N-type TiO2 Research Articles

Highly sensitive and rapid responding humidity sensors based on silver catalyzed Ag2S-TiO2 quantum dots prepared by SILAR.

We developed a resistive humidity sensor based on a heterojunction of silver sulfide (Ag2S) quantum dots (QDs) and TiO2 because of its specificity to water vapor adsorption and its insensitivity to environmental gases. The QDs were grown on a mesoporous TiO2 layer using the successive ionic layer adsorption and reaction (SILAR) method. The boundary condition between TiO2 and Ag2S provides a tunable energy gap by adjusting the number of SILAR cycles. Besides, the large surface-to-volume ratio of QDs provides a strong water vapor adsorption ability and electron transfer. Nano-silver precipitated during the SILAR process provides free electrons and lowers the Fermi level to between n-type TiO2 and p-type Ag2S. The resistance response increased significantly to 4600 and the reaction equilibrium time decreased greatly to 7 seconds due to the presence of nano-silver. Finally, the Ag2S QDs possess a best sensing range of 13–90%. To sum up, Ag2S QDs are high sensitivity and selectivity humidity sensors.

Effect of the Niobium Doping Concentration on the Charge Storage Mechanism of Mesoporous Anatase Beads as an Anode for High-Rate Li-Ion Batteries

A promising strategy to improve the rate performance of Li-ion batteries is to enhance and facilitate the insertion of Li ions into nanostructured oxides like TiO2. In this work, we present a systematic study of pentavalent-doped anatase TiO2 materials for third-generation high-rate Li-ion batteries. Mesoporous niobium-doped anatase beads (Nb-doped TiO2) with different Nb5+ doping (n-type) concentrations (0.1, 1.0, and 10% at.) were synthesized via an improved template approach followed by hydrothermal treatment. The formation of intrinsic n-type defects and oxygen vacancies under RT conditions gives rise to a metallic-type conduction due to a shift of the Fermi energy level. The increase in the metallic character, confirmed by electrochemical impedance spectroscopy, enhances the performance of the anatase bead electrodes in terms of rate capability and provides higher capacities both at low and fast charging rates. The experimental data were supported by density functional theory (DFT) calculations showing how a different n-type doping can be correlated to the same electrochemical effect on the final device. The Nb-doped TiO2 electrode materials exhibit an improved cycling stability at all the doping concentrations by overcoming the capacity fade shown in the case of pure TiO2 beads. The 0.1% Nb-doped TiO2-based electrodes exhibit the highest reversible capacities of 180 mAh g–1 at 1C (330 mA g–1) after 500 cycles and 110 mAh g–1 at 10C (3300 mA g–1) after 1000 cycles. Our experimental and computational results highlight the possibility of using n-type doped TiO2 materials as anodes in high-rate Li-ion batteries.

Collisional Electron Transfer Route between Homogeneous Porphyrin Dye and Catalytic TiO2/Re(I) Particles for CO2 Reduction

Dye detachment issue in the TiO2-mediated dye-sensitized photocatalytic system engenders an electron injection route based on collisional quenching between the detached solution-phase dye and dispersed n-type TiO2 particles, in addition to the general fast electron injection pathway from dye chemisorbed on TiO2. For porphyrin-sensitized hetero-binary hybrids prepared by mixing a solution-phase Zn porphyrin sensitizer (ZnP) and heterogeneous Re(I) molecular catalyst-immobilized TiO2 particles (TiO2/Re(I)), we found that without any dye immobilization on the TiO2 surface, the dissolved porphyrin dye can effectively transport its excited-state electrons to the heterogeneous catalytic TiO2/Re(I) particles via a collisional electron transfer pathway, which is relatively unstudied and thus an interesting topic in the dye-sensitized semiconductor photocatalytic system. The better light-harvesting ability of porphyrin in solution and the TiO2-induced stabilization of the molecular Re(I) catalyst raised the photochemical CO2-to-CO conversion activity of the semiheterogeneous system (porphyrin + TiO2/Re(I) catalyst) above that of the homogeneous system (porphyrin + Re(I) catalyst) and the heterogeneous ternary hybrid (porphyrin/TiO2/Re(I) catalyst).

Direct Observation of Photoinduced Charge Separation at Transition-Metal Nitride-Semiconductor Interfaces.

Optically excited hot carriers from metallic nanostructures forming metal-semiconductor heterostructures are advantageous for enhancing photoelectric conversion in the sub-band gap photon energy regime. Plasmonic gold has been widely used for hot carrier excitation, but recent works have demonstrated that plasmonic transition-metal nitrides have higher efficiencies in injecting hot electrons to adjacent n-type semiconductors and are more cost-effective. To collect direct evidence of hot carrier excitation from nanostructures, imaging of hot carriers is essential. In this work, photoexcited Kelvin probe force microscopy (KPFM) is used to image hot carriers excited in transition-metal nitride nanostructures forming heterostructures with semiconductors. Among available transition-metal nitrides, we select zirconium nitride (ZrN) for this study. Additionally, both p-type and n-type titanium dioxides (TiO2) are selected to study the transport of hot holes and hot electrons. The KPFM results indicate that for ZrN and p-type TiO2 heterostructures, hot holes are injected into the p-type TiO2 across the Schottky contact. In the case of ZrN and n-type TiO2 heterostructures, hot electrons are injected into the n-type TiO2 across the ohmic contact. Because transition-metal nitrides are known to be more effective than gold at injecting hot carriers into adjacent semiconductors, unambiguously determining the mechanisms of hot carrier transportation of transition-metal nitrides using photoexcited KPFM will facilitate additional studies on hot carrier applications with transition-metal nitrides.

Charge Transfer Kinetics in the Dark at Oxide Semiconductor/ electrolyte Interfaces

Among all the requisite properties of an inorganic semiconductor, the dynamics of interfacial charge transfer is an important common denominator for numerous technologically important applications such as PEC water splitting, photocatalytic pollutant degradation, or photovoltaic solar energy conversion.Most attention in this regard has been paid to the dynamics of minority carrier transfer; only sporadic studies have focused on majority carrier transfer across the solid/electrolyte interface. However, recent studies have underlined the growing realization that the charge transfer kinetics of both minority and majority carriers are often coupled. Performance optimization of the interfaces must address both these charge transfer pathways such that deleterious carrier recombination can be minimized. Therefore, this study addresses the fundamental and experimental understanding of interfacial charge transfer dynamics at semiconductor/electrolyte interfaces in the dark . A variety of interfaces were studied to gain a unified and self-consistent picture.Firstly, binary n-type TiO2 and WO3 semiconductors were chosen because of their excellent chemical/photoelectrochemical (PEC) stability, high PEC activity, and overall robustness over a wide pH range. Secondly, binary and ternary p-type semiconductors such as copper bismuth oxide (CuBi2O4),silver vanadate (AgVO3),and copper (II) oxide (CuO) were selected to compare their charge transfer kinetics in the dark. Such comparative studies are conspicuously absent in the literature, and in particular, dark current-forward bias potential measurements are lacking for these compounds. Tafel analyses were used to evaluate the standard rate constant, k 0 and the exchange current density, jo in all these cases. Based on these kinetics data, a general conclusion could be made that p-type oxide semiconductors exhibited faster kinetics than their n-type counterparts. For comparison, Pt and fluorine doped tin oxide (FTO) electrodes were included as benchmarks in these experiments. The data also indicated that heterogeneous charge transfer at metal/electrolyte interfaces had faster kinetics compared to the semiconductor/electrolyte interfaces. This contrasting and self-consistent behavior stems from surface state density variations in the two sets of cases. The practical implications of these data are finally discussed.

A novel gas flow-through photocatalytic reactor based on copper-functionalized nanomembranes for the photoreduction of CO2 to C1-C2 carboxylic acids and C1-C3 alcohols

A novel concept of gas flow-through photo(electro)catalytic reactor based on copper-functionalized nanomembranes for the conversion of CO2 is presented. The nanomembranes are based on aligned TiO2 nanotube arrays grown over a microperforated metallic substrate, acting as an electron collector and to provide the necessary robustness, which are then functionalized by copper oxide (Cu2O or CuO) electrodeposition. For comparison, the behavior of copper oxide electrodeposited over the bare microperforated metallic substrate is also given. The concept is quite different from conventional photocatalytic approaches. Due to the peculiar characteristics and conditions in the photoreactor (working under a cross-flow of gaseous CO2 saturated with water passing through the nanomembrane photocatalyst layer), it is possible to evidence for the first time the highly selective CO2 conversion to C1-C2 carboxylic acids (formic, acetic and oxalic acids) without formation of H2, CO, CH4 or other hydrocarbons. Copper-oxide introduces an additional reaction pathway to C1-C3 alcohols (methanol, ethanol and isopropanol) or derived products (methyl formate). The best performances are obtained with p-type Cu2O over n-type TiO2 nanotubes (Faradaic Efficiency -FE- = 42% to methanol and 44% to acetic acid) due to the creation of a p-n-type heterojunction that improves visible light harvesting, giving an apparent quantum yield (ratio between electrons reacted and photons absorbed) with solar illumination of about 21%. FE up to 47% to methanol or 73% to acetic acid are observed among the other tested samples. The relevance of these results to the mechanism of CO2 conversion is also discussed.

Photocatalytic landfill leachate treatment using P-type TiO2 nanoparticles under visible light irradiation

Landfill leachate treatment is a necessary measure for environmental protection and supporting sustainable development. Photocatalytic treatment method using N- or P-type TiO2 nanoparticles has been proposed as an efficient method for the treatment of recalcitrant pollutants. Since main oxidizing agents in the photocatalytic treatment by N- and P-type TiO2 are different, investigating their performance for the photocatalytic treatment of landfill leachate is necessary. Therefore, the purpose of this study is to evaluate the performance of P-type TiO2 nanoparticles for the photocatalytic treatment of landfill leachate under visible light irradiation. Silicon (Si) element was considered as TiO2 dopant, and Si-doped TiO2 nanoparticles were synthesized by sol–gel method. Four effective parameters on the photocatalytic treatment process, i.e., the dopant content of Si (Si wt.%), calcination temperature (T), pH, and exposure time, were considered as independent variables, and temporal normalized concentration of leachate residual COD was considered as dependent variable. Decision tree (M5P) model was applied for modeling the photocatalytic process of landfill leachate treatment using the data of 167 experiments. Based on the results, the optimum value of pH, calcination temperature, and dopant content for Si-doped TiO2 nanoparticles are 6, 500 °C, and 2.5 weight percentage, respectively, and the leachate COD removal efficiency at these conditions is about 85% for leachate with 600 mg/L initial COD. Therefore, Si dopant considerably enhances the photocatalytic activity of TiO2 nanoparticles under visible light irradiation. This photocatalytic process can be efficiently applied for landfill leachate treatment. Finally, the performance of Si-doped TiO2 nanoparticles as P-type TiO2 was compared with the performance of tungsten (W)-doped TiO2 nanoparticles as N-type TiO2 for leachate COD removal. Results showed that both types of nanoparticles have a similar performance for oxidizing the leachate COD, and there is no significant difference between them.

Transition-Metal Oxides for Kesterite Solar Cells Developed on Transparent Substrates.

Fabrication on transparent soda-lime glass/fluorine-doped tin oxide (FTO) substrates opens the way to advanced applications for kesterite solar cells such as semitransparent, bifacial, and tandem devices, which are key to the future of the PV market. However, the complex behavior of the p-kesterite/n-FTO back-interface potentially limits the power conversion efficiency of such devices. Overcoming this issue requires careful interface engineering. This work empirically explores the use of transition-metal oxides (TMOs) and Mo-based nanolayers to improve the back-interface of Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 solar cells fabricated on transparent glass/FTO substrates. Although the use of TMOs alone is found to be highly detrimental to the devices inducing complex current-blocking behaviors, the use of Mo:Na nanolayers and their combination with n-type TMOs TiO2 and V2O5 are shown to be a very promising strategy to improve the limited performance of kesterite devices fabricated on transparent substrates. The optoelectronic, morphological, structural, and in-depth compositional characterization performed on the devices suggests that the improvements observed are related to a combination of shunt insulation and recombination reduction. This way, record efficiencies of 6.1, 6.2, and 7.9% are obtained for Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 devices, respectively, giving proof of the potential of TMOs for the development of kesterite solar cells on transparent substrates.

The Use of Silane-Aniline as Coupling Agent between Titanium (IV) Oxide Core and Polyaniline Emeraldine Salt Shell

Stable electronic configuration between the interface of an n-type oxide semiconductor core and a p-type polymer shell is necessary in order to guarantee a consistent functioning core-shell structure. This research aims to use silane-aniline to link between an n-type Titanium (IV) oxide (TiO2) core and p-type polyaniline emeraldine salt (PANI-ES) shell. Core-shell structure was created by functionalizing TiO2 powders with silane aniline molecules using simple soaking technique and then polymerizing the attached aniline molecules using an oxidative technique. Infrared spectroscopy reveals the presence of Si-O bonds signifying the presence of linkage between the inorganic core and polymeric shell. Polymerization of the attached aniline molecules may have led to coupling of aromatic rings to form long polymeric structures which caused widening and shifting of aromatic rings’ IR peak to lower wavenumber. In conclusion, silane-aniline was successfully utilized to connect the n-type TiO2 core and p-type PANI-ES shell.

Fabrication and characterization of Schottky barrier diodes on rutile TiO2

Schottky barrier diodes (SBDs) were fabricated by depositing Pd, Pt or Ni on single crystal, conductive n-type rutile TiO2 using e-beam evaporation. As-grown and nominally undoped rutile TiO2 single crystals are semi-insulating, and were heat-treated in forming gas flow, N2 flow or H2 gas to obtain conductive n-type crystals displaying electrical conductivities in the range of . Additionally, SBDs were deposited on Nb-doped conductive n-type rutile TiO2 with a conductivity of around . Generally, SBDs displaying a rectification of up to eight orders of magnitude were obtained, when comparing the current under reverse and forward bias. The extracted ideality factors were in the range of . From Capacitance-Voltage measurements, the built-in voltage was derived to be around , depending on the doping concentration of the specific TiO2 single crystal. Series resistances as low as were achieved. A considerable variation in the electrical characteristics of different SBDs deposited on the same crystal was found, regardless of the metal or doping strategy used. Moreover, the SBD characteristics change over time, particularly seen as a degradation in rectification, mainly related to an increase in the current under reverse bias. Additional surface treatments such as boiling in H2O2 and etching in HF do not have a significant effect on the quality of the SBDs. Clear indications for poor adhesion between TiO2 and Pd are shown. In conclusion, we demonstrate the fabrication of SBDs which are suitable for studying the fundamental properties of metal/TiO2 junctions and the characteristics of electrically-active defects in TiO2 using space-charge spectroscopy.

Enhanced thermoelectric performance of Bi2Se3/TiO2 composite

Bi2(Te,Se)3 alloys are conventional commercial thermoelectric materials for solid-state refrigeration around room temperature. In recent years, much attention has been paid to various advanced thermoelectric composite materials due to the unique thermoelectric properties. In this work, Bi2Se3/TiO2 composites were prepared by hot pressing the plate-like Bi2Se3 powders coated in situ with hydrolyzed hytetabutyl-n-butyl titanate (TNBT), and therefore numerous TiO2 in micrometer size could be formed on the interface of Bi2Se3 grains. The carrier concentration in Bi2Se3 matrix is optimized subject to the addition of n-type semiconductor TiO2, contributing to a significant improved power factor. In the meantime, the lattice thermal conductivity is also suppressed due to the enhanced phonon scattering at Bi2Se3/TiO2 interface and amorphous TiO2 particles. As a consequence, a peak figure of merit (zT) of 0.41 is obtained at 525 K in Bi2Se3/15 mol% TiO2 composites, nearly 50% augment over the pristine Bi2Se3 binary compound.

Phosphorus-doped graphene quantum dots loaded on TiO2 for enhanced photodegradation

Reducing the direct recombination of the photogenerated electron-hole pairs in a photocatalytic system is important to improve the photocatalytic efficiency. Transferring the photogenerated carriers to other adsorbates is a usual way to reduce the direct recombination probability. By synthesizing p-type phosphorus-doped graphene quantum dots (P-GQDs) to form p-n junctions with n-type TiO2 nanocomposites, the photogenerated holes of TiO2 can be effectively transferred to P-GQDs, thus the direct carrier recombination of TiO2 is decreased, resulting in the conspicuous improvement of the Methyl Orange (MO) photodegradation efficiency to 95.5% in 14 min. This work provides a new type of p-n junction in highly efficient photodegradation system.

Visible-light-driven pollutants degradation with carbon quantum dots/N-TiO2 under mild condition: Facile preparation, dramatic performance and deep mechanism insight

Because pure TiO2 has high photogenerated charge carriers recombination rate and inferior visible light capture capability, the optical activity is very weak. N doping can generate a lower energy gap energy and carbon quantum dots (CDs) have excellent properties that can transfer electrons smoothly and reserve electrons quickly, so we think that doping of N into TiO2 and loading of CDs can modify TiO2. We synthesized a brand new carbon quantum dots/N-TiO2(CDs/N-TiO2) by mechanically mixing carbon quantum dots with N-TiO2 instead of the conventional calcination or solvothermal step. The degradation ratio of RhB(10 mg/L) was increased from 6.66 % and 19.97 %–99.8 % in 5 min under visible light when compared with TiO2 and N-TiO2. The kinetic constants of RhB degradation by 30CDs/N-TiO2 are 85.52 and 25.40 times higher than those of TiO2 and N-TiO2, respectively. Besides, Cr(Ⅵ) (20 mg/L) photoreduction can be completely achieved in 4 min under solar light irradiation. Besides, We analyzed the behavior of photogenerated charge carriers by the surface photovoltage spectra (SPV) and transient photovoltage spectra (TPV) measurement analyses, showing the deep mechanism of photodegradation process of dye. Doping of nitrogen into TiO2 can extend the photo absorption range of TiO2 and let n-type TiO2 show p-type conducting character that makes it easier to transfer electrons to the CDs. Loading of CDs can enhance the electron-hole pairs separation efficiency.

Influence of Nb-doping on the local structure and thermoelectric properties of transparent TiO2:Nb thin films

Abstract Transparent n-type niobium-doped titanium dioxide thin films (TiO2:1.5 at.%Nb) with pronounced thermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering. The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques. The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Ti and Nb K-edges. A set of radial distribution functions were extracted from the simultaneous analysis of EXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopant atoms modify the local environment of the films, but their average structure remains close to that of the anatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very high absolute Seebeck coefficient (S = 155 μV/K) for n-type TiO2 was achieved with Nb doping, yielding a maximum power factor and thermoelectric figure of merit of 0.5 mW m−1 K−2 and 0.18 at a temperature of 300 K, respectively, for a 150 nm thick film. From frequency-domain thermoreflectance experiments, a thermal conductivity value of 1.3 W m−1 K−1 was obtained for the optimized TiO2:Nb film.

Light-Controlled Nanoparticle Collision Experiments.

Electrochemical monitoring of catalytically amplified collisions of individual metal nanoparticles (NP) with ultramicroelectrodes (UME) has been extensively used to study electrocatalysis, mass-transport, and charge-transfer processes at the single NP level. More recently, photoelectrochemical collision experiments were carried out with semiconductive NPs. Here, we introduce two new types of light-controlled nanoimpact experiments. The first experiment involves localized photodeposition of catalyst (Pt) on TiO2 NPs with a glass-sheathed carbon fiber simultaneously serving as the light guide and collector UME. The collisions of in situ prepared Pt@TiO2 NPs with the carbon surface produced blips of water oxidation current, while the activity of pristine TiO2 NPs was too low to yield measurable signal. In another experiment, collisions of catalytic (Ir oxide) NPs with the semiconductor (Nb doped n-type TiO2 rutile single crystal) electrode are monitored by measuring the photocurrent of water oxidation.

High-Performance Phase-Pure SnS Photocathodes for Photoelectrochemical Water Splitting Obtained via Molecular Ink-Derived Seed-Assisted Growth of Nanoplates.

Although tin monosulfide (SnS) is one of the promising earth-abundant semiconducting materials for photoelectrochemical water splitting, the performance of SnS photocathodes remains poor. Herein, we report a stepwise approach for the fabrication of highly efficient photocathodes based on SnS nanoplates via elaborate modulation of molecular solutions. It is demonstrated that phase-pure SnS nanoplates without detrimental secondary phases (such as SnS2 and Sn2S3) can be readily obtained by adjusting the amounts of Sn and S in the precursor solution. Additionally, the orientation of SnS nanoplates is controlled by implementing different types of SnS seed layers. The orientations of the SnS seed layers are changed according to the molecular shapes of the Sn-S bonds in the molecular solutions, depending on the relative nucleophilicity of the molecular moieties formed by specific thiol-amine reactions. The molecular Sn-S sheets in the seed ink was obtained by the reaction in a solvent mixture of thiogylcolic acid and ethanolamine. By contrast, the short Sn-S molecular rods result from the reaction in a solvent mixture of 2-mercaptoethanol and ethylenediamine. Interestingly, the relatively short rodlike morphology of the SnS seed induces the growth of SnS nanostructures faceted by preferred (111) and (101) planes, leading to fast charge transport. With the formation of a proper band alignment with n-type CdS and TiO2, the preferred (111)- and (101)-oriented SnS nanoplate-based photocathode exhibited a photocurrent density of -19 mA cm-2 at 0 V versus a reversible hydrogen electrode, establishing a new benchmark for SnS photocathodes.

An experimental study on the blinking suppression mechanism of organic-inorganic formamidinium lead halide perovskite quantum dots on N-Type semiconductors

Lead halide perovskite has emerged as a potential material for a wide range of applications, including solar cells, light-emitting diode displays, lasing, and single photon emitters. To optimize their utilization in optoelectronic devices, the fundamental photophysical properties, especially their charge carrier transition and blinking behaviors, must be elucidated. In this study, we investigate the blinking behaviors of single formamidinium bromide perovskite quantum dots (FAPbBr3 PQDs) on the n-type TiO2 substrate. It is suggested that the electrons from TiO2 fill the trap states of FAPbBr3 PQD during Fermi-level equilibrium, which can reduce the possibility of capturing the hot electrons from PQD into the trap states. In addition, charge separation and charge recombination processes between PQD and TiO2 are expected to shorten the duration of the OFF state, thus stabilizing the fluorescence of PQDs.

Effective combination of CuFeO2 with high temperature resistant Nb-doped TiO2 nanotube arrays for CO2 photoelectric reduction

Herein, we report a simple approach to synthesize CuFeO2/TNNTs photocathodes composed of high-temperature resistance n-type Nb-doped TiO2 nanotube arrays (TNNTs) and p-type CuFeO2 for CO2 reduction. TNNTs were prepared by anodic oxidation on TiNb alloy sheets and CuFeO2/TNNTs were then prepared by coating precursor liquid onto TNNTs followed by heat treatment in argon atmosphere. The microstructures of CuFeO2/TNNTs and TNNTs before and after heat treatment were investigated by SEM and TEM. The phase compositions of CuFeO2/TNNTs were studied by XRD and XPS, and the light absorption performance were tested by UV–vis diffuse reflectance spectrum. Results show that TNNTs exhibit a regular nanotube arrays structure and this structure is well remained after the calcination at 650 °C. In addition, TNNTs show similar semiconductor properties to n-type TiO2, which enables them to be integrated with p-type CuFeO2 to obtain composite photocathodes with a p-n junction. The synthesized CuFeO2/TNNTs photocathode is well crystallized because no other crystalline iron or copper compounds are included in the prepared photocathode. Furthermore, the photocathode shows high light absorption and fast carrier transport due to the appropriate band gap and p-n junction. As a result, high photoelectrocatalytic CO2 reduction performance with high selectivity to ethanol is obtained on this photocathode.

CuO/ZnO/TiO2 photocathodes for a self-sustaining photocell: Efficient solar energy conversion without external bias and under visible light

We report the results of a p-CuO nanoflake photocathode combined with an n-type TiO2 nanorod-based photoanode in a solar-water-splitting photocell, operating without external bias under visible light illumination. Both p-CuO nanoflakes and n-TiO2 nanorods were successfully fabricated by a low-cost solution-based method on transparent conductive substrates. Photocorrosion of the CuO electrode was suppressed by coating with a 200-nm ZnO/TiO2 protective film, which demonstrated a stability of over 70%. The visible-light response of single crystalline n-TiO2 nanorods was enhanced by sensitization with CdS/CdSe nanoparticles. Finally, the two n- and p-type photoelectrodes were short-circuited in the photocell, and their current-voltage (I–V) characteristics evaluated under visible-light illumination. The results of the I–V measurements reveal that the performance of the photocell strongly depends on the electrochemical properties of each electrode. The photocell comprising highly stable p-CuO and visible-light-active n-TiO2-based photoelectrodes operating without external bias demonstrated a short-circuit current and photoconversion efficiency of ~1 mA and 0.57%, respectively, under visible-light illumination.

Investigating the high-temperature thermoelectric properties of n -type rutile TiO2

Transition metal oxides are considered promising thermoelectric materials for harvesting high-temperature waste heat due to their stability, abundance and low toxicity. Despite their typically strong ionic character, they can exhibit surprisingly high power factors $\sigma S^2$, as in n-type SrTiO$_3$ for instance. Thus, it is worth examining other transition metal oxides that might surpass the performances of SrTiO$_3$. This theoretical paper investigates the thermoelectric properties of n-type rutile TiO$_2$, which is the most stable phase of titanium oxide up to 2000 K. The electronic structure is obtained through ab initio calculations, while the prominent features of strong electron-phonon interaction and defects states are modelled using a small number of parameters. The theoretical results are compared with a wealth of experimental data from the literature, yielding very good agreements over a wide range of carrier concentrations. This validates the hypothesis of band conduction in rutile TiO$_2$ and allows the prediction of the high-temperature thermoelectric properties.