TiO2 nanotubes incorporated with CdS for photocatalytic hydrogen production from splitting water under visible light irradiation

The CdS/TiO₂ composites were synthesized using titanate nanotubes (TiO₂NTs) with different pore diameters as the precursor by simple ion change and followed by sulfurization process at a moderate temperature. Some of results obtained from XRD, TEM, BET, UV–vis and PL analysis confirmed that cadmium sulfide nanoparticles (CdSNPs) incorporated into the titanium dioxide nanotubes. The photocatalytic production of H₂ was remarkably enhanced when CdS nanoparticles was incorporated into TiO₂NTs. The apparent quantum yield for hydrogen production reached about 43.4% under visible light around λ = 420 nm. The high activity might be attributed to the following reasons: (1) the quantum size effect and homogeneous distribution of CdSNPs; (2) the synergetic effects between CdS particles and TiO₂NTs, viz., the potential gradient at the interface between CdSNPs and TiO₂NTs.     

High performance hydrogen sensor based on Pd/TiO2 composite film

Hydrogen sensors with fast response and recovery rate based on nanoporous palladium (Pd) and titanium dioxide (TiO₂) composite films supported by anodic aluminum oxide (AAO) template have been demonstrated. Nanoporous TiO₂ film was sprayed on the porous AAO templates, followed by Pd film deposited on TiO₂ layer by DC magnetron sputtering. We have researched the detection performance of the hydrogen sensors depending on different thickness of TiO₂ layer from 6 to 30 nm with keeping the thickness of Pd as 30 nm. The results have demonstrated the sensors with 10 nm thickness of TiO₂ achieve the best performance with a response/recovery time as short as 4/8s at 0.8% and 0.4% hydrogen concentration, respectively. The sensors exhibited very good performance under hydrogen concentrations from 0.4% to 1.8%.     

Pt modified TiO2 nanotubes electrode: Preparation and electrocatalytic application for methanol oxidation

Pt nanoparticles decorated TiO₂ nanotubes (Pt/TiO₂NTs) modified electrode has been successfully synthesized by depositing Pt in TiO₂NTs, which were prepared by anodization of the Ti foil. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties. The Pt/TiO₂NTs electrode shows excellent electrocatalytic activity toward methanol oxidation reaction (MOR) in alkaline electrolyte without UV irradiation.     

Photoelectrochemical water splitting on highly smooth and ordered TiO2 nanotube arrays for hydrogen generation

To improve the photoelectrochemical (PEC) water splitting efficiency for hydrogen production, we reported the fabrication of lotus-root-shaped, highly smooth and ordered TiO₂ nanotube arrays (TiO₂ NTs) by a simple and effective two-step anodization method. The TiO₂ NTs prepared in the two-step anodization process (2-step TiO₂ NTs) showed better surface smoothness and tube orderliness than those of TiO₂ NTs prepared in one-step anodization process (1-step TiO₂ NTs). Under illumination of 100 mW/cm² (AM 1.5, simulated solar light) in 1 M KOH solution, water was oxidized on the 2-step TiO₂ NTs electrode with higher efficiency (incident-photon-to-current efficiency of 43.4% at 360 nm and photocurrent density of 0.90 mA/cm² at 1.23 V_RHE) than that on the 1-step TiO₂ NTs electrode. The effective photon-to-hydrogen conversion efficiency was found to be 0.18% and 0.49% for 1-step TiO₂ NTs and 2-step TiO₂ NTs, respectively. These results suggested that the structural smoothness and orderliness of TiO₂ NTs played an important role in improving the PEC water splitting application for hydrogen generation.     

Hydrogen storage in TiO2 functionalized (10, 10) single walled carbon nanotube (SWCNT) – First principles study

Hydrogen storage in titanium dioxide (TiO₂) functionalized (10, 10) armchair single walled carbon nanotube (SWCNT) is investigated through first principle calculations using density functional theory (DFT). This first principles study uses Vienna Ab-initio Simulation Package (VASP) with ultrasoft pseudopotentials and local density approximation (LDA). The necessary benchmark and other systematic calculations were carried out to project the hydrogen storage capability of the designed system. Interestingly, the TiO₂ molecules functionalized on the outer surface of SWCNT do not undergo any dimerization/clustering thus giving excellent stability and usable gravimetric hydrogen storage capacity of 5.7 wt.% and the value nearly fulfills the US DOE target (i.e. 6 wt.%). The band structure and density of states (DOS) plots suggest that the functionalization can lead a way to transform the nature (metallic → semiconducting) of the pristine SWCNT. The nominal values of H₂ storage capacity and binding energies give much hope for using CNT functionalized with TiO₂ as a practical and reversible hydrogen storage medium (HSM).     

Direct synthesis of nanocrystalline titanium dioxide/carbon composite and its catalytic effect on NaAlH4 for hydrogen storage

Nanocrystalline titanium dioxide/carbon composite (TiO₂/C) was synthesized through a direct solution-phase carburization using tetrabutyl titanate (Ti(OBu)₄) and resol as precursors. The prepared TiO₂/C composite was mainly in the anatase structure with an average particle size under 20 nm, which was then introduced in NaAlH₄ as a catalyst through ball milling. The desorption curves show that both nanocrystalline TiO₂/C and TiO₂ can obviously improve the kinetics of NaAlH₄, while NaAlH₄ with 3 mol% TiO₂/C exhibits better cycling stability than NaAlH₄ with 3 mol%TiO₂. The hydrogen storage capacity of NaAlH₄ with TiO₂/C remains stable after 5th cycle, and about 94% of initial hydrogen is released, while the capacity of NaAlH₄ with TiO₂ decreases continuously during cycling, and only 88% of initial hydrogen is released after 10th cycle. Furthermore, NaAlH₄ with 3 mol%TiO₂/C exhibits good reversibility at relatively low hydrogen pressures, and it can reload 4.16 and 1.63wt% hydrogen at 50 and 30 bar hydrogen pressures, respectively.     

The decoration of TiO2/reduced graphene oxide by Pd and Pt nanoparticles for hydrogen gas sensing

Reduced graphene oxide (RGO) was used to improve the hydrogen sensing properties of Pd and Pt-decorated TiO₂ nanoparticles by facile production routes. The TiO₂ nanoparticles were synthesized by sol–gel method and coupled on GO sheets via a photoreduction process. The Pd or Pt nanoparticles were decorated on the TiO₂/RGO hybrid structures by chemical reduction. X-ray photoelectron spectroscopy demonstrated that GO reduction is done by the TiO₂ nanoparticles and Ti–C bonds are formed between the TiO₂ and the RGO sheets as well. Gas sensing was studied with different concentrations of hydrogen ranging from 100 to 10,000 ppm at various temperatures. High sensitivity (92%) and fast response time (less than 20 s) at 500 ppm of hydrogen were observed for the sample with low concentration of Pd (2 wt.%) decorated on the TiO₂/RGO sample at a relatively low temperature (180 °C). The RGO sheets, by playing scaffold role in these hybrid structures, provide new pathways for gas diffusion and preferential channels for electrical current. Based on the proposed mechanisms, Pd/TiO₂/RGO sample indicated better sensing performance compared to the Pt/TiO₂/RGO. Greater rate of spill-over effect and dissociation of hydrogen molecules on Pd are considered as possible causes of the enhanced sensitivity in Pd/TiO₂/RGO.     

Significant enhancement of the electrochemical hydrogen uptake of reduced graphene oxide via boron-doping and decoration with Pd nanoparticles

Development of advanced hydrogen storage materials with high capacity and stability is vital to achieve an envisaged hydrogen economy. Here, we report a uniformly dispersed Pd nanoparticles on the boron-doped reduced graphene oxide (Pd/B-rGO) as a novel nanocomposite for efficient hydrogen storage. The effects of the incorporation of Pd NPs and the substitution of boron atoms into the graphene-based nanomaterial matrix on the electrochemical hydrogen up-taking and releasing were comparatively studied using electrochemical techniques, and duly supported by density functional theory (DFT) calculations. The discharge capacities of the Pd-rGO and Pd/B-rGO nanocomposites were determined to be over 45 and 128 times higher than that of the Pd NPs, respectively, showing that the B doping and the rGO support played significant roles in the enhancement of the hydrogen storage capability. Moreover, the galvanostatic charging and discharging cycling tests demonstrated a high stability and efficient kinetics of the Pd/B-rGO nanocomposite in the H₂SO₄ electrolyte for hydrogen up-taking and release.     

Optimization of TiH2 content for fast and efficient hydrogen cycling of MgH2-TiH2 nanocomposites

Magnesium hydride is extensively examined as a hydrogen store due to its high hydrogen content and low cost. However, high thermodynamic stability and sluggish kinetics hinder its practical application. To overcome this last drawback, different Ti amounts (y = 0, 0.025, 0.05, 0.1, 0.2 and 0.3) were added to magnesium to form (1-y)MgH₂+yTiH₂ nanocomposites (NC) by reactive ball milling under hydrogen gas. Thermodynamic stability of the MgH₂ phase in NCs was determined using a manometric Sieverts rig. Reversible hydrogen capacity and reaction kinetics were determined at 573 K over 20 sorption cycles under a limited reaction time of 15 min. On increasing Ti amount, reaction kinetics are enhanced both in absorption and desorption leading to a higher reversibility for hydrogen storage with the MgH₂ phase. However, titanium increases the molar weight of NCs and forms irreversible titanium hydride. The highest reversible capacity (4.9 wt% H) was obtained for the lowest here studied TiH₂ content (y = 0.025).     

Enhanced hydrogen uptake/release in 2LiH–MgB2 composite with titanium additives

The influence of different titanium additives on hydrogen sorption in LiH–MgB₂ system has been investigated. For all the composites LiH–MgB₂–X (X = TiF₄, TiO₂, TiN, and TiC), prepared by ball-milling in molar ratios 2:1:0.1, five hydrogen uptake/release cycles were performed. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and attenuated total reflection infrared spectroscopy (ATR-IR) have been used to characterize crystal phases developed during the hydrogen absorption–desorption cycles.     

Effect of g-C3N4 amount on green synthesized GdFeO3/g-C3N4 nanocomposites as promising compounds for solid-state hydrogen storage

Hydrogen energy is a key role in novel renewable energy production/consumption technologies. Traditional hydrogen energy systems are suffered from low density, high production cost, low efficiency, and storage complications. With the start of solid-state hydrogen storage technology, many of above deficiencies are fulfilled, however, there are several unknown points, particularly in metal oxides, which need more attention. Hydrogen sorption on the layered materials or inside porous materials is a hopeful key to drawbacks for high-performance hydrogen sorption. Hereupon, layered solids with the merit of hydrogen sorption are introduced, for the first time, including “nanostructured bi-metal oxide (BMO)” and “graphitic carbon nitride (CN)”. Perovskites are ceramic and they are hard materials so they could be a favorable candidate for solid-state hydrogen storage. g-C₃N₄ has attractive features including high surface area, chemical stability, small band gap, and low-cost synthesis methods but also has great potential as an electrode material for energy storage capacitors. The main motivation for this study comes from the potential applications for perovskite materials and graphitic carbon nitride for the solid-state hydrogen storage method. The Perovskite type GdFeO₃ nanostructures (as BMO) synthesized through sol-gel approach in front of natural source of Grape juice as both complexing agent and fuel. The experimental scrutinization ascertains an original fabrication of GdFeO₃ (GF) nanostructures in Grape juice at 800 °C, with an approximately uniform nanosized structure of 70 nm on average. The obtained pure GF nanostructures are then utilized for nanocomposite formation based on g-C₃N₄ (CN) with different amounts. The resulting nanocomposites with the ratio of 1:2 from GF:CN perform a preferable hydrogen sorption capacity, in terms of “maximum discharge capacity of 577 mAhg^?1” in 2 M KOH electrolyte. It should be declared that however, the discharge capacity of the nanostructured GF is 188 mAhg^?1. It can be emphasized that these GF/CN nanocomposites can be utilized as hopeful hosts in an electrochemical hydrogen storage setup due to the synergic effect of g-C₃N₄ with essential characteristics in cooperation with BMO nanostructures as acceptable electrocatalysts.     

Syngas production by electrocatalytic reduction of CO2 using Ag-decorated TiO2 nanotubes

Huge efforts have been done in the last years on electrochemical and photoelectrochemical reduction of CO₂ to offer a sustainable route to recycle CO₂. A promising route is to electrochemically reduce CO₂ into CO which, by combination with hydrogen, can be used as a feedstock to different added-value products or fuels. Herein, perpendicular oriented TiO₂ nanotubes (NTs) on the electrode plate were grown by anodic oxidation of titanium substrate and then decorated by a low loading of silver nanoparticles deposited by sputtering (i.e. Ag/TiO₂ NTs). Due to their quasi one-dimensional arrangement, TiO₂ NTs are able to provide higher surface area for Ag adhesion and superior electron transport properties than other Ti substrates (e.g. Ti foil and TiO₂ nanoparticles), as confirmed by electrochemical (CV, EIS, electrochemical active surface area) and chemical/morphological analysis (FESEM, TEM, EDS). These characteristics together with the role of the TiO₂ NTs to enhance the stability of CO₂^·- intermediate formed due to titania redox couple (Ti^IV/Ti^III) lead to an improvement of the CO production in the Ag/TiO₂ NTs electrodes. Particular attention has been devoted to reduce the loading of noble metal in the electrode(14.5 %w/%w) and to increase the catalysts active surface area in order to decrease the required overpotential.     

Nanostructured hydrogen storage materials prepared by high-energy reactive ball milling of magnesium and ferrovanadium

Hydrogen storage nanocomposites prepared by high energy reactive ball milling of magnesium and vanadium alloys in hydrogen (HRBM) are characterised by exceptionally fast hydrogenation rates and a significantly decreased hydride decomposition temperature. Replacement of vanadium in these materials with vanadium-rich Ferrovanadium (FeV, V80Fe20) is very cost efficient and is suggested as a durable way towards large scale applications of Mg-based hydrogen storage materials. The current work presents the results of the experimental study of Mg–(FeV) hydrogen storage nanocomposites prepared by HRBM of Mg powder and FeV (0–50 mol.%). The additives of FeV were shown to improve hydrogen sorption performance of Mg including facilitation of the hydrogenation during the HRBM and improvements of the dehydrogenation/re-hydrogenation kinetics. The improvements resemble the behaviour of pure vanadium metal, and the Mg–(FeV) nanocomposites exhibited a good stability of the hydrogen sorption performance during hydrogen absorption – desorption cycling at T = 350 °C caused by a stability of the cycling performance of the nanostructured FeV acting as a catalyst. Further improvement of the cycle stability including the increase of the reversible hydrogen storage capacity and acceleration of H₂ absorption kinetics during the cycling was observed for the composites containing carbon additives (activated carbon, graphite or multi-walled carbon nanotubes; 5 wt%), with the best performance achieved for activated carbon.     

Effect of anodization voltage on performance of TiO2 nanotube arrays for hydrogen generation in a two-compartment photoelectrochemical cell

Highly ordered TiO₂ nanotube arrays were prepared by anodic oxidation of Ti foil under different anodization voltages in ethylene glycol electrolyte. The morphology and photoelectrochemical performance of the TiO₂ nanotubes (NTs) samples were characterized by FESEM and electrochemical working station. Hydrogen production was measured by splitting water in the two-compartment photoelectrochemical (PEC) cell without any external applied voltage or sacrificial agent. The results indicated that anodization voltage significantly affects morphology structures, photoelectrochemical properties and hydrogen production of TiO₂ NTs. The pore diameter and layer thickness of TiO₂ samples increased linearly with the anodization voltage, which led to the enhancement of active surface area. Accordingly, the photocurrent response, photoconversion efficiency and hydrogen production of TiO₂ nanotubes were also linearly correlated with the anodization voltage.     

Effects of different palladium content loading on the hydrogen storage capacity of double-walled carbon nanotubes

The effects of different amounts palladium loading on the hydrogen sorption characteristics of double-walled carbon nanotubes (DWCNTs) have been investigated. The physical properties of the pristine DWCNTs and Pd/DWCNTs were systematically characterized by X-ray diffraction, transmission electron microscopy, and Brunauer–Emmett–Teller surface area measurements. Pd nanoparticles were loaded on DWCNT surfaces for the dissociation of H₂ into atomic hydrogen, which spills over to the defect sites on the DWCNTs. When we use different Pd content, the particle size and dispersion will be different, which affects the hydrogen storage capacity of the DWCNTs. In this work, the hydrogen storage capacities were measured at ambient temperature and found to be 1.7, 1.85, 3.0, and 2.0 wt% for pristine DWCNTS, 1.0 wt%Pd/DWCNTs, 2.0 wt%Pd/DWCNTs, and 3.0 wt%Pd/DWCNTs, respectively. We found that the hydrogen storage capacity can be enhanced by loading with Pd nanoparticles and selecting a suitable content. Furthermore, the sorption can be attributed to the chemical reaction between the atomic hydrogen and the dangling bonds of the DWCNTs.     

Photo-induced reforming of alcohols with improved hydrogen apparent quantum yield on TiO2 nanotubes loaded with ultra-small Pt nanoparticles

Photo-induced reforming of methanol, ethanol, glycerol and phenol at room temperature for hydrogen production was investigated with the use of ultra-small Pt nanoparticles (NPs) loaded on TiO₂ nanotubes (NTs). The Pt NPs with diameters between 1.1 and 1.3 nm were deposited on TiO₂ NTs by DC-magnetron sputtering (DC-MS) technique. The photocatalytic hydrogen rate achieved an optimum value for a loading of about 1 wt% of Pt. Apparent quantum yield for hydrogen generation was measured for methanol and ethanol water solutions reaching a maximum of 16% under irradiation with a wavelength of 313 nm in methanol/water solution (1/8 v/v). Pt NPs loaded on TiO₂ NTs represented also a true water splitting catalyst under UV irradiation and pure distilled water. DC-MS method appears to be a technologically simple, ecologically benign and potentially low-cost process for production of an efficient photocatalyst loaded with ultra-small NPs with precise size control.     

A nanoreactor based on SrTiO3 coupled TiO2 nanotubes confined Au nanoparticles for photocatalytic hydrogen evolution

A TiO₂ nanotube-based nanoreactor was designed and fabricated by facile two steps synthesis: firstly, hydrothermal synthesized SrTiO₃ was deposited on TiO₂ nanotubes (TiO₂NTs). Secondly, the Au nanoparticles (NPs) were encapsulated inside the TiO₂NTs followed by vacuum-assisted impregnation. The as-synthesized composites were characterized using Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and Ultraviolet–visible absorption spectroscopy (UV–vis). The photocatalytic performance was evaluated by the hydrogen evolution reaction. The results revealed that the SrTiO₃ modified TiO₂NTs confined Au NPs (STO-TiO₂NTs@Au) achieved an enhanced hydrogen evolution rate at 7200 μmol h⁻¹ g⁻¹, which was 2.2 times higher than that of bald TiO₂NTs@Au at 3300 μmol h⁻¹ g⁻¹. The improved photocatalytic activity could be attributed to the synergistic effect of the electron-donating of SrTiO₃ and TiO₂NTs confinement. The as-designed nanoreactor structure provides an example of efficient carriers' separation photocatalyst.     

Hybrid inverted organic photovoltaic cells based on nanoporous TiO2 films and organic small molecules

Solar cells based on nanoporous TiO₂ films with an inverted structure of indium tin oxide (ITO)/TiO₂/copper phthalocyanine (CuPc):fullerene (C₆₀)/CuPc/poly(3,4-oxyethyleneoxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Au were fabricated. The best overall photovoltaic performance undergoing a series of device optimization was achieved with the device of ITO/dense TiO₂ (30 nm)/nanoporous TiO₂ (130 nm)/C₆₀:CuPc (1:6 weight) (20 nm)/CuPc (20 nm)/PEDOT:PSS (50 nm)/Au (30 nm). The device using the nanoporous TiO₂ films has better photovoltaic properties compared to those using dense TiO₂ films. Higher photovoltaic performances were obtained by introducing a coevaporated layer of C₆₀:CuPc between TiO₂ and CuPc. The stability of inverted structure was better than that of the normal device, which gives a promising way for fabrication of solar cells with improved stability.     

Effect of different reductants for palladium loading on hydrogen storage capacity of double-walled carbon nanotubes

The effects of different reductants for palladium loading on the hydrogen sorption characteristics of double-walled carbon nanotubes (DWCNTs) have been investigated. Pd nanoparticles were loaded on DWCNT surfaces for dissociation of H₂ into atomic hydrogen, which spills over to the defect sites on the DWCNTs. When we use different reductants, the reduction capabilities and other effects of the different reductants are different, which affects the hydrogen storage capacity of the DWCNTs. In this work, the amount of hydrogen storage capacity was determined (by AMC Gas Reactor Controller) to be 1.7, 2.0, 2.55, and 3.0 wt% for pristine DWCNTS and for 2.0%Pd/DWCNTs using H₂, l-ascorbic acid, and NaBH₄ as reductants, respectively. We found that the hydrogen storage capacity can be enhanced by loading with 2% Pd nanoparticles and selecting a suitable reductant. Furthermore, the sorption can be attributed to the chemical reaction between atomic hydrogen and the dangling bonds of the DWCNTs.     

A green and facile synthesis of TiO2/graphene nanocomposites and their photocatalytic activity for hydrogen evolution

This work reports a green and facile approach to synthesize chemically bonded TiO₂/graphene sheets (GS) nanocomposites using a one-step hydrothermal method. The as-prepared composites were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and ultraviolet visible (UV-Vis) diffuse reflectance spectra. The photocatalytic activity was evaluated by hydrogen evolution from water splitting under UV-Vis light illumination. An enhancement of photocatalytic hydrogen evolution was observed over the TiO₂/GS composite photocatalysts, as 1.6 times larger for TiO₂/2.0 wt%GS than that of Degussa P25. This fabrication process features the reduction of graphene oxide and formation of TiO₂ simultaneously leading to the well dispersion of generated TiO₂ nanoparticles on the surface of GS.