Anatase Polymorph Research Articles

Photocatalytic Performance of Highly Active Brookite in the Degradation of Hazardous Organic Compounds Compared to Anatase and Rutile

The photocatalytic activity of brookite was studied and compared with anatase, rutile, and commercial titania P25 (Degussa). Brookite exhibited relatively high activity in the degradation of different hazardous compounds under sunlight equivalent conditions. Brookite and other titania polymorphs anatase and rutile were hydrothermally synthesized under the similar reaction conditions starting with the same amorphous titania precursor. The highly crystalline titania polymorphs were characterized by XRD, SEM, TG-DSC, Raman- and diffuse reflectance UV–vis spectroscopy. Brookite (B) and anatase (A) crystallized in form of agglomerated spherical-shaped nanoparticles of ca. 10nm in size. Rutile (R) formed up to 500nm large rod-like nanocrystals. The band gaps of the titania polymorphs were about 3.25–3.34eV. The aromatic ring opening in different hazardous compounds was monitored by UV–vis absorption spectroscopy and the mineralization was determined by total organic carbon (TOC) measurements. Additionally, the formation of intermediates was studied by electrospray ionization time-of-flight mass spectra (ESI-TOF-MS). The recalcitrance of organic compounds against the photocatalytic degradation increases in the following order: cinnamic acid<ibuprofen<phenol. The general order of photocatalytic activity was B≈A>R.

Effect of silica/titania ratio on enhanced photooxidation of industrial hazardous materials by microwave treated mesoporous SBA-15/TiO2 nanocomposites

In this study microwave assisted technique has been adopted for the synthesis of different weight ratios of TiO2 dispersed on Santa barbara amorphous-15 (SBA-15) support. Morphological study revealed TiO2 particles (4–10 nm) uniformly distributed on SBA-15 while increases in SBA-15 content results in higher specific surface area (524–237 m2/g). The diffraction intensity of 101 plane of anatase polymorph was seen increasing with increase in TiO2 ratio. All the photocatalysts were having a mesoporous nature and follow the Langmuir IV isotherm, SBA-15 posses the highest pore volume (0.93 cm3 g−1) which consistently decreased with TiO2 content and was lowest (0.50 cm3 g−1) in case of 5 wt% of TiO2 followed by P25 (0.45 cm3 g−1) while pore diameter increased after TiO2 incorporation due to pore strain. The photocatalytic activity of the nanocomposites were analysed for the photodegradation of alizarin dye and pentachlorophenol under UV light irradiation. The reaction kinetics suggested the highest efficiency (98 % for alizarin and 94 % for PCP) of 5 wt% TiO2 compared to other photocatalysts, these nanocomposites were reused for several cycles, which is most important for heterogeneous photocatalytic degradation reaction. This study demonstrates the synthesis of silica embedded TiO2 nanocomposites by microwave assisted technique and their catalytic influence on degradation of organic dyes and pollutants. Higher loading of titania (SBA-15/TiO2, 1:5) results better catalytic performance than commercial nano TiO2 (P25).

Electronic properties of atomic layer deposition films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy

The TiO2 films are prepared by atomic layer deposition (ALD) method using titanium isopropoxide precursors at 250 °C and analyzed using resonant photoemission spectroscopy (resPES). We report on the Ti2p and O1s core levels, on the valence band (VB) spectra and x-ray absorption spectroscopy (XAS) data, and on the resonant photoelectron spectroscopy (resPES) profiles at the O1s and the Ti3p absorption edges. We determine the elemental abundance, the position of the VB maxima, the partial density of states (PDOS) in the VB and in the conduction band (CB) and collect these data in a band scheme. In addition, we analyze the band-gap states as well as the intrinsic states due to polarons and charge-transfer excitations. These states are found to cause multiple Auger decay processes upon resonant excitation. We identify several of these processes and determine their relative contribution to the Auger signal quantitatively. As our resPES data allow a quantitative analysis of these defect states, we determine the relative abundance of the PDOS in the VB and in CB and also the charge neutrality level.The anatase and rutile polymorphs of TiO2 are analyzed in the same way as the TiO2 ALD layer. The electronic properties of the TiO2 ALD layer are compared with the anatase and rutile polymorphs of TiO2. In our comparative study, we find that ALD has its own characteristic electronic structure that is distinct from that of anatase and rutile. However, many details of the electronic structure are comparable and we benefit from our spectroscopic data and our careful analysis to find these differences. These can be attributed to a stronger hybridization of the O2p and Ti3d4s states for the ALD films when compared to the anatase and rutile polymorphs.

Computational Approach for Epitaxial Polymorph Stabilization through Substrate Selection.

With the ultimate goal of finding new polymorphs through targeted synthesis conditions and techniques, we outline a computational framework to select optimal substrates for epitaxial growth using first principle calculations of formation energies, elastic strain energy, and topological information. To demonstrate the approach, we study the stabilization of metastable VO2 compounds which provides a rich chemical and structural polymorph space. We find that common polymorph statistics, lattice matching, and energy above hull considerations recommends homostructural growth on TiO2 substrates, where the VO2 brookite phase would be preferentially grown on the a-c TiO2 brookite plane while the columbite and anatase structures favor the a-b plane on the respective TiO2 phases. Overall, we find that a model which incorporates a geometric unit cell area matching between the substrate and the target film as well as the resulting strain energy density of the film provide qualitative agreement with experimental observations for the heterostructural growth of known VO2 polymorphs: rutile, A and B phases. The minimal interfacial geometry matching and estimated strain energy criteria provide several suggestions for substrates and substrate-film orientations for the heterostructural growth of the hitherto hypothetical anatase, brookite, and columbite polymorphs. These criteria serve as a preliminary guidance for the experimental efforts stabilizing new materials and/or polymorphs through epitaxy. The current screening algorithm is being integrated within the Materials Project online framework and data and hence publicly available.

Asymmetric and symmetric absorption peaks observed in infrared spectra of CO2 adsorbed on TiO2 nanotubes.

Infrared spectra of CO2 physisorbed on titania nanotubes (TiNTs), predominantly in the anatase polymorph, were measured at 81 K. Asymmetric and symmetric absorption peaks due to the antisymmetric stretch vibration (ν3) of CO2 were observed at 2340 cm(-1) and 2350 cm(-1), respectively. On the basis of the exposure- and time-dependence of the spectrum, the 2340 cm(-1) peak was attributed to CO2 at the defective sites related to subsurface O vacancies (Vos) while the 2350 cm(-1) peak was assigned to that at the fivefold coordinated Ti(4+) sites. It was found that the generalized Fano line shape was well fitted to the 2340 cm(-1) peak. We also observed an absorption peak at 2372 cm(-1), which was attributed to the combination band of ν3 and the external mode of CO2 at Ti(4+).

Low temperature synthesis of N-doped TiO2 with rice-like morphology through peroxo assisted hydrothermal route: Materials characterization and photocatalytic properties

Nanorice-shaped N:TiO2 photocatalysts have been prepared by the peroxo assisted hydrothermal method using stabilized titanium complex as a precursor and urea as a N source. The N:TiO2 nanorices were characterised by XRD, FE-SEM, HRTEM, XPS, UV–vis spectroscopy, Raman spectroscopy and measurements of photocatalytic degradation of organic molecules (atrazine and RhB dye) under the UV and visible-light irradiation. XRD analyses showed that pristine TiO2 crystallizes into anatase polymorph and that the N-doping process at 5% introduced a degree of disorder on the TiO2 crystalline structure. XPS study revealed the successful incorporation of the nitrogen atoms at the interstitial sites of the TiO2 crystal lattice. Microscopy studies revealed that the particle size was in the range 50–80nm for the pristine TiO2. The photocatalysts were assembled in the form of nanorices with a high surface area (102m2g−1). The successful incorporation of nitrogen atoms into the TiO2 crystal lattice is expected to be responsible for enhanced photocatalytic activity of the as-prepared samples for the degradation of pollutants (RhB and atrazine) under UV and visible light irradiation. The rate of OH radicals formation under visible-light irradiation was examined and found to be correlated with the photocatalytic activity per unit surface area. The N:TiO2 particles with nanorice morphology was efficient photocatalysts for decomposition of organic dyes under UV and visible-light exposure while pristine TiO2 photocatalyst did not show any significant photocatalytic activity when stimulated by visible-light. The 3% doped N:TiO2 sample exhibited the highest photocatalytic activity among all synthesized photocatalysts.

Role of surface water molecules in stabilizing trapped hole centres in titanium dioxide (anatase) as monitored by electron paramagnetic resonance

Abstract A key factor affecting the photo-efficiency of TiO2 is strictly related to the fate of charge carriers, electrons (e−) and holes (h+), generated upon band gap excitation. In the present paper we point our attention to the nature of the hole trapping sites in the anatase polymorph monitored coupling the conventional continuous wave EPR (CW-EPR) technique with pulse electron nuclear double resonance (ENDOR) experiments. The attention is focused on the role of surface adsorbed water (both in molecular and in dissociated form) in the stabilization of photogenerated hole centres. CW-EPR results indicate that two distinct O − hole centres can be identified in Anatase (O −surf. and O −subsurf.) and that the quantitative ratio (measured in terms of spectral intensity) of these two species is markedly conditioned by the presence of surface physisorbed water. For the first time a h+-proton distance, evaluated via ENDOR measurement, is reported.

Crystalline structure and morphology of TiO2 thin films deposited by means of hollow cathode plasma jet with supporting anode

TiO2 thin films with developed structure were deposited by means of a hollow cathode plasma jet (HCPJ) in a DC regime with a supporting anode. The influence of the plasma temperature on the surface morphology and crystalline structure of the thin films under different deposition conditions was studied. Diagnostics of the thin films structure was carried out using XRD, SEM, EDX and TEM methods. One batch of samples was annealed at a temperature of 400 °C in atmospheric conditions as a comparison with the crystalline structure and morphology of unannealed samples. The presence of two crystalline polymorphs of rutile and anatase in the films was discussed. The vacuum system was improved for an extended deposition of non-conductive materials without terminating the discharge and cleaning of the deposition chamber. The aim of this investigation was to prepare the vacuum system for the fabrication of photo electrodes which are the main functional part in dye-sensitized solar cells. The test DSSCs (dye-sensitized solar cells) were prepared from low-cost materials (raspberry/hibiscus natural dye-sensitizers and candle soot counter electrode) in order to check the quality of the films, with a highest conversion efficiency η = 0.66% and a fill factor FF = 62%.

Optimization and Characterization of Anatase Formed on Anodized Titanium in Phosphoric Acid

Titanium (Ti) is widely used in dental and orthopedic implants because of its good biocombatibility and high corrosion resistance. Titanium oxide (TiO2) has shown to exhibit strong physicochemical bonding between Ti implant and living bone because of its ability to induce bone-like apatite in a body environment. Ti is always coated by an oxide surface layer of 1.5-10 nm thickness. TiO2 crystalline structures; anatase and rutile present several distinctive features, such as photocatalytic behaviour, superhydrophilicity and biocompatible properties. Anodic oxidation is used to modify the surface of pure titanium in a phosphuric acid electrolyte in order to maximize and characterize the TiO2 anatase crystalline phase. In the present work, thick films of the anatase polymorph of TiO2 were formed on commercially pure Ti foil under potentials 200 V-350 V at current densities 40 and 60 mA/cm2 for 10 min. Multiple characterization techniques were used. Glancing angle X-ray diffraction (GAXRD) is used to obtain crystalline phases, field emission scanning electron microscope (FESEM) is used to obtain surface images and water contact angle (WCA) is used to obtain the wettability of the oxide surface. According to GAXRD results the intensity of the major peak increased with increasing applied voltage and current density while decrease with molar concentration. This means that the amount and/or crystallinity of anatase are/is influenced with these parameters. The coated oxides obtained small amount of anatase is comparing to films anodized in H2SO4 electrolyte. Which confirm that slower crystallization in H3PO4 than in H2SO4. FESEM images obtained that as the voltage increased, the film breaks down locally and results in a porous surface. The porosity and the pore size increase with the increasing voltage. The pore size diameter at 300V for 0.3 M can reach up to 1μm. As for WCA results the coated samples at higher voltages (250 V, 300 V and 350 V) and molar concentration 0.3 M have shown more hydrophilic surface, with sample anodized at 350 V at 0.3 M have the lowest contact angle, thus the highest surface energy. While samples anodized at 200 V voltage observed more hydrophobic surface with sample anodized at 200 V at 0.1 M have the lower wettability, thus the lowest surface energy.

Photocatalytic Nb2O5-doped TiO2 nanoparticles for glazed ceramic tiles

TiO2 nanoparticles are currently used as coating for self-cleaning building products. In order to achieve high self-cleaning efficiency for outdoor applications, it is important that titania is present as anatase phase. Moreover, it is desirable that the particle sizes are in nano-range, so that a large enough surface area is available for enhanced catalytic performance. In this work, TiO2 nanoparticles doped with 0–5mol% Nb2O5 were synthesized by co-precipitation. Nb2O5 postponed the anatase to rutile transformation of TiO2 by about 200°C, such that after calcination at 700°C, no rutile was detected for 5mol% Nb2O5-doped TiO2, while undoped TiO2 presented 90wt% of the rutile phase. A systematic decreasing on crystallite size and increasing on specific surface area of TiO2 were observed with higher concentration of Nb2O5 dopant. Photocatalytic activity of anatase polymorph was measured by the decomposition rate of methylene blue under ultraviolet and daylight illumination and compared to commercial standard catalyst (P25). The results showed enhanced catalysis under UV and visible light for Nb2O5-doped TiO2 as compared to pure TiO2. In addition, 5mol% Nb2O5-doped TiO2 presented higher photocatalytic activity than P25 under visible light. The enhanced performance was attributed to surface chemistry change associated with a slight shift in the band gap.

Influence of substrate temperature and silver-doping on the structural and optical properties of TiO2 films

Evaporation of titanium together with activated oxygen is used to grow TiO2 films and simultaneously with silver to grow Ag–TiO2 films (5at.% Ag) onto sapphire substrates at three different substrate temperatures: −190, 30, and 200°C. The obtained films were characterized by X-ray powder diffraction, Raman, X-ray photoelectron, ultraviolet–visible spectroscopy, and transmission electron microscope investigations. The properties of TiO2 films varied with the substrate temperature. Amorphous, transparent TiO2 films were grown at −190°C and opaque, polycrystalline films at 200°C, respectively. Surprisingly, at room temperature black, amorphous TiO2 films are obtained which transform at 350°C into a mixture of the anatase and brookite polymorph. In the amorphous state of the TiO2 films a predefined rutile arrangement is suggested by Raman investigations, and the contraction of the lattice constant c of anatase phases (tetragonal, space group I 41/amd) depending on the substrate temperature is experimentally observed. The silver-doped TiO2 films deposited at −190 and 30°C contain Ag-particles with 2nm in size inside the TiO2 matrix, which after annealing segregate under increasing particle sizes. The silver-doping stabilizes the anatase polymorph and yields to reduced titanium species in the films especially during deposition at 30°C. The Ag–TiO2 films deposited at −190°C are transparent up to 350°C. In the undoped as well as silver-doped TiO2 films the rutile polymorph is directly formed at 200°C as main phase.

Synthesis of Lithium Titanate (Li4Ti5O12) through Hydrothermal Process by using Lithium Hydroxide (LiOH) and Titanium Dioxide (TiO2) Xerogel

Lithium Titanate (Li4Ti5O12) or (LTO) has a potential as an anode material for a high performance lithium ion battery. In this work, LTO was synthesized by a hydrothermal method using Titanium Dioxide (TiO2) xerogel prepared by a sol-gel method and Lithium Hydroxide (LiOH). The sol-gel process was used to synthesize TiO2 xerogel from a titanium tetra-nbutoxide/Ti(OC4H9)4 precursor. An anatase polymorph was obtained by calcining the TiO2 xerogel at a low temperature, i.e.: 300 o C and then the hydrothermal reaction was undertaken with 5M LiOH aqueous solution in a hydrothermal process at 135 o C for 15 hours to form Li4Ti5O12. The sintering process was conducted at a temperature range varying from 550 o C, 650 o C, and 750 o C, respectively to determine the optimum characteristics of Li4Ti5O12. The characterization was based on Scanning Thermal Analysis (STA), X-ray Powder Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) testing results. The highest intensity of XRD peaks and FTIR spectra of the LTO were found at the highest sintering temperature (750 o C). As a trade-off, however, the obtained LTO/Li4Ti5O12 possesses the smallest BET surface area (< 0.001 m 2 /g) with the highest crystallite size (56.45 nm).

Stable Co‐Catalyst‐Free Photocatalytic H2 Evolution From Oxidized Titanium Nitride Nanopowders

AbstractA simple strategy is used to thermally oxidize TiN nanopowder (∼20 nm) to an anatase phase of a TiO2:Ti3+:N compound. In contrast to the rutile phase of such a compound, this photocatalyst provides activity for hydrogen evolution under AM1.5 conditions, without the use of any noble metal co‐catalyst. Moreover the photocatalyst is active and stable over extended periods of time (tested for 4 months). Importantly, to achieve successful conversion to the active anatase polymorph, sufficiently small starting particles of TiN are needed. The key factor for catalysis is the stabilization of the co‐catalytically active Ti3+ species against oxidation by nitrogen present in the starting material.

Optimization and Characterization of Anatase Formed on Anodized Titanium in Sulfuric Acid

Titanium (Ti) is widely used in dental and orthopedic implants because of its good biocombatibility and high corrosion resistance. Titanium oxide (TiO2) has shown to exhibit strong physicochemical bonding between Ti implant and living bone because of its ability to induce bone-like apatite in a body environment. Ti is always coated by an oxide surface layer of 1.5-10 nm thickness. TiO2 crystalline structures; anatase and rutile present several distinctive features, such as photocatalytic behaviour, superhydrophilicity and biocompatible properties. Anodic oxidation is used to modify the surface of pure titanium in a sulphuric acid electrolyte in order to maximize and characterize the TiO2 anatase crystalline phase. In the present work, thick films of the anatase polymorph of TiO2 were formed on commercially pure Ti foil under potentials 100V-140V at current densities 40 and 60 mA/cm2 for 10 min. Multiple characterisation techniques were used and found that the maximum level of significantly formed anatase intensity where no significant rutile formation is observed at potential 140 V according to Glancing angle X-ray diffraction (GAXRD). Field Emission Scanning Electron Microscope (FESEM) images have shown porous surfaces as the applied voltage increased. Water contact angle (WCA) values observed hydrophilicity on the coated surfaces with samples anodized at 120 V have the highest wettability.

Stable Co-Catalyst-Free Photocatalytic H2 Evolution From Oxidized Titanium Nitride Nanopowders.

A simple strategy is used to thermally oxidize TiN nanopowder (∼20 nm) to an anatase phase of a TiO2:Ti(3+):N compound. In contrast to the rutile phase of such a compound, this photocatalyst provides activity for hydrogen evolution under AM1.5 conditions, without the use of any noble metal co-catalyst. Moreover the photocatalyst is active and stable over extended periods of time (tested for 4 months). Importantly, to achieve successful conversion to the active anatase polymorph, sufficiently small starting particles of TiN are needed. The key factor for catalysis is the stabilization of the co-catalytically active Ti(3+) species against oxidation by nitrogen present in the starting material.

Simple synthesis of anatase/rutile/brookite TiO2 nanocomposite with superior mineralization potential for photocatalytic degradation of water pollutants

In this study, we report a simple synthesis procedure of anatase/rutile/brookite TiO2 nanocomposite material, designed for efficient transformation of emerging water pollutants (e.g., bisphenol (A)) to CO2 and H2O as final products of complete photo-oxidation. Sol–gel procedure with a subsequent hydrothermal treatment carried out at mild temperature and in the presence of 3M HCl led to the formation of TiO2 nanomaterial, which consists of anatase (43%), rutile (24%) and brookite (33%) polymorph phases within the same material. For the purpose of efficient evaluation of nanocomposite activity, individual polymorphs of anatase, rutile and brookite were also prepared using the same precursor material. Individual polymorph phases within the nanocomposite material crystallized separately and formed mixed agglomerates; the polymorphs were regularly shaped and randomly distributed in agglomerates, where some of the anatase particles exhibited truncated octahedron morphology, rutile was in the form of tetragonal prisms with pyramidal termination and brookite was shaped as blocky particles, which were found to be the smallest within the nanocomposite material (∼20nm). Newly synthesized TiO2 nanocomposite was highly active in terms of mineralization, since after 60min of irradiation under UV light almost 60% of water dissolved pollutant bisphenol A was successfully transformed into CO2 in H2O. On the other hand, the benchmark TiO2 P25 Degussa catalyst reached a lower extent of mineralization, which is due to significantly less expressed resistance to accumulation of carbonaceous deposits on the catalyst surface.

Band Alignment and Controllable Electron Migration between Rutile and Anatase TiO2.

TiO2 is the most promising semiconductor for photocatalytic splitting of water for hydrogen and degradation of pollutants. The highly photocatalytic active form is its mixed phase of two polymorphs anatase and rutile rather than their pristine compositions. Such a synergetic effect is understood by the staggered band alignment favorable to spatial charge separation. However, electron migration in either direction between the two phases has been reported, the reason of which is still unknown. We determined the band alignment by a novel method, i.e., transient infrared absorption-excitation energy scanning spectra, showing their conduction bands being aligned, thus the electron migration direction is controlled by dynamical factors, such as varying the particle size of anatase, putting electron or hole scavengers on either the surface of anatase or rutile phases, or both. A quantitative criterion capable of predicting the migration direction under various conditions including particle size and surface chemical reactions is proposed, the predictions have been verified experimentally in several typical cases. This would give rise to a great potential in designing more effective titania photocatalysts.

Comparing Quasiparticle H2O Level Alignment on Anatase and Rutile TiO2

Knowledge of the molecular frontier levels' alignment in the ground state can be used to predict the photocatalytic activity of an interface. The position of the adsorbate's highest occupied molecular orbital (HOMO) levels relative to the substrate's valence band maximum (VBM) in the interface describes the favorability of photogenerated hole transfer from the VBM to the adsorbed molecule. This is a key quantity for assessing and comparing H$_2$O photooxidation activities on two prototypical photocatalytic TiO$_2$ surfaces: anatase (A)-TiO$_2$(101) and rutile (R)-TiO$_2$(110). Using the projected density of states (DOS) from state-of-the-art quasiparticle (QP) $G_0W_0$ calculations, we assess the relative photocatalytic activity of intact and dissociated H$_2$O on coordinately unsaturated (Ti$_{\textit{cus}}$) sites of idealized stoichiometric A-TiO$_2$(101)/R-TiO$_2$(110) and bridging O vacancies (O$_{\textit{br}}^{\textit{vac}}$) of defective A-TiO$_{2-x}$(101)/R-TiO$_{2-x}$(110) surfaces ($x=\frac{1}{4},\frac{1}{8}$) for various coverages. Such a many-body treatment is necessary to correctly describe the anisotropic screening of electron-electron interactions at a photocatalytic interface, and hence obtain accurate interfacial level alignments. The more favorable ground state HOMO level alignment for A-TiO$_2$(101) may explain why the anatase polymorph shows higher photocatalytic activities than the rutile polymorph. Our results indicate that (1) hole trapping is more favored on A-TiO$_2$(101) than R-TiO$_2$(110) and (2) HO@Ti$_{\textit{cus}}$ is more photocatalytically active than intact H$_2$O@Ti$_{\textit{cus}}$.

Behavior of Titania Nanoparticles in Cross-linking Hydroxypropyl Guar Used in Hydraulic Fracturing Fluids For Oil Recovery

Fluids pumped in hydraulic fracturing operations constitute highly viscous gels achieved via cross-linking of the polysaccharide derivative hydroxypropyl guar (HPG), e.g., with titanium or zirconium complexes. In this study, the mechanism underlying the cross-linking effect was clarified experimentally for the titanium system. It was found that the cross-linking effect is not based on a ligand exchange reaction with the cis-hydroxy functionalities present in HPG but instead relies on TiO2 nanoparticles resulting from hydrolysis of the Ti complexes. For example, 6 nm titania nanospheres (anatase polymorph) synthesized via acid hydrolysis of tetraisopropyl orthotitanate can increase the viscosity of a HPG solution by a factor of 25. However, this effect was observed only at pH = 2–4 where the nanoparticles are stable. At higher pH values, electrostatic repulsion between the nanoparticles decreases, resulting in agglomeration as was observed via zeta potential and pH-dependent particle size measurement. Such...

Electrochemical Activity of Titanium Dioxide Toward Oxygen Reduction and Evolution Reactions

We report on the electrochemical activity of TiO2 polymorphs toward oxygen reduction and evolution reactions in a CsH2PO4 solid acid electrochemical system. Oxygen reduction and evolution are catalytically challenging reactions relevant to the fuel cell and water splitting applications. Because of the strong O=O bond, oxygen reduction is a slow reaction even on a Pt surface. In fuel cells, the oxygen reduction reaction (ORR) requires high loadings of the precious Pt catalyst. Even at the operating temperature of the super-protonic CsH2PO4 solid acid, ca. 240 °C, the ORR remains sluggish. Titanium dioxide has been studied extensively as a promising, low cost (photo)catalyst for water splitting. TiO2 activity toward oxygen led us to examine its catalytic performance for the oxygen reactions in the CsH2PO4 electrochemical system. Solid state TiO2 catalysts on carbon based supports show a range of activity depending on the relative ratio of the rutile to anatase polymorphs. Rutile phase exhibits a lower overpotential for the ORR. The activity of the catalysts are also controlled by the type of the carbon based interconnects used in the fabrication of the composite electrodes. Interconnects facilitate the interaction between CsH2PO4 and TiO2 particles. Catalysis only occurs on TiO2 particles that are connected to the CsH2PO4 electrolyte, and are also accessible to the O2 gas. We will discuss the selective activity of pure and mixed phases of TiO2 rutile and anatase polymorphs toward oxygen reduction and evolution reactions.