Hydrogen Release Rate Research Articles

AuPd Nanoparticles Anchored on Nitrogen-Decorated Carbon Nanosheets with Highly Efficient and Selective Catalysis for the Dehydrogenation of Formic Acid

Formic acid (FA), a sustainable and safe hydrogen storage vector, has the advantages of nontoxicity, high hydrogen content (4.4 wt %) and low cost. However, the dehydrogenation of formic acid at near room temperature remains a big challenge in terms of favorable hydrogen release rate and CO-absence hydrogen production. Herein, a series of nitrogen-decorated carbon nanosheets (n-CNS) supported AuPd nanoparticles (NPs) were designed and employed as efficient catalysts to dehydrogenate FA for the first time. The catalyst AuPd NPs supported on n-CNS synthesized at hydrothermal temperature of 160 °C (AuPd/n-CNS-Th-160) exhibits excellent catalytic activity toward the dehydrogenation of FA compared with AuPd/g-carbon nitride (AuPd/g-C3N4) and commercial Pd/C catalysts, reaching an initial turnover frequency (TOF) of 527 h–1, 100% hydrogen generation and selectivity at room temperature (25 °C), while the TOF achieves even 1896 h–1 at 60 °C. The enhanced catalytic performance can be attributed to the coordinated ...

Controlled hydrogen release from metastable hydrides

Metastable hydrides are an interesting class of hydrogen carrier since many offer high volumetric and gravimetric hydrogen densities and rapid hydrogen release rates at low temperatures. Unlike reversible metal hydrides, which operate near equilibrium, metastable hydrogen carriers rely on kinetic barriers to limit or prevent the release of hydrogen and can be prepared in a stabilized state far from equilibrium. Despite the advantage of low temperature hydrogen release, this type of one-way thermolysis reaction can be difficult to control since the hydrogen release rate varies with temperature and composition. Here we developed a kinetic rate equation from a series of isothermal measurements, which describes the relationship between temperature, hydrogen release rate and composition for aluminum hydride. This equation is necessary to thermally control the rate of hydrogen release throughout decomposition. This equation was used to run a fuel cell at a controlled rate of ∼1 wt%/hr. Although the equation established in this paper relates specifically to aluminum hydride, the method used is applicable to other metastable hydrides.

Effect of Foaming Temperature on Bubble Size Distribution of Liquid Aluminium Foam: Modeling and Experimental Studies

The present study examines the effect of foaming temperature on the final foam expansion and the bubble size distribution of liquid aluminium foam through mathematical modeling and validation experiments. The model calculates the rate of hydrogen release from the foaming agent (TiH2) particles, super saturation of the melt, nucleation and growth of bubbles and finally, evaluates the evolving bubble size distribution using a population balance approach. The model does not consider bubble coalescence and breakage and uses only solute diffusion for bubble growth. The simulation is performed for two conditions; firstly, for pure temperature effects and secondly, for temperature and TiH2 quantity combined effects. Upon comparison of simulation results with the experiments, following important observations are made; firstly, the predicted total number of bubbles is found to be one order of magnitude higher than the experiments while the predicted average size is one order of magnitude lower. Secondly, the spread of the predicted distributions is observed to be much narrower. These discrepancies are considered to be due to bubble coalescence and coarsening which are not modeled and shown to be strongly influenced by the foaming temperature.

Investigation of Hydrogen Release Rate from Electrodes of Nickel-Cadmium Batteries at Their Thermal Decomposition

Investigation of Hydrogen Release Rate from Electrodes of Nickel-Cadmium Batteries at Their Thermal Decomposition

Dendritic Co0.52Cu0.48 and Ni0.19Cu0.81 alloys as hydrogen generation catalysts via hydrolysis of ammonia borane

Dendritic CoCu and NiCu alloys were employed as hydrogen generation catalysts via hydrolysis of ammonia borane (NH3BH3, AB). Dendritic Co0.52Cu0.48 and Ni0.19Cu0.81 alloys were successfully synthesized with starch by a facile and efficient in situ method at room temperature. The structure, morphology, and chemical composition of the as-obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X ray spectroscopy (EDX), transmission electron microscopy (TEM) inductively coupled plasma emission spectroscopy (ICP) and X-ray photoelectron spectroscopy (XPS). The characterization results revealed a dendritic and uniform distribution for the as-synthesized nanoparticles (NPs). Good performance towards the hydrolysis of AB was observed in all cases, although Co0.52Cu0.48 showed the highest hydrogen release rate (r, 2179 mL min−1·g−1) and the lowest activation energy (Ea, 37.3 kJ mol−1) among the samples prepared. The surface structure of the alloys and the reticular density of the different crystal faces were studied with the aim to explain the catalytic performance of the samples.

Hydrogen production by low-temperature oxidation of coal: Exploration of the relationship between aliphatic C[sbnd]H conversion and molecular hydrogen release

Molecular hydrogen, released by coal combustion, is closely related to mine safety. In this study, the evaluation of emission characteristics of hydrogen in the low-temperature (T ≤ 200 °C) oxidation process of coal was first introduced in the use of batch reactors. The effects of coal rank, coal temperature, and particle size on hydrogen release were systematically investigated. Results showed that the release of hydrogen at low temperature was linearly related to oxygen consumption and did not really depend on the mass of coal. Coal samples with higher rank and under the condition of higher temperature produced more amount of hydrogen. When the particle size was large, the rate of hydrogen release exhibited a dependence on particle size, while for the coal samples with very fine particles (less than 0.12 mm in diameter), it was much more difficult to release hydrogen and the rate of hydrogen release was independent of the particle size. Moreover, in-situ fourier transform infrared spectroscopy was employed to analyze aliphatic CH stretching vibration from 2800 to 3000 cm−1. The conversion rates of three types of CH groups during coal oxidation were analyzed and calculated. The results indicated that methylene group exhibited the highest conversion rate; however, hydrogen release was more likely to involve the conversion of hydrogen radicals from functional group containing methane bond. Finally, the intrinsic relationship between the conversion of aliphatic CH and the release of hydrogen was quantified based on theory of oxidation kinetics.

Ruthenium nanoparticles immobilized on surfactant-directed polypyrrole as an effective and reusable catalyst for hydrogen generation

An effective catalyst with high activity and stability is required to produce hydrogen from the hydrolysis of sodium borohydride (NaBH4) for the portable fuel cell applications. In this study, the synthesis of highly effective, stable and reusable polypyrrole (PPy) supported ruthenium nanoparticles (NPs) is presented. PPy powders with porous structure were prepared by the chemical oxidative polymerization, followed by the deposition of Ru NPs using the wet impregnation—reduction method. Due to the synergistic effect of Ru NPs with PPy, the as-synthesized catalyst exerts good catalytic activity, with the hydrogen release rate of 22.74 ± 0.84 L min−1 g Ru −1 and activation energy of 39.08 ± 1.69 kJ mol−1, which is lower than most of the reported activation energy values. This novel Ru/PPy catalyst is a promising candidate for small portable hydrogen generators by NaBH4 hydrolysis. Structural, morphological and textural properties of the catalysts were investigated by analytical techniques. Moreover, the effects of reaction temperature, NaOH and NaBH4 concentrations on catalytic activity were also investigated.

Simulation of thermal desorption spectrum of hydrogen from austenite embedded in the martensite matrix

Thermal desorption spectra of hydrogen of martensite (or ferrite), austenite and a composite of them in which austenite is a minor phase are simulated using McNabb–Foster theory. Whereas the peak temperature of desorption rate is markedly dependent upon the specimen thickness in all specimens, it did not decrease below a certain limit in thin martensite specimens where hydrogen desorption is controlled by detrapping of hydrogen from the trap site. The peak temperature in the two-phase specimen depends strongly upon the thickness of austenite if the initial amount of hydrogen in the ferrite matrix can be ignored, becoming close to or lower than the room temperature for the austenite thickness less than ∼10 μm. For larger austenite particles the release rate of hydrogen from the austenite governs the peak temperature. For small particles such as interlath retained austenite the release time of hydrogen from the particle is so short that re-capture of hydrogen at matrix dislocations and martensite/austenite interfaces can enhance the peak of martensite and/or cause an independent peak at a higher temperature.

Air and water oxidation of aluminum flake particles

The article deals with the oxidation of aluminum flake particles with specific surface area ranged from 0.37m2/g to 0.73m2/g. The investigated powders which consisted of the above mentioned flake particles contained metal aluminum in high values (95–98 mass %). The powders possess a high hydrogen release rate (up to 27cm3/min) by the interaction with calcium hydroxide water solution. The powders under study revealed a high reactivity while oxidized in a non-isothermal mode in air. The reactivity parameter values for aluminum flake particles can be compared to those of aluminum spherical nanoparticles. The application of these aluminum flake particles were possible in two directions due to their high metal content in combination with low specific surface area and high reactivity: pyrotechnics and cellular concrete production.

Hydrogen jet fires in a passively ventilated enclosure

This paper describes a combined experimental, analytical and numerical modelling investigation into hydrogen jet fires in a passively ventilated enclosure. The work was funded by the EU Fuel Cells and Hydrogen Joint Undertaking project Hyindoor. It is relevant to situations where hydrogen is stored or used indoors. In such situations passive ventilation can be used to prevent the formation of a flammable atmosphere following a release of hydrogen. Whilst a significant amount of work has been reported on unignited releases in passively ventilated enclosures and on outdoor hydrogen jet fires, very little is known about the behaviour of hydrogen jet fires in passively ventilated enclosures. This paper considers the effects of passive ventilation openings on the behaviour of hydrogen jet fires. A series of hydrogen jet fire experiments were carried out using a 31 m3 passively ventilated enclosure. The test programme included subsonic and chocked flow releases with varying hydrogen release rates and vent configurations. In most of the tests the hydrogen release rate was sufficiently low and the vent area sufficiently large to lead to a well-ventilated jet fire. In a limited number of tests the vent area was reduced, allowing under-ventilated conditions to be investigated. The behaviour of a jet fire in a passively ventilated enclosure depends on the hydrogen release rate, the vent area and the thermal properties of the enclosure. An analytical model was used to quantify the relative importance of the hydrogen release rate and vent area, whilst the influence of the thermal properties of the enclosure were investigated using a CFD model. Overall, the results indicate that passive ventilation openings that are sufficiently large to safely ventilate an unignited release will tend to be large enough to prevent a jet fire from becoming under-ventilated.

Increase in Hydrogen Release Rate of MgH<SUB>2</SUB> by Grinding in a Hydrogen Atmosphere with Ni Added

Increase in Hydrogen Release Rate of MgH<SUB>2</SUB> by Grinding in a Hydrogen Atmosphere with Ni Added

Assessment of similarity relations using helium for prediction of hydrogen dispersion and safety in an enclosure

The ability to predict the concentration of hydrogen in a partially confined space is significant to the safe use of hydrogen-related products such as fuel cell vehicles. Hydrogen release and subsequent dispersion are frequently investigated using commercially-available computational fluid dynamic (CFD) models once those are calibrated with available experimental data. Due to the explosion safety concerns of using hydrogen, accidental scenarios are often replicated with helium as a hydrogen simulant in experiments. Currently, there is no validated, theoretical analogy to correlate the helium data in order to predict the spatial and temporal distribution of hydrogen in the enclosure. The aim of this paper is to assess different theoretical relationships for the similarity between hydrogen and helium leakage in an enclosure. Experiments were first carried out to obtain measured data with helium leakage in a set of scenarios and to validate the present CFD model. Three methods, namely equal volumetric flow rate, equal buoyancy and a newly proposed correlation derived from equal concentration, were employed to determine the equivalent hydrogen release rate, using which the validated CFD model was then used, with the physical property values for hydrogen, to stimulate hydrogen dispersion as compared to that of helium. The accuracy of these different methods at different stage of release and location is discussed. The present result thus provides a guide when using helium experiment to validate hydrogen simulation in different scenarios, which is of importance to the investigation of hydrogen safety.

Multi-scale and spatially resolved hydrogen mapping in a Ni–Nb model alloy reveals the role of the δ phase in hydrogen embrittlement of alloy 718

We investigated the hydrogen distribution and desorption behavior in an electrochemically hydrogen-charged binary Ni–Nb model alloy to study the role of δ phase in hydrogen embrittlement of alloy 718. We focus on two aspects, namely, (1) mapping the hydrogen distribution with spatial resolution enabling the observation of the relations between desorption profiles and desorption sites; and (2) correlating these observations with mechanical testing results to reveal the degradation mechanisms. The trapping states of hydrogen in the alloy were globally analyzed by Thermal Desorption Spectroscopy (TDS). Additionally, spatially resolved hydrogen mapping was conducted using silver decoration, Scanning Kelvin Probe Force Microscopy (SKPFM) and Secondary Ion Mass Spectrometry (SIMS): The Ag decoration method revealed rapid effusion of hydrogen at room temperature from the γ-matrix. The corresponding kinetics was resolved in both, space and time by the SKPFM measurements. At room temperature the hydrogen release from the γ-matrix steadily decreased until about 100 h and then was taken over by the δ phase from which the hydrogen was released much slower. For avoiding misinterpretation of hydrogen signals stemming from environmental effects we also charged specimens with deuterium. The deuterium distribution in the microstructure was studied by SIMS. The combined results reveal that hydrogen dissolves more preferably inside the γ-matrix and is diffusible at room temperature while the δ phase acts as a deeper trapping site for hydrogen. With this joint and spatially resolving approach we observed the microstructure- and time-dependent distribution and release rate of hydrogen with high spatial and temporal resolution. Correlating the obtained results with mechanical testing of the hydrogen-charged samples shows that hydrogen enhanced decohesion (HEDE) occurring at the δ/matrix interfaces promotes the embrittlement.

On the thermochemical hydrogen release rate and activity transport in a supercritical water‐cooled reactor

Hydrogen evolution and activity release rates for stainless steel SS316 and nickel‐based Alloy 800H at the supercritical water‐cooled reactor (SCWR) conditions were estimated, together with amount of oxygen absorbed into the passivation oxide layers formed on both materials. Hydrogen evolution from an oxidized SS316 surface was found to be about six times larger than from Alloy 800H at constant temperature and pressure of 650 °C and 25 MPa. The largest 60Co activity release rate due to corrosion was estimated to be for SS316 at 650 °C and at pH10. Because of a single loop design, the radioactive corrosion products of in‐core surfaces of the SCWR are expected to be carried out‐of‐core with the supercritical coolant.

Thermal coupling of PEM fuel cell and metal hydride hydrogen storage using heat pipes

This paper presents a mathematical model to study opportunities for simultaneous passive thermal management of an integrated PEM fuel cell and metal hydrogen (MH) storage system by thermal bridging of these two components, using heat pipes. The thermal coupling arrangement is expected to be promising, because, as more power is drawn from the PEMFC, more heat is generated that can be used to enhance the rate of release of hydrogen from the MH storage. Heat pipes can provide an effective passive thermal bridge for this purpose on account of their high thermal conductivity, and thus avoid parasitic energy penalties associated with active methods of cooling. The main components modelled analytically in MATLAB in this study are the PEMFC, heat pipes, and MH hydrogen storage. This simulation has been used to size the heat pipe system needed for thermal coupling of a 500 W PEMFC and MH storage canisters. The performance improvement of the MH system after receiving the fuel cell heat, and the cooling capacity of the MH system to be used as heat sink for thermal management of the fuel cell stack, has been studied. The MH canisters used to supply hydrogen to this stack each had the maximum supply capability of 2.5 slpm at 25 °C, while the fuel cell demand was 7.2 slpm at its rated power (500 W). The results show that just under 20% of the total cooling load of the stack (i.e. ∼880 W) at its maximum power point is demanded by the MH canisters (∼170 W) to achieve the required hydrogen discharge rate of 7.2 slpm at 35 °C provided the MH canisters are thermally well insulated.

Experimental and numerical investigation of the cryogenic hydrogen storage processes over MOF-5

The processes of hydrogen charging to and discharging from a 3-L cryogenic tank have been studied experimentally and numerically. This study investigated the impacts of factors such as mass flow rate, outlet opening time, bed density, and heating power on the hydrogen charging and discharging processes. For charging, it was found that the flow-through cooling technique could remove the adsorption heat in the process, but some issues such as channeling phenomenon and large thermal mass of the system need to be addressed. Low initial bed temperature is beneficial for hydrogen storage in terms of the efficiency of charging operation. When the bed density of metal organic framework-5 (MOF-5) is increased from 164 kg/m3 to 174 kg/m3, the total storage of hydrogen within the tank increases accordingly. It is found that pressure is the major factor that determines the storage of hydrogen, which increases significantly with the pressure within the tank. For discharging, high pressure in the storage tank can be used to release hydrogen for a certain period of time without heating. However, in order to maintain the desired hydrogen discharge rate, a heat source is eventually needed. This heat must be supplied in order to desorb the additional hydrogen from the system. To deal with the channeling phenomenon in the charging process, cyclic charging was tested and adopted.

Catalytic hydrolysis of sodium borohydride via nanostructured cobalt–boron catalysts

In this study, nanostructured Co–B/Cu sheet catalysts were successfully fabricated using electroless plating method at ambient temperature. The results illustrated that the morphology, composition, structure and surface roughness of the catalysts were immensely dependent upon the concentration of BH4−. The as-prepared catalyst with the average size of about 52.2 nm exhibited significantly enhanced catalytic activity during hydrolytic dehydrogenation of sodium borohydride. The hydrogen release rate was 7935.6 mL min−1 g−1 and the activation energy was 43.3 kJ mol−1. This enhanced catalytic activity was attributed to the small particle size and the high surface roughness, which provided many defects (such as angle, step, or edge etc.), offering more active sites on the catalyst surface. Meanwhile, it was found that the excess amount of BH4− used to synthesize the catalysts was not increasing the catalytic activity, when the reduction agent BH4− concentration was over 0.8 g L−1. Furthermore, the Co–B catalyst deposited 0.8 g L−1 BH4− retained about 80% catalytic activity of its initial activity after 5 cycles, which indicated that the hydrogen release rate decreased gradually. The reason might be due to the damage of nanostructure and the decrease of Co species and boron species in concentration after 5 cycles.

Nanostructured cobalt–phosphorous catalysts for hydrogen generation from hydrolysis of sodium borohydride solution

Nanostructured Co–P/Cu sheet catalysts were successfully synthesized by electroless plating method. The effects of the deposition temperature on microstructures of Co–P catalysts and their catalytic properties for hydrogen generation from NaBH4 solution were systematically investigated. By tuning the deposition temperature, the morphology of the surface of the Co–P catalysts changed significantly, such as nanoplatelets, nanospheres, pores and nanoclews. When the deposition temperature was 50 °C, the as-prepared Co–P catalyst with novel hierarchical architectures exhibited enhanced catalytic performance during the hydrolysis of NaBH4. The hydrogen release rate of 2275.1 mL min−1 g−1 was achieved. This enhanced activity might be due to the novel hierarchical architectures, small size of Co phase precipitated from the amorphous Co–P phase, or the high surface roughness, which provided many defects (such as angle, step, or edge etc.) and formed more active sites on the catalyst surface. Meanwhile, the lower apparent activation energy of 27.9 kJ mol−1 was calculated. Furthermore, the Co–P catalyst retained about 67% catalytic activity of its first activity after 5 cycles, which illustrated that the hydrogen release rate decreased gradually. The reason might be due to the reduction of in the amount of P and Co on the catalytic surface analyzed by XPS.

Preparation and characterization of fishbone-like Co–B nanoparticles with high catalytic activity for hydrogen generation from NaBH4 solution

We demonstrate a facile preparation of fishbone-like Co–B nanoparticles via electroless plating method for the first time, as evidenced by XRD, SEM and AFM results. The catalytic activities of the obtained fishbone-like Co–B nanoparticles have been investigated for hydrogen generation from NaBH4 solution. The results reveal that the fishbone-like Co–B nanoparticles exhibit high catalytic activity during hydrolytic dehydrogenation of NaBH4. The hydrogen release rate and the activation energy are 10089.1mLmin−1g−1 and 34.2kJmol−1, respectively. More importantly, the fishbone-like Co–B nanoparticles have retained about 84.0% catalytic activity of its first activity after 5 cycles, which illustrates that the Co–B catalysts composed of fishbone-like catalysts show much improved reusability contrast to those common Co–B catalysts reported in the literature.

Improved dehydrogenation performance of LiBH4 by 3D hierarchical flower-like MoS2 spheres additives

In this work, 3D hierarchical flower-like MoS2 spheres are successfully fabricated via a hydrothermal method followed by a heat treatment. The obtained product is composed of few-layered MoS2 nanosheets with enlarged interlayer distance (ca. 0.66 nm) of the (002) plane. Meanwhile, the hydrogen storage properties of the as-prepared MoS2 ball milled with LiBH4 are systematically investigated. The results of temperature programmed desorption (TPD) and isothermal measurement suggest that the LiBH4–MoS2 (as-prepared) mixture exhibits favorable dehydrogenation properties in both lowering the hydrogen release temperature and improving kinetics of hydrogen release rate. LiBH4–MoS2 (as-prepared) sample (the preparation mass ratio is 1:1) starts to release hydrogen at 171 °C, and roughly 5.6 wt% hydrogen is released within 1 h when isothermally heated to 320 °C, which presents superior dehydrogenation performance compared to that of the bulk LiBH4. The excellent dehydrogenation performance of the LiBH4–MoS2 (as-prepared) mixture may be attributed to the high active site density and enlarged interlayer distance of the MoS2 nanosheets, 3D architectures and hierarchical structures.