In-situ characterization of hydrogen-induced defects in palladium by positron annihilation and acoustic emission

Positron annihilation spectroscopy was employed for characterization of hydrogen-induced defects in Pd. Positron annihilation studies were performed in-situ during electrochemical hydrogen charging and were combined with measurement of acoustic emission, which is a non-destructive technique capable of monitoring of collective dislocation motion. It was found that hydrogen loading introduced defects into Pd lattice, namely vacancies and dislocations. At low concentrations (α-phase) hydrogen loading created vacancies associated with hydrogen. Stresses induced by growing α'-phase particles led to plastic deformation and introduced dislocations into the sample. Moreover, additional vacancies were introduced into the sample by crossing dislocations. Vickers hardness testing revealed that hydrogen absorbed in interstitial sites causes solid solution hardening. Further hardening was caused by dislocations when α'-phase particles are formed. Pd sample completely transformed into the α'-phase was subsequently unloaded. Decomposition of α'-phase particles during unloading caused further increase of dislocation density and led to an additional hardening. Loading-unloading of Pd sample with hydrogen continuously generates dislocations and makes the sample harder.     

Dissociation of H2S in non-equilibrium gliding arc “tornado” discharge

The process of hydrogen sulfide, H₂S, dissociation was studied in a non-equilibrium gliding arc “tornado” (GAT) plasma discharge. Utilizing GAT ensured uniform H₂S gas treatment in the reactor. In addition, it created a low temperature zone near the cylindrical wall of the reactor, while maintaining a high temperature zone near the reactor axis. An energy cost of 1.2 eV per H₂ molecule was achieved in this plasma system at atmospheric pressure. These results are particularly important for the oil industry, which consumes large amounts of hydrogen in oil hydro-treatment, and for gas industry because of the high H₂S content in “sour” gas.     

Redistribution of hydrogen in calibrated wire

The model formed by distributing the concentration of hydrogen in a wire influenced by acidic removal of scales and further calibration has been developed. It is shown that hydrogen strengthens steel, developing homogeneous and inhomogeneous solid solutions, and blocking the movement of dislocations. Besides, hydrogen causes steel to be brittle, forming micropores and microcracks. The transition from strengthening to brittleness of steel occurs with a slight change of hydrogen concentration and alloy elements. The developed electron-microscopic investigations of steels, of ferrite–pearlite class influenced by hydrogenation, brought to light the specific role of hydrogen in the formation of substructure during drawing, and further deformation by compression.     

Ultraviolet activation of thermal decomposition of α-alane

We investigated activation of thermal dehydriding of α-AlH₃ crystal by preliminary irradiation by ultraviolet light using thermal desorption spectroscopy, barometry, and cathode luminescence methods. It is shown that hydrogen vacancies appear due to irradiation; they serve as points where metal nuclei probably appear, so dehydriding becomes significantly faster. Possible explanation of transformation of hydrogen vacancies to metal phase nuclei is suggested: new vacancies are more likely to appear near the first one compared to remote places. Using density functional theory method we calculated the electronic structure of stoichiometric α-AlH₃ and α-AlH₃ with a hydrogen atom removed from a regular lattice site with a vacancy in place of it. It is suggested that an appearance of a new vacancy near the first vacancy needs less energy compared to the first one. From cathode luminescence data we see that appearance of vacancies can also be activated thermally. The model of hydrogen desorption from α-AlH₃ activated by UV light is suggested and kinetic parameters of desorption are evaluated.     

Catalytic mechanisms of TiH2 thin layer on dehydrogenation behavior of fluorite-type MgH2: A first principles study

DFT calculations were carried out to investigate hydrogen release and diffusion behaviors. Results demonstrated that MgH₂/TiH₂ interface is thermodynamically stable with negative adhesion energy of −1.33 J/m² with respect to the individual MgH₂ and TiH₂ slabs. The formation of MgH₂/TiH₂ interface alters the interstice structure and space of the interstitial sites where H atoms located and then significantly lowers the dehydrogenation energy of hydrogen releasing from both the MgH₂ and TiH₂ slabs nearby the interface comparing the bulk MgH₂ and TiH_2. The smallest dehydrogenation energy of 0.06 eV/H could be reached when H releases from MgH₂ side. The study also illustrates that the existence of the MgH₂/TiH₂ interface promotes the diffusion of hydrogen vacancy. The lowest diffusion barrier of hydrogen vacancy in the MgH₂ slab (from the sublayer to the frontier layer to the interface) is estimated as 0.21 eV. Based on the present study, one can deduce that the dehydrogenation of the MgH₂/TiH₂ system will start by H releasing from MgH₂ slab, which generates H vacancies near the interface, then the interior H of MgH₂ migrates to the H vacancies (diffuse of H vacancies in the opposite direction) and releases. The TiH₂ acts as a catalyst promoting the generation and diffusion of H vacancies in MgH₂. Therefore synthesizing of MgH₂/TiH₂/MgH₂ sandwich structure could be an effective approach to promote the dehydrogenation process of MgH₂, and an ideal structure owning geometric hydrogen capacity of 6.45 wt%.     

Li-decorated porous graphene as a high-performance hydrogen storage material: A first-principles study

Development of novel carbon-based nanoporous materials with high reversible capacity and excellent cycling stability is a hot topic in the field of hydrogen delivery and storage. In this work, first-principles calculations are carried out to discuss the hydrogen storage properties of Li-decorated porous graphene (Li-PG). The binding energies, electronic structures, storage capacities of hydrogen on different sites are investigated in details. The computational results show that with the increase of lithium doping concentration, the electron concentration of donor atoms exceeds the N_c value, and as a consequence, the PG changes from the p-type semiconductor to the n-type degenerate semiconductor. The maximum hydrogen adsorption configurations of H1a-H'1b and H2a-H'2b systems are obtained, and the average binding energy of per H₂ molecule is 0.245 eV and 0.263 eV, respectively. Furthermore, ab inito MD simulation results show that the H1-H'1 and H2-H'2 systems can hold up to sixteen and fifteen H₂ molecules, which corresponds to a hydrogen storage capacity of 10.89 wt% and 10.79 wt% at T = 300 K (no external pressure), respectively.     

Variation of creation and annealing character of light induced metastable defects in a-Si1−xCx:H alloys

The creation and annealing kinetics of light induced metastable defects were studied in a set of good quality a-Si_1−xC_x:H alloys (x0.11) using the constant photocurrent method (CPM) at room temperature. Light induced metastable defects created at room temperature started annealing at higher temperatures, when the alloys had high carbon content. The annealing activation energy distribution functions of the hydrogenated amorphous silicon–carbon alloys were calculated using the method proposed by Hata and Wagner (J. App. Phys. 72 (1992) 2857). The annealing activation energy distribution function is a narrow Gaussian peaked at about 1 eV for the unalloyed sample. For the alloys, the peak position shifts to higher energies and the half-width of the distribution decreases with increasing carbon content. The results obtained are discussed within the framework of the “weak-bond breaking” (Phys. Rev. B 32 (1985) 23), and the “hydrogen-collision” (Phys. Rev. 59(8) (1999) 5498) models.     

Model systems in photoelectrochemical energy conversion

Several model photoelectrochemical energy conversion systems are devised and analyzed, based on properties of liquid junction-solid state semi-conductor photoactive “membranes”. The systems are classified in terms of the following output objectives: electric power, short term chemical energy storage, desalted water from a saline source, acid-base production from a saline source, and hydrogen and oxygen from water. Multicompartment photoelectrochemical cells designed to achieve these objectives are made from various combinations of the photoactive component and ion selective membranes. All of the objectives are projected as technically feasible, but only the electric power and desalting are projected as economically feasible based on state-of-the-art technology. The properties of conceptual new solid state membranes needed to meet economic objectives in the other cases are analyzed.     

Hydrogen adsorption on and diffusion through MoS2 monolayer: First-principles study

We investigate the hydrogen adsorption on and diffusion through the MoS₂ monolayer based on density-functional theory. We show that the hydrogen atom prefers to bond to the S atom at the monolayer, leading to enhanced conductivity. The hydrogen atom can also adsorb at the middle of the hexagon ring by overcoming an energy barrier of 0.57 eV at a strain of 8%. Also, we show that the MoS₂ monolayer is flexible and any mechanical deformation of the monolayer is reversible because the extension of the Mo–S bond is much smaller than the applied strain. The monolayer can block the diffusion of hydrogen molecule from one side to the other due to a high energy barrier (6.56 eV). However, the barrier can be reduced to 1.38 eV at a strain of 30% and even totally removed by creating S vacancies and applying a strain of 15%. The MoS₂ monolayer may find applications in sensors to detect hydrogen, and as mechanical valve to control the concentration of hydrogen gas.     

Effects of post-deposition treatment on the PL spectra and the hydrogen content of CuInS2 absorber layers

CuInS₂ absorber layers for thin-film solar cells are examined in this work. The influence of post-deposition annealing in hydrogen and oxygen atmosphere is studied by means of photoluminescence (PL) and nuclear reaction analysis (NRA). The intensity of a PL peak at 1.445 eV can be drastically influenced by post-deposition treatments. This transition is ascribed to the donor-acceptor pair recombination between a sulfur vacancy and a copper vacancy. From the measurements, a simple defect model is deduced which assumes the occupation of sulfur vacancies by oxygen. The sulfur vacancy can be activated by hydrogen annealing and passivated by oxygen annealing.     

Catalyst Induced Hydrino Transition (CIHT) electrochemical cell

Atomic hydrogen is predicted to form fractional Rydberg energy states H(1/p) called ‘hydrino atoms’ wherein n = 1/2,1/3,1/4,…,1/p (p ≤ 137 is an integer) replaces the well‐known parameter n = integer in the Rydberg equation for hydrogen excited states. The transition of H to a stable hydrino state H[a_H/p = m + 1] having a binding energy of p² × 13.6 eV occurs by a nonradiative resonance energy transfer of m × 27.2 eV (m is an integer) to a matched energy acceptor such as nascent H₂O which has a potential energy of 81.6 eV (m = 3) to form an intermediate that decays with the emission of continuum bands with short wavelength cutoffs and energies of m² × 13.6 eV. The predicted H(1/4) continuum radiation in the region 10 to 30 nm was observed first at BlackLight Power, Inc. (BLP) and reproduced at the Harvard Center for Astrophysics (CfA) wherein H₂O catalyst was formed by a hydrogen reduction reaction at the anode of a hydrogen pinch plasma. By the same mechanism, the nascent H₂O molecule formed by an oxidation reaction of OH^? at a hydrogen anode is predicted to serve as a catalyst to form H(1/4) with an energy release of 204 eV compared to the 1.48 eV required to produce H from electrolysis of H₂O. CIHT cells, each comprising a Ni anode, NiO cathode, a LiOH–LiBr eutectic mixture as the electrolyte, and MgO matrix exploit hydrino formation as a half‐cell reaction to serve as a new electrical energy source. The cells were operated under intermittent H₂O electrolysis to generate H at the anode and then discharged to form hydrinos wherein trace H₂O vapor was supplied as entrained in an inert gas flow in otherwise closed cells. Net electrical production over the electrolysis input was measured using an Arbin BT 2000 (<0.1% error) and confirmed using a digital oscilloscope, wherein no theoretical conventional energy was possible. Materials characterizations included those that quantified any compositional change of the electrolyte by elemental analysis using ICPMS, XRF, and XRD, and SEM were performed on the anode. The electrical energies were continuously output over long‐duration, measured on different systems, configurations, and modes of operation and were typically multiples of the electrical input that in most cases exceed the input by a factor of greater than 10. Calorimetry of solid fuels that exploited the same catalyst and a similar reaction mechanism showed excess thermal energy greater than 10 times the maximum possible from any conventional reaction. The predicted molecular hydrino H₂(1/4) was identified as a product of CIHT cells and solid fuels by MAS ¹H NMR, ToF‐SIMS, ESI‐ToFMS, electron‐beam excitation emission spectroscopy, Raman spectroscopy, photoluminescence emission spectroscopy, FTIR, and XPS. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of microstructure-driven hydrogen distribution on environmental hydrogen embrittlement of an Al–Cu–Mg alloy

The hydrogen trap sites and corresponding hydrogen binding energies in an Al–Cu–Mg alloy with the different microstructures were investigated to unravel the environmental hydrogen embrittlement (HE) behavior of the alloy. The results showed that hydrogen can reside at interstitial lattices, dislocations, S′-phase, and vacancies. In the aged specimen with the highest hydrogen content, it was firstly reported that hydrogen resided at S′-phase particles with relatively high binding energy, which is a determinant factor on HE resistance of the alloy. In the cold-rolled specimen, high content of hydrogen trapped at dislocations with a reversible nature leads to intergranular hydrogen-assisted cracking. In the solution-treated specimen, hydrogen migration to the surface due to low trap density results in low hydrogen content and prevents the GBs from reaching critical hydrogen concentration. The obtained results clearly reveal that trap site density, and the nature of trap sites can determine environmental HE susceptibility of the alloy.     

Solute hydrogen effects on plastic deformation mechanisms of α-Fe with twist grain boundary

The deformation mechanisms in the α-Fe twist bi-crystals (TBCs) containing differently angled twist grain boundaries (TGBs) are investigated carefully using the molecular dynamics modeling, with especial concerns on how solute hydrogen affects them. The results show that there are three main deformations in the TBCs, i.e. the dislocation glide-dominated mechanism, the twining-dominated mechanism, the dislocation glide and twining co-dominated mechanism, depending upon both the twist angle and the loading direction. In the dislocation glide-dominated TBCs, solute hydrogen increases the dislocation nucleation strength, dislocation mobility and dislocation density, further increases the vacancies concentration due to frequent interactions of solute hydrogen atoms with dislocations. In the dislocation glide and twining co-dominated TBCs, the solute hydrogen has weaker effect on the increase of dislocations density and the decrease of twins fraction with increasing tensile strain. However, in the twining-dominated TBCs, solute hydrogen assists the deformation twinning but doesn't increase significantly the vacancies concentration. So, it seems that twinning deformation is beneficial to resist hydrogen embrittlement (HE). These knowledge is helpful for us to understand the HE mechanism and develop new hydrogen-resistant high-strength materials.     

Effect of thermo hydrogen treatment on lattice defects and microstructure refinement of Ti6Al4V alloy

An investigation of a rolled Ti6Al4V alloy after thermo hydrogen treatment was performed. The effect of hydrogen content on the types and amount of lattice defects, the microstructure refinement after hydrogenation–dehydrogenation processing and the refining mechanisms were studied. The results show that the types of defects are at first vacancies and dislocations, and then they are mainly dislocations with increasing of hydrogen content. The amount of defects increases gradually with increasing of hydrogen content. After thermo hydrogen treatment, the rolled microstructure of Ti6Al4V alloy is refined.     

Design and optimization of solar industrial hot water systems with storage

This paper presents a new method for the design and optimization of solar industrial process hot water systems with storage. The single-pass open-loop design thermally “decouples” collectors from storage, hence insuring that collectors always heat the coldest fluid possible and that stored heat can be completely depleted by the nighttime load. So the single-pass open-loop design, in spite of the relatively low flow rates entailed, operates at higher system efficiency than conventional system designs. One solved example for an an industrial hot water application shows that the single-pass open-loop design delivers about 30 per cent more useful energy with roughly 30 per cent less storage than the conventional design. Moreover, storage tanks do not have to stand high pressures and can thus be significantly cheaper than in conventional systems. The effects of collector operating time, heat exchangers, and secondary system losses are also treated. The new method is extended to cover systems that require weekend storage. The introduction of weekend storage may be cost effective because it enables the designer to reduce collector area without reducing the yearly useful energy delivered by the system.     

Photoinduced hydrogen evolution by use of porphyrin, EDTA, viologens and hydrogenase in solutions and Langmuir–Blodgett films

Photoinduced hydrogen evolution was investigated by use of a zinc porphyrin, EDTA, viologens and hydrogenase (H₂ase) in the solutions and Langmuir–Blodgett (LB) films. An almost linear increase of hydrogen evolution rate was observed with the increase of H₂ase concentrations from 1 to 5 μg/ml. For the zinc porphyrin, EDTA and methyl viologen, when their concentrations increased to a given value, hydrogen evolution did not show obvious increase. Phospholipid-porphyrin mixed LB films were prepared and used as photosensitizer for the photoinduced hydrogen evolution. Spectroscopic studies of the deoxygenated solutions indicated a “new” absorption band (in the solutions) or sharp peaks (in the LB films) when the sample solutions were irradiated, which was ascribed to the formation of an excited complex of porphyrin–EDTA (or -EDTA breakdown products). This excited complex was unstable to air.     

A multi-agent system for energy management of distributed power sources

The field of energy management is an area increasingly studied. However, most solutions are based on centralized systems and barely fulfil criterion like fault tolerance or adaptability. Also, these systems are often difficult to design because of the “top–down” approach used: the designer generally knows how each component has to respond separately, but a centralized management system focuses his attention solely on the overall reaction of the system. That is why a distributed management solution based on the paradigm of Multi-Agent Systems (MASs) is proposed in this paper. In addition to a more natural conception, based on a “bottom–up” approach, this solution ensures better system reliability. After reviewing the previous works, an application of MAS to power management in a hybrid power source is presented. Then, the system is tested using a simulation model. The results show that this approach is perfectly valid and can respond to most problems of centralized energy management systems (EMSs).     

Towards high-efficiency thin-film silicon solar cells with the “micromorph” concept

Tandem solar cells with a microcrystalline silicon bottom cell (1 eV gap) and an amorphous-silicon top cell (1.7 eV gap) have recently been introduced by the authors; they were designated as “micromorph” tandem cells. As of now, stabilised efficiencies of 11.2% have been achieved for micromorph tandem cells, whereas a 10.7% cell is confirmed by ISE Freiburg. Micromorph cells show a rather low relative temperature coefficient of 0.27%/K. Applying the grain-boundary trapping model so far developed for CVD polysilicon to hydrogenated microcrystalline silicon deposited by VHF plasma, an upper limit for the average defect density of around 2 × 10¹⁶/cm³ could be deduced; this fact suggests a rather effective hydrogen passivation of the grain-boundaries. First TEM investigations on μc-Si : H p-i-n cells support earlier findings of a pronounced columnar grain structure. Using Ar dilution, deposition rates of up to 9 Å/s for microcrystalline silicon could be achieved.     

A comparative study of optical, electrical and structural properties of CuGaSe2 and CuGaTe2 thin films

The growth conditions, the composition and the structural, optical and electrical properties of thin films of CuGaSe₂ and CuGaTe₂ have been studied using “flash” and “slow” evaporation in vacuum. Single phase films, when analyzing the absorption coefficient, present several energy gaps. For CuGaSe₂, they are 1.59, 1.66, 2.03 and 2.11 eV, for CuGaTe₂ 1.23 and 1.89 eV. Both the CuGaSe₂ and CuGaTe₂ evaporated films are p-type; the resistivities, carrier densities and mobilities are appropriate for thin film solar cells.