Preparation of porous ZnO/SnO2 compound films by sol-dipping template method

Abstract

Porous ZnO/SnO₂ compound film was prepared by sol-dipping template method. The morphology and characteristics of the film were analysed by SEM and X-ray diffraction (XRD). The results showed that precursor sol concentration played an important role in the formation of porous structure. The thickness of inorganic wall increases with increasing sol concentration. The suitable sol concentration, which has a satisfactory permeation and a good pore structure, is about 0·4M. X-ray diffraction pattern showed that ZnO and SnO₂ were wurtzite and rutile structure respectively.     

Novel non-alloy Ru/Pd composite membrane fabricated by electroless plating for hydrogen separation

This study presents a new non-alloy Ru/Pd composite membrane fabricated by electroless plating for hydrogen separation. It shows that palladium and ruthenium can be deposited on an aluminum-oxide-modified porous Hastalloy by using our new EDTA-free plating bath at room temperature and 358 K, respectively. A 6.8 μm thick non-alloy Ru/Pd membrane film could be plated and helium leak test confirmed that the membrane was free of defects. Hydrogen permeation test showed that the membrane had a hydrogen permeation flux of 4.5 × 10⁻¹ mol m⁻² s⁻¹ at a temperature of 773 K and a pressure difference of 100 kPa. The hydrogen permeability normalized value with thickness of the membrane was 1.4 times higher than our pure Pd membrane having similar structure. The EDX profiles of the front and back side membrane, cross-sectional EDX line scanning and XRD profile show that there was no alloying progress between the palladium and ruthenium layer after hydrogen permeation test at 773 K.     

Preparation of palladium membrane on Pd/silicalite-1 zeolite particles modified macroporous alumina substrate for hydrogen separation

A palladium composite membrane was successfully fabricated by electroless plating on a macroporous alumina tube. Pd/silicalite-1 zeolite particles were employed to reduce the pore size of the alumina support and improve its surface roughness. Moreover, the Pd⁰ existed in the Sil-1 particle can avoid the time consuming sensitization and activation steps for palladium seeding. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) analysis were conducted for analyzing the detailed microstructure of the palladium composite membrane. The hydrogen permeation performance of the resulting palladium membrane was investigated at temperatures of 623 K, 673 K, 723 K and 773 K. The hydrogen permeance of 1.95 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ with an H₂/N₂ ideal selectivity of 1165 for the palladium membrane was obtained at 773 K. Furthermore, the resulting palladium membrane was stable for a long-term operation of 15 days at 673 K.     

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%.     

Effect of PBI-HFA surface treatments on Pd/PBI-HFA composite gas separation membranes

For pure hydrogen separation, palladium was deposited on surface-treated polybenzimidazole (PBI-HFA, 4,4′-(hexafluroisopropylidene)bis(benzoic acid)) via the vacuum electroless plating technique (VELP). Since the hydrophobic characteristics of the polymer surface restrict strong adhesion of Pd on it and cause the peel-off of Pd film, various surface treatments have been employed. To increase the number of Pd anchoring sites on the PBI-HFA surface, mechanical abrasion (polishing) was applied, and to increase the hydrophilicity of the PBI-HFA surface, wet-chemical and O₂ plasma treatment (dry etching) were used. The thickness and effective permeating area of the deposited Pd films on the PBI-HFA membranes were estimated to be in the range of 160–340 nm and 8.3 cm², respectively. Among the tested membranes, membranes with Pd layers deposited on O₂ plasma treated PBI-HFA surfaces had the most uniform microstructure and the least number of defects compared to the other membranes. Gas permeation experiments were performed as a function of temperature and pressure. The gases used in the permeation measurements were H₂, N₂, CO₂, and CO (99.9% purity). A Pd-O₂30 m membrane, fabricated by O₂ plasma surface treatment during 30 min, exhibited superior gas separation performance (H₂ permeability of 275.5 Barrer), and proved to be impermeable to carbon monoxide. Enhancement of H₂ permselectivity of Pd/PBI-HFA composite membrane treated by O₂ plasma shows promising hydrogen separation membrane.     

Influence of the type of siliceous material used as intermediate layer in the preparation of hydrogen selective palladium composite membranes over a porous stainless steel support

In this work, several composite membranes were prepared by Pd electroless plating over modified porous stainless steel tubes (PSS). The influence of different siliceous materials used as intermediate layers was analyzed in their hydrogen permeation properties. The addition of three intermediate siliceous layers over the external surface of PSS (amorphous silica, silicalite-1 and HMS) was employed to reduce both roughness and pore size of the commercial PSS supports. These modifications allow the deposition of a thinner and continuous layer of palladium by electroless plating deposition. The technique used to prepare these silica layers on the porous stainless steel tubes is based on a controlled dip-coating process starting from the precursor gel of each silica material. The composite membranes were characterized by SEM, AFM, XRD and FT-IR. Moreover they were tested in a gas permeation set-up to determine the hydrogen and nitrogen permeability and selectivity. Roughness and porosity of original PSS supports were reduced after the incorporation of all types of silica layers, mainly for silicalite-1. As a consequence, the palladium deposition by electroless plating was clearly influenced by the feature of the intermediate layer incorporated. A defect free thin palladium layer with a thickness of ca. 5 μm over the support modified with silicalite-1 was obtained, showing a permeance of 1.423·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 and a complete ideal permselectivity of hydrogen.     

Graphite coating on alumina substrate for the fabrication of hydrogen selective membranes

Development of composite membranes is a suitable alternative to improve the hydrogen flux through palladium membranes. The porous substrate should not represent a barrier to gas permeation, but the roughness of its surface should be sufficiently smooth for the deposition of a thin and defect-free metal layer. In this study, the performances of the modification of the outer surface of an asymmetric alumina hollow fibre substrate by the deposition of a graphite layer were evaluated. The roughness of the substrate outer surface was reduced from 120 to 37 nm after graphite coating. After graphite coating, the hydrogen permeance through the composite membrane produced with 2 Pd plating cycles was of 1.02 × 10^?3 mol s^?1 m^?2 kPa^?1 at 450 °C and with infinite H₂/N₂ selectivity. Similar hydrogen permeance was obtained with the composite membrane without graphite coating, also at infinite H₂/N₂ selectivity, but 3 Pd plating cycles were necessary. Thus, graphite coating on asymmetric alumina hollow fibres is a suitable alternative to reduce the required palladium amount to produce hydrogen selective membranes.     

Current carrying friction and wear characteristics of Ti3AlC2 by novel method of infiltration sintering

Abstract

High purity Ti₃AlC₂ samples were prepared by an infiltration sintering method. The current carrying friction and wear characteristics of high pure bulk Ti₃AlC₂ dry sliding against a GCr₁₅ bearing steel disc were experimentally investigated on a pin-on-disk type tester at several sliding speeds from 20 to 60 m s^?1, different electric currents from 0 to 100 A and normal pressures from 0·1 to 0·6 MPa. It was found that the highly pure Ti₃AlC₂ exhibits an increasing friction coefficient (0·11–0·65) and an increasing wear rate (2·13–7·75×10^?6 mm³ N^?1 m^?1) with the electric current increasing from 0 to 100 A; the normal pressure (0·1–0·6 MPa) and the sliding speed (20–60 m s^?1) also have a complex but relatively weak influence on them. The minimum value of friction coefficient was 0·11 when the sliding electric current, speed and normal pressure were set to 0 A, 60 m s^?1 and 0·6 MPa; the wear rate reached the maximum value 7·75×10^?6 mm³ N^?1 m ^?1 when the sliding electric current, speed and normal pressure respectively were set to 100 A, 60 m s^?1 and 0·6 MPa. The low friction coefficient can be attributed to the presence of a continuous frictional oxide film consisting of an amorphous mixture of Al, Ti and Fe oxides on the friction surface, which have a significant antifriction effect on the friction surfaces. The percentage of oxide film cover was relatively higher when the electric current was 0 A, while the percentage of oxide film cover decreased with increasing electric current. The increase in the wear rate was ascribed to the ablation of the electric arc when the electric current was high.     

Photoelectrocatalytic activity of spray deposited ZnO thin films against E. coli Davis

Abstract

Zinc oxide (ZnO) thin films have been deposited onto fluorine doped tin oxide coated glass substrates by economical chemical spray pyrolysis technique. Films were deposited using various quantities of solution from 50 to 200 cc (substrate temperature 400°C, solution concentration 0·2M) in order to achieve different thicknesses. The films were characterised by X-ray diffraction, SEM, AFM and optical absorption techniques. The films exhibit a hexagonal wurtzite crystal structure with preferred (002) orientation. Morphological study showed a smooth and nanocrystalline surface of ZnO films. Direct optical band gap energy of ZnO thin films is found to be 3·24 eV. The average transmission is of the order of 87% in the visible region. The photoelectrocatalytic response of the film against Escherichia coli Davis is studied using a specially designed photoelectrochemical (PEC) reactor module. Thickness and UV light dependent photoelectrocatalytic bactericidal properties of ZnO thin films have been investigated. It shows that biased 1·1 μm thick ZnO thin films with 2 mW cm^?2 UV light intensity give better bactericidal response compared to others. The relative percentage of killing of bacteria is 19·81% due to UV illumination, 52·71% due to UV illumination and passing over ZnO surface and 95·03% due to UV illumination and passing through PEC reactor with ZnO thin film after 2·5 h. It can be concluded that the ZnO thin film with photochemical reactor can be used in a water purifier to get bacteria free drinking water.     

Long term integrity against corrosion of titanium used for TRU waste container

Abstract

Commercial grade pure titanium containing palladium (Ti-Grade 17) may be used for transuranic waste containers. The long term integrity of Ti-Grade 17 against corrosion was studied in the concrete permeated alkaline sodium water environment of 0·6 mol [Cl^?]+0·223 mol [OH^?] at various temperatures up to 80°C. The study focused on the stability of the passive oxide film, the susceptibility to crevice corrosion and cracks in the titanium hydride (TiH₂) layer. General corrosion depth for sustained passivation may be determined as i_pass times the evaluation period of 10⁴ years, with addition of the electric quantity for the destruction and repair of passivation film. Crevice corrosion sensitivity is not affected by processes such as welding, cold work and heat treatment. Cathodic reactions essential for maintaining the passive state produce hydrogen that, to some extent, is adsorbed to form a hydride layer. This layer subsequently undergoes cracking to cause reduction in the critical hydride layer thickness δ_c of 10 μm. The crack depth becomes as much as 100 μm at 2000 years.     

Spectrally selective copper oxide films

Copper oxide coatings have been produced on aluminium substrates by the spray pyrolysis technique. Studies have been carried out to observe the variations of solar absorptance (α_S) and thermal emittance (ε_T) with different concentrations of the spraying solution for different coating thicknesses. The effect of baking temperature on the optical properties of the coatings has also been studied. Under optimum conditions, with a baking temperature of 350°C and a spray concentration of 0·005m, a solar absorptance of 0·90 with a corresponding thermal emittance of 0·15 is obtained for a film 1·35 μm thick. Structural studies carried out with X-ray diffraction and electron diffraction techniques have shown that the monovalent oxide CuO is the clear dominating constituent of the oxide layer with a small percentage of the divalent Cu₂O. The stagnation temperature measurements give a maximum stagnation temperature of 120·8°C for the selective surface whereas, under identical conditions, it is 106·8°C for a non-selective black surface.     

On the long-term stability of Pd-membranes with TiO2 intermediate layers for H2 purification

This work addresses the use of TiO₂-based particles as an intermediate layer for reaching fully dense Pd-membranes by Electroless Pore-Plating for long-time hydrogen separation. Two different intermediate layers formed by raw and Pd-doped TiO₂ particles were considered. The estimated Pd-thickness of the composite membrane was reduced in half when the ceramic particles were doped with Pd nuclei before their incorporation onto the porous support by vacuum-assisted dip-coating. The real thickness of the top Pd-film was even lower (around 3 μm), as evidenced by the cross-section SEM images. However, a certain amount of palladium penetrates in some points of the porous structure of the support up to 50 μm in depth. In this manner, despite saving a noticeable amount of palladium during the membrane fabrication, lower H₂-permeance was found while permeating pure hydrogen from the inner to the outer surface of the membrane at 400 °C (3.55·10^?4 against 4.59·10^?4 mol m^?2 s^?1 Pa^?0.5). Certain concentration-polarization was found in the case of feeding binary H₂–N₂ mixtures for all the conditions, especially in the case of reaching the porous support before the Pd-film during the permeation process. Similarly, the effect of using sweep gas is more significant when applied on the side where the Pd-film is placed. Besides, both membranes showed good mechanical stability for around 200 h, obtaining a complete H₂/N₂ ideal separation factor for the entire set of experiments. At this point, this value decreased up to around 400 for the membrane prepared with raw TiO₂ particles as intermediate layer (TiO₂/Pd). At the same time, complete selectivity was maintained up to 1000 h in case of using doped TiO₂ particles (Pd–TiO₂/Pd). However, a specific decrease in the H₂-permeate flux was found while operating at 450 °C due to a possible alloy between palladium and titanium that is not formed at a lower temperature (400 °C). Therefore, Pd–TiO₂/Pd membranes prepared by Electroless Pore-Plating could be very attractive to be used under stable operation in either independent separators or membrane reactors in which moderate temperatures are required.     

Electroless Pd membrane deposition on alumina modified porous Hastelloy substrate with EDTA-free bath

This study demonstrates palladium membranes can be electrolessly plated on aluminum oxide-modified porous Hastelloy with hydrazine using an EDTA-free bath. The plating bath temperature affected the membrane surface morphology, with the palladium grain size increasing with increasing temperature. A 7.5 μm thick membrane plating was obtained at room temperature. Helium leak testing confirmed that the membrane was free of defects. Hydrogen permeation test showed that the membrane had a hydrogen permeation flux of 3.3 × 10⁻¹ mol m⁻² s⁻¹ at a temperature of 823 K and at a pressure difference of 100 kPa. There was no measurable interdiffusion between the membrane film and the porous Hastalloy substrate at 823 K. This room temperature membrane plating method provides several advantages such as very high selectivity, stability, favorable energy efficiency and simplicity.     

Effect of catalytic Pd coating on the hydrogen storage performances of ZrCo alloy by electroless plating method

The effects of Pd coating with different deposition concentration (PdCl₂ 0.2 g L^?1, 0.6 g L^?1, 1.0 g L^?1) on the surface morphology, microstructure and hydrogen storage performances of ZrCo alloy have been investigated. Results show that spherical Pd particles have been deposited on the surface of ZrCo alloy successfully, which transfer from sparse arrangement to continuous and compact film with increasing deposition concentration of PdCl₂. The hydriding kinetic property of all Pd coated alloys is improved compared with the bare alloy, which is due to the catalyst effect of Pd coating. The hydriding rate of the samples firstly increases and then decreases with increasing deposition concentration, which is closely related to the surface morphology and thickness of Pd coating. The hydriding kinetic property of the samples is greatly improved after 5 cycles, although Pd particles on the alloy surface peel off to some extent. This phenomenon indicates that the accumulated fresh surface during cycling makes a greater contribution to the improved hydriding kinetic property and the catalyst effect of Pd coating is weakened during cycling.     

Improved formic acid oxidation using electrodeposited Pd–Cd electrocatalysts in sulfuric acid solution

In the present research, nanostructured Pd–Cd alloy electrocatalysts with different compositions were produced using the electrodeposition process. The morphology of the samples was studied by scanning electron microscopy analysis. Also, the elemental composition of the samples was determined by energy-dispersive X-ray spectroscopy and elemental mapping tests. Tafel polarization and electrochemical impedance spectroscopy methods were employed to determine the electrochemical corrosion properties of the synthesized samples in a solution containing 0.5 M sulfuric acid and 0.1 M formic acid. The linear sweep voltammetry, cyclic voltammetry, and chronoamperometry techniques were also employed to evaluate the electrocatalytic activity of prepared samples toward the oxidation of formic acid. In this respect, the influence of some factors such as formic acid and sulfuric acid concentrations and also potential scan rate was investigated. Compared to the pure Pd sample, the Pd–Cd samples were more reactive for the oxidation of formic acid. Besides, the sample with a lower amount of Pd (Pd_1·3Cd) demonstrated much higher electrocatalytic activity than the Pd_7·1Cd and Pd_2·1Cd samples. The observed high mass activity of 15.06 A mg^?1_Pd for the Pd_1·3Cd sample which is 21.1 times higher than Pd/C is an interesting result of this study.     

Ag modified LSCF as cathode material for protonic conducting SOFCs

Abstract

BaCe_0·7Zr_0·1Y_0·2O_3?δ (BCZY) electrolyte and La_0·6Sr_0·4Co_0·2Fe_0·8O_3?δ (LSCF) cathode perovskite materials were synthesised using the citrate–nitrate combustion method. NiO–BCZY anode supported thin film sold oxide fuel cells (SOFCs) was fabricated using spin coating and co-sintering process. LSCF exhibited good chemical stability in H₂O containing atmosphere and chemical compatibility with BCZY proton conducting material. The electrochemical performance of the Ag–LSCF composite cathode was dependent on the Ag content. The thin film proton conducting SOFC displayed highest maximum power density of 563 mW cm^?2 at 700°C for 10 wt-%Ag–(LSCF+BCZY) composite cathode.     

Cracked palladium films on an elastomeric substrate for use as hydrogen sensors

We have investigated a lithography-free technique for On-Off type hydrogen sensors using a cracked palladium (Pd) film on an elastomeric substrate. Cracks were induced in a sputtered Pd film simply by undergoing hydrogen absorption and desorption processes. Compared to the same thickness of a Pd film on a Si/SiO₂ substrate that relied on the electron scattering mechanism, a cracked Pd film on an elastomeric substrate operated as a reversible On-Off hydrogen sensor based on the crack open-close mechanism when exposed to hydrogen. The thickness of a Pd film on the elastomeric substrate plays a significant role in determining the sensing mode of the cracked Pd film. The cracked Pd film with a thickness of 9–11 nm on the elastomeric substrate showed reversible and perfect On-Off responses under a wide range of hydrogen concentrations with large current variations and a fast response time of less than 1 s.     

Effects of sputtering pressure on properties of Al doped ZnO thin films dynamically deposited by rf magnetron sputtering

Abstract

Aluminium doped zinc oxide (AZO) films were dynamically deposited by rf magnetron sputtering under various sputtering pressures in the range of 0·3–2·0 Pa. The effect of the Ar sputtering pressure on the structural, electrical and optical properties of the AZO films was systematically investigated by X-ray diffractometry, scanning electron microscope, four-point probe measurement and UV–vis spectrophotometer. As the sputtering pressures decrease, the crystallite sizes of the films became larger, while their deposition rate turns higher. Under the condition of lower sputtering pressures, a decrease in the resistivity was observed due to an increase in carrier concentration. The AZO film deposited at 0·5 Pa in the dynamic mode has shown the lowest resistivity of 9·5×10^?4 Ω cm. This work was performed in a dynamic deposition system in order to produce a large area of AZO films, which is more important in practical fields to improve productivity.     

Si doped ZnO thin films for transparent conducting oxides

Abstract

Transparent conductive silicon doped zinc oxide (SZO, 3%Si) thin films are grown by direct current magnetron sputtering on glass substrates at room temperature. Experimental results show that the sputtering time has a significance impact on the growth rate, crystal quality and electrical properties of the films, and have little impact on the optical properties of the films. The growth rate decreases with the sputtering time. The resistivity of ZnO/Si films decreases as the sputtering time increases from 8 to 20 min. However, as the sputtering time increases further, the electrical resistivity increases instead. When other sputtering conditions are kept unchanged, it is found that the optimum sputtering time is 20 min and the achieved lowest resistivity is 4·92×10^?4 Ω cm (sheet resistance?=?11·5 Ω/sq for thickness 427·5 nm). The UV-vis transmission spectrum shows that all film samples present a transmission of above 90·0% in the visible range.     

Preparation of semiconducting copolymer and its application in nanocrystalline TiO2 solar cells

Abstract

The past decade has witnessed increasing attention in the nanocrystalline TiO₂ solar cells (TSSCs). In this work, we have studied a novel TiO₂/PCBM/PPy solar cell based on blends of the semiconducting copolymer polypyrrole (PPy) and [6,6]-phenyl C₆₁ butyric acid methyl (PCBM) coated titanium dioxide (TiO₂) nanocrystal film to substitute the I₃^?/I^? redox electrolyte and the dye using in DSSCs. The research by incident photon to current efficiency spectra shows that the TiO₂ films had a stronger absorption in 300–500 nm light range. The performance of the resulting photovoltaic devices was investigated, and the effects of the PCBM/PPy ratio by photocurrent–voltage characteristics were researched. By the optimised PCBM/PPy ratio was 3∶1, The TSSC exhibited a short circuit current of 1·28 mA cm^?2, an open circuit voltage of 0·788 V, a fill factor of 0·654 and a light to electric energy conversion efficiency of 0·622% under a simulated solar light irradiation of 100 mW cm^?2.