In2O3:H transparent conductive oxide films with high mobility and near infrared transparency for optoelectronic applications

Abstract

Hydrogen doped In₂O₃ (In₂O₃:H) films show high conductivity, small dispersion of refractive index and very low extinction coefficient in the visible to near infrared wavelengths. The improved properties make this transparent conducting oxide an ideal candidate for a window electrode of optoelectronic devices. This article describes the control of microstructure of In₂O₃:H, the relationship between the structure and transport properties and the Si based solar cells incorporating the In₂O₃:H window electrode.     

Improvement of H2/O2 chemical kinetic mechanism for high pressure combustion

An updated H₂/O₂ kinetic mechanism was proposed by incorporating carefully selected reaction rate coefficient and great progress in radical chain mechanisms, in which the uncertainties of rate coefficient were discussed. The performance of the current mechanism was compared to other H₂ mechanism and validated against a wide range kinetic targets, including oxidation, decomposition in shock waves, ignition, flame speed and flame structure. Results show that the current mechanism obtains an overall improvement of performance, especially for the flame speed. By using the updated binary diffusion coefficient from ab initio calculations and the chemically termolecular reactions, the current mechanism presents better agreement with the new experimental flame speed at atmospheric pressure and obtains the improved performance with respect to the negative pressure dependence of high-pressure H₂ flame. Furthermore, the flame speed predictions are strongly sensitive to the H₂O third body efficiency in the H₂ mechanism, affecting the water-contained H₂ flame. The modeling results of rapid compression machine ignition show that present mechanism can more accurately predicts the ignition delay under engine-like conditions. However, all three mechanisms cannot accurately reproduce the negative pressure dependence behavior of mass burning rate in high-pressure H₂ flame, which may be attributed to the fact that the important reaction O + OH(+M) = HO₂(+M) that significantly affects lean high-pressure H₂ flame is not included in current mechanism. Consequently, continuous works should be emphasized on the reactions that are important but neglected in H₂ mechanism. All these not only develop an improved H₂ reaction mechanism for high-pressure combustion, but also point out the direction for refining the H₂ mechanism.     

PdAgAu alloy with high resistance to corrosion by H2S

PdAgAu alloy films were prepared on porous stainless steel supports by sequential electroless deposition. Two specific compositions, Pd₈₃Ag₂Au₁₅ and Pd₇₄Ag₁₄Au₁₂, were studied for their sulfur tolerance. The alloys and a reference Pd foil were exposed to 1000H₂S/H₂ at 623 K for periods of 3 and 30 h. The microstructure, morphology and bulk composition of both non-exposed and H₂S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD and SEM analysis revealed time-dependent growth of a bulk Pd₄S phase on the Pd foil during H₂S exposure. In contrast, the PdAgAu ternary alloys displayed the same FCC structure before and after H₂S exposure. In agreement with the XRD and SEM results, sulfur was not detected in the bulk of either ternary alloy samples by EDS, even after 30 h of H₂S exposure. X-ray photoelectron spectroscopy (XPS) depth profiles were acquired for both PdAgAu alloys after 3 and 30 h of exposure to characterize sulfur contamination near their surfaces. Very low S 2p and S 2s XPS signals were observed at the top-surfaces of the PdAgAu alloys, and those signals disappeared before the etch depth reached ∼10 nm, even for samples exposed to H₂S for 30 h. The depth profile analyses also revealed silver and gold segregation to the surface of the alloys; preferential location of Au on the alloys surface may be related to their resistance to bulk sulfide formation. In preliminary tests, a PdAgAu alloy membrane displayed higher initial H₂ permeability than a similarly prepared pure Pd sample and, consistent with resistance to bulk sulfide formation, lower permeability loss in H₂S than pure Pd.     

Hydrogen gas sensor based on mesoporous In2O3 with fast response/recovery and ppb level detection limit

Hydrogen gas sensors were fabricated using mesoporous In₂O₃ synthesized using hydrothermal reaction and calcination processes. Their best performance for the hydrogen detection was found at a working temperature of 260 °C with a high response of 18.0 toward 500 ppm hydrogen, fast response/recovery times (e.g. 1.7 s/1.5 s for 500 ppm hydrogen), and a low detection limit down to 10 ppb. Using air as the carrier gas, the mesoporous In₂O₃ sensors exhibited good reversibility and repeatability towards hydrogen gas. They also showed a good selectivity for hydrogen compared to other commonly investigated gases including NH₃, CO, ethyl alcohol, ethyl acetate, styrene, CH₂Cl₂ and formaldehyde. In addition, the sensors showed good long-term stability. The good sensing performance of these hydrogen sensors is attributed to the formation of mesoporous structures, large specific surface areas and numerous chemisorbed oxygen ions on the surfaces of the mesoporous In₂O₃.     

Hydrogen permeation behavior and mechanism of Cr2O3/Al2O3 bipolar oxide film under plasma discharging environment

To improve the thermal stability between aluminide and stainless steel substrate and obtain thermodynamically stable phase of alpha-Al₂O₃, a new Cr₂O₃/Al₂O₃ bipolar oxide barrier was proposed, in which metallic Al was sputtered on the preoxidation coating of electroplated chromium and then oxidizing by oxygen plasma. It was found that Cr₂O₃ film exhibits P-type semiconducting properties while Al₂O₃ acts as N-type. Hydrogen discharging plasma was used to simulate the in-pile hydrogen permeation. Raman spectra and atomic force microscopy (AFM) were employed to analyze phase structure and surface morphology. Electrochemical impedance spectroscopy and Mott–Schottky were utilized to qualitatively evaluate effective thickness and the integrity for the oxide film. The depth profile and surface chemical states of involving elements were analyzed by auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), respectively. The result shows that Cr₂O₃/Al₂O₃ bipolar oxides have improved hydrogen permeation resistance and would be a potential candidate for barrier application.     

Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this work, CdS nanoparticles (NPs) have been immobilized on hydrogenated three-dimensional (3D) branched TiO₂ nanorod arrays, resulting in a highly efficient photocatalyst, i.e, CdS/H-3D-TiO₂. In addition, electrochemical reduction of H⁺ ion is identified as a limiting step in the photocatalytic generation of H₂ at this catalyst, while here a Pt wired photocatalysis system (CdS/H-3D-TiO₂/Pt-wire) is designed to overcome this barrier. Without the application of potential bias, visible light photocatalytic hydrogen production rate of CdS/H-3D-TiO₂/Pt-wire is 18.42 μmol cm^?2 h^?1, which is 11.2 times that of CdS/H-3D-TiO₂ without Pt (1.64 μmol cm^?2 h^?1). The Pt wire acts as an electron super highway between the FTO substrate and H⁺ ions to evacuate the generated electrons to H⁺ ions and catalyze the reduction reaction and consequently generate H₂ gas. This work successfully offers a novel direction for dramatic improvement in H₂ generation efficiency in photocatalysis field.     

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.     

Hydrogen gas sensing properties of microwave-assisted 2D Hybrid Pd/rGO: Effect of temperature,humidity and UV illumination

A novel microwave assisted two-dimensional (2D) hybrid material based on nanostructured reduced graphene oxide (rGO) doped with Pd nanoparticles (Pd/rGO) has been synthesised to investigate its hydrogen sensing performance at different operational conditions. The sensing performance has been evaluated at various operating temperatures (room temperature up to 120 °C), hydrogen concentrations (up to 1%), and relative humidity (up to ~44%). The material characterization of the hybrid Pd/rGO analysed by different techniques which confirms homogeneous distribution of Pd NPs (<35 nm) on the multi-layered porous structure of the rGO nanosheets (NSs) and forming the hybrid Pd/rGO NSs. Moreover, the fundamental hydrogen sensing mechanism as well as recovery enhancement by ultraviolet (UV) light are investigated. This work offers an environmentally friendly and energy-saving synthesis approach for hydrogen sensing with excellent control over experimental parameters which can lead to fabrication of a highly selective and sensitive hydrogen sensor.     

In2Se3/CdS nanocomposites as high efficiency photocatalysts for hydrogen production under visible light irradiation

Hydrogen energy is an important clean energy. Using visible light to produce hydrogen by semiconductor photocatalysts is one of the current research hotspots. In this work, In₂Se₃/CdS nanocomposite photocatalysts with different mass content of CdS are prepared. The In₂Se₃/CdS photocatalyst with 85.25% CdS mass content exhibits the optimal photocatalytic hydrogen evolution activity (1.632 mmol g^?1 h^?1), which is much higher than that of CdS (0.715 mmol g^?1 h^?1) and In₂Se₃ (trace). Moreover, the In₂Se₃/CdS photocatalyst still maintains a high hydrogen evolution rate after five cycles. The high photocatalytic activity and stability of the In₂Se₃/CdS nanocomposite is due to the formation of heterojunction between In₂Se₃ and CdS. The existence of heterojunction is confirmed by high resolution transmission electron microscopy image and X-ray photoelectron spectra. Theoretical calculations and experimental results indicate that the electron transfer route at the heterojunction is step-scheme. The step-scheme helps the separation of photogenerated electrons and holes, and maximize the hydrogen evolution activity. This work provides a high efficiency step-scheme photocatalyst for hydrogen production.     

2-D WO3 decorated with Pd for rapid gasochromic and electrical hydrogen sensing

The ultrathin two-dimensional (2D) nanomaterials display unique properties owing to their ultrahigh specific surface area and strong quantum confinement of electrons in two dimensions. In this work, we fabricated a rapid gasochromic and electrical hydrogen sensing system containing 2D WO₃ and Pd nanoparticles. 2D WO₃ nano-plates (NP) are synthesized using sol–gel method and Pd nanoparticles are coated on WO₃ by green photochemical deposition method. The sensor is fabricated by dispersing the 2D WO₃/Pd composite on filter paper. In presence of hydrogen gas, 2D WO₃/Pd composite produces visible change in color from brown to dark blue. With the fabricated sensor, as low as 0.1% H₂ gas in air at room temperature can be easily detected using electrical sensing scheme whereas for higher concentration from 1 to 100%, eye readable gasochromic scheme can be utilized. The use of 2D WO₃ decreased the response time in great deal compared to WO₃ nanoparticles indicating the advantage of 2D structure in fabricating rapid response H₂ sensors. The proposed method is simple and can be easily employed to large scale fabrication system for commercial applications.     

Pd/NH2-KIE-6 catalysts with exceptional catalytic activity for additive-free formic acid dehydrogenation at room temperature: Controlling Pd nanoparticle size by stirring time and types of Pd precursors

Pd nanoparticle size is one of important factors to determine the catalytic activity of formic acid dehydrogenation catalysts. Thus various approaches to minimization of Pd nanoparticles have been attempted. In this study, we first tried to decrease Pd nanoparticles size and increase Pd dispersion of Pd/NH₂-mesoporous silica (Pd/NH₂-KIE-6) catalysts by controlling only stirring time and types of Pd precursors. It was demonstrated that the stirring time and types of Pd precursors significantly affect the performance of the catalysts. As a result, the Pd/NH₂-KIE-6 exhibited the highest catalytic activity (TOF: 8185 mol H₂ mol catalyst^?1 h^?1) ever reported for additive-free formic acid dehydrogenation at room temperature. In addition, the Pd/NH₂-KIE-6 provided higher TOF even than the case with additives such as sodium formate. Considering that the catalytic activity of Pd-based catalysts for formic acid dehydrogenation was previously controlled by promoter, support type and surface chemistry of supports, controlling the stirring time and types of Pd precursors is novel and very intriguing solutions to go beyond the current kinetic limitation for formic acid dehydrogenation.     

Effects of density ratio and differential diffusion on flame accelerative propagation of H2/O2/N2 mixtures

The effects of density ratio and differential diffusion on premixed flame propagation of H₂/O₂/N₂ mixtures are investigated by constant volume combustion chamber. The density ratio and differential diffusion are controlled independently by adjusting the O₂/N₂ ratio and equivalence ratio. Results show that the density ratio has no effect on turbulent burning velocity while the differential diffusion has a promotion effect on turbulent burning velocity. The onsets of laminar flame acceleration are promoted by both density ratio and differential ratio. The turbulent flames perform a continuous acceleration propagation and the dependence between flame propagation speed and flame radius can be characterized as (dR/dt)/(σ·S_L) ～ R^0.33～0.37, which is lower than the 1/2 power law. The acceleration parameters of laminar flames and turbulent flames (u^’/S_L = 1) are around 0.17 and 0.36 respectively, and both of them are not affected by density ratio and differential diffusion. The empirical formula m = 0.19·(u^’/S_L)^0.4+0.17 is concluded to quantitatively describe the accelerative characteristics of laminar and turbulent flames. The current study indicates that the acceleration of laminar flames is mainly induced by flame intrinsic instability, and the latter can affect the acceleration onset but not affect the fractal excess. The acceleration of turbulent flames is dominated by turbulent stretch, while the effects of density ratio and differential diffusion can be ignored.     

Oxide ionic conductivity and crystallographic properties of tetragonal type Bi2O3-based solid electrolyte doped with Ho2O3

Abstract

In the present work, the authors have investigated the binary system of (Bi₂O₃)_1–x(Ho₂O₃)_x. For the stabilisation of the tetragonal type solid solution, small amounts of Ho₂O₃ were doped into the monoclinic Bi₂O₃ via solid state reactions in the stoichiometric range 0·01≤x≤0·1. The crystal formula of the formed solid solution was determined as Bi(III)_4–4xHo(II)_4xO_6–2xVo_(2+2x) (where Vo is the oxide ion vacancy) according to the XRD and SEM microprobe results. In the crystal formula, stoichiometric values of x were 0·04≤x≤0·08, 0·03≤x≤0·09, 0·02≤x≤0·09 and 0·04≤x≤0·09 for annealing temperatures at 750, 800, 805 (quench) and 760°C (quench) respectively. The four probe electrical conductivity measurements showed that the studied system had an oxide ionic type electrical conductivity behaviour, which is increased with increasing dopant concentration and temperature. The obtained solid electrolyte system has an oxygen non-stoichiometry characteristic, and it contains O^2– vacancies, which have disordered arrangements in its tetragonal crystal structure. The increase in the amount of Ho₂O₃ doping and temperature causes an increasing degree of the disordering of oxygen vacancies and a decrease in the activation energy E_a.     

Non-monotonic behaviors of laminar burning velocities of H2/O2/He mixtures at elevated pressures and temperatures

Both experimental and calculated laminar burning velocities of H₂/O₂/He mixtures were obtained, with equivalence ratios of 0.6–4.0, initial pressures of 0.1 MPa–0.5 MPa, initial temperature of 373 K, and dilution ratio of 7.0. Laminar burning velocities changed non-monotonically with the increasing initial pressures at equivalence ratios of 1.0–3.0. The decrease of overall reaction orders can explain the non-monotonic relationship between the laminar burning velocities and initial pressures. Consumption and production of both H and HO₂ radicals were also obtained to explain the decrease of overall reaction order. The competition of H and HO₂ radical between elemental reactions were also discussed. The three body reaction R15 (H + O₂(+M) = HO₂(+M)) gained more H radical in the competition with R1 (H + O₂ = O + OH), producing more HO₂ radical. Through the reaction pathway analysis, the restraint in production of both OH and H leaded to a reducing radical pool. The poorer reaction pool would restrain the overall reaction and lead to the reduction of overall reaction order and the non-monotonic behavior of the laminar burning velocity.     

铝锂/镁合金与H_2O反应的热力学分析

根据吉布斯能最小原理,利用FactSage计算研究了Al-Li-H2O体系和Al-Mg-H2O反应体系的热力参数,研究了温度、合金组成和H2O量的影响。结果表明:Al-Li-H2O体系氧化反应可以自发进行,随着温度的升高反应放出的热量减少;合金组成中Al含量越高,生成的H2越少;随着Li含量增大,固态产物由Al2O3向LiAlO2、Li2O转变。Al-Mg-H2O体系氧化反应可以自发进行,随着温度的升高反应放出的热量减少;合金组成中Al含量越高生成的H2越多;随着Mg含量增大,最终固态产物由Al2O3向MgAl2O4、MgO转变。Al中添加Li或Mg因产物发生转变而对制氢反应有促进作用;H2O量增加有助于反应最终温度的降低,温差为1800~2000 K,对金属制氢的实施应用有指导意义。     

Mechanochemical modification of LiAlH4 with Fe2O3 - A combined DFT and experimental study

LiAlH₄ is a promising material for hydrogen storage, having the theoretical gravimetric density of 10.6 wt% H₂. In order to decrease the temperature where hydrogen is released, we investigated the catalytic influence of Fe₂O₃ on LiAlH₄ dehydrogenation, as a model case for understanding the effects transition oxide additives have in the catalysis process. Quick mechanochemical synthesis of LiAlH₄ + 5 wt% Fe₂O₃ led to the significant decrease of the hydrogen desorption temperature, and desorption of over 7 wt%H₂ in the temperature range 143–154 °C. Density functional theory (DFT)-based calculations with Tran-Blaha modified Becke-Johnson functional (TBmBJ) address the electronic structure of LiAlH₄ and Li₃AlH₆. ⁵⁷Fe Mössbauer study shows the change in the oxidational state of iron during hydrogen desorption, while the ¹H NMR study reveals the presence of paramagnetic species that affect relaxation. The electron transfer from hydrides is discussed as the proposed mechanism of destabilization of LiAlH₄ + 5 wt% Fe₂O₃.     

Local levels in La1-xSrxScO3-x/2 band-gap under interaction with components of O2, H2, H2O atmospheres

The paper studies the electronic structure of proton-conducting oxides based on the lanthanum scandate La_1-xSr_xScO_3-x/2 for advancing in understanding the mechanisms of hydrogen uptake from dry and humid atmospheres into the lattice of oxides with a perovskite structure. The process of protons incorporation from H₂O containing atmospheres is considered to describe by the reaction ${\text{H}}_2\text{O}+{\text{O}}_{\text{O}}^{\times }+{\text{V}}_{\text{O}}^{??}=2{\text{OH}}_{\text{O}}^{?}$. However, there is no established concept of a mechanism for proton uptake from a dry H₂ atmosphere. At such an uptake, a positively charged proton defect will be formed in the oxide lattice, and a negative charge must appear for compensation of the excess positive charge. Formally, the reaction of this process can be represented as $\frac{1}{2}{\text{H}}_2+{\text{O}}_{\text{O}}^{\times }={\text{OH}}_{\text{O}}^{?}+{\text{e}}^{\text{′}}$. In this case an uncompensated electron appears, and the question arises as to where it is localized. In order to answer this question, it is necessary to study the electronic structure of perovskites.With increasing in dopant concentration x the absorption band at 5.6 eV overlapping with the edge of fundamental absorption increases. Most probably it can be related with oxygen vacancies. When protons are incorporated from the H₂ atmosphere into the La_1-xSr_xScO_3-x/2 lattice, the absorption intensity in this band decreases, which can be due to the transition of the defects causing this band to another charge state. In addition, specific defects that absorb in the red and IR region at hν < 2.2 eV are formed. They are found to be located deep enough in the bang-gap and not to be an electronic traps. It is also shown that in La_1-xSr_xScO_3-x/2 there are electron traps located at a depth of 2–4.5 eV in the band-gap relative to the bottom of the conduction band. On the basis of the obtained data, it can be assumed that these defects are somehow associated with oxygen vacancies, but their charge state is not obvious. It is important that these traps participate in the capture of uncompensated electrons during the proton uptake from the H₂ atmosphere.     

Much enhanced electrocatalysis of Pt/PtO2 and low platinum loading Pt/PtO2-Fe3O4 dumbbell nanoparticles

Pt/PtO₂ nanoparticles (NPs) have been prepared by a simple synthetic strategy, easily able to control nanoparticles (NPs) size, consisting in the thermolysis of a suitable precursor in organic solvent under a low oxygen enriched atmosphere. An excellent combination of a low tafel slope of 31 mV/dec with a negligible overpotential was measured for our Pt/PtO₂ NPs, due to PtO₂ resulting in electron rich Pt island, showing activity higher than that of common Pt. Additionally, the paper proves that it is possible to improve platinum/platinum oxide activity through control of NPs size and reduce platinum loading through its junction and interaction with a further metal oxide. Very high hydrogen production rate of 3.35 mL cm^?2 h^?1 at ?0.024 V, obtained by means of an on-line mass spectrometry analysis, to corroborate the results with a realistic hydrogen production estimation, was measured for Pt/PtO₂ electrode. Moreover, Pt/PtO₂ was stable in corrosive acidic solution during electrolysis under high current density.     

Thermal desorption processes of H2 and CH4 from Li2ZrO3 and Li4SiO4 materials absorbed H2O and CO2 in air at room temperature

The thermal desorption processes of hydrogen (H₂) and methane (CH₄) from lithium-based materials, Li₂ZrO₃ and Li₄SiO₄, exposed to air at room temperature of 293 K with a relative humidity of 80%, were investigated using gas chromatography (GC). The GC analysis revealed that the absolute values of the released H₂ and CH₄ gases at 523 K were approximately 7.42 × 10^?6 and 1.54 × 10^?6 ml/g for Li₂ZrO₃, and 3.24 × 10^?6 and 0 ml/g for Li₄SiO₄. The amounts of H₂ and CH₄ released increased with increase in annealing temperatures and considerably depended on absorption properties of water (H₂O) and carbon dioxide (CO₂) present in air at room temperature. The production of CH₄ at low temperature is due to the intermediate species including CH_x precursors produced by the reaction between H split from H₂O and Li₂CO₃ resulting in the CO₂ absorption of Li₂ZrO₃ and Li₄SiO₄ materials.     

Ceria-promoted Ni@Al2O3 core-shell catalyst for steam reforming of acetic acid with enhanced activity and coke resistance

A series of Ni@Al₂O₃ core-shell catalysts with ceria added to the surface of Ni nanoparticles or inside the alumina shell were prepared, and the effect of ceria addition on the performance of the catalyst in the steam reforming of acetic acid was investigated. The prepared catalysts were characterized by BET, XRD, HRTEM, H₂-TPR and DTG. The addition of ceria to the surface of nickel nanoparticles greatly enhanced the activity of catalyst owing to the presence of the mobile oxygen, which migrated from the ceria lattice. Among the prepared catalysts, the Ni@Al10Ce catalyst showed the highest activity with a conversion of acetic acid up to 97.0% even at a low temperature (650 °C). The molar ratio of CO₂/CO was also improved due to the oxidation of CO by the mobile oxygen into CO₂. The coke formation on the core-shell catalysts was significantly inhibited by the addition of ceria to the surface of nickel nanoparticles due to the oxidation of carbon species by the mobile oxygen in the ceria lattice. However, the Ni@Al10Ce-a catalyst with ceria added to the alumina shell showed a low activity and the formation of a large amount of coke. It is suggested that only the ceria in close to the Ni surface has the promoting effect on the catalytic performance of the Ni@Al₂O₃ catalyst in the steam reforming of acetic acid.