Study and modeling of hydrogen release from Ti,Zr, Ni,Pd, Pt during linear heating

New the experimental results of thermally stimulated hydrogen release (TCHR) from plane-parallel plates of Ti, Zr, Ni, Pd, Pt metals with various thicknesses (0.05–1 mm), pre-saturated with hydrogen, under linear heating (1 °C s^?1) presented. The electrolytic and Sieverts method for saturate were used. Theoretical models for diffusion and desorption hydrogen release from flat metal samples into vacuum with linear heating were developed. In this case, the processes of diffusion and thermal desorption were taken into account to select the optimal conditions and experimental methods. The TSHR spectra simulated using the MATLAB software package to test the consistency of theory with experiment. By modeling in MATLAB using both the developed models and experimental TSHR spectra, the activation energies of desorption, diffusion and decomposition of hydrides, as well as the preexponential factors in the diffusion and kinetic equations, were determined.     

Scope of doped mesoporous (<10 nm) surfactant‐modified alumina templated carbons for hydrogen storage applications

Metal (Ni/Pd) and nitrogen codoped mesoporous templated carbons were synthesized using low‐cost surfactant‐modified mesoporous alumina as a hard template via chemical vapor deposition for hydrogen storage application. Initially, high surface area (1508 m²/g) nitrogen‐doped templated carbon was successfully prepared. Pore volume was also significant (1.64 cm³/g). The codoping with metals (Ni or Pd) reduced both the area and pore volume. All the codoped carbons were mesoporous (2‐8 nm). Aggregated morphology was observed for nitrogen‐doped carbon; tubular or noodle shape appeared on codoping with metals. The dispersion of Pd metal within the carbon framework was highest. The 2 wt% Pd codoped carbon showed the highest hydrogen uptake of 5 wt% (?196°C; 25 bar). This may be attributed to its most number of active sites corresponding to the highest metal dispersion and amount of nitrogen present. The cyclic stability of the samples was also good with only 3% to 5% loss in storage capacity up to 10 cycles.     

Extraordinary catalytic effect of Laves phase Cr and Mn alloys on hydrogen dissociation and absorption

In activation of hydrogen storage alloys, the nickel-group metals, especially Pd, act as the catalysts to dissociate hydrogen and turn the alloys into successful hydrogen absorbers. The Laves phase Sc and Zr alloys with Cr–Mn as common components exhibit extraordinary hydrogen activation properties matching Pd. Through a cracking mechanism, the bulk samples of these alloys rapidly absorb hydrogen at sub-atmospheric pressures and room-temperature, achieve absorption performance of those Pd surface-modified alloys, meanwhile retaining good reversibility. Among them, the ScCrMn exhibits significantly higher absorption rate than Pd, whereas, the ZrCrMn shows similar absorption kinetics and reversibility to Pd. The shortest initial-activation-time, highest initial-activation-rate and lowest allowed-activation-pressure achieved by ScCrMn are 15 s, −16.6 kPa/s and 0.46 kPa, respectively, in comparison with those of 18 s, 3.2 kPa/s and 0.13 kPa for Pd powder measured under equivalent conditions. The findings and associated magnetization measurements indicate that Cr and Mn upon alloying with certain lower valence metals possess surface electronic structures highly beneficial to hydrogen dissociation.     

Evaluation of catalyst activity for release of hydrogen from liquid organic hydrogen carriers

This contribution investigate the effect of parameters for production of hydrogen by catalytic dehydrogenation of perhydrodibenzyltoluene (H18-DBT). The sensitivity of the dehydrogenation reaction to temperature (290–320 °C) is justified by an increase in degree of dehydrogenation (DoD) from 40 to 90% when using 1 wt % Pt/Al₂O₃ catalyst. However, the increase in temperature increases the hydrogen production rate and decreases the hydrogen purity by increasing the formation of by-products. In addition, the DoD of 96% is obtained when 2 wt % Pt/Al₂O₃ is used at 320 °C. The DoD obtained for Pd, Pt, and Pt–Pd catalysts is 11, 82 and 6%, respectively. Therefore, Pd is not a metal of choice for dehydrogenation of H18-DBT, in both monometallic and bimetallic system. The ab-initio density functional theory (DFT) calculations are consistent with this observation. Furthermore, dehydrogenation of H18-DBT followed 1st order reaction kinetics and the activation energies for 1 wt % Pt/Al₂O₃, 1 wt % Pd/Al₂O₃ and 1:1 wt % Pt–Pd/Al₂O₃ catalysts are: 205, 84 and 66 kJ/mol, respectively.     

Influence of noble metals on the electronic and optical properties of LiH hydride: First-principles calculations

Lithium hydride (LiH) has attracted attention because of its high density hydrogen storage energy. However, the poor dehydrogenation properties cannot be used as an effective hydrogen storage material. In this paper, we apply the first-principles calculations to study the influence of noble metals on the electronic and optical properties of LiH hydride. Here, five noble metals TM(TM = Ag, Au, Pd, Pt and Ru) are considered. The calculated result shows that the noble metals are thermodynamic stability in LiH hydride. In particular, it is found that only the Pt-doped LiH is a dynamical stability compared to the other noble metals doping. Here, the calculated band gap of the pure LiH is 3.002 eV. Interestingly, these noble metals are beneficial to improve the electronic transfer (near Fermi level) of LiH because the introduction of noble metal induces the H-1s state to the Fermi level, making the band gap of the noble metal doped LiH disappear. In addition, we study the influence of noble metal Pt on the optical properties of LiH. It is found that the Pt doping can enhance the optical activity of LiH for visible light and infrared light, presumably caused by the addition of d state.     

Fabrication and characterization of NiCoZn-M (M: Ag, Pd and Pt) electrocatalysts as cathode materials for electrochemical hydrogen production

Ag, Pd and Pt-modified alkaline leached NiCoZn composite coatings were prepared on a copper specimen by electrochemical technique. The chemical composition of layers before and after leaching as well as after noble metal modification was determined by energy dispersive X-ray spectroscopy (EDX). The surface morphologies of the composite coatings were examined with the help of scanning electron microscopy (SEM). The hydrogen evolution activity of the electrodes was studied in 1 M KOH solution. For this purpose, cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques were used. Furthermore, the change of hydrogen evolution activity of the electrodes as a function of operation time in alkaline solution was also investigated. Surface morphologies showed that the composite coatings prepared to have compact and porous surface. EDX analysis confirmed the presence of Ag, Pd and Pt metals over the NiCoZn layer. The co-deposition of nickel, cobalt and zinc on copper surface and subsequently alkaline leaching of zinc rendered cathode material very active in hydrogen evolution. The modification of alkaline leached NiCoZn ternary coating by deposition of small amounts of Ag, Pd and Pt can further enhance the hydrogen evolution performance of this Raney-type electrode when compared to NiCoZn individually. The order of hydrogen evolution activity of catalysts studied is Ni < NiCoZn < NiCoZn-Pd < NiCoZn-Ag < NiCoZn-Pt. The long-term electrolysis tests showed that the Pt-modified electrode has the better time stability than the others. The superiority of Pt-modified catalyst explained by well known intrinsic catalytic activity of Pt.     

Hydrogen sorption in transition metal modified mesoporous materials

Ni, Rh and Pd incorporated mesoporous MCM-41, MCM-48, HMS and SBA-15 samples were synthesized and were characterized using XRD, ICP/EDX and N₂ adsorption–desorption at 77.4 K. The hydrogen adsorption studies in the synthesized materials were performed at 77.4 K (up to 112 kPa) and 303 K (up to 4000 kPa). The hydrogen adsorption isotherms of pristine and transition metals incorporated mesoporous materials at 77.4 K were completely reversible reflecting physisorption of hydrogen in these materials. The hydrogen adsorption isotherms at 303 K were not reversible showing the chemisorption of hydrogen in these materials at 303 K. Hydrogen sorption studies showed that transition metal modification improved the hydrogen storage capacity of mesoporous materials at 303 K. The desorption of the adsorbed hydrogen by heating up to 500 K from the mesoporous materials were also carried out for studying the recovery of adsorbed hydrogen from transition metal incorporated mesoporous materials.     

Biomass-derived hierarchical porous CdS/M/TiO2 (M = Au,Ag, pt,pd) ternary heterojunctions for photocatalytic hydrogen evolution

We demonstrate a general method for the synthesis of biomass-derived hierarchical porous CdS/M/TiO₂ (M = Au, Ag, Pt, Pd) ternary heterojunctions for efficient photocatalytic hydrogen evolution. A typical biomass—wood are used as the raw sources while five species of wood (Fir, Ash, White Pine, Lauan and Shiraki) are chosen as templates for the synthesis of hierarchical porous TiO₂. The as-obtained products inherited the hierarchical porous features with pores ranging from micrometers to nanometers, with improved photocatalytic hydrogen evolution activity than non-templated counterparts. Noble metals M (M = Pt, Au, Ag, Pd) and CdS are loaded via a two-step photodeposition method to form core (metal)/shell (CdS) structures. The photocatalytic modules—CdS(shell)/metal (core)/TiO₂ heterostructures, have demonstrated to increase visible light harvesting significantly and to increase the photocatalytic hydrogen evolution activity. The H₂ evolution rates of CdS/Pd/TiO₂ ternary heterostructures are about 6.7 times of CdS/TiO₂ binary heterojunctions and 4 times higher than Pd/CdS/TiO₂ due to the vertical electron transfer process. The design of such system is beneficial for enhanced activity from morphology control and composition adjustment, which would provide some new pathways for the design of promising photocatalytic systems for enhanced performance.     

Spillover enhanced hydrogen uptake of Pt/Pd doped corncob-derived activated carbon with ultra-high surface area at high pressure

Corncob-derived activated carbon (CAC) was prepared by potassium hydroxide activation. The Pt/Pd-doped CAC samples were prepared by two-step reduction method (ethylene glycol reduction plus hydrogen reduction). The as-obtained samples were characterized by N₂-sorption, TEM and XRD. The results show the texture of CAC is varied after doping Pt/Pd. The Pd particles are easier to grow up than Pt particles on the surface of activated carbon. For containing Pt samples, the pore size distributions are different from original sample and Pd loaded sample. The hydrogen uptake results show excess hydrogen uptake capacity on the Pt/Pd-doped CAC samples are higher than pure CAC at 298 K, which should be attributed to hydrogen spillover effects. The 2.5%Pt and 2.5%Pd hybrid doped CAC sample shows the highest hydrogen uptake capacity (1.65 wt%) at 298 K and 180 bar, The particle size and distribution of Pt/Pd catalysts could play a crucial role on hydrogen uptake by spillover. The total hydrogen storage capacity analysis show that total H₂ storage capacities for all samples are similar, and spillover enhanced H₂ uptakes of metal-doped samples could not well support total H₂ storage capacity. The total pore volume of porous materials also is a key factor to affect total hydrogen storage capacity.     

Catalytic dehydrogenation of cyclohexane over Ag-M/ACC catalysts for hydrogen supply

Dehydrogenation of cyclohexane to benzene has been carried out over Ag supported on activated carbon cloth (Ag/ACC) catalysts using a spray- pulse reactor. Hydrogen evolution was studied for hydrogen storage and supply system applications. The maximum rate of hydrogen evolution rate using monometallic Ag/ACC catalysts was 6.9 mmol/g_met/min for Ag loading of 10 wt%. An enhanced hydrogen evolution was observed by adding a small amount of noble metal (1 wt% Pt, Pd, Rh) to the Ag based catalysts. A synergistic effect was observed in the case of the Pt promoted catalysts on the hydrogen production were twice as compared to 10 wt% Ag catalyst only.     

SOFC stacks for mobile applications with excellent robustness towards thermal stresses

Solid oxide fuel cells (SOFC) are attractive power units for mobile applications, like auxiliary power units or range extenders, due to high electrical efficiencies, avoidance of noble metals, fuel flexibility ranging from hydrogen to hydrogen carriers such as ammonia, methanol or e-gas, and tolerance towards CO and other fuel impurities. Among challenges hindering more wide-spread use are the robustness under thermal cycling. The current study employs short stacks containing anode or metal supported SOFCs, which were subjected to thermal cycles in a furnace and under more realistic conditions without external furnace. Heating from 100 °C to operating temperature was accomplished by sending hot air through the cathode compartment and heating from bottom (and top) of the stack, reaching a fastest ramping time of ca. 1 h. The stacks remained intact under severe temperature gradients of at least 20 °C/cm for anode supported and 30 °C/cm for metal supported SOFCs.     

Cu-based tri-metallic nanoparticles with noble metals (Ag,Pd, and Ir) and their catalytic activities for hydrogen generation

The growth of simple and cost effective heterogeneous catalysts for the release of hydrogen is the key technological challenge for the fuel-cell based hydrogen economy. Stepwise metal displacement plating method was used for the fabrication of Cu⁰-based nanoparticles, Cu–Ag–Ir, Cu–Pd–Ir, and Cu–Ag–Pd to generate hydrogen from hydrazine hydrogen storage material. The preliminary indications of CuNPs production were the appearance of red-chocolate color with NaBH₄, sodium dodecyl sulfate (SDS) under light emitting diode (LED) irradiation. Ag and Pd were deposited on the surface of Cu⁰ by rapid reduction with NaBH₄ in SDS. Catalytic activity of trimetallic (Cu–Pd–Ir, Cu–Ag–Ir, Cu–Ag–Pd)) were higher than that of bimetallic (Cu–Ag, Cu–Ir, and Cu–Pd) due to the synergistic effect and electron interactions between the three metals. The catalytic performance of these materials depends on the structure of outer, and middle metal layers over a Cu inner metal. The nessler's reagent solution was employed to trap ammonia formation along with evolution of hydrogen generation. Cu₂₅–Pd₂₅–Ir₅₀ exhibited the superior catalytic activity, with rate constant of 5.6 × 10⁻⁴ s⁻¹ at 303 K, activation energy of 32 kJ/mol, activation enthalpy of 30 kJ/mol, and turn over frequency of 350 h⁻¹.     

Effect of Pt–Pd/C coupled catalyst loading and polybenzimidazole ionomer binder on oxygen reduction reaction in high-temperature PEMFC

Polybenzimidazole (PBI) was studied as an ionomer binder at varying ratios (1–7) in a 20–40 wt% Pt–Pd/C cathode-coupled catalyst layer for the oxygen reduction reaction (ORR) in a high-temperature proton exchange membrane fuel cell (HT-PEMFC). Catalytic activity was examined by CV and LSV, while the properties of the catalysts were characterized by FESEM-EDX, N₂ adsorption–desorption, XRD and FTIR. The results showed that the distribution of metals on the carbon surface, carbon wall thickness and the interaction between ionomer and coupled catalysts affected the ORR performance. The fabricated membrane electrode assembly with 5:95 PBI: 30 wt% Pt–Pd/C catalyst ratio exhibited the best performance and highest durability for HT-PEMFC at 170 °C, yielding a power density of 1.30 Wcm⁻² with 0.02 mg_Pt/cm Pt loading. This performance of ultra-low metal loading of coupled Pt–Pd/C electrocatalyst with PBI binder was comparable to those reported by other studies, highlighting a promising catalyst for fuel cell application.     

Intermetallics as cathode materials in the electrolytic hydrogen production

The intermetallics of transition metals have been investigated as cathode materials for the production of hydrogen by electrolysis from water–KOH solutions, in an attempt to increase the electrolytic process efficiency. We found that the best effect among all investigated cathodes (Hf₂Fe, Zr–Pt, Nb–Pd(I), Pd–Ta, Nb–Pd(II), Ti–Pt) exhibits the Hf₂Fe phase. These materials were compared with conventional cathodes (Fe and Ni), often used in the alkaline electrolysis. A significant upgrade of the electrolytic efficiency using intermetallics, either in pure KOH electrolyte or in combination with ionic activators added in situ, was achieved.The effects of these cathode materials on the process efficiency were discussed in the context of transition metal features that issue from their electronic configuration.     

Transition metal/carbon nanoparticle composite catalysts as platinum substitutes for bioelectrochemical hydrogen production using microbial electrolysis cells

Various metal nanoparticle catalysts supported on Vulcan XC-72 and carbon-nanomaterial-based catalysts were fabricated and compared and assessed as substitutes of platinum in microbial electrolysis cells (MECs). The metal-nanoparticle-loaded cathodes exhibited relatively better hydrogen production and electrochemical properties than cathodes coated with carbon nanoparticles (CNPs) and carbon nanotubes (CNTs) did. Catalysts containing Pt (alone or mixed with other metals) most effectively produced hydrogen in terms of overall conversion efficiency, followed by Ni alone or combined with other metals in the order: Pt/C (80.6%) > PtNi/C (76.8%) > PtCu/C (72.6%) > Ni/C (73.0%) > Cu/C (65.8%) > CNPs (47.0%) > CNTs (38.9%) > plain carbon felt (38.7%). Further, in terms of long-term catalytic stability, Ni-based catalysts degraded to a lesser extent over time than did the Cu/C catalyst (which showed the maximum degradation). Overall, the hydrogen generation efficiency, catalyst stability, and current density of the Ni-based catalysts were almost comparable to those of Pt catalysts. Thus, Ni is an effective and inexpensive alternative to Pt catalysts for hydrogen production by MECs.     

Preparation of Pt/Ce–Zr–Y mixed oxide/anodized aluminium oxide catalysts for hydrogen passive autocatalytic recombination

The use of a Pt-based catalyst was evaluated for autocatalytic hydrogen recombination. The Pt was supported on a mixture of Ce-, Zr- and Y-oxides (CZY) to yield nanosized Pt particles. The Pt/CZY/AAO catalyst was then prepared by the spray-deposition of the Pt/CZY intermediate onto an anodized aluminium oxide (AAO) layer on a metallic aluminum core. The Pt/CZY/AAO catalyst (3 × 1 cm) was evaluated for hydrogen combustion (1–8 vol% hydrogen in the air) in a recombiner section testing station. The thermal distribution throughout the catalyst surface was investigated using an infrared camera. The maximum temperature gradient (ΔT) for the examined hydrogen concentrations did not exceed 36 °C. The Pt/CZY/AAO catalyst was also evaluated for prolonged hydrogen combustion duration to assess its durability. An average combustion temperature of 239.0 ± 10.0 °C was maintained for 53 days of catalytic hydrogen combustion, suggesting that there was limited, or no, catalyst deactivation. Finally, a Pt/CZY/AAO catalytic plate (14.0 × 4.5 cm) was prepared to investigate the thermal distribution. An average surface temperature of 212.5 °C and a maximum ΔT of 5.4 °C was obtained throughout the catalyst surface at a 3 vol% hydrogen concentration.     

Promotional effect of auxiliary metals Bi on Pt,Pd, and Ag on Au,for glycerol electrolysis

In the search for active, stable, and selective electrocatalysts for glycerol electro-oxidation, this study focuses on the favorable effect that the addition of auxiliary metals, Bi for Pt and Pd, and Ag for Au, exerts on these three aspects. Electrocatalysts (Pt/C, Pt₃Bi/C, PtBi/C, Au/C, Au₃Ag/C, Pd/C and Pd₃Bi/C) were successfully prepared by chemical reduction with NaBH₄, resulting in nanoparticulate materials. Furthermore, in the case of the Pd₃Bi/C, a high degree of Pd–Bi alloy was achieved. When applied to glycerol electrochemical reforming, the electrochemical performance was enhanced so reducing the energy requirements for hydrogen production. Furthermore, in 24 h potentiostatic electrolysis, a smaller decay of the current was observed compared to the monometallic material, especially in the case of the Au₃Ag/C and Pd₃Bi/C electrocatalysts. Finally, the presence of the auxiliary metals altered the selectivity of the glycerol electro-oxidation. Bismuth added to Pt and Pd leads to an increase in the selectivity toward C₃ carboxylates, especially potassium tartronate in Pt–Bi materials operating at 30 °C. When the temperature is increased, this effect is counterbalanced by the larger amount of energy available, leading to a more heterogeneous product distribution in which oxalate and formate appear in higher percentages. Conversely, Ag leads to a more complex distribution product with large percentages of oxalate and formate.     

Enhanced response speed of SAW based hydrogen sensor employing a micro-heater

To feature fast hydrogen detection, a new design of surface acoustic wave (SAW) based hydrogen sensor integrated with a micro-heater is proposed in this paper. A 200 MHz delay-line patterned SAW sensing chip coated Pd/Ni alloy hydrogen sensitive film and a micro-heater are prepared on a Y35^oX quartz wafer. The hydrogen gas adsorption in Pd/Ni thin-film modulates the SAW propagation, and against the temperature interference, the corresponding changes in acoustic attenuation are collected as the sensor signal. The Micro-heater is designed to catalysis the gas-sensitive effect by regulating the working temperature, and the influence law of heating temperature towards response speed is revealed theoretically, allowing determination of the optimal working temperature. The experimental results verify the theoretical prediction. Fast response (t₉₀ < 2 s), lower power consumption (<1.35 W), and the low detection limit (<15 ppm) are achieved at low working temperature of 75 °C. Furthermore, very low crossed humidity sensitivity and excellent long-term stability are observed.     

Dissolution,diffusion, and penetration of H in the group VB metals investigated by first-principles method

The group VB metals (V, Nb, Ta) are referred to as one of the most valuable hydrogen separation membrane materials because of their advantages over Pd. To evaluate the hydrogen-permeation performance of the three metals, their structure stability, H-solubility, H-diffusivity, H-permeability, and elastic stiffness tensors have been investigated using the first-principles method. Our results reveal that the tetrahedral interstitial site (TIS) is favorable position for H-occupying, but mainly because H-solution enthalpy is the lowest. H-diffusion coefficient follows the order of V > Nb > Ta, H-permeability and H-permeation flux follow the order of Nb > V > Ta. The attractive interactions between H atoms are weak, so it is impossible to form H₂ molecules inside the metals, and all metal hydride phases present good ductility. The calculated Debye temperature is basically consistent with the experimental value. These results provide fundamental data for the further design of alloy membranes based on VB metals.