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In recent years, the defect engineering of titania via reduction treatments has shown a high potential for enabling efficient and co-catalyst-free photocatalytic H2 generation from methanol/water solutions. However, defect engineering simultaneously alters several properties of TiO2. Here, we use pristine (white) and hydrogenated (gray) anatase nanosheets with dominant (001) facets. By comparing electrical conductivity, photocurrent spectra, transient photocurrent response, and photocatalytic H2 evolution, we show that the increased conductivity or broad visible light absorption of gray titania is not responsible for its increased activity. Instead, the true bottleneck is the hole transfer rate that is significantly accelerated while using gray instead of white modification. Moreover, the hole transfer reaction causes the accumulation of the reaction products in pure water, hindering the photocatalytic H2 evolution over time. These combined factors explain the superior performance of gray titania over white titania in photoelectrochemical or photocatalytic water splitting.

TiO2-based catalyst supports in polymer electrolyte membrane fuel cells (PEMFCs) are widely investigated and provide an alternative to corrosion-susceptible carbon-based catalyst supports. For PEMF...

ACS catalysis 12, 33 - 41 (2022). doi:10.1021/acscatal.2c04481, Trapping sites in single atom (SA) catalysts are critical to the stabilization and reactivity of isolated atoms. Herein, we show that anchoring of Pt SAs on TiO$_2$ nanosheets is strongly aided by lattice incorporated fluorine species. Tailoring the speciation of fluorine on TiO$_2$ nanosheets is a key factor for uniform and stable dispersion of the Pt SAs and high efficiency in Pt SA co-catalyzed photocatalytic H$_2$ production. Fluorine-stabilized uniformly dispersed Pt SAs on the (001) surface of TiO$_2$ can provide a remarkable photocatalytic activity (a H$_2$ production rate of 45.3 mmol h$^{–1}$ mg$^{–1}$ Pt for 65 mW/cm2 365 nm light). This high (maximized) efficiency can be achieved with a remarkably low loading amount of Pt SAs on TiO$_2$ nanosheets (0.03 wt %), which is far superior to Pt nanoparticles on a TiO$_2$ nanosheet with the same or a higher loading amount. F-stabilized Pt SAs on TiO$_2$ nanosheets also exhibit an excellent stability in long-term photocatalytic reactions., Published by ACS, Washington, DC

In the present work the authors show that anodic TiO

Photoelectrochemical (PEC) water splitting is a promising method for the conversion of solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α-Fe2 O3 ) is one of the most attractive materials for a highly efficient charge carrier generation and collection due to its large specific surface area and the short minority carrier diffusion length. In the present work, the PEC water splitting performance of nanostructured α-Fe2 O3 is investigated which was prepared by anodization followed by annealing in a low oxygen ambient (0.03 % O2 in Ar). It was found that low oxygen annealing can activate a significant PEC response of α-Fe2 O3 even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The photocurrent of the α-Fe2 O3 annealed in the low oxygen at 1.5 V vs. RHE results as 0.5 mA cm-2 , being 20 times higher than that of annealing in air. The obtained results show that the α-Fe2 O3 annealed in low oxygen contains beneficial defects and promotes the transport of holes; it can be attributed to the improvement of conductivity due to the introduction of suitable oxygen vacancies in the α-Fe2 O3 . Additionally, we demonstrate the photocurrent of α-Fe2 O3 annealed in low oxygen ambient can be further enhanced by Zn-Co LDH, which is a co-catalyst of oxygen evolution reaction. This indicates low oxygen annealing generates a promising method to obtain an excellent PEC water splitting performance from α-Fe2 O3 photoanodes.

Photoelectrochemical (PEC) water splitting is a promising method for conversing solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite ($\alpha$-Fe$_2$O$_3$) is one of the most attractive materials for highly efficient charge carrier generation and collection due to its large specific surface area and shortening minority carrier diffusion length required to reach the surface. In the present work, PEC water splitting performance of $\alpha$-Fe$_2$O$_3$ prepared by anodization of thin iron layers on an FTO glass and subsequent annealing in low O$_2$-Ar ambient with only 0.03% O$_2$ was investigated. The key finding is that annealing the anodic nanostructures with low oxygen concentration provides a strongly enhanced PEC performance compared with classic air annealing. The photocurrent of the former at 1.5 V vs. RHE results in 1.1 mA/cm2, being 11 times higher than that of the latter. The enhancement of the PEC performance for $\alpha$-Fe$_2$O$_3$ annealed in low oxygen atmosphere can be attributed to controlled morphology, Sn doping, and introduction of oxygen vacancies, which contribute to the enhancement of the hole flux from the photogenerated site to the reactive surface and additionally lead to an enhanced hole transfer at the interface between the $\alpha$-Fe$_2$O$_3$ and the electrolyte. From the obtained results, it is evident that low oxygen annealing is a surprisingly effective method of defect engineering and optimizing $\alpha$-Fe$_2$O$_3$ electrodes for a maximized PEC water splitting performance.

Defined substoichiometric titanium oxides (Ti$_x$O$_{2x-1}$ with $3 < x < 10$) called Magneli phases have been investigated mostly for their unusual high conductivity and metal-like behavior. In photocatalysis, Magneli phase containing titania particles have been reported to provide favorable charge separation resulting in enhanced reaction efficiency. In the current work we describe a one-step synthesis of Magneli-containing mixed phase nanoparticles that carry directly integrated minute amounts of Pt. Phase optimized nanoparticles that contain only a few hundred ppm Pt are very effective photocatalysts for H$_2$ evolution (they provide a 50-100 times higher H$_2$ evolution than plain anatase loaded with a similar amount of Pt). These photocatalysts are synthesized in a setup combining a hot-wall reactor that is used for TiOx synthesis with a spark generator producing Pt nanoparticles. Different reactor temperatures result in various phase ratios between anatase and Magneli phases. The titania nanoparticles (ca. 24 - 53 nm) were characterized using XRD, HRTEM, XPS and EPR spectra as well as ICP-OES analysis. The best photocatalyst prepared at 900$^\circ$C (which consists of mixed phase particles of 32% anatase, 11% rutile and 57% Magneli phases loaded with 290 ppm of Pt) can provide a photocatalytic H$_2$ evolution rate of ca. 5432 micromol h$^{-1} g$^{-1}$ for UV and ca. 1670 micromol h$^{-1} g$^{-1}$ for AM1.5 illumination. For powders converted to higher amounts of Magneli phases (1000$^\circ$C and 1100$^\circ$C), a drastic loss of the photocatalytic H$_2$ generation activity is observed. Thus, the high photocatalytic efficiency under best conditions is ascribed to an effective synergy between multi-junctions of Magneli titania and Pt that enable a much more effective charge separation and reaction than conventional Pt/anatase junctions.

In the present work, we compare the photoresponse of vertically erected (VE) single crystal anatase layers with that of widely used TiO2 nanotube layers. These VE-anatase layers were grown hydrothermally, directly on fluorine-doped tin oxide (FTO) glass, and consist of an array of anatase single crystal flakes with preferred (0 0 1) facets. As formed, these single crystal layers are fluorine terminated – this termination can be removed by a thermal treatment in air. We compare the photocurrent magnitude and photocurrent transients using intensity-modulated photocurrent spectroscopy (IMPS). We find that the “de-fluorinated” VE-anatase layers show significantly higher photocurrents than the comparable nanotube layers. This high efficiency of the VE-anatase layers is due to the electron transport being 100 times faster in these single crystal electrodes, provided that the blocking fluorine termination is removed.

For more than 20 years, Pt/TiO$_2$ represents the benchmark photocatalyst/co-catalyst platform for photocatalytic hydrogen (H$_2$) generation. Here, single atom (SA) Pt is decorated on different polymorphs of TiO$_2$ (anatase, rutile, and the mixed phase of P25) using a simple immersion anchoring approach. On P25 and anatase, Pt SAs act as highly effective co-catalyst for pure water splitting with a photocatalytic H$_2$ evolution activity (4600 µmol h$^{−1}$ g$^{−1}$)—on both polymorphs, SA deposition yields a significantly more active photocatalyst than those decorated with classic Pt nanoparticles or conventional SA deposition approaches. On rutile, Pt SAs provide hardly any co-catalytic effect. Most remarkable, for P25, the loading of Pt SAs from precursor solution with a very low concentration (

Summary Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.

In this work, we grow intrinsically Cu-doped TiO2 nanotubes (TiNTs) by self-organizing anodization of Ti–Cu binary alloys. We demonstrate that up to a copper concentration of 1.5 at.% in the alloy, self-ordered Cu2+-doped nanotubes can be grown. Under UV illumination the Cu2+ ion-doped oxide structures can be converted to nanotubes that carry metallic nanoparticles (NPs) uniformly decorated on top of the TiNTs. We investigate the formation of these metallic nanoparticles under UV illumination by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The resulting intrinsic copper-doped and decorated TiNTs have a strongly enhanced photocatalytic activity for H2 evolution in comparison to pristine TiNTs. Key is the light-induced conversion of the intrinsic Cu dopant to metallic copper nanoparticles that act as a stable co-catalyst for H2 generation. Keywords: TiO2, Cu doped TiO2, Photocatalytic activity, Intrinsic copper decoration

Here we report that both-end open anodic TiO2 nanotube membranes, after sensitization with a Ru(II)-based dye, exhibit visible-light switching properties for flow-through the nanotube channels. Under illumination, the gate is in an open state providing ∼four-times faster permeation of small molecules through the membrane compared to a dark state. Switching is reversible with no apparent dye degradation being observed. Gating is possible not only of permeating dye molecules but also of nanoprobes such as polystyrene nanospheres. Supported by quantitative modelling, we attribute the switching mechanism to light-induced changes of the charge distribution at the dye/TiO2 interface which in turn alters the hydrodynamics within the anodic tube membranes. This demonstrates that these simple dye-sensitized nanotube membranes can be used as an optically addressable flow-through gate in nanofluidics.

In this work we describe the synthesis and electrochemical properties of nitridated hierarchical TiO$_2$ nanotubes as an electrode for supercapacitors. The hierarchical TiO$_2$ nanostructures are formed by a controlled layer-by-layer TiO2 nanoparticle decoration on self-organized spaced TiO$_2$ nanotubes. These structures are then annealed in NH$_3$ atmosphere at elevated temperature to convert the material to a nitride structure -- this drastically enhances their electron-transport properties. The areal capacitance of hierarchical structures can be tuned by changing the number of decorated TiO$_2$ nanoparticle layers. The capacitance enhancement of the hierarchical structures reaches a maximum when the surface area through nanoparticle deposition is highest and the conductivity via nitridation is optimized.

In this work we study the depth composition of anodic TiO2 nanotube layers. We use elemental depth profiling with Glow Discharge Optical Emission Spectroscopy and calibrate the results of this technique with X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). We establish optimized sputtering conditions for nanotubular structures using the pulsed RF mode, which causes minimized structural damage during the depth profiling of the nanotubular structures. This allows to obtain calibrated sputter rates that account for the nanotubular “porous” morphology. Most importantly, sputter-artifact free compositional profiles of these high aspect ratio 3D structures are obtained, as well as, in combination with SEM, elegant depth sectional imaging.

In the present work we grow anodic TiO2 nanotube layer with a tube diameter > 500 nm and an open tube mouth. We use this morphology in dye-sensitized solar cells (DSSCs) and show that these tubes allow the construction of hybrid hierarchical photoanode structures of nanotubes with a defined and wall-conformal TiO2 nanoparticle decoration. At the same time, the large diameter allows the successful establishment of an additional (insulating) blocking layer of SiO2 or Al2O3 on the tube wall. We show that this combination of hierarchical structure and blocking layer significantly enhances the solar cell efficiency by suppressing recombination reactions. In such a DSSC structure, the solar cell efficiency under back side illumination with AM1.5 illumination is enhanced from 3% for the neat tube to 5 % for the hierarchical structure, to 7 % when additionally a blocking layer is attached.

In the present work we show how to achieve different nanotube morphologies (namely, not only single- and double-walled tubes, but also a tube-in-tube configuration) by combining specific anodization parameters. We characterize as-grown tube layers in terms of morphology, chemical composition and properties. As-grown tubes exhibit a double-walled morphology, that is, they consist of an inner and an outer shell. The low quality inner shell can be removed by an optimized chemical treatment thus leading to nanotubes of a higher quality oxide and with a single-walled nature. Double-walled tubes grown at low electrolyte temperature provide a thick inner shell that after adequate annealing can form a unique tube-in-tube morphology.

Recently, sodium ion batteries (SIBs) have been widely investigated as one of the most promising candidates for replacing lithium ion batteries (LIBs). For SIBs or LIBs, designing a stable and uniform solid electrolyte interphase (SEI) at the electrode–electrolyte interface is the key factor to provide high capacity, long‐term cycling, and high‐rate performance. In this paper, it is described how a remarkably enhanced SEI layer can be obtained on TiO2 nanotube (TiO2 NTs) arrays that allows for a strongly improved performance of sodium battery systems. Key is that a Li+ pre‐insertion in TiO2 NTs can condition the SEI for Na+ replacement. SIBs constructed with Li‐pre‐inserted NTs deliver an exceptional Na+ cycling stability (e.g., 99.9 ± 0.1% capacity retention during 250 cycles at a current rate of 50 mA g−1) and an excellent rate capability (e.g., 132 mA h g−1 at a current rate of 1 A g−1). The key factor in this outstanding performance is that Li‐pre‐insertion into TiO2 NTs leads not only to an enhanced electronic conductivity in the tubes, but also expands the anatase lattice for facilitated subsequent Na+ cycling.

In this work, we report on the electrochemical behavior of nitrided spaced TiO$_2$ nanotubes conformally coated with a nanocrystalline Nb$_2$O$_5$ layer and find for these hierarchical structures an excellent supercapacitor performance. Highly aligned conductive 1D electrodes were obtained by a three step process: i) growth of self-organized nanotubes with defined and adjustable intertube spacing, ii) conformal Nb$_2$O$_5$ decoration in the tube interspace (while providing full electrolyte access to the entire active area), and iii) high temperature nitridation. Key is the growth of a nanotube array with regular tube-to-tube interspacing that enables an optimized decoration with secondary materials such as Nb$_2$O$_5$. We observe an increase in electrode capacitance from 158 $\mu$F cm-2 for bare TiO$_2$ NTs, to 1536 $\mu$F cm-2 for TiO$_2$/Nb$_2$O$_5$ NTs, to finally 37 mF cm-2 for Nb$_2$O$_5$ decorated and then nitrided nanotubes. This drastic increase can be ascribed firstly to the defined spacing established between the tube arrays that then allows for a conformal coating with a secondary active coating. Secondly, nitridation causes a drastic increase of the electron conductivity of the entire scaffold and thus reduces resistive losses.

Photoelectrochemical (PEC) water splitting is a promising method for the conversion of solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α‐Fe2O3) is one of the most attractive materials for a highly efficient charge carrier generation and collection due to its large specific surface area and the short minority carrier diffusion length. In the present work, the PEC water splitting performance of nanostructured α‐Fe2O3 is investigated which was prepared by anodization followed by annealing in a low oxygen ambient (0.03 % O2 in Ar). It was found that low oxygen annealing can activate a significant PEC response of α‐Fe2O3 even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The photocurrent of the α‐Fe2O3 annealed in the low oxygen at 1.5 V vs. RHE results as 0.5 mA cm−2, being 20 times higher than that of annealing in air. The obtained results show that the α‐Fe2O3 annealed in low oxygen contains beneficial defects and promotes the transport of holes; it can be attributed to the improvement of conductivity due to the introduction of suitable oxygen vacancies in the α‐Fe2O3. Additionally, we demonstrate the photocurrent of α‐Fe2O3 annealed in low oxygen ambient can be further enhanced by Zn‐Co LDH, which is a co‐catalyst of oxygen evolution reaction. This indicates low oxygen annealing generates a promising method to obtain an excellent PEC water splitting performance from α‐Fe2O3 photoanodes., Low oxygen annealing can activate a significant photoelectrochemical response of α‐Fe2O3 even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The α‐Fe2O3 annealed in low oxygen ambient contains beneficial defects and promotes the transport of photogenerated holes; it can be attributed to the introduction of suitable oxygen vacancies in the α‐Fe2O3.

Here we report that both-end open anodic TiO

Single atom (SA) catalysis, over the last 10 years, has become a forefront in heterogeneous catalysis, electrocatalysis, and most recently also in photocatalysis. Most crucial when engineering a SA catalyst/support system is the creation of defined anchoring points on the support surface to stabilize reactive SA sites. Here, a so far unexplored but evidently very effective approach to trap and stabilize SAs on a broadly used photocatalyst platform is introduced. In self-organized anodic TiO2 nanotubes, a high degree of stress is incorporated in the amorphous oxide during nanotube growth. During crystallization (by thermal annealing), this leads to a high density of Ti3+-O-v, surface defects that are hardly present in other common titania nanostructures (as nanoparticles). These defects are highly effective for SA iridium trapping. Thus a SA-Ir photocatalyst with a higher photocatalytic activity than for any classic co-catalyst arrangement on the semiconductive substrate is obtained. Hence, a tool for SA trapping on titania-based back-contacted platforms is provided for wide application in electrochemistry and photoelectrochemistry. Moreover, it is shown that stably trapped SAs provide virtually all photocatalytic reactivity, with turnover frequencies in the order of 4 x 10(6) h(-1) in spite of representing only a small fraction of the initially loaded SAs. Web of Science 31 30 art. no. 2102843

We report on free-standing Ta3N5 nanotubular membranes with open top and bottom, used as visible-light-active, flow-through photocatalytic micro-reactors. We grow first a robust anodic Ta2O5 layer, lift-off a membrane and convert to Ta3N5. Such membranes can easily, in a flow-through mode, degrade methylene blue under visible light (wavelength >400 nm) or solar illumination.

'Black' TiO2 -in the widest sense, TiO2 reduced by various treatments-has attracted tremendous scientific interest in recent years because of some outstanding properties; most remarkably in photocatalysis. While the material effects visible light absorption (the blacker, the better), black titania produced by high pressure hydrogenation was recently reported to show another highly interesting feature; noble-metal-free photocatalytic H2 generation. In a systematic investigation of high-temperature hydrogen treatments of anatase nanoparticles, TEM, XRD, EPR, XPS, and photoelectrochemistry are used to characterize different degrees of surface hydrogenation, surface termination, electrical conductivity, and structural defects in the differently treated materials. The materials' intrinsic activity for photocatalytic hydrogen evolution is coupled neither with their visible light absorption behavior nor the formation of amorphous material, but rather must be ascribed to optimized and specific defect formation (gray is better than black). This finding is further confirmed by using a mesoporous anatase matrix as a hydrogenation precursor, which, after conversion to the gray state, even further enhances the overall photocatalytic hydrogen evolution activity.

In this work we introduce the use of TiN/Ti2N layers as a back contact for Ta3N5 membranes of lifted-off anodic Ta3N5 nanotubular layers. In photoelectrochemical H2 generation experiments under simulated AM 1.5G light, a shift in the onset potential of anodic photocurrents to lower potentials is observed, as well as a higher magnitude of the photocurrents compared to a conventional Ta3N5 nanotubular layer (Ta3N5/Ta, ~0.5 VRHE). We ascribe this beneficial effect to the improved conductive properties of the TiNx-based back contact layer that enables a facilitated electron transport from the tantalum nitride based materials to the conductive substrate. Keywords: Tantalum nitride, Nanotubular membranes, Titanium nitride, Water splitting

We report the fabrication of defect-free crystalline TiO2 nanotube (NT) membranes that maintain a full anatase phase composition up to an annealing temperature of 950 °C. Key is the use of a lactic acid electrolyte for the growth of the anodic nanotube layers. These nanotube layers are mechanically sufficiently robust to fabricate, by chemical etching, lift-off and annealing, both-end-open membranes that feature no morphological damage over their entire surface area and thickness. We illustrate the beneficial use of the pure anatase membranes for a flow-through photocatalytic application, i.e., the photodegradation of Acid Orange 7. However, it is anticipated that these pure anatase membranes will also have a wide range of uses in photo(electrochemical) applications of TiO2. Keywords: TiO2 nanotubes, Robust nanotube membranes, Anatase, Organic dye photodegradation

In the present work we grow self-organized TiO2 nanotube arrays with a defined and controlled regular spacing between individual nanotubes. These defined intertube gaps allow one to build up hierarchical 1D-branched structures, conformally coated on the nanotube walls using a layer by layer nanoparticle TiO2 decoration of the individual tubes, i.e. having not only a high control over the TiO2 nanotube host structure but also on the harvesting layers. After optimizing the intertube spacing, we build host–guest arrays that show a drastically enhanced performance in photocatalytic H2 generation, compared to any arrangement of conventional TiO2 nanotubes or conventional TiO2 nanoparticle layers. We show this beneficial effect to be due to a combination of an increased large surface area (mainly provided by the nanoparticle layers) with a fast transport of the harvested charge within the passivated 1D nanotubes. We anticipate that this type of hierarchical structures based on TiO2 nanotubes with adjustable spacing will find even wider application, as they provide an unprecedented controllable combination of surface area and carrier transport.

In the present work we grow anodic self-organized Ta2O5 nanotube layers, which are converted by ammonolysis to Ta3 N5 nanotubes, and then are used as photoanodes for photoanalytic water splitting. We introduce a two-step anodization process that not only improves order (reduced growth defects) and overall light absorption in the nanotube layers, but also provides a significantly reduced interface charge resistance at the nitride/metal interface due to subnitride (TaNx ) formation. As a result, such nanotube anodes afford a 15-fold increase of the photocurrent compared with conventional nanotubular Ta3 N5 electrodes under AM 1.5 G simulated sunlight (100 mW cm(-2)) conditions.

In the present work we report significant enhancement of the photoelectrochemical properties of self- organized TiO2 nanotubes by a combined "de-coring" of classic nanotubes followed by an appropiate TiCl4 treatment. We show that, except for the expected particle decoration, a key effect of the TiCl4 treatment is that the electron transport characteristics in TiO2 nanotubes can be drastically improved, for example, we observe an enhancement of up to 70 % in electron-transport times.

In the present work we investigate the utilization of Pt nanoparticles produced by atomic layer deposition (ALD) within anodic TiO2 nanotube (NT) layers for photocatalytic H2 production. By varying the number of ALD cycles, Pt nanoparticles with different diameters were produced, uniformly decorating the tube walls. The Pt nanoparticle size (2–15nm), the Pt mass loading and areal density were strongly dependent on the number of Pt ALD cycles. The deposited Pt nanoparticles turned out to be highly effective as a co-catalyst for photocatalytic H2 generation. The most effective performance for solar light photocatalysis was reached after 26 ALD cycles (yielding an optimal area coverage with particles of diameter ≈7nm). For UV light, the optimum photocatalytic efficiency was reached after 40 ALD cycles. Keywords: TiO2 nanotubes, Platinum, Photocatalysis, H2 evolution, Atomic layer deposition

Titania is one of the key materials used in 1, 2 and 3D nanostructures as electron transport media in energy conversion devices. In the present work we show that the electronic properties of TiO2 nanotubes can be drastically improved by inducing a nanotwinned grain structure in the nanotube wall. This structure can be exclusively induced for “single-walled” nanotubes with a high temperature treatment in pure oxygen atmospheres. Nanotubes with a twinned grain structure within the tube wall show a strongly enhanced conductivity and photogenerated charge transport compared to classic nanotubes. We exemplify this remarkable improvement in the electronic properties by using nanotwinned TiO2 nanotubes in dye-sensitized solar cells where a significant increase in efficiency of up to 10.2% is achieved.

We report on free-standing Ta

Herein, we grew anodic TiO

In this study, hierarchically porous carbon nanofibers (HPCNFs) containing numerous electroactive heteroatoms are prepared by controlling carbonization and chemical activation. The HPCNFs have a large surface area of 2862.1 m 2 g −1 , hierarchical porous structure, and 20.6 at% electroactive oxygen atoms. These HPCNFs exhibit excellent electrochemical performance, and their thermal treatment with melamine results in nitrogen-doped HPCNFs (N-HPCNFs) with 9.1 at% nitrogen and improved electrical property (1.8 × 10 2 Ω □ −1 ). The electrochemical performance of N-HPCNFs is better than that of HPCNFs, displaying specific energy of 113 Wh kg −1 , specific power of 105 kW kg −1 , and stable cycle life of over 5000 cycles.

In the present work we report on TiO2 nanotube arrays (TNTAs) that were converted to a conductive scaffold established via an optimized reduction treatment in Ar/H2. These conductive TNTAs are then employed for RuO2 nanoparticle decoration. The effect of the Ar/H2 treatment is evaluated by electron energy loss spectroscopy (EELS) and electron paramagnetic resonance (EPR). The results show that, under ideal conditions, buried Ti3+ states are formed, with a higher concentration in the inner shell of the nanotube. Together with the capacitive and conductive performance, investigated by solid-state conductivity and electrochemical measurements, we find that 20 μm long TNTAs, annealed at 550 °C in Ar/H2, yield an optimized and stable structure that provides a remarkably low resistivity of 13.5 KΩ/tube (vs. 70.2 MΩ for non-treated nanotubes). In cycling experiment, with a loading of only 0.048 mg cm−2 RuO2 a specific capacitance of 1297 F g−1 can be reached. The reason for this highly efficient use of RuO2 is that the conducting core-shell scaffold provides a unique, well dispersed RuO2 nanoparticle structure (∼2.8 nm), which is responsible for the high specific capacitance, and moreover yields an excellent long-term cycling stability.

In the present work we introduce the formation of highly ordered single-walled TiO2 nanotubes based on anodizing nanoimprinted titanium substrates. In a first step, anodization on nanoimprinted substrates leads to the formation of highly ordered TiO2 nanotubes. These as-formed TiO2 nanotubes have a double-walled nature. After an optimized chemical treatment in piranha solution, the inner wall is removed and an array of single-walled TiO2 nanotubes is obtained that has a high degree of hexagonal ordering. These single walled arrangements show an enhanced photocatalytic activity for H2 evolution in comparison with classic self-ordered TiO2 nanotubes. Keywords: Nanoimprinting, Anodization, Single walled TiO2 nanotube, Photocatalysis

The electrical transport properties of anodically grown TiO2 nanotubes was investigated. Amorphous nanotubes were anodically grown on titanium foil and transformed through annealing into the anatase phase. Amorphous and polycrystalline single nanotubes were isolated and contacted for measurements of the electrical resistance. Non-linear current-voltage characteristics were explained using the fluctuation induced tunneling conduction model. A clear enhancement of the conductance was induced in an insulating anatase nanotube through low-energy Ar/H ion irradiation. Confocal Raman spectroscopy shows that the annealed samples were in anatase phase and a blueshift due to phonon confinement was observed., Comment: 7 pages, 5 figures

IrO2, a water electrolysis catalyst, has been known to be effective in preventing corrosion of the carbon support in proton exchange membrane fuel cells (PEMFCs). Particulate IrO2 can agglomerate easily, which can decrease substantially the catalytic surface area required for oxygen evolution reaction, causing the loss of catalytic efficiency. Furthermore, agglomerated IrO2 nanoparticles can have an adverse effect on the oxygen reduction reaction by covering the active surface area of the Pt/C cathode catalyst, which is a damaging factor for the intrinsic performance of PEMFC. Carbon-supported iridium oxide, IrO2/C, which can prevent the agglomeration of Ir nanoparticles more effectively, was synthesized to overcome these problems. Compared to the cell with the Pt/C cathode only, the cell with 10 wt.% IrO2 particles and Pt/C cathode showed stronger durability during fuel starvation but the cell performance at normal operation decreased severely by 35%. The cell with the same amount of IrO2 dispersed on a carbon support, 10 wt.% IrO2/C, showed similar durability during fuel starvation maintaining the cell performance comparable to the cell using a Pt/C cathode only. Carbon-supported IrO2, IrO2/C, was more effective than IrO2 particles in both maintaining the intrinsic performance and improving the cell durability during fuel starvation.

In the present work we grow self-organized TiO

'Black' TiO

In the present work we introduce a path to the controlled construction of DSSCs based on hierarchically structured single walled, self-organized TiO2 layers. In a first step we describe a simple approach to selectively remove the inner detrimental shell of anodic TiO2 nanotubes (NTs). This then allows controlled well-defined layer-by-layer decoration of these TiO2-NT walls with TiO2 nanoparticles (this in contrast to conventional TiO2 nanotubes). We show that such defined multiple layered decoration can be optimized to build dye sensitized solar cells that (under back-side illumination conditions) can yield solar light conversion efficiencies in the range of 8 %. The beneficial effects observed can be ascribed to a combination of three factors : 1) improved electronic properties of the single walled tubes themselves, 2) a further improvement of the electronic properties by the defined TiCl4 treatment, and 3) a higher specific dye loading that becomes possible for the layer-by-layer decorated single walled tubes., Comment: arXiv admin note: text overlap with arXiv:1610.06437

Subnitrides strongly enhance the efficiency of Ta3 N5 -nanotube photoanodes in photochemical water splitting. The fabrication of Ta3 N5 nanotube layers with a controlled subnitride layer at the interface to the back contact is demonstrated. The insertion of this subnitride layer has a strong influence on the electron transfer to the back contact, and as a result leads to a drastic shift in photocurrent onset potential and a considerable enhancement of photocurrent conversion efficiency.