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In this article, we report a simple ex situ Sn-doping method on hematite nanoflakes (coded as MSnO2-H) that can protect the nanoflake (NF) morphology against the 800 degrees C high-temperature annealing process and activate the photoresponse of hematite until 800 nm wavelength excitation. MSnO2-H has been fabricated by dropping SnCl4 ethanol solution on hematite nanoflakes homogeneously grown over the conductive FTO glass substrate and annealed at 500 degrees C to synthesize the SnO2 nanoparticles on hematite NFs. The Sn-treated samples were then placed in a furnace again, and the sintering process was conducted at 800 degrees C for 15 min. During this step, structure deformation of hematite occurs normally due to the grain boundary motion and oriented attachment. However, in the case of MSnO2-H, the outer SnO2 nanoparticles efficiently prevented a shape deformation and maintained the nanoflake shape owing to the encapsulation of hematite NFs. Furthermore, the interface of hematite/SnO2 nanoparticles became the spots for a heavy Sn ion doping. We demonstrated the generation of the newly localized states, resulting in an extension of the photoresponse of hematite until 800 nm wavelength light irradiation. Furthermore, we demonstrated that SnO2 nanoparticles can effectively act as a passivation layer, which can reduce the onset potential of hematite for water splitting redox reactions. The optimized MSnO2-H nanostructures showed a 2.84 times higher photocurrent density and 300 mV reduced onset potential compared with a pristine hematite nanoflake photoanode. Web of Science

The use of metal composites based on plasmonic nanostructures partnered with catalytic counterparts has recently emerged as a promising approach in the field of plasmon-enhanced electrocatalysis. Here, we report on the role of the surface morphology, size, and anchored site of Pd catalysts coupled to plasmonic metasurfaces formed by periodic arrays of multimetallic Ni/Au nanopillars for formic acid electro-oxidation reaction (FAOR). We compare the activity of two kinds of metasurfaces differing in the positioning of the catalytic Pd nanoparticles. In the first case, the Pd nanoparticles have a polyhedron crystal morphology with exposed (200) facets and were deposited over the Ni/Au metasurfaces in a site-selective fashion by limiting their growth at the electromagnetic hot spots (Ni/Au–Pd@W). In contrast, the second case consists of spherical Pd nanoparticles grown in solution, which are homogeneously deposited onto the Ni/Au metasurface (Ni/Au–Pd@M). Ni/Au–Pd@W catalytic metasurfaces demonstrated higher light-enhanced FAOR activity (61%) in comparison to the Ni/Au–Pd@M sample (42%) for the direct dehydrogenation pathway. Moreover, the site-selective Pd deposition promotes the growth of nanoparticles favoring a more selective catalytic behavior and a lower degree of CO poisoning on Pd surface. The use of cyclic voltammetry, energy-resolved incident photon to current conversion efficiency, open circuit potential, and electrochemical impedance spectroscopy highlights the role of plasmonic near fields and hot holes in driving the catalytic enhancement under light conditions.

In this article, we report a simple

Titanium miniplates are biocompatible materials used in modern oral and maxillofacial surgery to treat facial bone fractures. However, plate removal is often required due to implant complications. Among them, a biofilm formation on an infected miniplate is associated with severe inflammation, which frequently results in implant failure. In light of this, new strategies to control or treat oral bacterial biofilm are of high interest. Herein, the authors exploit the ability of nanorobots against multispecies bacterial biofilm grown onto facial commercial titanium miniplate implants to simulate pathogenic conditions of the oral microenvironment. The strategy is based on the use of light-driven self-propelled tubular black-TiO2/Ag nanorobots, that unlike traditional ones, exhibit an extended absorption and motion actuation from UV to the visible-light range. The motion analysis is performed separately over UV, blue, and green light irradiation and shows different motion behaviors, including a fast rotational motion that decreases with increasing wavelengths. The biomass reduction is monitored by evaluating LIVE/DEAD fluorescent and digital microscope images of bacterial biofilm treated with the nanorobots under motion/no-motion conditions. The current study and the obtained results can bring significant improvements for effective therapy of infected metallic miniplates by biofilm.

A new P- and F-co-doped amorphous carbon nitride (PFCN) has been synthesized via sol-gel-mediated thermal condensation of dicyandiamide. Such synthesized P- and F-co-doped carbon nitride displayed a well-defined mesoporous nanostructure and enhanced visible light absorption region up to infrared with higher BET surface area of 260.93 m2 g-1 ; the highest recorded value for phosphorus-doped carbon nitride materials. Moreover, the formation mechanism is delineated and the role of templates was found to be essential not only in increasing the surface area but also in facilitating the co-doping of P and F atoms. Co-doping helped to narrow the optical band gap to 1.8 eV, thus enabling an excellent photocatalytic activity for the aqueous reduction of carbon dioxide into methanol under visible-light irradiation, which is fifteen times higher (119.56 μmol g-1 h-1 ) than the bare carbon nitride. P doping introduced Bronsted acidity into the material, turning it into an acid-base bifunctional catalyst. Consequently, the material was also investigated for the thermal conversion of common carbohydrates into furanics.

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.

In the present work the authors show that anodic TiO

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.

Valence engineering has been proved an effective approach to modify the electronic property of a catalyst and boost its oxygen evolution reaction (OER) activity, while the limited number of elements restricts the structural diversity and the active sites. Also, the catalyst performance and stability are greatly limited by cationic dissolution, ripening, or crystal migration in a catalytic system. Here we employed a widely used technique to fabricate heteroepitaxial pyrite selenide through dual-cation substitution and a boron dopant to achieve better activity and stability. The overpotential of Ni-pyrite selenide catalyst is decreased from 543 mV to 279.8 mV at 10 mA cm-2 with a Tafel slope from 161 to 59.5 mV dec-1. Our theoretical calculations suggest both cation and boron doping can effectively optimize adsorption energy of OER intermediates, promote the charge transfer among the heteroatoms, and improve their OER property. This work underscores the importance of modulating surface electronic structure with the use of multiple elements and provides a general guidance on the minimization of activity loss with valence engineering.

Copper oxide thin films were deposited by a reactive high power impulse magnetron sputtering (r-HIPIMS) on glass substrates with a SnO2:F (FTO) layer. The pulse magnetron discharge was analyzed via the radio frequency (RF) Sobolewski probe, used for the time-resolved measurement of ion flux density on the substrate. Pulsed discharge current and voltage waveforms were analyzed. It was found that the pulse magnetron discharge worked in a self-sputtering mode with a stable or slightly growing discharge current after pulse discharge stabilization. As-deposited copper oxide films exhibited a certain degree of crystallinity, as identified by XRD, which was further improved after postdeposition annealing at 550 °C in the air. After annealing, the mixture of CuO and Cu2O crystallites was usually found in the films and in a few cases CuO0.96 phase was detected. Deposited films exhibited a p-type conductivity and relatively high photocurrents in the cathodic region after the postdeposition annealing. The highest photocurrent density of ip≈ 1.1 mA cm−2 at potential −500 mV vs. Ag/AgCl was detected for films with a thickness of 1200 nm.

Hematite is a low band gap, earth abundant semiconductor and it is considered to be a promising choice for photoelectrochemical water splitting. However, as a bulk material its efficiency is low because of excessive bulk, surface, and interface recombination. In the present work, we propose a strategy to prepare a hematite (&alpha, Fe2O3) photoanode consisting of hematite nanorods grown onto an iron oxide blocking layer. This blocking layer is formed from a sputter deposited thin metallic iron film on fluorine doped tin oxide (FTO) by using cyclic voltammetry to fully convert the film into an anodic oxide. In a second step, hematite nanorods (NR) are grown onto the layer using a hydrothermal approach. In this geometry, the hematite sub-layer works as a barrier for electron back diffusion (a blocking layer). This suppresses recombination, and the maximum of the incident photon to current efficiency is increased from 12% to 17%. Under AM 1.5 conditions, the photocurrent density reaches approximately 1.2 mA/cm2 at 1.5 V vs. RHE and the onset potential changes to 0.8 V vs. RHE (using a Zn-Co co-catalyst).

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 (

A hybrid of GA@UiO-66-NH2 was synthesized based on the covalent assembly of graphene acid (GA) and the amine functionalized UiO-66 metal-organic framework through amide bonds. This strategy endows the material with unique properties, such as hierarchical pores, a porous conductive network decorated with functional groups, a high specific surface area, and a good chemical and thermal stability. The resultant hybrid has an electrical resistance of similar to 10(4) omega, whereas the pristine GA and UiO-66-NH2 possess an electrical resistance of similar to 10(2) omega and similar to 10(9) omega, respectively. The hybrid GA@UiO-66-NH2 was demonstrated for CO2 chemiresistive sensing and displayed a very fast response and quick recovery time of similar to 18 s for 100% CO2, at 200 degrees C. While the pristine GA exhibits negligible response under the same conditions, GA@UiO-66-NH2 exhibited a response of 10 +/- 0.6%. Further, in situ temperature dependent Raman studies during CO2 exposure confirm the presence of strong hydrogen bonding interaction between CO2 and the amide functionality present on GA@UiO-66-NH2. The resulting gas sensing characteristics of GA@UiO-66-NH2 are majorly attributed to the better interaction of CO2 at the amide/amine functional groups and the readily accessible hierarchical pores. This design strategy opens new horizons in the development of covalently linked hybrids with hierarchical porous conductive networks which can help to improve the gas sensing properties of MOF-based materials. Web of Science 9 32 17441 17434

A new P- and F-co-doped amorphous carbon nitride (PFCN) has been synthesized via sol-gel-mediated thermal condensation of dicyandiamide. Such synthesized P- and F-co-doped carbon nitride displayed a well-defined mesoporous nanostructure and enhanced visible light absorption region up to infrared with higher BET surface area of 260.93 m

Metallic Fe-Ti alloy thin films were deposited by high-power impulse magnetron sputtering (HiPIMS) on a glass substrate with an FTO electrode. Two-component alloys were prepared by sputtering of a single target, which was composed from two sectors made from different elements: iron disc and titanium ring. Chemical composition of alloy thin films was controlled by the width of titanium ring that partially covered iron target. These alloy thin films were anodized in fluorine-containing electrolyte with the aim to create mixed oxide nanostructures. Anodized layers were amorphous and transparent. After calcination, the layers consisted of crystalline Fe2O3 although TiO2 was still amorphous. Photoelectrochemical characterization show that increasing amount of titanium in the alloy results in the fabrication of Fe2O3/TiO2 nanostructures with higher photocurrent compared to those prepared from pure iron by the same anodization technique.

The pyrite iron disulfide thin films are regarded as suitable candidates for construction of low-cost photoelectrochemical (PEC) solar cells. Iron oxide hematite has attracted much attention as possibly convenient material for hydrogen production via PEC water splitting. We refer on preparation of pyrite thin films via thermal sulfidation of hematite films synthetized by a physical methodology of high power impulse magnetron sputtering (HiPIMS) and purely chemical approach of sol-gel. We studied for the first time the correlation between PEC functionality of hematite films and after their sulfidation into pyrite. The highest PEC activity of hematite films of 560 μA cm−2 at 700 mV vs. Ag/AgCl was achieved with the HiPIMS photoelectrodes. The photoefficiency dropped dramatically to 4 μA cm−2 at 600 mV vs. Ag/AgCl after the sulfidation. A significant increase of grains‘ size, residual unreacted hematite, surface defects were the main reasons for the poor photoactivity. The sol-gel produced hematite yielded photocurrent of 30 μA cm−2 and a slight increase to 40 μA cm−2 (recorded at 500 mV vs. Ag/AgCl) of the corresponding pyrite version. Both these electrodes showed also similar morphological characteristics. The structural, electronic and optical properties of the deposited films were determined using various methods e.g. Raman spectroscopy, SEM, and PDS.

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.

In the present work the authors show that anodic TiO2 nanotubes (NT) show excellent harvesting properties for Pt single atoms (Pt SAs) from highly dilute Pt solutions. The tube walls of anodic nanotubes, after adequate annealing to anatase, provide ample of suitable trapping sites—that is, surface Ti3+‐Ov (Ov: oxygen vacancy) defects that are highly effective to extract and accumulate Pt in the form of SAs. A saturated (maximized) SA density can be achieved by an overnight immersion of a TiO2 NT layer to a H2PtCl6 solution with a concentration that is as low as 0.01 mm Pt. Such TiO2 NTs with surface trapped Pt SAs provide a maximized high activity for photocatalytic H2 generation (reaching a turnover frequency (TOF) of 1.24 × 106 h−1 at a density of 1.4 × 105 Pt atoms µm−2)—a higher loading with Pt nanoparticles does not further increase the photocatalytic activity. Overall, these findings show that anodic TiO2 nanotubes provide a remarkable substrate for Pt extraction and recovery from very dilute solutions that directly results in a highly efficient photocatalyst, fabricated by a simple immersion technique.

Titanium dioxide in the form of one-dimensional (1D) nanostructure arrays represent widely studied morphological arrangement for light harvesting and charge transfer applications such as photocatalysis and photoelectrochemistry (PEC). Here we report a comparative structural and PEC study of variously grown 1D TiO2 nanostructures including i) nanorod arrays prepared by a hydrothermal method (TNR), ii) nanotube arrays fabricated by a two-step hydrothermal method using a ZnO nanorod array film as a template (THNT) and finally iii) nanotubes grown by self-organized electrochemical anodization of Ti films deposited on the FTO substrate (TNT). These nanostructures are assumed to be utilized as photoanodes in PEC water splitting devices. Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), TEM images and UV–vis absorption spectra were used to characterize TiO2 nanostructures. The SEM and TEM morphology images revealed that the main difference among the nanostructures grown on the FTO are the shape and diameter of the individual nanotubes/nanorods and also the array’s density in the range of TNR > THNT > TNT and the degree of organization in the range of TNT > TNR > THNT. The obtained photocurrents at 0 V vs. Ag/AgCl increased in the order of THNT (110 μA cm−2)

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.

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.

Solar driven photoelectrochemical water splitting (PEC-WS) using semiconductor photoelectrodes represents a promising approach for a sustainable and environmentally friendly production of renewable energy vectors and fuel sources, such as dihydrogen (H2). In this context, titanium dioxide (TiO$_2$) and iron oxide (hematite, $\alpha$-Fe$_2$O$_3$) are among the most investigated candidates as photoanode materials, mainly owing to their resistance to photocorrosion, non-toxicity, natural abundance, and low production cost. Major drawbacks are, however, an inherently low electrical conductivity and a limited hole diffusion length that significantly affect the performance of TiO$_2$ and $\alpha$-Fe$_2$O$_3$ in PEC devices. To this regard, one-dimensional (1D) nanostructuring is typically applied as it provides several superior features such as a significant enlargement of the material surface area, extended contact between the semiconductor and the electrolyte and, most remarkably, preferential electrical transport that overall suppress charge carrier recombination and improve TiO$_2$ and $\alpha$-Fe$_2$O$_3$ photo-electrocatalytic properties. The present review describes various synthetic methods, properties and PEC applications of 1D-photoanodes (nanotubes, nanorods, nanofibers, nanowires) based on titania, hematite, and on $\alpha$-Fe$_2$O$_3$/TiO$_2$ heterostructures. Various routes towards modification and enhancement of PEC activity of 1D photoanodes are also discussed including doping, decoration with co-catalysts and heterojunction engineering. Finally, the challenges related to the optimization of charge transfer kinetics in both oxides are highlighted.

TiO 2 nanotube (TNT) arrays directly grown on a transparent conductive support such as e.g. a layer of fluorine doped tin oxide (FTO) are highly desirable for solar energy application including dye-sensitized solar cells (DSSC) and photoelectrochemical water splitting (PEC-WS). In this paper we report on the fabrication of fully transparent TNT arrays formed by complete self-organizing electrochemical anodization of metallic Ti thin layers deposited on the FTO glass substrate by using electron beam evaporation and/or magnetron sputtering. It is clearly shown for the first time that the quality of the deposited titanium film (e.g. amount and size of pinholes) governs its adherence to the substrate and subsequently the anodization process itself. Mechanical properties of the deposited Ti films were investigated by tribology experiments. The main difference between the sputtered and evaporated titanium layers are the lower film density and considerably higher amount of pinholes of the latter. The grown TNT films were further characterized by SEM, X-ray diffraction, and UV–Vis spectroscopy. The sputtered layers overperformed the evaporated layers by 20% when applied for DSSC. An even greater difference was observed in the case of aqueous electrolyte based PEC-WS, where the sputtered layers showed five times higher activity.

A variety of Titanium dioxide (TiO 2 ) phases and nanostructures have been explored for their applications in photoelectrochemical cells (PECs) for solar-driven water splitting. In this case, anatase phase and TiO 2 nanotubes offer significant advantages especially for PEC-based applications. Though, significant efforts have already been engaged to combine the advantages from both the fields, poor activation and the high electron-hole pair recombination rate of TiO 2 electrodes, originating from intrinsic physicochemical properties, limits its practical use. As an alternative, we report directly grown TiO 2 nanotubes (synthesized on Fluorine doped Tin Oxide (FTO) via facile electrospinning technique) on carbon nanofibers, using hydrothermal method. The hierarchical branch type configuration has an intimate contact between the TiO 2 nanotube and carbon nanofiber backbone and offers higher photocatalytic activity than their respective individual components (namely TiO 2 nanotubes and carbon nanostructures).

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 this paper we present a plasma deposition technique that allows the reactive deposition of oxide layers with extremely high deposition rate. The new approach combines reactive sputtering by DC hollow cathode discharge with thermal evaporation from the hot surface of the hollow cathode. As an example of successful fast deposition, photoactive films of titanium dioxide (TiO2) with various thicknesses were deposited using this technique. The uncooled titanium nozzle served as a hot hollow cathode and simultaneously as an inert gas (Ar) inlet. The reactive gas (O2) was introduced into the vacuum chamber through a separate inlet. During deposition, the temperature of the titanium hollow cathode reached up to 1600 °C, depending on the discharge parameters. This made it possible to combine the ion sputtering of hot titanium cathode with its thermal surface evaporation, which significantly increased the TiO2 deposition rate. The highest achieved deposition rate was 567 nm/min (34 μm/h), which (with respect to the geometry of this process) corresponds to total volume of the deposited TiO2 material 1.2 mm3/min per 1 kW of absorbed power. Despite extremely high thermal flux to the substrate, TiO2 films were successfully deposited even on temperature-sensitive PET foil. The as-deposited and post-annealed TiO2 films prepared on fluorine doped tin oxide (FTO) substrates and glass were subject to further analyses including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and photoelectrochemical (PEC) measurements. Whereas the as-deposited TiO2 films had an amorphous (or nearly amorphous) structure, which exhibited only weak photoactivity, after annealing their PEC activity increased by an order of magnitude.

Thin layers of ZnO were prepared by using a special modification of the plasma-enhanced chemical vapor deposition known as surfatron. This technique utilizes the principle of surface-wave discharge powered by microwave magnetron generator. Two types of substrate holder regimes (static and movable) were intentionally employed for the preparation of two types of surface morphologies. A series of ZnO films were yielded with thicknesses ranging from 60 nm to 1500 nm. The layers were analyzed by profilometry, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, UV-light adsorption and by a number of electrochemical tests. All prepared samples were crystalline and possessing different surface morphologies. It was shown that the electrochemical response of the films was directly reflecting their surface morphology.

Hematite, α-Fe2O3, is considered as one of the most promising materials for sustainable hydrogen production via photoelectrochemical water splitting with a theoretical solar-to-hydrogen efficiency of 17%. However, the poor electrical conductivity of hematite is a substantial limitation reducing its efficiency in real experimental conditions. Despite of computing models suggesting that the electrical conductivity is extremely anisotropic, revealing up to 4 orders of magnitude higher electron transport with conduction along the (110) hematite crystal plane, synthetic approaches allowing the sole growth in that direction have not been reported yet. Here, we present a strategy for controlling the crystal orientation of very thin hematite films by adjusting energy of ion flux during advanced pulsed reactive magnetron sputtering technique. The texture and effect of the deposition mode on the film properties were monitored by XRD, conversion electron Mössbauer spectroscopy, XPS, SEM, AFM, PEC water splitting, IPCE, transient photocurrent measurements, and Mott-Schottky analysis. The precise control of the synthetic conditions allowed to fabricate hematite photoanodes exhibiting fully textured structures along (110) and (104) crystal planes with huge differences in photocurrents of 0.65 and 0.02 mA cm(-2) (both at 1.55 V versus RHE), respectively. The photocurrent registered for fully textured (110) film is among record values reported for thin planar films. Moreover, the developed fine-tuning of crystal orientation having a huge impact on the photoefficiency would induce further improvement of thin hematite films mainly if cation doping will be combined with the controllable texture.

A nanoparticle photocatalysts based on silver-doped titanium dioxide were synthesized using a modified sol–gel route and also a dip-and-pull step photochemical method. The catalysts were characterized by UV/Vis absorption spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, electron microprobe analysis, and Raman spectroscopy. The effects of the experimental parameters on the photoreactivity of the catalysts were evaluated for the decolorization of Rhodamine B in water and by photoelectrochemistry. The activity results show that silver doping significantly promotes the photoreactivity of the titanium dioxide catalyst with some phase transformation from anatase to brookite. The enhanced photoactivity of new nanoparticulate photocatalysts is predominantly attributable to an improvement in crystallinity, band gap lowering, the nature of precursor materials used, and also the method of doping.

The work deals with fabrication of iron oxide (α-Fe 2 O 3 ) hematite films by a novel high-power impulse magnetron sputtering method (HiPIMS). Hematite is regarded as a highly promising material for sustainable production of hydrogen via photoelectrochemical (PEC) water splitting. Some of the crucial issues of hematite are a large overpotential needed to develop the water oxidation photocurrent onset, high extent of surface defects acting as traps, and a short diffusion length (2–4 nm) of photogenerated holes. We report on minimizing these limits by deposition of highly photoactive nanocrystalline very thin (∼30 nm) absorbing hematite films by HiPIMS and their passivation by ultra-thin (∼2 nm) atomic layer deposited (ALD) isocrystalline alumina oxide (α-Al 2 O 3 ) films. A new approach of one-step annealing of this bilayer system is introduced. The films were judged on the basis of physical properties such as crystalline structure, optical absorption, surface topography, and electronic properties. The functional properties were investigated under simulated photoelectrochemical (PEC) water-splitting conditions. The shift by 1 V vs. RHE and the maximal photocurrent value of 0.48 mA cm −2 at 1.23 V vs. RHE were achieved.

WO3 crystalline semiconductor thin films for water-splitting applications were prepared by pulsed unbalanced reactive magnetron sputtering with W target and Ar + O2 gas mixture. Postdeposition annealing at temperature of 450 °C was applied to the WO3 samples to improve their crystallinity and semiconductor properties. Various pulsing modes were tested in deposition experiments with different pulsing frequencies, discharge power applied in pulse, and average applied power. To determine the influence of the plasma parameters on the deposition process, the pulsed and average ion flux density on the substrate were measured using an ion probe. The WO3 films had monoclinic crystalline structure after the annealing process. Different crystallite orientations were found for different modes of discharge pulsing. Preferential orientation of the (200) plane parallel to the substrate surface was identified for higher frequency of discharge pulsing with lower substrate pulsed ion flux but higher average substrate ion flux. The WO3 films with this type of texture had the highest photocurrents in photoelectrochemical (PEC) measurements.

Solar driven photoelectrochemical water splitting (PEC-WS) using semiconductor photoelectrodes represents a promising approach for a sustainable and environmentally friendly production of renewable energy vectors and fuel sources, such as dihydrogen (H

The uniform pinhole-free iron disulfide (FeS2) pyrite thin films were fabricated. In the first step the FeO(OH)x xerogel solution was synthetized by means of a novel epoxy catalyzed sol–gel method and next spin-coated onto various substrates to form the thin films. In the second step the xerogel coatings were annealed to yield hematite (α-Fe2O3) films, which were transformed into pyrite by chemical sulfurization. Among the main deposition parameters studied were the temperature of xerogel–hematite transformation and the optimal sufulrization temperature and duration. It has been observed that 15 min sulfurization at the temperature of 450 °C provided the pyrite films of sufficient quality. The estimated optical band gap of 0.98 eV is very close to the theoretical value of 0.95 eV. Auger electron spectroscopy showed almost ideal stoichiometry of FeS2. However a trace amount of oxygen (approximately 0.5 at.%) present in the film was still detected. The photoinduced functionality of the films was assessed based on photoelectrochemical experiments. In order to demonstrate the ability of pyrite to photosensitize a large band gap semiconductor, a bilayer system of TiO2 anatase/FeS2 pyrite was prepared. The highest photocurrent reached was 45 μA cm−2 at the light intensity of 10.5 mW cm−2.

Multi plasma jet system with 4 independent nozzles working on the principle of surface-wave discharge (SWD) has been developed. The system was optimized and used for plasma-enhanced chemical vapor deposition (PECVD) of nominally pure and Al and Mn doped ZnO thin films. The surfatron source was powered by a microwave magnetron generator working at a frequency of 2.45 GHz with the output power of 300 W per surfatron. The time-resolved properties of low-pressure plasma jet working under deposition conditions in pulse mode were studied using Langmuir probe. It was found that the plasma density inside the active plasma jet is about 10 17 m −3 and electron effective temperature can reach approximately 3 eV. The set of ZnO samples with a thickness of 300 nm were prepared on Si, ITO and quartz substrate and were analyzed by XRD, SEM, EDX, UV-light amperometry and optical ellipsometry. All samples under study were crystalline in nature, revealed n -type conductivity, were photo-electrochemically active and have optical band gap close to 3.5 eV. The deposition condition had a strong influence on the grain size and surface morphology.

The fabrication of crystalline α-Fe2O3 hematite thin films by means of novel high power impulse magnetron sputtering (HiPIMS) and high power hollow cathode plasma jets system is reported. The coatings are based on low temperature pulsed-plasma reactive sputtering. These methods were compared with a more common method of medium frequency (MF) pulsed reactive DC magnetron sputtering. Although both high power methods yielded crystalline structure of the films already during the depositions, the films had to be thermally treated at elevated temperature in order to improve their physical (crystallinity) and electronic properties. The deposition methods used and the effect of the post deposition thermal annealing were judged on the basis of physical properties such as crystalline structure, optical absorption, surface topography, electronic properties, and electrical behavior. The functional properties were investigated under simulated photoelectrochemical water splitting conditions. Despite the revealed hematite phase of the as-deposited films, these were almost photoelectrochemically inactive. The annealing improved crystal structure of the deposited films and increased their dark conductivity. Furthermore the annealing initiated the diffusion of tin atoms from FTO (fluorine doped tin oxide) substrate into the film increasing its extrinsic conductivity. These improvements lead to higher photoefficiency.

Hybrid metal–organic frameworks (MOFs) demonstrate great promise as ideal electrode materials for energy‐related applications. Herein, a well‐organized interleaved composite of graphene‐like nanosheets embedded with MnO2 nanoparticles (MnO2@C‐NS) using a manganese‐based MOF and employed as a promising anode material for Li‐ion hybrid capacitor (LIHC) is engineered. This unique hybrid architecture shows intriguing electrochemical properties including high reversible specific capacity 1054 mAh g−1 (close to the theoretical capacity of MnO2, 1232 mAh g−1) at 0.1 A g−1 with remarkable rate capability and cyclic stability (90% over 1000 cycles). Such a remarkable performance may be assigned to the hierarchical porous ultrathin carbon nanosheets and tightly attached MnO2 nanoparticles, which provide structural stability and low contact resistance during repetitive lithiation/delithiation processes. Moreover, a novel LIHC is assembled using a MnO2@C‐NS anode and MOF derived ultrathin nanoporous carbon nanosheets (derived from other potassium‐based MOFs) cathode materials. The LIHC full‐cell delivers an ultrahigh specific energy of 166 Wh kg−1 at 550 W kg−1 and maintained to 49.2 Wh kg−1 even at high specific power of 3.5 kW kg−1 as well as long cycling stability (91% over 5000 cycles). This work opens new opportunities for designing advanced MOF derived electrodes for next‐generation energy storage devices., D.P.D. acknowledges Queensland University of Technology and Australian Research Council (ARC) for the Future Fellowship (FT180100058). K.J. is grateful to the Alexander von Humboldt (AvH) foundation for the post‐doctoral fellowship. The authors also gratefully acknowledge support from the Ministry of Education, Youth and Sports of the Czech Republic (LO1305) and the assistance provided by the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic under Project No. LM2015073. The authors also gratefully acknowledge support by the Catalysis Research Centre at Technische Universität München (TUM) for analytical support and the support by the Operational Programme Research, Development and Education—European Regional Development Fund, Project Nos. CZ.02.1.01/0.0/0.0/15_003/0000416 of the Ministry of Education, Youth and Sports of the Czech Republic.

Semiconducting hematite Fe2O3 thin films were fabricated by means of reactive sputtering in a high power DC pulsed magnetron (HIPIMS) and in a DC pulsed hollow cathode plasma jet sputtering system. Fused silica slides (quartz) were used as substrates. Both plasma processes were monitored with the help of a quartz crystal monitor (QCM) that was also fitted with magnetic field electron suppression filter and biased collecting electrode. This set up measured the deposition rate and the ratio of ionized to neutral fluxes of depositing particles on the substrate during the coating process. The deposition methods were compared in terms of the properties of produced films such as crystalline structure, optical absorption and surface topography. The as-deposited hematite Fe2O3 thin films (without annealing) and after their thermal treatment (with annealing) were examined.

A hybrid high-power impulse magnetron sputtering (HiPIMS) + mid-frequency (MF) magnetron sputtering system was used for the deposition of crystalline TiO 2 thin films at a low substrate temperature. Ion velocity distribution functions (IVDFs) were measured in a pulsed magnetron discharge at substrate positions depending on the type of plasma excitation and on the working gas mixtures. Several different pulsed discharge configurations were used: (i) HiPIMS, (ii) pulsed bipolar MF with frequency 350 kHz and (iii) both HiPIMS + MF connected in parallel to the magnetron cathode. The timing of HiPIMS excitation was set to period time T = 10 ms with “ON” time T ON = 100 μs. Ti targets were sputtered in three different types of atmospheres: (i) inert pure Ar, (ii) a reactive mixture of Ar + O 2 and (iii) a reactive mixture of Ar + O 2 + N 2 with a constant gas pressure p = 1 Pa. All IVDFs were measured using a time-resolved retarding field energy analyzer (RFEA) located in the substrate position. TiO 2 thin films were deposited under identical experimental conditions on silica (SiO 2 ) glass substrate, glass with an indium tin oxide (ITO) electrode and polycarbonate polymer foil. The thin film properties are discussed with respect to the measured plasma parameters. It is shown that the combination of HiPIMS + MF excitation in a reactive atmosphere effectively reduces the delay between the edge of cathode voltage and current onset. The highest ion energy was reached in the case of an inert Ar atmosphere due to the highest ratio of fast Ti + ions in the overall ion flux. All TiO 2 thin films deposited in reactive atmospheres formed pure rutile phase regardless of the excitation mode; however, those films deposited by a HiPIMS + MF excitation mode exhibited the greatest ability to produce a photocurrent. Furthermore, HiPIMS + MF was the best setting for the deposition of crystalline TiO 2 on polycarbonate foil because of the low heating flux on the substrate and suitable plasma parameters leading to the formation of the rutile phase.

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe2O3 nanoflakes branched on TiO2 nanotubes. The novel α-Fe2O3/TiO2 hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO2 nanotubes. An enhanced separation of photogenerated charge carriers is here proposed as the main factor for the observed photo-activities: electrons photogenerated in TiO2 are efficiently collected at FTO, while holes are transferred to the α-Fe2O3 nanobranches that serve as charge mediators to the electrolyte. The morphology of α-Fe2O3 that varies from ultrathin nanoflakes to nanorod/nanofiber structures depending on the Fe precursor concentration was shown to have a significant impact on the photo-induced activity of the α-Fe2O3/TiO2 composites. In particular, it is shown that for an optimized photo-electrochemical structure, a combination of critical factors should be achieved such as (i) TiO2 light absorption and photo-activation vs. α-Fe2O3-induced shadowing effect and (ii) the availability of free TiO2 surface vs. α-Fe2O3-coated surface. Finally, theoretical analysis, based on DFT calculations, confirmed the optical properties experimentally determined for the α-Fe2O3/TiO2 hierarchical nanostructures. We anticipate that this new multi-step hydrothermal process can be a blueprint for the design and development of other hierarchical heterogeneous metal oxide electrodes suitable for photo-electrochemical applications.

The photoinduced self-cleaning and super-hydrophilic properties of titania (TiO2) coated glasses are considered to be utilized in many applications. The photocatalytic activity of titania is inherent to the glass composition and to the deposition method. Particularly sodium ions diffused to the titania film from the substrate have tremendous impact on its crystallinity. The deposition method influences surface, structure, and the density of the film. This study aims to provide new findings regarding the mechanism of crystallization of sol–gel synthesized titania and its thin films deposited by means of two different methods (dip-coating and spin-coating) onto the glass substrate with a high content of sodium ions (soda-lime glass) and without sodium ions (quartz glass). The main attention is devoted to Raman spectroscopy and Raman point-to-point mapping of the films. The content and the chemical state of the sodium ions were judged using the XPS. It is shown that the dip-coating method led to dense compact material. In this case the crystallization is localized in randomly distributed centers of nucleation. Contrary the spin-coated samples embodied a web-like pattern of cracks, from which the crystallization proceeds throughout the film. Additionally SEM, AFM, XRD, GDS, UV–VIS methods were performed to support the results.

CuIn 1− x Al x S 2 thin films ( x = 0, 0.09, 0.27, 0.46, 0.64, 0.82 and 1) with thicknesses of approximately 1 μm were formed by the sulfurization of DC sputtered Cu–In–Al precursors. All samples were sulfurized in a graphite container for 90 min at 650 °C in a 150 kPa Ar + S atmosphere. Final films were studied via X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-Raman spectroscopy. It was found that all samples were polycrystalline in nature and their lattice parameters varied slightly nonlinearly from { a = 5.49 A, c = 11.02 A} for CuInS 2 to { a = 5.30 A, c = 10.36 A} for CuAlS 2 . No unwanted phases such as Cu 2− x S or others were observed. Raman were recorded at a room temperature and the most intensive and dominant A 1 phonon frequency varied nonlinearly from 294 cm −1 (CuInS 2 ) to 314 cm −1 (CuAlS 2 ).

The basic objective of this work is related to the research on the design of hierarchic multilayer systems with the assumed final functionality utilized for microelectronics and photovoltaics. We report on photoelectrochemical functionality of the multilayer system consisting of carbon nanofibers (CNFs)/photoactive anatase TiO 2 /conductive ZnO thin films. The CNFs’ layers were obtained by annealing the polyacrylonitrile (PAN) web deposited by the electrospinning method. Titanium dioxide and zinc oxide layers were deposited by means of a hollow cathode cold plasma deposition system. Raman spectra confirmed carbon nanofibers, crystalline TiO 2 and ZnO forming individual layers as well as the final multilayer assembly. A mixture of various Zn x Ti y O z phases was also observed. These structures were produced due to the reactions between the highly energetic zinc ions generated in the plasma environment and the TiO 2 layer. The same phenomenon is probably responsible for the doping of TiO 2 by carbon atoms originating from CNFs and leading to a significant decrease of the photocatalytic activity.

This study reports the preparation of thin nanoparticulate films of titanium dioxide and its modified version doped with a transition metal. The behavior of prepared films was described by means of their photocatalytic and photo-induced electrochemical properties. The TiO 2 and M/TiO 2 (M = Ag, Zr, Fe) thin films were produced via a standard sol–gel method using titanium n -butoxide, acetylacetone, and transition metal acetylacetonates as precursors. Prepared films were analyzed by a series of techniques involving XRD, Raman spectroscopy, SEM, AFM, and XPS. Their photocatalytic activity was monitored with the aid of decomposition of the model compound Rhodamine B in water. All films were then tested for their photo-induced electrochemical properties based on evaluation of polarization curves (photocurrents). The highest reaction rate constant (0.0101 min −1 ), which was even higher than that for pure TiO 2 , was obtained for the Ag/TiO 2 sample. The highest quantum yield of the charge collection was determined for the undoped TiO 2 film.

Here, a Sb-doped SnO2 (ATO) nanorod underneath an α-Fe2 O3 nanorod sheathed with TiO2 for photoelectrochemical (PEC) water splitting is reported. The experimental results, corroborated with theoretical analysis, demonstrate that the ATO nanorod underlayer effect on the α-Fe2 O3 nanorod sheathed with TiO2 enhances the PEC water splitting performance. The growth of the well-defined ATO nanorods is reported as a conductive underlayer to improve α-Fe2 O3 PEC water oxidation performance. The α-Fe2 O3 nanorods grown on the ATO nanorods exhibit improved performance for PEC water oxidation compared to α-Fe2 O3 grown on flat fluorine-doped tin oxide glass. Furthermore, a simple and facile TiCl4 chemical treatment further introduces TiO2 passivation layer formation on the α-Fe2 O3 to reduce surface recombination. As a result, these unique nanostructures show dramatically improved photocurrent density (139% higher than that of the pure hematite nanorods).

Thin films of SiC have been deposited using a hollow cathode sputtering technique. Several methods have been used including DC, RF, and pulsed sputtering. The films reported here have been deposited using DC and pulsed sputtering.

The low temperature double hollow cathode plasma jet method for producing photoresponding thin transparent layers of TiO 2− x N x is reported. This technique allows involvement of thermally sensitive materials as supports. Dependence of the properties of the films on the applied RF field power was clearly demonstrated. Produced films were first characterized with the aid of a number of characterization methods (AFM, SEM, XRD, photothermal deflection spectroscopy (PDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and UV–vis), then their photocurrent generation efficiencies upon illumination with spectrally well defined narrow light beams were described. These tests based on the recorded polarization curves revealed a significant dependence of the scanning direction (anodic and/or cathodic) on the E on (photocurrent onset) and an appearance of the photocurrent maxima. Open circuit potential (OCP), cyclic voltammetry and amperometry tests were also performed. The RF power magnitude was identified as the parameter affecting substantially the photoinduced properties of the produced films.