-like and P-like Dirac cones, and hence massless Dirac electrons. Hence, we are developing a new class of 2-D semiconductors with all useful semiconductor properties, strong-spin orbit coupling and Dirac-type charge carriers. We also present the first results on the electronic density of states, obtained by scanning probe microscopy and spectroscopy.
Low-Dimensional Semiconductor Superlattices Formed by Geometric Control over Nanocrystal Attachment W. H. Evers, B. Goris, S. Bals, M. Casavola, J. de Graaf, R. v. Roij, M. Dijkstra, and D. Vanmaekelbergh Nano Letters 2013 doi: 10.1021/
FE-3:IL02 Development of Plasmonic Photocatalysts for Environmental Application
E. KOWALSKA, B. OHTANI, Catalysis Research Center, Hokkaido University, Sapporo, Japan; A. MARKOWSKA-SZCZUPAK, West Pomeranian University of Technology, Szczecin, Poland; L. ROSA, S. JUODKAZIS, Centre for Micro-Photonics, Swinburne University of Technology, Hawthorn, Australia
Regarding catalytic and plasmonic properties of gold nanoparticles (NPs), the novel area of research on photocatalytic gold properties has been recently started. In contrast with catalytically active gold NPs, where nano-sized gold is recommended, our results showed that polydispersity of deposited gold NPs on semiconducting support was beneficial for photocatalytic activity under visible light irradiation. It is thought that wide size/shape distribution of gold NPs, and thus the ability of absorption of light in a wide wavelengths range is responsible for the high level of photoactivity. The action spectrum analysis has proved that visible light-induced oxidation of organics by gold-modified titania is initiated by excitation of gold surface plasmon.
Plasmonic photocatalysts composed of titania and silver, gold or copper NPs have also showed high antiseptic properties under visible light irradiation, due to possible synergism between antiseptic properties of: i) photo-generated active oxygen species on the surface of semiconductor and ii) metal NPs in dark conditions and under irradiation (plasmonic heating).
FE-3:IL03 Photocatalytic Air Treatment of VOCs and Bioaerosols in Real Indoor Air Conditions
B. SANCHEZ1, M.C. CANELA2, S. SUÁREZ1, C.R. NUNES2, M. SÁNCHEZ, I. JANSSON1, 1CIEMAT-Photocatalytic Treatment of Pollutants in Air, Madrid, Spain; 2Environmental Chemistry Research Group - Universidade Estadual do Norte Fluminense. Campos dos Goytacazes, Brazil
The Indoor air quality (IAQ) is related in many cases with the presence of high levels of volatile organic compounds (VOCs) and various types of particles as bioaerosols (bacteria and fungi). On the basis of the ongoing study ENERCLEAN (Energy optimization of Indoor Air Quality) the characterization of the seasonal variability of Indoor VOCs has been performed. The main objective of the project is the design, construction, installation and testing in actual working conditions of a photocatalytic air treatment inside. This project has two main stages: To characterize the existing pollution and in a second phase characterize its degradation.
On the first phase sampling has been conducted over one year one week a month, three days a week, 24 hours per day for VOCs and every 2 hours between 9 and 19:00h for bioaerosols.
On the second phase a new system has been designed, constructed, installed and tested in a business office. The photocatalytic material applied as a coating on the surface of aluminum monoliths shaped as honeycomb has proven to be effective for treating many of the compounds detected.
A detailed description of the evolution of VOCs and bioaerosols from November 2011 to date and the efficiency of the photocatalytic device developed will be presented at CIMTEC2014.
FE-3:IL05 New Tandem Devices for Water Splitting
P.C.K. VESBORG1, B. SEGER1, T. PEDERSEN1, A.B. LAURSEN2, O. HANSEN1, I. CHORKENDORFF1, 1Technical University of Denmark, Kgs. Lyngby, Denmark; 2Rutgers, USA
In order to achieve overall photoelectrochemical water splitting there is in principle a substantial efficiency advantage to using a two-photon (tandem) approach over a single-photon approach - despite the fact that twice the number of photons are needed in the tandem case.
This is because the large voltage required to split water in practice make all but the violet and ultraviolet photons useless in the single-photon case whereas a tandem system may utilize even the red part of the solar spectrum.
Here we present recent progress made in the field of photocathodes for tandem water splitting. Based on highly oxidation-prone materials such as silicon, substantial improvements towards corrosion protection and electrocatalytic activity have been made. We also present advantages of an "inverted" approach where the high band-gap material is the cathode (instead of the standard approach where the high-gap material is the anode).
FE-3:IL06 Hybrid Materials with Organized Nanoscale Architecture for Solar Energy Applications
C. JANAKY, G.F. SAMU, K. RAJESHWAR, Dept. of Physical Chemistry and Materials Science, University of Szeged, Szeged, Hungary; Dept. Chemistry and Biochemistry, University of Texas at Arlington, Arlington, TX, USA
Conducting polymers can be employed as solid-state hole-transporter materials in dye-sensitized solar cells (DSSCs) using quantum dots (QDs) as sensitizer. To assemble these architectures, as the first step, electrochemical anodization is employed to synthesize interconnected oxide SCs (e.g. TiO2 nanotube arrays). As the second step, the sensitizer is anchored onto the oxide surface through hydrothermal synthesis. Finally, the CP component is in situ generated inside the decorated oxide nanostructure, using electrochemical and photoelectrochemical methods. These methods result in high pore-filling ratios, and in an intimate contact between the organic and inorganic components both at the physical and electronic levels which is likely to contribute to an improved solar cell performance.
As the second topic we present photoelectrochemical water oxidation on nanoporous WO3 films, decorated with RuO2 nanoparticles. The RuO2 electrocatalyst substantially increased photoanodic current flow through facile transfer of photogenerated holes from WO3 to the solution, thereby improving interfacial charge transfer kinetics. Through optimization of the composition of the hybrid material, the incident photon-to-charge carrier efficiency (IPCE) was increased close to the theoretical 100% limit.
FE-3:L08 Bio-organic Hybrid Photoconverters from Organic Dyes and a Bacterial Photoenzyme
G. FARINOLA1, 2, A. OPERAMOLLA1, O. HASSAN OMAR2, F. MILANO3, R.R. TANGORRA1, R. RAGNI1, S. LA GATTA1, A. AGOSTIANO1, 3, M. TROTTA3, 1Dipartimento di Chimica Università degli Studi di Bari Aldo Moro, Bari, Italy; 2CNR ICCOM Bari, Bari, Italy; 3CNR IPCF Bari, Bari, Italy
The Reaction Centers (RCs) of photosynthetic organisms are efficient billion-of-years optimized photoenzymes for conversion of absorbed light into charge separated states. Combination of such effective photoenzymes with p-conjugated molecules appears an intriguing strategy to obtain a new generation of versatile hybrid bio-electronic materials for application ranging from photoconversion to photocatalysis and sensing.
We present here the design and synthesis of hybrid bio-organic photosynthetic complexes by combination of the Reaction Center (RC) of the photosynthetic bacterium Rhodobacter sphaeroides R26 with tailored molecular semiconductors. The organic molecules can act as antennas to extend the light harvesting capability of the RC, thus enhancing its photoconversion performances , but can be also used for charge transfer processes to external electron acceptors.
We have developed protocols that enable to obtain tailored bio-organic complexes, exhibiting optimized interactions of the functional light absorbing molecules with the RC. We also demonstrate that such hybrid architectures can be incorporated in the functional membrane of tailored polymersomes, still maintaining their full functionality, or even be anchored on electrodes surfaces.
 F. Milano, R.R. Tangorra, O. Hassan Omar, R. Ragni, A. Operamolla, A. Agostiano, G.M. Farinola, M. Trotta Angew. Chem. Int. Ed. 51, 11019 (2012)
FE-3:L09 Development of Self-supporting TiO2 Foams
T. TYTGAT, S. LENAERTS, Dept. of Bio-science Engineering, University Antwerp, Antwerp, Belgium
The number of real life photocatalytic applications is limited because several disadvantages remain unsolved. An important problem is the immobilisation of the catalyst. The release of nanoparticles needs to be limited because they can be harmful to humans and the environment.
A protocol to produce self-supporting TiO2 foam was adapted to increase activity, rigidity and porosity. To improve the rigidity, the calcination temperature of the material was altered, resulting in materials with an increased strength. Next the effect of acidity on the foam structure was studied. When adding a base to the synthesis protocol, the structure of the foam was altered with important impact on porosity and therefore activity. The photocatalytic activity was determined and a relation between activity and density was found.
Finally several foams were selected and tested in a continuous gas phase system. The activity in a flow-through experiment was unsatisfying therefore the tests were repeated in a recirculating system. In this case, optimal degradation was observed for the foam with the highest surface area but with a low rigidity.
FE-3:L11 Degradation of Pesticides, Dye Molecules and Relevant Surface Interactions with Mesoporous Titania
M. MEIRE, P. LOMMENS, I. VAN DRIESSCHE, SCRiPTS, Department of Inorganic and Physical Chemistry, Ghent University, Ghent, Belgium; I. ASCOOP, P. VAN DER VOORT, COMOC, Department of Inorganic and Physical Chemistry, Ghent University, Ghent, Belgium
Titania is the most widely studied and applied material for photocatalytic applications. Enhancing the surface area of a titania catalyst could significantly increase its activity as photocatalytic reactions typically proceed on or near the surface of the material.
In this report, mesoporous titania is used in water purification applications. The photocatalytic activity of different mesoporous TiO2 samples obtained from various synthesis approaches is tested by following the degradation of methylene blue and some highly mobile pesticides present in surface waters under UV illumination. Not only the specific surface area of the samples determines their efficiency, also the crystallinity and chemical nature of their surface are crucial. Therefore, we use Rietveld analysis to determine the crystallinity of the samples. IR spectroscopy reveals that titanol groups present on the surface play an important role in the activity of the material. This means that to further enhance the activity of the material, a lot of attention needs to be paid to the surface of TiO2 and the interactions of the organic pollutants and the surface of mesoporous titania. In the case of the degradation of the pesticides, the intermediate species are determined to make sure no toxic species are obtained.
FE-3:IL12 The Photocatalytic Properties of Gypsum Plaster Containing Co-modified TiO2-N,C and its Application in Synthetic Dye Removal
M. JANUS1, E. KUSIAK-NEJMAN2, K. BUBACZ2, A. CZYZEWSKI2, J. ZATORSKA2, A.W. MORAWSKI2, 1West Pomerania University of Technology, Department of Sanitary Engineering, Szczecin, Poland; 2West Pomerania University of Technology, Szczecin, Institute of Chemical and Environmental Engineering, Szczecin, Poland
Titanium dioxide was modified by nitrogen and carbon at 100 °C for 1.5 h. The source of nitrogen and carbon in the co-modified TiO2 was ammonia gas and ethanol. The prepared photocatalyst (TiO2-N,C) has been used as an additive in gypsum, in order to benefit photocatalytic activity of the building material. Starting TiO2 was supplied from the Chemical Factory "POLICE" S.A., Poland.
The modified photocatalyst and two reference materials (commercial Evonik P 25 and starting TiO2) were mechanically mixed with gypsum in 10% weight ratio. The photocatalytic properties of the gypsum plasters were studied through the photooxidation of Reactive Red 198 dye. The rate of degradation was determined by UV-Vis/DR spectroscopy and the obtained results will be presented. The highest rate of dye photocatalytic degradation (92% after 10 h of UV irradiation) was observed for gypsum plaster with modified TiO2-N,C photocatalyst. It was determined that the addition of co-modified TiO2-N,C to gypsum plaster has noticeably enhanced its photocatalytic properties. It ought to be stated that the gypsum plaster with commercial P25 revealed significantly lower removal rate of RR 198 (54.5%) than the prepared one.
Acknowledgement: Project was founded by The National Centre for Research and Development.
FE-3:IL14 Photocatalytic Materials Based on F-doped or codoped TiO2
M.V. DOZZI, E. SELLI, Department of Chemistry, University of Milan, Milano, Italy; B. Ohtani, Catalysis Research Center, Hokkaido University, Sapporo, Japan
The photocatalytic activity of an extended series of singly doped or co-doped TiO2 photocatalysts prepared by the sol-gel method starting from different amounts of N, F, S and B dopants and calcined at different temperatures in the 500-700 °C range, was investigated, also as a function of the irradiation wavelength, in both thermodynamically down-hill reactions (formic and acetic acid degradation in aqueous suspension, gas phase mineralization of acetaldehyde) and up-hill reactions for solar fuels production (H2 production from methanol-water vapor mixtures). By comparing the absorption spectra of the materials with their action spectra in acetic acid oxidation, inactive light absorption, i.e. not leading to any photocatalytic reaction, could be clearly distinguished from effective photoactivity. An in depth HRTEM analysis provided novel information on the peculiar effects that fluorine doping has on the bulk structure of these materials. Time resolved photo-luminescence (PL) analysis in the pico-second range revealed that both PL spectral shapes and lifetimes are strongly affected by the presence of dopants and by the calcination temperature, and that a correlation exists between the longer-living luminescence component and the photocatalytic activity of the materials.
FE:P02 Hydrothermal Synthesis and Photocatalytic Properties of Pyrochlore Sm2Zr2O7 Nanoparticles
HAIBO JIN, JINGBO LI, PENGWAN CHEN; WENBIN CAO, School of Materials Science and Engineering, Beijing Institute of Technology; School of Materials Science and Engineering, University of Science & Technology Beijing, China
Pyrochlore Sm2Zr2O7 nanoparticles were synthesized by a facile hydrothermal method and their photocatalytic properties were investigated. The effects of pH value, hydrothermal temperature and reaction time on the structures and morphologies of the resultant products were investigated. An optimum hydrothermal process was proposed based on the investigations and pyrochlore Sm2Zr2O7 nanoparticles with an average size less than 18 nm was successfully obtained. The investigations showed that the structural stability of Sm2Zr2O7 nanoparticles depended on the crystallite size. The nanoparticles with the size larger than 10 nm have the pyrochlore structure, however, the less-size nanoparticles are fluorite. The absorption spectrum of the Sm2Zr2O7 nanoparticles evidenced the existence of an absorption edge in the visible-light range, indicating the possibility of visible-light photocatalytic activity of Sm2Zr2O7 nanoparticles. The observation of photodegradation of congo red organic dye revealed excellent photocatalytic activity of the nanosize Sm2Zr2O7 particles.
FE:P04 AAO as the Support for Titania Photocatalysts
M. STODOLNY, K. DYBA, M. LANIECKI, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland
Nanostructured materials opened a new chapter in many areas of science including the photocatalysis. The new nanomaterials are more active than their classical equivalents. This is a result of better utilization of the adsorption energy and better efficiency in charge separation and the electrons transport. Unfortunately, the method allowing for the synthesis of the nanomaterials in a highly controlled way are not widely available. In consequence the need for sophisticated synthetic and measuring apparatus significantly increases the costs. The hard template technique can be a solution. One of these templates may be the anodic aluminum oxide. The AAO is relatively easy to obtain with tailored parameters. Therefore, this material was used in this study as a template for supporting photoactive catalyst in the form of structured TiO2. The spin coating, deep coating and electro-deposition techniques were used in order to deposit titania onto aluminia. The obtained materials were tested to determine the structure(XRD, ASAP, SEM) and energy levels (UV-Vis). Photocatalytic activity was tested in the water splitting reaction in presence of a sacrificial agent. The best results concerning the structure and photocatalytic activity (hydrogen) were obtained for electrodeposited samples.
FE:P08 Influence of SiO2 Thin Films on Optical Properties and Conversion Efficiency of ITO Based Thin Films for Photovoltaic Applications
JONG SU WOO, GUN EIK JANG, Department of Materials Engineering, Chungbuk National University, Cheongju, Korea
For the purpose of increasing the transparence in dye-sensitized solar cell(DSSC)’s conductive films, indium tin oxide(ITO) thin films with composition of 10wt% SnO2 and 90wt% In2O3 were deposited by DC magnetron sputtering on SiO2 coated glass substrates. Then SiO2 blocking layers were deposited on the SiO2/ITO coated glasses. The properties of multi-layered films [SiO2/ITO/SiO2/glass] prepared at a substrate temperature of 300℃ were systematically analyzed by X-ray diffraction, atomic force microscopy, and optical and electrical measurement. From the XRD result, the ITO film exhibited a crystalline phase with (400) and (222) preferred orientation at 2θ = 30.4° and 2θ = 35.3° respectively. Compared with single layer ITO film, the multi-layered films increased up to 8% in optical transmittance. The Photocurrent-voltage (I-V) characteristics of the DSSCs were measured under AM 1.5, 100mW/cm2 (1 sun) using a solar simulator.
FE:P09 16c Substituted CsTaWO6: The Influence of Different d0 Metal-Ions on the Photocatalytic Activity of Mixed Oxides with the Defect-Pyrochlore Structure
L. SCHWERTMANN1, R. MARSCHALL2, M. WARK3, 1Laboratory of Industrial Chemistry, Ruhr-University Bochum, Bochum, Germany; 2Justus-Liebig-University Giessen, Giessen, Germany; 3Institute for Chemistry, Carl von Ossietzky University Oldenburg, Oldenburg, Germany
CsTaWO6 is a photocatalyst of high potential for H2 generation with vis-light. This material exhibits a defect-pyrochlore structure and a band gap (Eg) of 3.6 eV. The rigid but open 3-D framework, which consists of corner-sharing TaO6- and WO6-octahedra, is considered to be a pre-condition for high photocatalytic activity . The resulting channels are well suited for homogeneous doping reactions as shown by Marschall et al.. The N- and/or S-doped materials (reduced Eg), are able to generate H2 in the range of vis-light without using a co-catalyst. To get a better understanding of the material, the metal-ions on 16c position were systematically changed. Other d0 metal-ions from the same period were chosen in order to investigate the influence of each element on photocatalytic activity (substituting Nb for Ta, and Mo for W). Due to changes of the band structure by introducing Mo, photoexcited e- in the CB of CsTaMoO6 are no longer able to reduce H+ or to break down pollutants via O2-. formation. However, the Eg is reduced compared to CsTaWO6, thus the ability to generate O2 in vis-light was investigated.
 L. Schwertmann et al., RSC Adv., (2013), 3, 18908.
 R. Abe et al., J. Phys. Chem., (2006), 110, 2219.
 R. Marschall et al., J. Mater. Chem., (2011), 21, 887
FE:P12 Mechanism of Li-storage in TiO2 (B) and TiO2 (anatase)
M. ZUKALOVA, B. LASKOVA, A. ZUKAL, M. BOUSA, L. KAVAN, J. Heyrovsky Institute of Physical Chemistry of the ASCR, v. v. i., Prague, Czech Republic
TiO2 (B) is metastable modification of titanium dioxide, adopting the monoclinic structure. Zukalova et al. found that Li-insertion into TiO2 (B) is characterized by unusually large faradaic pseudocapacitance. This peculiar effect was ascribed to Li-accommodation in open channels of TiO2 (B) structure allowing fast Li-transport in TiO2 (B) lattice along the b axis (perpendicular to (010) face). Analysis of cyclic voltammograms of Li insertion into TiO2 (B) and anatase provides information about capacitive contributions to overall charge of Li-storage. The enhancement of 30% is found in capacitive contributions (normalized to the total stored charges) in TiO2 (B) compared to that in anatase, in spite of ca. three times smaller surface area of the former. Different charging mechanism explains facilitated Li- insertion in TiO2 (B). The difference is caused mainly by pseudocapacitive Li-storage in the bulk TiO2 (B). Deconvolution of cyclic voltammograms also indicates different capacitive contributions of the two voltammetric peaks, S1 and S2 of TiO2 (B). These results provide novel insight into the Li-storage in TiO2 (B) and its difference from that in anatase.
This work was supported by the Grant Agency of the Czech Republic (contracts No. 13-07724S and P108/12/0814).