On-board Hydrogen Storage Research Articles

Preliminary hazard identification for qualitative risk assessment on onboard hydrogen storage and supply systems of hydrogen fuel cell vehicles

Due to the ever-increasing stringency of environmental policy requirements, hydrogen fuel cell vehicles (HFCVs), which are intended to serve as a substitute for conventional automobiles, are continuously evolving as a new promising technology. It is essential to conduct hazard identification as an early phase in the development of HFCVs in order to describe possible hazards and identify potential safety concerns. The onboard hydrogen storage and supply system is an essential component of HFCVs, serving to store hydrogen and provide it to the fuel cell system to guarantee its proper functioning. In this context, the research is conducted by establishing models of onboard hydrogen storage and supply system that reflected their specifications and elements. In this study, the methods of hazard and operability study (HAZOP) and failure mode and effect analysis (FMEA) are employed to identify and analyze the potential accident scenarios. The risk of each potential accident scenario, including whether to implement safety measures, is analyzed and classified as risk matrix. Medium- and high-risk scenarios in the absence of safety measures include accidental burst of the hydrogen cylinder, debonding of plastic liners and metal bosses, release of hydrogen from a thermally activated pressure relief device or pressure relief device, tiny release of hydrogen from improperly attached tube fittings, and small release of hydrogen from valves with seal failures. Comparing the findings of risk matrices with and without safety measures confirms that the safety measures lower the risk levels of the onboard hydrogen storage and supply systems to a tolerable level.

Design of High Specific Power Solid Oxide Fuel Cells

Fuel-Cell Electric-Vehicle demonstrated by PCI was fueled with military-spec F-24/JP-8 and does not require on-board hydrogen storage. An onboard fuel reformer with integrated sulfur trap was used for processing these fuels. The 10-kW electric generator included a SOFC and balance of plant components. It was hybridized with a rechargeable battery for startup, peak loads, and load following. The power produced was sufficient for vehicle propulsion and export power. Both 28-32 VDC and 110 VAC for charging batteries and supporting external load demands were available onboard. Initial off-road demonstrations were successfully conducted at PCI and customer sites. This prototype unit showed the feasibility of utilizing hydrocarbon fuels with on-board reforming and SOFC stack to generate power suitable for mobile applications while the system weight and start-up time still need to be improved. To reduce the system weight and start-up time, we are separately investigating advanced SOFC’s that show potential to address the known limitations of the state-of-the-art technology. These advanced SOFC’s demonstrated potential for fast start-up and high-power density on the cell level at 750-800°C of operating temperatures. By optimizing the configuration and design, the system performance is expected to be further improved.

Determining the possibility of the appearance of a combustible medium in the hydrogen storage and supply system

The object of this study is the process of functioning of the hydrogen storage and supply system. The issue of fire-explosive events in the hydrogen storage and supply system is investigated. A set of mathematical models has been built to determine the probability of a combustible medium in the hydrogen storage and supply system. This set includes partial mathematical models for the main elements of the system, which are united by a generalized mathematical model. When constructing partial mathematical models, the probabilities of trouble-free operation of the main elements of the system are used, which include a pipeline and a gas generator with a pressure stabilization circuit. The probability of trouble-free operation is represented in the form of two multiplicative components that take into account catastrophic and parametric failures of the main elements of the system. When determining the probability of trouble-free operation of the main elements of the system in relation to parametric failures, the integral (generalized) parameters were used. In particular, for a gas generator, such parameters are its time constants. The current values of time constants of the gas generator are determined according to the developed algorithm whose feature is the use for its implementation of the values of the amplitude-frequency characteristics of the system, which are determined at three a priori given frequencies. For a typical version of the on-board hydrogen storage and supply system, quantitative indicators of the likelihood of a combustible medium are given. It is shown that if the parametric failures of the main elements of the system are not taken into account, an error occurs, the value of which is 30.0 %. The results could be used to obtain an express assessment of the level of fire hazard of hydrogen storage and supply systems at different stages of their life cycle.

Thermodynamic parametric analysis of refueling heavy-duty hydrogen fuel-cell electric vehicles

Reliable design and safe operation of heavy-duty hydrogen refueling stations are essential for the successful deployment of heavy-duty fuel cell electric vehicles (FCEVs). Fueling heavy-duty FCEVs is different from light-duty vehicles in terms of the dispensed hydrogen quantities and fueling rates, requiring tailored fueling station design for each vehicle class. In particular, the selection and design of the onboard hydrogen storage tank system and the fueling performance requirements influence the safe design of hydrogen fueling stations. A thermodynamic modeling and analysis are performed to evaluate the impact of various fueling parameters and boundary conditions on the fueling performance of heavy-duty FCEVs. We studied the effect of dispenser pressure ramp rate and precooling temperature, initial tank temperature and pressure, ambient temperature, and onboard storage design parameters, such as onboard storage pipe diameter and length, on the fueling rate and final vehicle state-of-charge, while observing prescribed tank pressure and temperature safety limits. An important finding was the sensitivity of the temporal fueling rate profile and the final tank state of charge to the design factors impacting pressure drop between the dispenser and vehicle tank, including onboard storage pipe diameter selection, and flow coefficients of nozzle, valves, and fittings. The fueling rate profile impacts the design and cost of the hydrogen precooling unit upstream of the dispenser.

Research on Temperature Rise of Type IV Composite Hydrogen Storage Cylinders in Hydrogen Fast-Filling Process

The internal pressure and temperature of type IV on-board hydrogen storage cylinders constantly change during the hydrogen fast-filling process. In this work, a 2D axisymmetric computational fluid dynamics (CFD) model is established to study the temperature rise of hydrogen storage cylinders during the fast-filling process. The hydrogen filling rate, ambient temperature, volume, and hydrogen inlet temperature were investigated to evaluate their effects on temperature rise inside the cylinders. The effects of the inlet pressure rise and pre-cooling patterns on the temperature rise of large-volume type IV hydrogen storage cylinders are analyzed, and the optimal filling strategy is determined. The research results show that a greater filling rate causes a higher hydrogen temperature rise at the end. The ambient temperature increases linearly with the maximum hydrogen temperature and decreases linearly with the state of charge (SOC). As the volume increases, the temperature rise of the cylinder increases. Reducing the inlet hydrogen temperature helps control the temperature rise, and the hydrogen inlet pre-cooling temperature required for large-volume cylinders is lower. If the filling time remains unchanged, a high pressure rise rate should be avoided, and a linear pressure rise pattern is optimal. Reducing the initial cooling energy is key to optimizing the filling strategy.

Dehydrogenation of Alkali Metal Aluminum Hydrides MAlH4 (M = Li, Na, K, and Cs): Insight from First-Principles Calculations

Complex aluminum hydrides with high hydrogen capacity are among the most promising solid-state hydrogen storage materials. The present study determines the thermal stability, hydrogen dissociation energy, and electronic structures of alkali metal aluminum hydrides, MAlH4 (M = Li, Na, K, and Cs), using first-principles density functional theory calculations in an attempt to gain insight into the dehydrogenation mechanism of these hydrides. The results show that the hydrogen dissociation energy (Ed-H2) of MAlH4 (M = Li, Na, K, and Cs) correlates with the Pauling electronegativity of cation M (χP); that is, the Ed-H2 (average value) decreases, i.e., 1.211 eV (LiAlH4) < 1.281 eV (NaAlH4) < 1.291 eV (KAlH4) < 1.361 eV (CsAlH4), with the increasing χP value, i.e., 0.98 (Li) > 0.93 (Na) > 0.82 (K) > 0.79 (Cs). The main reason for this finding is that alkali alanate MAlH4 at higher cation electronegativity is thermally less stable and held by weaker Al-H covalent and H-H ionic interactions. Our work contributes to the design of alkali metal aluminum hydrides with a favorable dehydrogenation, which is useful for on-board hydrogen storage.

Ultimate pressure-bearing capacity of Type III onboard high-pressure hydrogen storage tanks under typical accident scenarios

Sufficient pressure-bearing performance was the basis for ensuring the safety of hydrogen storage tanks in service for the entire life cycle. The aim of this study was to analyze the ultimate pressure-bearing capacity of tanks under possible working conditions, such as room temperature, fire, and after flame exposure. The results show that the actual burst pressure of a Type III tank of 48 L and 70 MPa at room temperature was 209.80 MPa, which had sufficient explosion-proof behavior. Compared with the room temperature, the critical failure pressure of the tank under fire conditions dropped sharply by ca. 63.1 %, which readily induced pressure-bearing failure. However, after cooling to room temperature, the residual burst pressure of the tank thermally damaged by fire was only roughly 14.5 % lower than the ultimate pressure-bearing pressure at room temperature, and still maintained a certain strength. The grey correlation analysis model of influencing factors on the ultimate pressure-bearing performance of tanks in normal temperature and fire environments was established for the first time. This paper reports quantitatively that, in addition to the nominal working pressure, the design wall thickness of the tank at room temperature has the most prominent effect on the pressure-bearing performance. While the initial filling pressure and flame exposure time in fire environments were considered to be the key factors affecting the pressure bearing performance.

An Overview of the Recent Advances in Composite Materials and Artificial Intelligence for Hydrogen Storage Vessels Design

The environmental impact of CO2 emissions is widely acknowledged, making the development of alternative propulsion systems a priority. Hydrogen is a potential candidate to replace fossil fuels for transport applications, with three technologies considered for the onboard storage of hydrogen: storage in the form of a compressed gas, storage as a cryogenic liquid, and storage as a solid. These technologies are now competing to meet the requirements of vehicle manufacturers; each has its own unique challenges that must be understood to direct future research and development efforts. This paper reviews technological developments for Hydrogen Storage Vessel (HSV) designs, including their technical performance, manufacturing costs, safety, and environmental impact. More specifically, an up-to-date review of fiber-reinforced polymer composite HSVs was explored, including the end-of-life recycling options. A review of current numerical models for HSVs was conducted, including the use of artificial intelligence techniques to assess the performance of composite HSVs, leading to more sophisticated designs for achieving a more sustainable future.

Ti-decorated nitrogen-rich BeN4 monolayer for reversible hydrogen storage: DFT investigations

The metal-decorated two-dimensional materials have the potential to be considered as onboard hydrogen storage materials, as they have a high surface area and fast kinetics. Here, the application of titanium atom (Ti) decoration on the nitrogen-rich BeN4 monolayer for hydrogen storage is studied by means of Density Functional Theory (DFT). BeN4 is made up of five and six-membered rings and has been synthesized using high-pressure nanofabrication in the recent past. The binding energy of the Ti-decorated BeN4 monolayer comes out to be −2.04 eV indicating that an energetically stable complex is formed after metal decoration. The spin-polarized partial density of states (PDOS) implies that semimetal BeN4 becomes magnetic after Ti decoration. The charge transfer analysis validates transfer of charge from the Ti metal atom toward the BeN4 monolayer. The Ti-decorated BeN4 (BeN4 + Ti) can bind seven hydrogen molecules via Kubas interactions with average adsorption energy and desorption temperature of −0.36 eV/H2 and 512 K, correspondingly satisfying DOE’s criteria. The ab initio molecular dynamics (AIMD) simulations ensure the structural integrity of the BeN4 + Ti complex at 300 K. The high diffusion energy barrier reduces the probability of metal–metal clustering formation. The storage capacity of the BeN4 + Ti complex comes out to be 14.21 gravimetric wt% of hydrogen. The present electronic and molecular level study signifies that the Ti-decorated nitrogen-rich BeN4 monolayer has the potential to fulfill the requirements to be considered as an energy storage material.

Methane reforming in microchannels: Application to the methanol synthesis

Methanol as a simple hydrocarbon containing oxygen is one of the most consumed gas chemicals all around the world. It is a versatile fuel that can be used in fuel cells such as direct methanol fuel cells and downstream proton exchange membrane fuel cells, combustion engines, or even as on-board hydrogen storage. In the chemical industry, methanol is also a vital intermediate employed in a variety of applications and feedstocks. The production of heat upon the synthesis of methanol enhances the temperature of the reactor, lowers the conversion rate, and hastens the deactivation of the catalyst. More isothermal process conditions can be achieved by using microchannel reactors in the methanol synthesis. Because of the small channel's dimensions, the reactor has a high surface-to-volume ratio, which greatly enhances the heat and mass transfer. The rapid heat and mass transfer of substances caused by diffusion in small lateral dimensions results in narrower residence-time distribution in the reactor for gas-phase reactions. The purpose of this work is to investigate the methane-reforming process in microchannels with application in the methanol synthesis process in recent years.

Combined composites layup architecture and mechanical evaluation of type IV pressure vessels: A novel analytical approach

Strict requirements for cost and reliability of compressed gaseous pressure vessels as on-board hydrogen storage necessitates in-depth understanding on the mechanical responses of the composite structure. General numerical methodology to assess this involves a two-step setup: composite layup generation and mechanical property calculation, which becomes highly time and resource-consuming, particularly if multiple designs are scanned for optimization. This study presents a multi-functional analytical tool, combining both aforementioned steps in a single modeling framework. The model enables quick prediction of the strain/stress distribution in correlation with uncomplicated inputs describing the layup design, i.e. stacking sequence with desired winding angles. Additionally, the mechanical evaluation specially focuses on the dome region whose calculation has hardly been inspected analytically in the literature. The results are validated against a three-dimensional finite element calculation implemented in Ansys Workbench, showing qualitative and quantitative agreement. Overall, the study paves the way for composite tank design using analytical approaches, with easy implementation, minimum computational cost and great transparency.

Research on the airtight helium leak detection test device of fully-wrapped carbon fiber reinforced cylinders with a plastic liner for the on-board storage of compressed hydrogen

Research on the airtight helium leak detection test device of fully-wrapped carbon fiber reinforced cylinders with a plastic liner for the on-board storage of compressed hydrogen

Quantitative Risk Assessment Methodology for Hydrogen Tank Rupture in a Tunnel Fire

This study presents a methodology of a quantitative risk assessment for the scenario of an onboard hydrogen storage tank rupture and tunnel fire incident. The application of the methodology is demonstrated on a road tunnel. The consequence analysis is carried out for the rupture of a 70 MPa, 62.4-litre hydrogen storage tank in a fire, that has a thermally activated pressure relief device (TPRD) failed or blocked during an incident. Scenarios with two states of charge (SoC) of the tank, i.e., SoC = 99% and SoC = 59%, are investigated. The risks in terms of fatalities per vehicle per year and the cost per incident are assessed. It is found that for the reduction in the risk with the hydrogen-powered vehicle in a road tunnel fire incident to the acceptable level of 10−5 fatality/vehicle/year, the fire-resistance rating (FRR) of the hydrogen storage tank should exceed 84 min. The FRR increase to this level reduces the societal risk to an acceptable level. The increase in the FRR to 91 min reduces the risk in terms of the cost of the incident to GBP 300, following the threshold cost of minor injury published by the UK Health and Safety Executive. The Frequency–Number (F–N) of the fatalities curve is developed to demonstrate the effect of mitigation measures on the risk reduction to socially acceptable levels. The performed sensitivity study confirms that with the broad range of input parameters, including the fire brigade response time, the risk of rupture of standard hydrogen tank-TPRD systems inside the road tunnel is unacceptable. One of the solutions enabling an inherently safer use of hydrogen-powered vehicles in tunnels is the implementation of breakthrough safety technology—the explosion free in a fire self-venting (TPRD-less) tanks.

Hydrogen production from ammonia-rich combustion for fuel reforming under high temperature and high pressure conditions

Ammonia is a promising carbon-free fuel for internal combustion engines. However, the low reactivity and combustion sluggishness make ammonia difficult to be used in a single-fuel way. A small amount of hydrogen addition has been demonstrated beneficial to improving ammonia’s reactivity and engine performance. To overcome the safety and cost issues of onboard hydrogen storage on vehicles, we propose to produce hydrogen by in-cylinder ammonia reforming through ammonia-rich combustion. This paper presents an investigation on the hydrogen production from ammonia-rich combustion on a rapid compression machine (RCM) over conditions with varying pressures (22–36 bar), temperatures (1200–1300 K), and equivalence ratios (1.75–2.25). Both major combustion reactants (NH3) and products (H2 and N2) were analyzed using a fast sampling system and gas chromatography (GC). Chemical analysis was also conducted to interpret the experimental results. The results showed that current ammonia mechanisms were inadequate to predict the ignition delay time and the hydrogen production trend under engine-relevant and fuel-rich conditions. The experimental hydrogen production increased with the increasing initial temperature, which could be ascribed to the increase in reaction rate constants of key reactions. For the effect of pressure, the hydrogen production was found to first increase and then decrease as the initial pressure increased, which failed to be predicted by simulations. In the tested equivalence ratio range, a moderate fuel-rich equivalence ratio of two produced the highest hydrogen, in which the combined impact of key radical pool buildup (NH3 and NH2) and the change in reaction ratios of key reactions (NH2 + H->NH + H2) was responsible.

Tailoring MgH2 for hydrogen storage through nanoengineering and catalysis

Hydrogen energy has been recognized as “Ultimate Power Source” in the 21st century, which could be the best solution to the looming energy crisis and climate degeneration in the near future. Due to its high safety, low price, abundant resources and decent hydrogen storage density, magnesium based solid-state hydrogen storage materials are becoming the leading candidate for onboard hydrogen storage. However, the high operation temperature and slow reaction rate of MgH 2 , as a result of the large formation enthalpy and high reaction activation energy, respectively, are the first and most difficult problems we need to face and overcome to realize its industrialization. Herein, a state-of-the-art review on tailoring the stable thermodynamics and sluggish kinetics of hydrogen storage in MgH 2 , particularly through nanoengnieering and catalysis is presented, aiming to provide references and solutions for its promotion and application. Promising methods to overcome the challenges faced by MgH 2 /Mg, such as bidirectional catalysts and nanoconfinement with in-situ catalysis are compared and the required improvements are discussed to stimulate further discussions and ideas in the rational design of MgH 2 /Mg systems with ability for hydrogen release/uptake at lower temperatures and cycle stability in the near future.

A Promising Energy Storage System Based on High-Capacity Metal Hydrides

In this paper, based on the study of hydrogen accumulation in the electrodes of nickel–cadmium batteries, a high-capacity hydrogen storage system (HSS) is proposed. It has been experimentally proven that hydrogen accumulates in the electrodes of nickel–cadmium batteries in large quantities over the course of their operation. It has been shown that hydrogen accumulates in metal–ceramic matrices of sintered oxide–nickel electrodes in the form of metal hydrides. The gravimetric capacity of the nickel matrix is 20.3 wt% and the volumetric capacity is 406 kg m−3. The obtained gravimetric capacities for metal–ceramic matrices exceed almost four times the criteria for onboard hydrogen storage systems established by the US Department of Energy (DOE), as well as previously obtained results for any reversible hydrogen accumulation materials. In addition, in our previous papers, it was proved that if we use thermal runaway for the desorption of hydrogen from metal hydrides then the kinetic and thermodynamic criteria established by the US DOE may be significantly exceeded. Thus, within the framework of the proposed HSS, using the electrochemical method of hydrogen accumulation and the thermal runaway process, one can not only achieve all of the criteria established by the US DOE for HSS but also significantly exceed them.

Techno-Economic Analysis of Hydrogen Storage Technologies for Railway Engineering: A Review

According to the specific requirements of railway engineering, a techno-economic comparison for onboard hydrogen storage technologies is conducted to discuss their feasibility and potentials for hydrogen-powered hybrid trains. Physical storage methods, including compressed hydrogen (CH2), liquid hydrogen (LH2), and cryo-compressed hydrogen (CcH2), and material-based (chemical) storage methods, such as ammonia, liquid organic hydrogen carriages (LOHCs), and metal hydrides, are carefully discussed in terms of their operational conditions, energy capacity, and economic costs. CH2 technology is the most mature now but its storage density cannot reach the final target, which is the same problem for intermetallic compounds. In contrast, LH2, CcH2, and complex hydrides are attractive for their high storage density. Nevertheless, the harsh working conditions of complex hydrides hinder their vehicular application. Ammonia has advantages in energy capacity, utilisation efficiency and cost, especially being directly utilised by fuel cells. LOHCs are now considered as a potential candidate for hydrogen transport. Simplifying the dehydrogenation process is the important prerequisite for its vehicular employment. Recently, increasing novel hydrogen-powered trains based on different hydrogen storage routes are being tested and optimised across the world. It can be forecasted that hydrogen energy will be a significant booster to railway decarbonisation.

Design tool for estimating adsorbent hydrogen storage system characteristics for light-duty fuel cell vehicles

This work combines materials development with hydrogen storage technology advancements to address onboard hydrogen storage challenges in light-duty vehicle applications. These systems are comprised of the vehicle requirements design space, balance of plant requirements, storage system components, and materials engineering culminating in the development of an Adsorbent System Design Tool that serves as a preprocessor to the storage system and vehicle-level models created within the Hydrogen Storage Engineering Center of Excellence. Computational and experimental efforts were integrated to evaluate, design, analyze, and scale potential hydrogen storage systems and their supporting components against the Department of Energy 2020 and Ultimate Technical Targets for Hydrogen Storage Systems for Light Duty Vehicles. Ultimately, the Adsorbent System Design Tool was created to assist material developers in assessing initial design parameters that would be required to estimate the performance of the hydrogen storage system once integrated with the full fuel cell system.

An Electrochemical Ethylamine/Acetonitrile Redox Method for Ambient Hydrogen Storage

Hydrogen is an appealing energy carrier that can potentially replace conventional fossil fuels in the development of a clean, sustainable hydrogen economy, which would resolve environmental problems caused by the combustion of the non-renewable resources while also meeting the rising demand for energy. However, hydrogen storage has remained a major roadblock in the hydrogen economy development. As a matter of fact, the state-of-the-art methods fall short of the 2025 Department of Energy (DOE) onboard hydrogen storage target of 5.5 wt.% under 85 °C and 12 bars.Herein we report a new, electrochemical ethylamine/acetonitrile redox method for efficient, high-capacity hydrogen storage under completely ambient conditions. The amine/nitrile redox couple is selected due to their moderate chemical polarity and relatively simple hydrogenation and dehydrogenation pathways, which would aid reaction activation and reduce the energy barrier. Electrochemical potential provides the driving force in CH3CH2NH2 dehydrogenation under ambient conditions, rather than high temperature and pressure that are typically required to thermally drive an endothermic process. We demonstrate an effective, complete cycle of CH3CN hydrogenation to CH3CH2NH2 for hydrogen uptake and CH3CH2NH2 dehydrogenation to CH3CN for hydrogen release at low overpotentials, using commercial Pt black catalyst in an electrochemical cell. The studied CH3CH2NH2/CH3CN system has a theoretical H2 storage capacity of 8.9 wt.%, well surpassing the 5.5 wt.% DOE target. This study offers a new, effective hydrogen storage strategy that can be extended to many other amine/nitrile redox systems and would help advance the hydrogen economy development.

Exploring Technological Solutions for Onboard Hydrogen Storage Systems Through a Heterogeneous Knowledge Network: From Current State to Future Research Opportunities

With the imminent threat of the energy crises, innovation in energy technologies is happening world-wide. The aim is to reduce our reliance on fossil fuels. Electric vehicles with fuel-cells that use hydrogen as an energy carrier are touted to be one of the most important potential replacements of the gasoline vehicle in both future transportation scenarios and emerging smart energy grids. However, hydrogen storage is a major technical barrier that lies between where we are now and the mass application of hydrogen energy. Further exploration of onboard hydrogen storage systems (OHSS) is urgently needed and, in this regard, a comprehensive technology opportunity analysis will help. Hence, with this research, we drew on scientific papers and patents related to OHSS and developed a novel methodology for investigating the past, present, and future development trends in OHSS. Specifically, we constructed a heterogeneous knowledge network using a unique multi-component structure with three core components: hydrogen carriers, hydrogen storage materials, and fuel cells. From this network, we extracted both the developed and underdeveloped technological solutions in the field and applied a well-designed evaluation system and prediction model to score the future development potential of these technological solutions. What emerged was the most promising directions of research in the short, medium, and long term. The results show that our methodology can effectively identify technology opportunities in OHSS, along with providing valuable decision support to researchers and enterprise managers associated with the development and application of OHSS.