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High energy shot peening (HESP) as a common near-surface severe plastic deformation (NS-SPD) was employed to create a severely deformed surface with ultrafine grains and dense crystallographic defects (e.g., grain boundaries, dislocations, and twins) on GTD-111 Ni superalloy. The fluoride-induced corrosion performance of HESPed GTD-111 and its solution-annealed counterpart is comparatively studied using immersion tests, grazing-incidence X-ray diffraction (GI-XRD) analysis, electrochemical techniques and glow discharge optical emission spectroscopy (GDOES). As supported by the immersion tests and electrochemical measurements, HESPed GTD-111 exhibits corrosion film with higher resistance and lower passivity current density at the expense of a higher initial corrosion rate. Both samples suffer pitting corrosion; however, the solution-annealed one shows deeper and larger pits. The dense distribution of crystallographic defects on the surface of HESPed sample significantly increases the diffusion of alloying elements to the corrosion front. The GDOES depth profiles reveal that (i) a thicker corrosion film with a higher contribution of alloying elements (namely, Cr, Ti, Co, and Al) is developed on the HESPed sample, and (ii) the corrosion films formed on the solution-annealed and HESPed samples consist of an outer F-rich part and an inner O-rich region. The protective mechanism of NS-SPD is discussed by a physical model.

In the present research, we investigate the synergistic effects of Ru-doping and Ar/H2 reduction treatment on the photoelectrochemical water splitting performance and hydrogen evolution rate of TiO...

Developing ultraefficient electrocatalytic materials for the hydrogen evolution reaction (HER) with low content of expensive platinum group metals (PGMs) via low-energy-input procedures is the key to the successful commercialization of green water electrolysis technologies for sustainable production of high-purity hydrogen. In this study, we report a facile room-temperature synthesis of ultrafine metallic Ir nanoparticles on conductive, proton-intercalated TiO2 nanotube (H-TNT) arrays via galvanic displacement. A series of experiments demonstrate that a controlled transformation of the H-TNT surface microstructure from neat open-top tubes to disordered nanostripe bundles (“nanograss”) is highly beneficial for providing an abundance of exposed Ir active sites. Consequently, for nanograss-engineered composites, outstanding HER activity metrics are achieved even at very low Ir(III) precursor concentrations. An optimum Ir@TNT cathode loaded with 5.7 μgIr cm−2 exhibits an overpotential of −63 mV at −100 mA cm−2 and a mass activity of 34 A mgIr−1 at −80 mV under acidic conditions, along with excellent catalytic durability and structural integrity. Density functional theory (DFT) simulations reveal that the hydrogen-rich TiO2 surface not only stabilizes the deposited Ir and weakens its H binding strength to a moderate intensity, but also actively takes part in the HER mechanism by refreshing the Ir catalytic sites near the Ir|H–TiO2 interface, thus substantially promoting H2 generation. The comprehensive characterization combined with theory provides an in-depth understanding of the electrocatalytic behavior of H-TNT supported PGM nanoparticles and demonstrates their high potential as competitive electrocatalyst systems for the HER.

The primary focus of the paper is the fabrication of nanotubes via a two steps anodizing procedure on a TiZr substrate followed subsequent annealing treatments and their effect on surface and biocompatibility. The two step anodizing process is optimized for obtaining uniform and ordered nanotubular structures, that are then annealed in air or reduced in an Ar/H2 environment. The high aspect ratio nanotubular structures (diameter 160 nm, length 9.4 μm) maintained their morphology after annealing or reduction. While the thermal treatments burned-off the fluoride, they converted the tubes to ZrTiO4 (annealing in air) or (Zr0.333 Ti0.666)O2 (reducing). Surface roughness and adhesion forces evaluation of the nanostructures was included in the AFM investigations, and show that these properties can be tuned. In vitro cell response to TiZr substrate and nanotubular coatings were analyzed using HGF-1 gingival fibroblasts cell line and LDH, nitric oxide (NO) and reactive oxygen species (ROS) tests. Regarding the hydrophilic balance of the studied samples, as expected it decreased after annealing and but increased after reduction, with only small change in the cell response. The results suggest that these coatings are biocompatible with human gingival fibroblast and can be used in biomedical applications without generating any considerable inflammatory process. Keywords: Anodizing, Thermal treatments, Roughness, Adhesion, Biocompatibility

TiO2 nanostructures represent a key platform for biomedical applications, due to the combination of biocompatibility and high surface area. Especially TiO2 nanotube layers have been widely investigated due to controllable nanotopographic effects as well as for electrodes in electrostimulation experiments. In the present work we produce Ar/H2-reduced 'black' TiO2 nanotube arrays with a strongly enhanced electrical conductivity and explore their interaction with mesenchymal stem cells when used as electrodes to apply electric fields (EF) across the cells. While we observe no significant change in cell adhesion and their focal contact formation on these high conductivity nanotubes, we do observe a rapid stem cell response when EF is engaged using the 'black' TiO2 nanotube arrays as electrodes. Compared to as-formed nanotube arrays, a faster stem cell growth was observed and a lower EF intensity caused an intracellular calcium level elevation. Our results indicate that the increased conductivity in TiO2 nanotubes significantly enhances the early stem cell response to minimal electric field stimuli. STATEMENT OF SIGNIFICANCE: The use of TiO2 nanostructures in biomedical applications is widely investigated, especially considering the nanostructured surface influence on the biomaterial-cell interactions. We have previously shown that an applied electric field (EF) on stem cells grown on TiO2 nanotubes leads to synergistic osteogenic stimulation in the absence of biochemical bone-inducing supplements. Here we report that black (i.e. highly conductive nanotubes obtained by reduction treatments) TiO2 nanotubes enable short-time EF effects on stem cells: we observe a faster stem cell growth and a significantly enhanced early stem cell response to minimal EF stimuli. The application of such nanostructures under electric field is promising for therapeutic interventions for bone regeneration and tissue engineering approaches.

In the present work, we investigate the efficiency of TiO2 photoelectrode layers on boron doped diamond foil (BDDF) in comparison with a classic conducting glass (FTO) back contact. Crystalline thin TiO2 layers were prepared on the substrates by two different methods: (i) deposition of metallic Ti thin films followed by thermal oxidation to form TiO2 (TO-TiO2), (ii) reactive sputter deposition of TiO2 thin films and crystallization of these layers (SP-TiO2). Optimized layers show that TO-TiO2 films on BDDF deliver a significantly higher incident photon to current efficiency (IPCE) compared to directly sputtered SP-TiO2 layers and these layers on BDDF also outperform conducting glass (FTO) as a back contact. We ascribe this beneficial effect of the BDDF back contact to the formation of an intermediate conductive phase of Ti-carbides at the TO-TiO2/BDDF interface.

Au nanoparticles at the surface of TiO2 can improve the photocatalytic H2 generation performances because of their electron transfer cocatalytic ability. The key to maximize the cocatalytic effect is a fine control over Au nanoparticle size and placement on the photocatalyst, in relation to parameters such as the TiO2 morphology, illumination wavelength and pathway, and light penetration depth in the photocatalyst. Here we present an approach for site-selective intrinsic decoration of anodic TiO2 nanotubes (TNs) with Au nanoparticles: we produce, by Ti and Au cosputtering, Ti–Au alloy layers that feature compositional gradients across their thickness; these layers, when anodized under self-ordering electrochemical conditions, can form Au-decorated TNs where the Au nanoparticle density and placement vary according to the Au concentration profile in the metal alloy substrates. Our results suggest that not only the amount but also the Au cocatalyst placement can strongly affect the photocatalytic H2 evolutio...

Recent work demonstrated that intrinsic Au nanoparticle decoration of TiO2 nanotube arrays (NTs) can be achieved by electrochemical anodization of Ti–Au alloy substrates. However, for a Ti–Au cast alloy produced by melt-alloying, the Au concentration cannot exceed the solubility limit of Au in Ti of 0.2 at.% – this sets constraints on the intrinsic Au nanoparticle loading on anodic TiO2 NTs. Here we explore “metastable” Ti–Au metal substrates that are produced by Ti and Au cosputtering and we establish Au concentrations that far exceed the solubility limit in cast Ti–Au alloys. We show the use of these “metastable” Ti–Au sputtered layers for the anodic formation of TiO2 NTs with a much higher density of Au nanoparticle loading than using classic alloys. Under optimized conditions (Au nanoparticle density) photocatalytic H2 production from such Au@TiO2 platforms provides a 15 times higher photocatalytic H2 evolution rate than the best rates achieved with conventional alloys.

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

The use of titanium dioxide (TiO2) for photocatalytic applications has been intensively investigated for years due to appropriate electronic properties, chemical and photocorrosion resistance, as well as the low cost of the material [1]. Although TiO2 has a suitable conduction band position for the photocatalytic H2 formation reaction, the hydrogen evolution reaction from water on a TiO2 surface is kinetically hampered. To tackle this problem, typically decoration with noble metals such as Pt, Pd, Au that act as a co-catalyst is employed. However, these noble metals are costly and a variety of pathways for replacing these elements have been explored. One of the promising substitutes for noble metals are copper and copper-compounds. The fabrication of copper co-catalyst loaded TiO2 nanotubes is conventionally carried out by chemical methods such as hydrothermal, impregnation, photo-deposition and electrochemical deposition [2]. However, a most straightforward and unique method to modify anodic TiO2 nanotube properties is employing, instead of pure Ti metallic substrate, a Ti‐X alloy in the anodization process, were X is another metal. During anodizing the second metal can be simultaneously oxidized and doped into the TiO2 lattice (in substitutional or interstitial position), giving the nanotubes a specific functionality [3–5]. A number of such intrinsically doped nanotube arrays have been reported, namely using Nb, Ta, Ru and etc., alloyed in Ti [3–5]. 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 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 provide a strongly enhanced photocatalytic activity for H2 evolution in comparison to pristine TiNTs. Key is the light induced conversion of the intrinsic Cu doping to metallic copper nanoparticles that act as a stable co-catalyst for H2 generation. [1] K. Lee, A. Mazare, P. Schmuki, Chem. Rev. 2014, 114, 9385–9454. [2] M. Janczarek, E. Kowalska, Catalysts. 2017, 7, 317-324. [3] P. Roy, C. Das, K. Lee, R. Hahn, T. Ruff, M. Moll, P. Schmuki, J. Am. Chem. Soc. 2011, 133, 5629–5631. [4] M. Altomare, K. Lee, M.S. Killian, E. Selli, P. Schmuki, Chem. - A Eur. J. 2013, 19, 5841–5844. [5] C. Das, P. Roy, M. Yang, H. Jha, P. Schmuki, Nanoscale. 2011, 3, 3094–3096. Figure 1

Single‐atom (SA) or single‐site catalysis (SACs) has over the past years become an increasingly fascinating topic in the catalysis field. SACs have allowed new approaches in heterogeneous catalysis, minimized the use of precious metals, and enabled an unprecedented control over atomistic effects, resulting in improved active sites, and at the same time enabled the design of metal–support interfaces with a high level of structural and chemical control [1,2]. A diverse range of supports and features is known to stabilize isolated metal atoms, notably through pinning at electronic and/or structural defects associated with coordinatively unsaturated sites. However, it is still difficult to create a high density of thermally stable support sites, and hence the fabrication and control of high SA loading remains a challenge [1,2]. In this work, an atomic‐scale defect engineering approach to form and control traps for SA sites as co‐catalyst for photocatalytic H2 generation is described. The control over defect types and density can be monitored by electron paramagnetic resonance spectroscopy (EPR) as the most precise method to study atomic scale defects [3]. Thin sputtered TiO2 layers are used as a model photocatalyst, and compared to the more frequently used (001) anatase sheets. To form stable SA co-catalysts, the TiO2 layers are reduced in Ar/H2 under different conditions (leading to different but defined Ti3+‐Ov surface defects), followed by immersion in a dilute solution containing Pt ion in this study. HAADF‐STEM results show that only on the thin‐film substrate can the density of SA sites be successfully controlled by the degree of reduction by annealing. An optimized SA‐Pt decoration can enhance the normalized photocatalytic activity of a TiO2 sputtered sample by a great extent in comparison to a conventional nanoparticle‐decorated TiO2 surface. Most interestingly, in the follow up work based on DFT calculations and experimental data we show that Pd single atom outperforms Pt as the most active co-catalyst for photocatalytic H2 evolution [4]. HAADF‐STEM, XPS, and EPR investigation jointly confirm the atomic nature of the decorated Pt and Pd on TiO2. Importantly, the density of the relevant surface exposed defect centers—thus the density of SA sites, which play the key role in photocatalytic activity—can be precisely optimized. [1] Sh. Mohajernia et al. Adv. Mater. 2020, 32 (16). [2] A. Wang, J. Li, and T. Zhang, Nat. Rev. Chem., 2(6). [3] Sh. Mohajernia et al. J. Mater. Chem. A, 2020, 8(1432) [4] G. Cha et al. iScience, 2021, 8 (24). Figure 1

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.

Reduced titanium dioxide has recently attracted large attention, particularly for its unique co-catalyst-free H$_2$ heterogeneous photocatalytic application. The enhanced photocatalytic activity of the reduced TiO$_2$ was previously ascribed to the introduction of point crystal defects (mainly Ti$_3^+$ centers), which result in the formation of intrinsic co-catalytic centers and enhanced visible light absorption. In this work, we systematically investigate the effect of different defects in the TiO$_{2-x}$ lattice on photocatalytic H$_2$ evolution. To introduce different types of defects, thermal annealing in air (oxidative), Ar (inert), Ar/H$_2$ (reducing), and H$_2$ (reducing) atmospheres were performed on commercially available anatase nanopowder. Then, the powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) to clarify the effect of treatment on material properties. Furthermore, the defect types were characterized by electron paramagnetic resonance (EPR) spectroscopy. We show that thermal annealing in different atmospheres can form different amounts of different defect types in the TiO$_2$ structure. The highest photocatalytic activation is achieved by annealing the anatase powder in a reducing atmosphere for an appropriate temperature/annealing time. By combining the results from H$_2$ generation and EPR analysis we show that the simultaneous presence of two types of defects, i.e. surface exposed Ti$_3^+$ and lattice embedded Ti$_3^+$ centers, in an optimum low concentration, is the determining factor for an optimized photocatalytic H$_2$ evolution rate. In fact, annealing anatase powder under the so-reported optimized conditions in reducing atmosphere leads to the generation of a considerable amount of H$_2$, with rates as high as 338 $\mu$molh-1g-1.

In this research, we investigate the effect of alkali metal cations including Li, Na and Cs in hydrothermal solution on the morphology, stability, and photoactivity of nanostructured TiO2 nanoflakes as a photoanode. The TiO2 nanoflakes are formed through hydrothermal treatment of Ti foil in 1.0 M LiOH, NaOH or CsOH at 100 °C for 3 h. By subsequent thermal reduction of the structure in an optimized Ar/H2 environment, conductive TiO2 nanoflakes were formed. The reduction treatment remarkably improves the photocurrent density of the TiO2 nanoflakes and has the highest impact on the sample treated in the NaOH alkali solution. For the nanoflakes produced in NaOH alkali solution, the bandgap is shifted to a lower value and the structure shows the most stable morphology after thermal treatment compared to nanoflakes formed in other alkali solutions. Such reduced hydrothermally treated nanoflakes formed in NaOH can generate a photocurrent density of approximately 1 mA/cm−2 vs. Ag/AgCl in 1.0 M KOH solution, which is six times higher than for pristine TiO2.

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.

Photocatalytic $H_2$ evolution reactions on pristine TiO$_2$ is characterized by low efficiencies due to trapping and recombination of charge carriers, and due to a sluggish kinetics of electron transfer. Noble metal (mainly Pt, Pd, Au) nanoparticles are typically decorated as cocatalyst on the TiO$_2$ surface to reach reasonable photocatalytic yields. However, owing to the high cost of noble metals, alternative metal cocatalysts are being developed. Here we introduce an approach to fabricate an efficient noble metal free photocatalytic platform for $H_2$ evolution based on alloyed NiCu cocatalytic nanoparticles at the surface of anodic TiO$_2$ nanotube arrays. NiCu bilayers are deposited onto the TiO$_2$ nanotubes by plasma sputtering. A subsequent thermal treatment is carried out that leads to dewetting, that is, owing to surface diffusion the Ni and Cu sputtered layers simultaneously mix with each other and split into NiCu nanoparticles at the nanotube surface. The approach allows for a full control over key features of the alloyed nanoparticles such as their composition, work function and cocatalytic ability towards $H_2$ generation. Dewetted-alloyed cocatalytic nanoparticles composed of equal Ni and Cu amounts not only are significantly more reactive than pure Ni or Cu nanoparticles, but also lead to $H_2$ generation rates that can be comparable to those obtained by conventional noble metal (Pt) decoration of TiO$_2$ nanotube arrays.

Single-atom (SA) catalysis is a novel frontline in the catalysis field due to the often drastically enhanced specific activity and selectivity of many catalytic reactions. Here, an atomic-scale defect engineering approach to form and control traps for platinum SA sites as co-catalyst for photocatalytic H

With a large-scale usage of portable electric appliances, a high demand for increasingly high density energy storage devices has emerged. MoO3 has, in principle, a large potential as negative electrode material in supercapacitive devices, due to high charge densities that can be obtained from its reversible redox reactions. Nevertheless, the extremely poor electrochemical stability of MoO3 in aqueous electrolytes prevents a practical use in high capacitance devices. In this work, we describe how to overcome this severe stability issue by forming amorphous molybdenum oxide/tantalum oxide nanotubes by anodic oxidation of a Mo-Ta alloy. The presence of a critical amount of Ta-oxide (> 20 at-%) prevents the electrochemical decay of the MoO3 phase and thus yields an extremely high stability. Due to the protection provided by tantalum oxide, no capacitance losses are measureable after 10000 charg-ing/discharging cycles.

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.

Au and Pt do not form homogeneous bulk alloys as they are thermodynamically not miscible. However, we show that anodic TiO2 nanotubes (NTs) can in situ be uniformly decorated with homogeneous AuPt alloy nanoparticles (NPs) during their anodic growth. For this, a metallic Ti substrate containing low amounts of dissolved Au (0.1 atom %) and Pt (0.1 atom %) is used for anodizing. The matrix metal (Ti) is converted to oxide, whereas at the oxide/metal interface direct noble metal particle formation and alloying of Au and Pt takes place; continuously these particles are then picked up by the growing nanotube wall. In our experiments, the AuPt alloy NPs have an average size of 4.2 nm, and at the end of the anodic process, these are regularly dispersed over the TiO2 nanotubes. These alloyed AuPt particles act as excellent co-catalyst in photocatalytic H2 generation, with a H2 production rate of 12.04 μL h–1 under solar light. This represents a strongly enhanced activity as compared to TiO2 NTs decorated with mon...

To control the degradation of magnesium alloys and improve the mechanical performance of common hydroxyapatite (HAp) coatings, a HAp coating containing multi-walled carbon nanotubes (MWCNT) was applied on AZ31 magnesium alloy using plasma spray technique. The coating properties including thickness and morphology, phase analysis and toughness were characterized through SEM, XRD, and indentation methods, respectively. Biodegradation behavior in the presence and absence of slow strain rate test (SSRT) was then thoroughly examined in a simulated body fluid (SBF). The results demonstrated that the stress corrosion cracking (SCC) susceptibility of AZ31 Mg alloy is decreased from 26.8% (HAp coated sample) to 9.8% (HAp/MWCNTs coated one). The combination of microscopic observations as well as mechanical-electrochemical degradation data for long exposure times, suggests that the bridging effect of MWCNTs among molten HAp splats plays a key role in the improvement of mechanical properties and consequently both electrochemical and stress corrosion performances of HAp coating.

Over the past years, α-Fe2 O3 (hematite) has re-emerged as a promising photoanode material in photoelectrochemical (PEC) water splitting. In spite of considerable success in obtaining relatively high solar conversion efficiency, the main drawbacks hindering practical application of hematite are its intrinsically hampered charge transport and sluggish oxygen evolution reaction (OER) kinetics on the photoelectrode surface. In the present work, we report a strategy that synergistically addresses both of these critical limitations. Our approach is based on three key features that are applied simultaneously: i) a careful nanostructuring of the hematite photoanode in the form of nanorods, ii) doping of hematite by Sn4+ ions using a controlled gradient, and iii) surface decoration of hematite by a new class of layered double hydroxide (LDH) OER co-catalysts based on Zn-Co LDH. All three interconnected forms of functionalization result in an extraordinary cathodic shift of the photocurrent onset potential by more than 300 mV and a PEC performance that reaches a photocurrent density of 2.00 mA cm-2 at 1.50 V vs. the reversible hydrogen electrode.

Cu-doping in titania is usually detrimental to the material’s photoconductivity which prevents the use of this combination in photoanodes. In this work, we produce TiO2 nanotube arrays intrinsically doped with copper and establish sufficient conductivity to use them as efficient photoanodes for methanol oxidation in a photoelectrochemical hydrogen generation setting. Firstly, Cu doped TiO2 nanotubes were produced by anodizing a Ti-Cu binary alloy. By subsequent thermal reduction of the structure in an Ar/H2 environment, conductive copper doped TiO2 nanotubes (TiCuTN-Ar/H2) can be achieved with an approximately 103 times higher conductivity than the non-reduced material. When these reduced Cu doped TiO2 nanotubes are used as photoanode, copper species embedded in the TiO2 wall catalyze the methanol oxidation reaction. As a result of the combined effect of conductivity and catalytic effect of Cu, such a reduced Cu:TiO2 nanotubes can generate a photocurrent of 0.76 mA.cm-2 at 1 V vs. RHE, under AM1.5 (100 mW/Cm2) irradiation – in a 50:50 MeOH/water solution – this is 33 times higher than for pristine Cu:TiO2 nanotubes.

Solutions that simulate hydrometallurgical base metal process streams with high nickel (Ni) and minor platinum (Pt) concentrations were used to create Pt/Ni nanoparticles on TiO2 nanotube surfaces. For this, electrochemical deposition – redox replacement (EDRR) was used that also allowed to control the nanoparticle size, density and Pt/Ni content of the deposited nanoparticles The Pt/Ni nanoparticle decorated titanium dioxide nanotubes (TiO2 nanotubes) become strongly activated for photocatalytic hydrogen (H2) evolution. Moreover, EDRR facilitates nanoparticle formation without the need for any additional chemicals and is more effective than electrodeposition alone. Actually, a 10,000-time enrichment level of Pt took place on the TiO2 surface when compared to Pt content in the solution with the EDRR method. The results show that hydrometallurgical streams offer great potential as an alternative raw material source for industrial catalyst production when coupled with redox replacement electrochemistry.

The present work describes a self-assembling photocatalytic system that is observed when illuminating grey titania nanoparticles in suspension with a plain aqueous Ni2+ solution. Such a suspension (in contrast to white titania), under UV illumination, increasingly produces H2 from neutral water. We show that the origin of this self-activation is not the light-induced deposition of Ni0 or another Ni-catalyst compound on the titania surface. Rather, in-situ electron paramagnetic resonance (EPR) clearly indicates that the activation is due to a light-induced formation of a suitable defect structure (Ti3+-OV) on grey titania, combined with the formation of an intermediate monovalent nickel (Ni(I)) electron transfer relay. Remarkably, the resulting Ni+/TiO2/Ti3+ photocatalyst operates in absence of any noble metal or sacrificial agent.

Single-atom (SA) catalysis is a novel frontline in the catalysis field due to the often drastically enhanced specific activity and selectivity of many catalytic reactions. Here, an atomic-scale defect engineering approach to form and control traps for platinum SA sites as co-catalyst for photocatalytic H2 generation is described. Thin sputtered TiO2 layers are used as a model photocatalyst, and compared to the more frequently used (001) anatase sheets. To form stable SA platinum, the TiO2 layers are reduced in Ar/H2 under different conditions (leading to different but defined Ti3+ -Ov surface defects), followed by immersion in a dilute hexachloroplatinic acid solution. HAADF-STEM results show that only on the thin-film substrate can the density of SA sites be successfully controlled by the degree of reduction by annealing. An optimized SA-Pt decoration can enhance the normalized photocatalytic activity of a TiO2 sputtered sample by 150 times in comparison to a conventional platinum-nanoparticle-decorated TiO2 surface. HAADF-STEM, XPS, and EPR investigation jointly confirm the atomic nature of the decorated Pt on TiO2 . Importantly, the density of the relevant surface exposed defect centers-thus the density of Pt-SA sites, which play the key role in photocatalytic activity-can be precisely optimized.

In the present work, we report the use of TiO2 nanotube (NT) layers with a regular intertube spacing that are decorated by Pt nanoparticles through the atomic layer deposition (ALD) of Pt. These Pt‐decorated spaced (SP) TiO2 NTs are subsequently explored for photocatalytic H2 evolution and are compared to classical close‐packed (CP) TiO2 NTs that are also decorated with various amounts of Pt by using ALD. On both tube types, by varying the number of ALD cycles, Pt nanoparticles of different sizes and areal densities are formed, uniformly decorating the inner and outer walls from tube top to tube bottom. The photocatalytic activity for H2 evolution strongly depends on the size and density of Pt nanoparticles, driven by the number of ALD cycles. We show that, for SP NTs, a much higher photocatalytic performance can be achieved with significantly smaller Pt nanoparticles (i.e. for fewer ALD cycles) compared to CP NTs.

Au and Pt do not form homogeneous bulk alloys as they are thermodynamically not miscible. However, we show that anodic TiO

Among several parameters that affect the yield of a photocatalytic process mediated by a metal oxide semiconductor, key is the efficient separation and transfer of photo-generated charge carriers. To overcome kinetic limitations and enable charge transfer, an effective strategy is to decorate the photocatalyst surface with cocatalytic nanoparticles of either a second semiconductor metal oxide or a noble metal. Nevertheless, classical deposition techniques based on powder technology approaches lead to randomly placed cocatalytic nanoparticles at the photocatalytic surface. The poor control over cocatalyst placement can drastically hamper the photocatalytic efficiencies, and can also prevent a full understanding of the charge carrier dynamics and photocatalytic mechanism. Here we investigate a highly defined charge separation platform for photocatalytic H2 evolution based on a Pt-WO3-TiO2 “stacked” structure constructed on anodically grown TiO2 nanotube arrays. Key is the formation of a site-selective and sequential W and Pt metal sputter-decoration only at the mouth of highly-ordered TiO2 nanotubes. After placing the W-Pt bilayer at the nanotubes mouth, a suitable thermal treatment forms a WO3 layer atop the nanotubes while the Pt film undergoes solid state dewetting into 2–6 nm-sized Pt nanoparticles. These structures show strongly improved photocatalytic H2 evolution efficiency compared to any other single-cocatalyst system (Pt-TiO2 and WO3-TiO2) and pristine TiO2 nanotubes. The photocatalytic activity improvement is ascribed to an enhanced charge carrier separation mechanism enabled by the well-defined TiO2-WO3-Pt architecture that provides swift electron transfer through WO3 and towards Pt for H2 evolution.

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.

In the present work we report on the key factors dictating the photoelectrochemical (PEC) performance of suboxide titania (TiO

In the present work we report on the key factors dictating the photo-electrochemical (PEC) performance of suboxide titania (TiOx) nanotubes. TiOx nanotubes were produced by a systematic variation of reduction heat treatments of TiO2 in Ar/H2. The properties of the TiOx tubes were investigated by electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), solid-state conductivity, reflectivity measurements, photocurrent spectroscopy, and photoelectrochemical hydrogen evolution. In line with earlier literature, these suboxide tubes show a drastically improved photoelectrochemical water splitting performance compared to non-reduced anatase TiO2 tubes. In this work we show that the key improvement in water splitting performance is due to the strongly improved conductivity of TiOx semimetalic tubes, reaching 13.5 KΩ/tube compared to 70 MΩ (for non-reduced anatase), and is not due to the enhanced visible light absorbance.

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 investigate the effect of the surface electrokinetic properties and presence of background ions on the flow of a marker dye through TiO2 nanotube membranes. We believe the results to be of high significance not only for filtration but also for the design of microphotoreactor application based on photoactive TiO2 nanotubes membrane. First, both-side open, high aspect ratio TiO2 nanotube membranes were obtained by fast anodization of Ti to self-aligned TiO2 nanotube layers, followed by a lift-off process. Then we investigated the permeation through the TiO2 nanotube membranes by diffusion of acid orange 7 (AO7) and extracted the dye diffusion rates. The effects of pH, ionic concentration, and size of ions were investigated, and the results were compared with theoretical modeling of the surface charge of TiO2 and the neighbouring electric double layer as a function of different species of ions; the modeling confirms the experimental data. We observed a remarkable influence of the background ion species, as well as of ion concentrations and pH in the feed solution on the diffusion rate of AO7. The results of modeling are well in line with the observed influence of TiO2 nanotube inner surface charge and effective size (hydrodynamic radius) of the ions in the background solution. It is also observed that the absolute permeate flux and the membrane’s permeability strongly depend on the electric and wetting conditions of the membrane surface. Keywords: TiO2 nanotube, Membrane, Electrochemical anodization

nanohydroxyapatite (n-HAP) was coated on to AZ31 magnesium alloy in order to reduce the surface corrosion rate and enhance the bio-compatibility. N-HAP was successfully coated by pulse electrodeposition technique. Morphology and composition of the coatings were investigated by scanning electron microscopy and X-ray diffraction methods, respectively. The corrosion behaviors of the coatings were studied by tafel polarization and impedance spectroscopy tests. Results demonstrated that the porosity of the nanostructure coating decrease in comparison with micro structure coating and therefore, corrosion resistance of AZ31 was improved significantly. Also, the adhesion of nanostructure coating was increased and thus it can be introduced as a suitable coating for body implants.

In this study, the inhibitive effect of synthesized 1-(7-methyl-5-morpholin-4-yl-thiazolo[4,5-d]pyrimidin-2-yl)-hydrazine (MMTPH) as a new corrosion inhibitor for mild steel in 0.5 M sulfuric acid medium is investigated employing potentiodynamic polarization, electrochemical impedance spectroscopy and linear polarization resistance techniques. The results show MMTPH reduces anodic dissolution, retards the hydrogen evolution reaction and its adsorption follows Langmuir’s adsorption isotherm. Any increase in temperature will in turn increase corrosion current densities; however, the presence of MMTPH hinders the rate. In solutions with inhibitor concentration of 200 ppm, temperature elevations as great as 30° (25–55 °C) result in a drop of about 45 % in inhibition efficiency (99–55 %). Thermodynamic adsorption parameters show that the MMTPH is absorbed by a spontaneous exothermic process and the adsorption mechanism is physical. Quantum chemical method shows that the MMTPH molecules can be directly adsorbed at the steel surface on the basis of donor–acceptor interactions between π-electrons of pyrimidine, N atoms of hydrazine and vacant d-orbitals of iron atoms.