China, People’s Republic
A Numerical Simulation on the Leakage Event of a High-Pressure Hydrogen Dispenser
Dec 2021
Publication
For the sake of the increasing demand of hydrogen fuel cell vehicles there are more concerns on the safety of hydrogen refueling stations. As one of the key pieces of equipment the hydrogen dispenser has drawn attention on this aspect since it involves massive manual operations and may be bothered by a high probability of failure. In this paper a numerical study is conducted to simulate the possible leakage events of the hydrogen dispenser based on a prototype in China whose working pressure is 70 MPa. The leakage accident is analyzed with respect to leakage sizes leak directions and the time to stop the leakage. It is found that due to the large mass flow rate under such high pressure the leak direction and the layout of the components inside the dispenser become insignificant and the ignitable clouds will form inside the dispenser in less than 1 s if there is a leakage of 1% size of the main tube. The ignitable clouds will form near the vent holes outside the dispenser which may dissipate quickly if the leakage is stopped. On the other hand the gas inside the dispenser will remain ignitable for a long time which asks for a design with no possible ignition source inside. The results can be useful in optimizing the design of the dispenser regarding the reaction time and sensitivity requirements of the leakage detector the size and amount of vent holes etc.
Improving Hydrogen Embrittlement Resistance of Hot-Stamped 1500 MPa Steel Parts That Have Undergone a Q&P Treatment by the Design of Retained Austenite and Martensite Matrix
Nov 2020
Publication
Hydrogen embrittlement is one of the largest obstacles against the commercialisation of ultra-high strength quenching and partitioning (Q&P) steels with ultimate tensile strength over 1500 MPa including the hot stamped steel parts that have undergone a Q&P treatment. In this work the influence of partitioning temperature on hydrogen embrittlement of ultra-high strength Q&P steels is studied by pre-charged tensile tests with both dog-bone and notched samples. It is found that hydrogen embrittlement resistance is enhanced by the higher partitioning temperature. Then the hydrogen embrittlement mechanism is analysed in terms of hydrogen retained austenite and martensite matrix. Thermal desorption analysis (TDA) shows that the hydrogen trapping properties are similar in the Q&P steels which cannot explain the enhancement of hydrogen embrittlement resistance. On the contrary it is found that the relatively low retained austenite stability after the higher temperature partitioning ensures more sufficient TRIP effect before hydrogen-induced fracture. Additionally dislocation recovery and solute carbon depletion at the higher partitioning temperature can reduce the flow stress of the martensite matrix improving its intrinsic toughness and reducing its hydrogen sensitivity both of which result in the higher hydrogen embrittlement resistance.
High CO2 Absorption Capacity of Metal-Based Ionic Liquids: A Molecular Dynamics Study
Apr 2020
Publication
The absorption of CO2 is of importance in carbon capture utilization and storage technology for greenhouse gas control. In the present work we clarified the mechanism of how metal-based ionic liquids (MBILs) Bmim[XCln]m (X is the metal atom) enhance the CO2 absorption capacity of ILs via performing molecular dynamics simulations. The sparse hydrogen bond interaction network constructed by CO2 and MBILs was identified through the radial distribution function and interaction energy of CO2-ion pairs which increase the absorption capacity of CO2 in MBILs. Then the dynamical properties including residence time and self-diffusion coefficient confirmed that MBILs could also promote the diffusion process of CO2 in ILs. That's to say the MBILs can enhance the CO2 absorption capacity and the diffusive ability simultaneously. Based on the analysis of structural energetic and dynamical properties the CO2 absorption capacity of MBILs increases in the order Cl− → [ZnCl4]2-→ [CuCl4]2-→ [CrCl4]- → [FeCl4]- revealing the fact that the short metal–Cl bond length and small anion volume could facilitate the performance of CO2 absorbing process. These findings show that the metal–Cl bond length and effective volume of the anion can be the effective factors to regulate the CO2 absorption process which can also shed light on the rational molecular design of MBILs for CO2 capture and other key chemical engineering processes such as IL-based gas sensors nano-electrical devices and so on.
Hydrolysis Hydrogen Production Mechanism of Mg10Ni10Ce Alloy Surface Modified by SnO2 Nanotubes in Different Aqueous Systems
May 2020
Publication
(Mg-10wt.%Ni)-10wt.%Ce (Mg10Ni10Ce) was ball-milled with SnO2 nanotubes and Mg10Ni10Ce-xSnO2 (x=0 5 10 and 15wt.%) composites have been prepared. The phase compositions microstructures morphologies and hydrolysis H2 generation performance in different aqueous systems (distilled water tap water and simulated seawater) have been investigated and the corresponding hydrolysis mechanism of Mg10Ni10Ce and Mg10Ni10Ce-SnO2 has been proposed. Adding a small amount of SnO2 nanotubes can significantly enhance the hydrolysis reaction of Mg10Ni10Ce especially the initial hydrolysis kinetics and the final H2 generation yield. Unfortunately the Mg10Ni10Ce-xSnO2 hardly react with distilled water at room temperature. The hydrolysis reaction rate of Mg10Ni10Ce-5SnO2 composite in tap water is still very slow with only 17.3% generation yield after 1 hour at 303 K. Fortunately in simulated seawater (3.5wt.% NaCl solution) the hydrolytic H2 generation behavior of the Mg10Ni10Ce-5SnO2 composite has been greatly improved which can release as high as 468.6 mL/g H2 with about 60.9% generation yield within 30 s at 303 K. The Cl- destroys the passivation layer on Mg-Ni-Ce alloy surface and the added SnO2 nanotubes accelerate the hydrolysis reaction rate and enhance the H2 generation yield. The Mg10Ni10Ce-5SnO2 composite can rapidly generate a large amount of H2 in simulate seawater in a short time which is expected to be applied on portable H2 generators in the future.
New Insights into the Electrochemical Behaviour of Porous Carbon Electrodes for Supercapacitors
Aug 2018
Publication
Activated carbons with different surface chemistry and porous textures were used to study the mechanism of electrochemical hydrogen and oxygen evolution in supercapacitor devices. Cellulose precursor materials were activated with different potassium hydroxide (KOH) ratios and the electrochemical behaviour was studied in 6 M KOH electrolyte. In situ Raman spectra were collected to obtain the structural changes of the activated carbons under severe electrochemical oxidation and reduction conditions and the obtained data were correlated to the cyclic voltammograms obtained at high anodic and cathodic potentials. Carbon-hydrogen bonds were detected for the materials activated at high KOH ratios which form reversibly under cathodic conditions. The influence of the specific surface area narrow microporosity and functional groups in the carbon electrodes on their chemical stability and hydrogen capture mechanism in supercapacitor applications has been revealed.
Hydrogen Storage Behavior of Nanocrystalline and Amorphous Mg–Ni–Cu–La Alloys
Sep 2020
Publication
Alloying and structural modification are two effective ways to enhance the hydrogen storage kinetics and decrease the thermal stability of Mg and Mg-based alloys. In order to enhance the characteristics of Mg2Ni-type alloys Cu and La were added to an Mg2Ni-type alloy and the sample alloys (Mg24Ni10Cu2)100−xLax (x = 0 5 10 15 20) were prepared by melt spinning. The influences of La content and spinning rate on the gaseous and electrochemical hydrogen storage properties of the sample alloys were explored in detail. The structural identification carried out by XRD and TEM indicates that the main phase of the alloys is Mg2Ni and the addition of La results in the formation of the secondary phases LaMg3 and La2Mg17. The as-spun alloys have amorphous and nanocrystalline structures and the addition of La promotes glass formation. The electrochemical properties examined by an automatic galvanostatic system show that the samples possess a good activation capability and achieve their maximal discharge capacities within three cycles. The discharge potential characteristics were vastly ameliorated by melt spinning and La addition. The discharge capacities of the samples achieve their maximal values as the La content changes and the discharge capacities always increase with increasing spinning rate. The addition of La leads to a decline in hydrogen absorption capacity but it can effectively enhance the rate of hydrogen absorption. The addition of La and melt spinning significantly increase the hydrogen desorption rate due to the reduced activation energy.
Risk Analysis on Mobile Hydrogen Refueling Stations in the World Expo Shanghai
Sep 2013
Publication
During the World Expo Shanghai there were one hundred fuel-cell sight-seeing cars in operation at the Expo Site. The sight-seeing cars were not allowed to drive out of the Expo Site and the stationary hydrogen refuelling station was not permitted to build at the Expo Site for the sake of safety. A flexible solution to refuel the cars was the application of mobile hydrogen refuelling stations. To better understand the hazards and risks associated with the mobile hydrogen refueling stations a risk analysis was preformed to improve the safety of the operations. The risks to the station personnel and to the public were discussed separately. Results show that the stationary risks of the mobile stations to the personnel and refueling customers are lower than the risk acceptance criteria over an order of magnitude so occupational risks and risks to customers are completely acceptable. The third party risks can be acceptable as long as the appropriate mitigation measures are implemented especially well designed parking area and operation time. Leak from boosters is the main risk contributor to the stationary risks because of its highest failure rates according to the generic data and its worst harm effects based on the consequence evaluations. As for the road risks of the mobile stations they can be acceptable as long as the appropriate mitigation measures are implemented especially well-designed moving path and transportation time.
Electrocatalysts Based on Metal@carbon Core@shell Nanocomposites: An Overview
Aug 2018
Publication
Developing low-cost high-performance catalysts is of fundamental significance for electrochemical energy conversion and storage. In recent years metal@carbon core@shell nanocomposites have emerged as a unique class of functional nanomaterials that show apparent electrocatalytic activity towards a range of reactions such as hydrogen evolution reaction oxygen evolution reaction oxygen reduction reaction and CO2 reduction reaction that are important in water splitting fuel cells and metal-air batteries. The activity is primarily attributed to interfacial charge transfer from the metal core to the carbon shell that manipulate the electronic interactions between the catalyst surface and reaction intermediates and varies with the structures and morphologies of the metal core (elemental composition core size etc.) and carbon shell (doping layer thickness etc.). Further manipulation can be achieved by the incorporation of a third structural component. A perspective is also included highlighting the current gap between theoretical modeling and experimental results and technical challenges for future research.
Improvement of Low Temperature Activity and Stability of Ni Catalysts with Addition of Pt for Hydrogen Production Via Steam Reforming of Ethylene Glycol
Nov 2018
Publication
Hydrogen production by steam reforming of ethylene glycol (EG) at 300 °C was investigated over SiO2 and CeO2 supported Pt–Ni bimetallic catalysts prepared by incipient wetness impregnation methods. It was observed that impregnation sequence of Pt and Ni can affect the performance of catalysts apparently. Catalyst with Pt first and then Ni addition showed higher EG conversion and H2 yield owing to the Ni enrichment on the surface and the proper interaction between Pt and Ni. It was observed that although SiO2 supported catalysts exhibited better activity and H2 selectivity CeO2 supported ones had better stability. This is attributed to the less coke formation on CeO2. Increasing Pt/Ni ratio enhanced the reaction activity and Pt3–Ni7 catalysts with 3 wt% Pt and 7 wt% Ni showed the highest activity and stability. Ni surficial enrichment facilitated the C—C bond rupture and water gas shift reactions; and Pt addition inhibited methanation reaction. Electron transfer and hydrogen spillover from Pt to Ni suppressed carbon deposition. These combined effects lead to the excellent performance of Pt3–Ni7 supported catalysts.
Catalysis of Oxides in Hydrogen Generation by the Reaction of Al with Water
Sep 2013
Publication
Hydrogen generation by the reaction of pure Al powder in water with the addition of Al(OH)3 γ- Al2O3 α-Al2O3 or TiO2 at mild temperatures was investigated. It was found that the reaction of Al with water is promoted and the reaction induction time decreases greatly by the above hydroxide and oxides. X-ray diffraction analyses revealed that the hydroxide and oxide phases have no any change during the Al-water reaction indicating that they are just as catalysts to assist the reaction of Al with water. A possible mechanism was proposed which shows that hydroxide and oxides could dissociate water molecules and promote the hydration of the passive oxide film on Al particle surfaces.
Explosion Venting of Rich Hydrogen-air Mixtures in a Cylindrical Vessel with Two Symmetrical Vents
Oct 2015
Publication
The safety issues related to explosion venting of hydrogen-air mixtures are significant and deserve more detailed investigation. Vented hydrogen-air explosion has been studied extensively in vessels with a single vent. However little attention has been paid to the cases with more than one vent. In this paper experiments about explosion venting of rich hydrogen-air mixtures were conducted in a cylindrical vessel with two symmetrical vents to investigate the effect of vent area and distribution on pressure build up and flame behaviours. Venting accelerates the flame front towards the vent but has nearly no effect on the opposite side. The maximum internal overpressure decreases and the maximum external flame length increases with the increase of vent area. Two pressure peaks can be identified outside of vessel which correspond to the external explosion and the burnt gas jet respectively. Compared with single vent two vents with same total vent area leads to nearly unchanged maximum internal and external overpressure but much smaller external flame length.
Reversible Ammonia-based and Liquid Organic Hydrogen Carriers for High-density Hydrogen Storage: Recent Progress
Feb 2019
Publication
Liquid hydrogen carriers are considered to be attractive hydrogen storage options because of their ease of integration into existing chemical transportation infrastructures when compared with liquid or compressed hydrogen. The development of such carriers forms part of the work of the International Energy Agency Task 32: Hydrogen-Based Energy Storage. Here we report the state-of-the-art for ammonia-based and liquid organic hydrogen carriers with a particular focus on the challenge of ensuring easily regenerable high-density hydrogen storage.
Novel Fuzzy Control Energy Management Strategy for Fuel Cell Hybrid Electric Vehicles Considering State of Health
Oct 2021
Publication
Due to the low efficiency and high pollution of conventional internal combustion engine vehicles the fuel cell hybrid electric vehicles are expected to play a key role in the future of clean energy transportation attributed to the long driving range short hydrogen refueling time and environmental advantages. The development of energy management strategies has an important impact on the economy and durability but most strategies ignore the aging of fuel cells and the corresponding impact on hydrogen consumption. In this paper a rule-based fuzzy control strategy is proposed based on the constructed data-driven online estimation model of fuel cell health. Then a genetic algorithm is used to optimize this fuzzy controller where the objective function is designed to consider both the economy and durability by combining the hydrogen consumption cost and the degradation cost characterized by the fuel cell health status. Considering that the rule-based strategy is more sensitive to operating conditions this paper uses an artificial neural network for predictive control. The results are compared with those obtained from the genetic algorithm optimized fuzzy controller and are found to be very similar where the prediction accuracy is assessed using MAPE RMSE and 10-fold cross-validation. Experiments show that the developed strategy has a good generalization capability for variable driving cycles.
Reversible Solid-oxide Cell Stack Based Power-to-x-to-power Systems: Comparison of Thermodynamic Performance
Jun 2020
Publication
The increasing penetration of variable renewable energies poses new challenges for grid management. The economic feasibility of grid-balancing plants may be limited by low annual operating hours if they work either only for power generation or only for power storage. This issue might be addressed by a dual-function power plant with power-to-x capability which can produce electricity or store excess renewable electricity into chemicals at different periods. Such a plant can be uniquely enabled by a solid-oxide cell stack which can switch between fuel cell and electrolysis with the same stack. This paper investigates the optimal conceptual design of this type of plant represented by power-to-x-to-power process chains with x being hydrogen syngas methane methanol and ammonia concerning the efficiency (on a lower heating value) and power densities. The results show that an increase in current density leads to an increased oxygen flow rate and a decreased reactant utilization at the stack level for its thermal management and an increased power density and a decreased efficiency at the system level. The power-generation efficiency is ranked as methane (65.9%) methanol (60.2%) ammonia (58.2%) hydrogen (58.3%) syngas (53.3%) at 0.4 A/cm2 due to the benefit of heat-to-chemical-energy conversion by chemical reformulating and the deterioration of electrochemical performance by the dilution of hydrogen. The power-storage efficiency is ranked as syngas (80%) hydrogen (74%) methane (72%) methanol (68%) ammonia (66%) at 0.7 A/cm2 mainly due to the benefit of co-electrolysis and the chemical energy loss occurring in the chemical synthesis reactions. The lost chemical energy improves plant-wise heat integration and compensates for its adverse effect on power-storage efficiency. Combining these efficiency numbers of the two modes results in a rank of round-trip efficiency: methane (47.5%)>syngas (43.3%) ≈ hydrogen (42.6%)>methanol (40.7%)>ammonia (38.6%). The pool of plant designs obtained lays the basis for the optimal deployment of this balancing technology for specific applications.
Empowering Hydrogen Storage Properties of Haeckelite Monolayers via Metal Atom Functionalization
Mar 2021
Publication
Using hydrogen as an energy carrier requires new technological solutions for its onboard storage. The exploration of two-dimensional (2D) materials for hydrogen storage technologies has been motivated by their open structures which facilitates fast hydrogen kinetics. Herein the hydrogen storage properties of lightweight metal functionalized r57 haeckelite sheets are studied using density functional theory (DFT) calculations. H2 molecules are adsorbed on pristine r57 via physisorption. The hydrogen storage capacity of r57 is improved by decorating it with alkali and alkaline-earth metals. In addition the in-plane substitution of r57 carbons with boron atoms (B@r57) both prevents the clustering of metals on the surface of 2D material and increases the hydrogen storage capacity by improving the adsorption thermodynamics of hydrogen molecules. Among the studied compounds B@r57-Li4 with its 10.0 wt% H2 content and 0.16 eV/H2 hydrogen binding energy is a promising candidate for hydrogen storage applications. A further investigation as based on the calculated electron localization functions atomic charges and electronic density of states confirm the electrostatic nature of interactions between the H2 molecules and the protruding metal atoms on 2D haeckelite sheets. All in all this work contributes to a better understanding of pure carbon and B-doped haeckelites for hydrogen storage.
Mechanical Properties and Hydrogen Embrittlement of Laser-Surface Melted AISI 430 Ferritic Stainless Steel
Feb 2020
Publication
Hydrogen was doped in austenitic stainless steel (ASS) 316L tensile samples produced by the laser-powder bed fusion (L-PBF) technique. For this aim an electrochemical method was conducted under a high current density of 100 mA/cm2 for three days to examine its sustainability under extreme hydrogen environments at ambient temperatures. The chemical composition of the starting powders contained a high amount of Ni approximately 12.9 wt.% as a strong austenite stabilizer. The tensile tests disclosed that hydrogen charging caused a minor reduction in the elongation to failure (approximately 3.5% on average) and ultimate tensile strength (UTS; approximately 2.1% on average) of the samples using a low strain rate of 1.2 × 10−4 s−1. It was also found that an increase in the strain rate from 1.2 × 10−4 s−1 to 4.8 × 10−4 s−1 led to a reduction of approximately 3.6% on average for the elongation to failure and 1.7% on average for UTS in the pre-charged samples. No trace of martensite was detected in the X-ray diffraction (XRD) analysis of the fractured samples thanks to the high Ni content which caused a minor reduction in UTS × uniform elongation (UE) (GPa%) after the H charging. Considerable surface tearing was observed for the pre-charged sample after the tensile deformation. Additionally some cracks were observed to be independent of the melt pool boundaries indicating that such boundaries cannot necessarily act as a suitable area for the crack propagation.
Towards the Rational Design of Stable Electrocatalysts for Green Hydrogen Production
Feb 2022
Publication
Now it is time to set up reliable water electrolysis stacks with active and robust electro‐ catalysts to produce green hydrogen. Compared with catalytic kinetics much less attention has been paid to catalyst stability and the weak understanding of the catalyst deactivation mechanism restricts the design of robust electrocatalysts. Herein we discuss the issues of catalysts’ stability evaluation and characterization and the degradation mechanism. The systematic understanding of the degradation mechanism would help us to formulate principles for the design of stable catalysts. Particularly we found that the dissolution rate for different 3d transition metals differed greatly: Fe dissolves 114 and 84 times faster than Co and Ni. Based on this trend we designed Fe@Ni and FeNi@Ni core‐shell structures to achieve excellent stability in a 1 A cm−2 current density as well as good catalytic activity at the same time
Particle Size and Crystal Phase Effects in Fischer-Tropsch Catalysts
Aug 2017
Publication
Fischer-Tropsch synthesis (FTS) is an increasingly important approach for producing liquid fuels and chemicals via syngas—that is synthesis gas a mixture of carbon monoxide and hydrogen—generated from coal natural gas or biomass. In FTS dispersed transition metal nanoparticles are used to catalyze the reactions underlying the formation of carbon-carbon bonds. Catalytic activity and selectivity are strongly correlated with the electronic and geometric structure of the nanoparticles which depend on the particle size morphology and crystallographic phase of the nanoparticles. In this article we review recent works dealing with the aspects of bulk and surface sensitivity of the FTS reaction. Understanding the different catalytic behavior in more detail as a function of these parameters may guide the design of more active selective and stable FTS catalysts.
Recent Development of Biomass Gasification for H2 Rich Gas Production
Mar 2022
Publication
Biomass gasification for hydrogen (H2) production provides outstanding advantages in terms of renewable energy resources carbon neutral high efficiency and environmental benefits. However the factors influencing H2 production from biomass gasification are complex which makes determining the optimal operating conditions challenging. Biomass gasification also poses challenges owing to the high associated tar content and low gas yield which need to be overcome. This review summarizes the influence of the gasification parameters on H2 production. Catalytic gasification technology and some of the latest catalysts such as composites and special structure catalysts are also summarized herein based on the requirements of high-purity H2 production. Moreover novel technologies such as staged gasification chemical looping gasification and adsorption-enhanced reforming for producing H2 rich gas are introduced. Finally the challenges and prospects associated with biomass gasification for H2 production are presented.
Low Temperature Autoignition of Diesel Fuel Under Dual Operation with Hydrogen and Hydrogen-carriers
Mar 2022
Publication
While electrification of light duty vehicles is becoming a real solution to abate local pollutant as well as greenhouse gases emission heavy duty applications (such as long distance freight and maritime transport) will keep requiring fuel-based propulsion systems. In these sectors dominated by compression ignition engines research on alternative biofuels and new combustion modes is still highly necessary. Dual-fuel combustion appears as a very promising concept to replace conventional diesel fuel by sustainable ones. Among the latter hydrogen-derived fuels (the so-called electrofuels or e-fuels) are maybe the most interesting. This work addresses the effect of partial substitution of diesel fuel by hydrogen and hydrogen-carriers (ammonia and methane) on the autoignition process under low temperature conditions. Tests were carried out in a constant volume combustion chamber at different temperatures (535 600 and 650 ◦C) and pressures (11 16 and 21 bar). While the cool flames timing and intensity was only slightly affected by the low reactivity fuel energy content the main ignition was delayed this effect being much more noticeable for ammonia followed by hydrogen and finally methane. Kinetic simulations showed a clear competition for active radicals between both fuels (diesel and low reactivity fuel). The combustion duration also increased with the hydrogen or hydrogen-carrier content which greatly points to the need of modifications in the injection strategy of compression ignition engines operating under dual mode. A correlation was proposed for estimating the autoignition delay time for dual-fuel lean combustion at low temperature.
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