Refuelling scenarios of a light urban fuel cell vehicle with metal hydride hydrogen storage. Comparison with compressed hydrogen storage counterpart

The high price of hydrogen fuel in the fuel cell vehicle refuelling market is highly dependent on the one hand from the production costs of hydrogen and on the other from the capital cost of a hydrogen refuelling station's components to support a safe and adequate refuelling process of contemporary fuel cell vehicles. The hydrogen storage technology dominated in the vehicle sector is currently based on high-pressure compressed hydrogen tanks to extend as much as possible the driving range of the vehicles. However, this technology mandates the use of large hydrogen compression and cooling systems as part of the refuelling infrastructure that consequently increase the final cost of the fuel. This study investigated the prospects of lowering the refuelling cost of small urban hydrogen vehicles through the utilisation of metal hydride hydrogen storage. The results showed that for low compression hydrogen storage, metal hydride storage is in favour in terms of the dispensed hydrogen fuel price, while its weight is highly comparable to the one of a compressed hydrogen tank. The final refuelling cost from the consumer's perspective however was found to be higher than the compressed gas due to the increased hydrogen quantity required to be stored in fully empty metal hydride tanks to meet the same demand.     

燃料电池车车载储氢系统的技术发展与应用现状

综述了燃料电池车车载储氢系统技术，包括高压氢、液氢、金属氢化物、低温吸附、纳米碳管高压吸附以及液体有机氢化物等的研究进展及其车载应用现状。参照燃料电池车对车载储氢系统单位重量储氢密度与体积储氢密度的目标要求，对目前已应用和处于研发阶段的一些储氢技术的性能指标和存在问题进行了分析讨论。同时对目前该领域的若干新的研究报道，如超高压轻质复合容器、混合储氢容器、b.c．c．储氢合金、超级活性碳和“浆液”双相储氢等，也作了简要介绍。     

Perspectives of high entropy alloys as hydrogen storage materials

Storage is a challenging issue that cuts across distribution, delivery, and safe end-uses of hydrogen as fuel. All the fuel cell vehicles are equipped with inefficient and unsafe high-pressure hydrogen cylinders. It is well known that storing such a highly flammable gas at high pressure is not safe. Only hydrogen can be stored safely as a form of metal hydrides, and all the investigated metal hydrides are inefficient in one way or another. Four essential hydrogen parameters for solid-state storage for fuel cell applications are high volumetric storage capacity, excellent heat transfer, and recharge time and feasible charging discharging temperatures. The available metal tanks have good gravimetric storage capacity but did not satisfy the prescribed criterion for good volumetric capacity necessary for mobile applications. Recently, some promising reports are published on the hydrogen storage properties of newly discovered High Entropy Alloys (HEAs). HEAs provide vast composition selection freedom for the formation of favorable simple solid solution phase for hydrogen storage. The four core effects of these alloys may also play a vital role in hydrogen storage properties. Here we reviewed and summarized the published results on hydrogen storage properties of HEAs to date. We underlined different essential aspects for the future development of HEAs as hydrogen storage materials. This review article discusses and describes the perspectives of HEAs in regards to the hydrogen storage applications of these alloys and will provide insight into the future development of hydrogen storage HEAs.     

Hydrogen patent portfolios in the automotive industry – The search for promising storage methods

In the development of hydrogen vehicle technologies, the automotive industry adopts a portfolio approach; a multitude of technological options is developed for hydrogen storage and conversion. Patent portfolios of car manufacturers are used as indicators of the variation and selection dynamics of different options. Convergence towards a single combination of storage and conversion technologies would indicate closeness to commercialization of hydrogen vehicles. Even though patent portfolios converge towards a single conversion option, the PEM fuel cell, storage patents only show divergence. This is very different from hydrogen prototype vehicles that have shown strong convergence towards high-pressure storage. These findings raise questions about the commercialization of hydrogen vehicles, as the industry is still searching for promising storage methods. As on-board storage methods are still in development, hydrogen refilling stations would best be kept open to all options rather than high-pressure systems alone.     

Thermodynamic analysis of the emptying process of compressed hydrogen tanks

During the driving of fuel cell vehicles, the fast depressurization of compressed hydrogen tanks plus the high storage pressure and the low thermal conductivity of carbon fiber reinforced plastic (CFRP) can lead to significant cooling of the tank. This can result in a temperature below −40 °C inside the compressed hydrogen tanks and cause safety problems. In this paper, a thermodynamic model that incorporates the nature of external natural convection was developed to describe the emptying process of compressed hydrogen tanks and was validated by experiments. Thermodynamic analyses of the emptying process were performed to study the global heat transfer characteristics and the effects of ambient temperature, defueling rate, defueling pattern, initial and final density of hydrogen gas, liner and CFRP thickness and the crosswind velocity on the final temperature decreases of hydrogen gas, the inner wall and the outer wall.     

The design and optimization of a cryogenic compressed hydrogen refueling process

Cryo-compressed hydrogen storage has excellent volume and mass hydrogen storage density, which is the most likely way to meet the storage requirements proposed by United States Department of Energy（DOE）. This paper contributes to propose and analyze a new cryogenic compressed hydrogen refueling station. The new type of low temperature and high-pressure hydrogenation station system can effectively reduce the problems such as too high liquefaction work when using liquid hydrogen as the gas source, the need to heat and regenerate to release hydrogen, and the damage of thermal stress on the storage tank during the filling process, so as to reduce the release of hydrogen and ensure the non-destructive filling of hydrogen. This paper focuses on the study of precooling process in filling. By establishing a heat transfer model, the dynamic trend of tank temperature with time in the precooling process of low-temperature and high-pressure hydrogen storage tank under constant pressure is studied. Two analysis methods are used to provide theoretical basis for the selection of inlet diameter of hydrogen storage tank. Through comparative analysis of the advantages and disadvantages of the two analysis methods, it is concluded that the analysis method of constant mass flow is more suitable for the selection in practical applications. According to it, the recommended diameter of the storage tank at the initial temperature of 300 K, 200 K and 100 K is selected, which are all 15 mm. It is further proved that the calculation method can meet the different storage tank states of hydrogen fuel cell vehicles when selecting the pipe diameter.     

Nanomaterials for on-board solid-state hydrogen storage applications

Hydrogen has the highest gravimetric density (energy density per unit mass) of any fuel. The combustion of hydrogen releases energy in the form of heat. When hydrogen reacts with oxygen in a fuel cell, the reaction releases energy in the form of electricity. Unlike hydrocarbon-based fuels, the generation of energy from either the combustion of hydrogen or the reaction of hydrogen with oxygen in a fuel cell is not accompanied by the emission of greenhouse gases. This makes hydrogen a promising solution to solve global warming issues. However, hydrogen has a low volumetric density (low energy density per unit volume) which makes storing or transporting hydrogen extremely difficult and expensive. To accelerate the utilization of hydrogen as an energy carrier, it is necessary to develop advanced hydrogen storage methods that have the potential to have a higher energy density.The hydrogen storage market is segmented by application into: (1) Stationary power: stored hydrogen is consumed for example in a fuel cell for use in backup power stations, refueling stations, power stations; (2) Portable power: hydrogen storage applications for electronic devices such as mobile phones, flash lights, and portable generators; and (3) Transportation: industries including automobiles, aerospace, unmanned aerial systems, and hydrogen tanks used throughout the hydrogen supply chain. The increasing development of light and heavy fuel cell vehicles is expected to drive the development of on-board solid-state hydrogen technologies.A large number of research groups worldwide for many years have been trying to develop materials having the right set of thermodynamic and kinetic properties, along with all of the physical properties (high gravimetric density, high volumetric density, etc.) to allow for low-pressure storage system in ambient conditions. However, to date, no material has been found that satisfies all the desired properties to be viably used in many applications. Even if we consider only three parameters namely gravimetric density, volumetric density, and system cost, no materials that can meet the ultimate targets of the U.S. Department of Energy (DOE) or the 2030 targets of the European Union's Fuel Cells and Hydrogen Joint Undertaking (FCH JU) and the New Energy and Industrial Technology Development Organization (NEDO) in Japan.The present article reviews advances in solid-state hydrogen storage technology and compares the opportunities and challenges of selected materials. The materials reviewed in this article have a wider spectrum than the materials reviewed in other existing articles, including carbon nanotubes (CNTs), metal–organic frameworks (MOFs), graphene, boron nitride (BN), fullerene, silicon, amorphous manganese hydride molecular sieve, and metal hydrides. Pioneering works, important breakthroughs, as well as the latest developments for promising materials are also reviewed.In addition, for the first time the targets set by several official regulatory agencies for solid-state hydrogen storage are summarized. Achievements in academic and industrial research are compared against these targets.The future prospects of promising materials are analyzed based on how its practical application can be implemented according to market needs.     

Impact of refueling parameters on storage density of compressed hydrogen storage Tank

Hydrogen fuel cell vehicle (HFCV) is one of the key contributors to sustainable development of the society. For commercial deployment and market acceptability of fuel cell vehicles, efficient storage of hydrogen with an optimum refueling is one of the important challenge. Compressed hydrogen storage in Type IV tanks is a mature and promising technology for on-board application. The fast refueling of the storage tank without overheating and overfilling is an essential requirement defined by SAE J2601. In this regard, station parameters such as hydrogen supply temperature, filling rate and vehicle tank parameters such as filling time strongly influences the storage capacity of the tank, affecting driving range of the fuel cell vehicle. This paper investigates the impact of these parameters on storage density of the tank defined in terms of state of charge. For this, refueling simulation based on SAE J2601 protocol has been performed using computational fluid dynamic approach to investigate the influence of station parameters on storage density of the tank. Further, the root cause analysis was carried out to investigate the contribution of station and vehicle tank parameters for enhancing the storage density of the tank. Finally, the regression model based on these refueling parameters was developed to predict the density attained at different filling conditions. The results confirmed the strong contribution of pressure, filling time, supply temperature and least contribution of temperature, filling rates in enhancing the storage density of the tank. The results can provide new insight into refueling behavior of the Type IV tank for fuel cell vehicle.     

Review on studies of the emptying process of compressed hydrogen tanks

Compressed hydrogen tanks are now widely used for onboard hydrogen storage in fuel cell vehicles (FCVs). However, because of the high storage pressure and the low thermal conductivity of carbon fibre reinforced polymer (CFRP), the emptying of such tanks during driving or emergency release can cause a significant temperature decrease and result in an in-tank gas temperature below the low safety temperature limit of ?40 °C even in warm weather. Once the gas temperature within the tank is lower than ?40 °C, the sealing elements at the boss of the tank may fail, and glass transition of the polymer liner of the type IV tank may occur; both can cause hydrogen leakage and severe safety problems. In this paper, the heat transfer correlations, thermodynamic analyses, computational fluid dynamics (CFD) simulations, experimental studies, and thermal management methods associated with the emptying process of compressed hydrogen tanks are comprehensively reviewed. Future research directions on this topic are suggested.     

Hydrogen storage technology: Current status and prospects

储氢技术作为氢气生产与使用之间的桥梁,至关重要。本文综述了目前常用的储氢技术,主要包括物理储氢、化学储氢与其它储氢。物理储氢主要包括高压气态储氢与低温液化储氢,具有低成本、易放氢、氢气浓度高等特点,但安全性较低。化学储氢包括有机液体储氢、液氨储氢、配位氢化物储氢、无机物储氢与甲醇储氢。其虽保证了安全性,但其放氢难,且易发生副反应,氢气浓度较低。其它储氢技术包括吸附储氢与水合物法储氢。吸附储氢技术的储氢效率受吸附剂的影响较大,且不同程度的存在放氢难、成本高、储氢密度不高等问题。水合物法储氢具有易脱氢、成本低、能耗低等特点,但其储氢密度较低。在此基础上,本文基于现状分析,简要展望了储氢技术今后的研究方向。     

High-pressure release and dispersion of hydrogen in a partially enclosed compartment: Effect of natural and forced ventilation

The study of compressed hydrogen releases from high-pressure storage systems has practical application for hydrogen and fuel cell technologies. Such releases may occur either due to accidental damage to a storage tank, connecting piping, or due to failure of a pressure release device (PRD). Understanding hydrogen behavior during and after the unintended release from a high-pressure storage device is important for development of appropriate hydrogen safety codes and standards and for the evaluation of risk mitigation requirements and technologies. In this paper, the natural and forced mixing and dispersion of hydrogen released from a high-pressure tank into a partially enclosed compartment is investigated using analytical models. Simple models are developed to estimate the volumetric flow rate through a choked nozzle of a high-pressure tank. The hydrogen released in the compartment is vented through buoyancy induced flow or through forced ventilation. The model is useful in understanding the important physical processes involved during the release and dispersion of hydrogen from a high-pressure tank into a compartment with vents at multiple levels. Parametric studies are presented to identify the relative importance of various parameters such as diameter of the release port and air changes per hour (ACH) characteristic of the enclosure. Compartment overpressure as a function of the size of the release port is predicted. Conditions that can lead to major damage of the compartment due to overpressure are identified. Results of the analytical model indicate that the fastest way to reduce flammable levels of hydrogen concentration in a compartment is by blowing through the vents. Model predictions for forced ventilation are presented which show that it is feasible to effectively and rapidly reduce the flammable concentration of hydrogen in the compartment following the release of hydrogen from a high-pressure tank.     

Ethanol–electric propulsion as a sustainable technological alternative for urban buses in Brazil

The option of fitting electric motors to vehicles that are more efficient and quieter than internal combustion engines has been hampered considerably, looking only at the use of conventional batteries supplying electricity. This is basically due to low gravimetric and volumetric energy densities of these devices that result in shorter autonomy, in addition to more weight and less usable space in the vehicle. An alternative that could make electric motors more attractive for vehicular applications by replacing batteries as the main electricity source is the fuel cell. Hydrogen is the main fuel used in these cells, but the hydrogen storage systems developed so far are heavier and bulkier than their equivalent for conventional liquid fuels such as diesel, gasoline and alcohol, despite heavier energy densities compared to batteries.This paper reviews technological aspects of fuel cells, the main storage systems for hydrogen and other energy sources, data on fuel use and the types of vehicles most commonly used in the Brazilian road transportation sector, followed by an overview of the insertion of hybrid ethanol–electric buses in Brazil.     

Affordable hydrogen supply pathways for fuel cell vehicles

Fuel cell vehicles can be powered directly by hydrogen stored on the vehicle, or indirectly by extracting hydrogen from onboard liquid fuels such as methanol or gasoline. The direct hydrogen fuel cell vehicle is preferred, since it would be less complex, have better fuel economy, lower greenhouse gas emissions, greater oil import reductions and would lead to a sustainable transportation system once renewable energy was used to produce hydrogen. The two oft-cited concerns with direct hydrogen fuel cell vehicles are onboard hydrogen storage and the lack of hydrogen supply options. Directed Technologies, Inc., working with the Ford Motor Company under a Department of Energy cost shared contract to develop direct hydrogen fuel cell vehicles, has addressed both perceived roadblocks to direct hydrogen fuel cell vehicles. We describe realistic, cost effective options for both onboard hydrogen storage and for economically viable hydrogen infrastructure development.     

An overview of hydrogen as a vehicle fuel

As hydrogen fuel cell vehicles move from manifestation to commercialization, the users expect safe, convenient and customer-friendly fuelling. Hydrogen quality affects fuel cell stack performance and lifetime, as well as other factors such as valve operation. In this paper, previous researcher's development on hydrogen as a possible major fuel of the future has been studied thoroughly. Hydrogen is one of the energy carriers which can replace fossil fuel and can be used as fuel in an internal combustion engines and as a fuel cell in vehicles. To use hydrogen as a fuel of internal combustion engine, engine design should be considered for avoiding abnormal combustion. As a result it can improve engine efficiency, power output and reduce NO_x emissions. The emission of fuel cell is low as compared to conventional vehicles but as penalty, fuel cell vehicles need additional space and weight to install the battery and storage tank, thus increases it production cost. The production of hydrogen can be ‘carbon-free’ only if it is generated by employing genuinely carbon-free renewable energy sources. The acceptability of hydrogen technology depends on the knowledge and awareness of the hydrogen benefits towards environment and human life. Recent study shows that people still do not have the sufficient information of hydrogen.     

A literature review of failure prediction and analysis methods for composite high-pressure hydrogen storage tanks

With the development of hydrogen fuel cell vehicles, the on-board hydrogen storage technology with safety, efficiency and economy has become a fundamental part. Low cost, light weight and good safety performance are required for the on-board hydrogen storage tanks. The composite high-pressure hydrogen storage tank has been recognized as an efficient solution that could address these problems. However, the complex working environment of hydrogen-thermo-mechanism presents challenge to the failure analysis and predictive model establishment of the composite hydrogen storage tanks. The crucial parameters or indicators for tank's failure analysis include burst pressure, damage state and fatigue lifetime, etc. So this paper gives a comprehensive review on the failure behavior analysis methods and prediction models of composite high-pressure hydrogen storage tanks from the literature. First, the failure analysis methods of composite high-pressure hydrogen storage tanks are summarized. Second, the latest literature regarding failure mode predictive methods and models of type III and type IV tanks are reviewed. The different failure criteria are compared and summarized, including some new failure criteria. These criteria enable failure analysis methods to obtain the interaction information on the interaction between the microscopic and macroscopic aspects of the composite. Damage evolution model and constitutive model are summarized. The post-initial failure behavior of the composite laminates structure is simulated by the material property degradation method (MPDM), especially the continuum damage mechanics (CDM) in conjunction with commercial finite element (FE) analysis method. The process of progressive failure analysis of composite tank is summarized as a reference for subsequent failure analysis. The future work of progressive failure analysis should focus on the initial failure of the composite material and microscopic failure mechanisms. The burst, fiber damage and fatigue life are the mainly investigated failure modes for type III composite hydrogen storage tank. For Type IV, the mainly researched failure modes are the collapse and blistering of the liner, burst and damage. The different finite element analysis methods and failure predictive models were classified and summarized. Further improvements were required for the simulation models of full-scale structure of the tank in the working environment or under the complex fiber winding modes. The liner of the type IV cylinder is completely distinct from that of the type III, therefore the behavior of collapse and blistering of the liner needs to be further investigated. The factors that affect collapse and blistering should be explored. The future research need focus on controlling these factors and monitoring the effects of these factors towards structural strength.     

The design of long-life,high-efficiency PEM fuel cell power supplies for low power sensor networks

Field sensor networks have important applications in environmental monitoring, wildlife preservation, in disaster monitoring and in border security. The reduced cost of electronics, sensors and actuators make it possible to deploy hundreds if not thousands of these sensor modules. However, power technology has not kept pace. Current power supply technologies such as batteries limit many applications due to their low specific energy. Photovoltaics typically requires large bulky panels and is dependent on varying solar insolation and therefore requires backup power sources. Polymer Electrolyte Membrane (PEM) fuel cells are a promising alternative, because they are clean, quiet and operate at high efficiencies. However, challenges remain in achieving long lives due to factors such as degradation and hydrogen storage. In this work, we devise a framework for designing fuel cells power supplies for field sensor networks. This design framework utilize lithium hydride hydrogen storage technology that offers high energy density of up to 5000 Wh/kg. Using this design framework, we identify operating conditions to maximize the life of the power supply, meet the required power output and minimize fuel consumption. We devise a series of controllers to achieve this capability and demonstrate it using a bench-top experiment that operated for 5000 h. The laboratory experiments point towards a pathway to demonstrate these fuel cell power supplies in the field. Our studies show that the proposed PEM fuel cell hybrid system fueled using lithium hydride offers at least a 3 fold reduction in mass compared to state-of-the-art batteries and 3-5 fold reduction in mass compared to current fuel cell technologies.     

Design of a hydrogen community

This paper discusses the conceptual design of a scalable and reproducible hydrogen fueling station at Santa Monica, California. Hydrogen production using renewable energy sources such as biogas, which accounts for 100% of the total production, has been discussed. The fueling station consists of a direct fuel cell (DFC) 300 fuel cell for on-site generation of 136 kg/day of hydrogen and 300 kW of electric power, five hydrogen storage tanks (storage capacity of 198 kg of H₂ at 350 and 700 bar), four compressors which assist in dispensing 400 kg of hydrogen in 14 h, two hydrogen dispensers operating at 350 bar and 700 bar independently and a SAE J2600 compliant hydrogen nozzle. Potential early market customers for hydrogen fuel cells and their daily fuel requirements have been computed. The safety codes, potential failure modes and the methods to mitigate risks have been explained. A well-to-wheel analysis is performed to compare the emissions and the total energy requirements of conventional gasoline and fuel cell vehicles.     

Performances comparison of adsorption hydrogen storage tanks at a wide temperature and pressure zone

Large-scale application of hydrogen requires safe, reliable and efficient storage technologies. Among the existing hydrogen storage technologies, cryo-compressed hydrogen (CcH₂) storage has the advantages of high hydrogen storage density, low energy consumption and no ortho-para hydrogen conversion. But it still needs higher hydrogen storage pressure when reaching higher hydrogen storage density. In order to reduce hydrogen storage pressure and improve storage density, solid adsorption technology is introduced in CcH₂. Activated carbon and metal-organic framework materials (MOFs) are employed as adsorbents in this paper. The gravimetric/volumetric hydrogen storage capacities of different adsorption tanks are studied and compared with the hydrogen storage conditions of 1–55 MPa at 77–298 K. The results show that the hydrogen storage density of CcH₂ combined with adsorption is higher than that of pure adsorption hydrogen storage, and the storage pressure is lower than that of pure CcH₂ under the same hydrogen storage capacity. And the combination of two hydrogen storage technologies can achieve a high hydrogen storage capacity equivalent to that of liquid hydrogen at a lower pressure.     

Hydrogen storage – Industrial prospectives

The topic of this paper is to give an historical and technical overview of hydrogen storage vessels and to detail the specific issues and constraints of hydrogen energy uses. Hydrogen, as an industrial gas, is stored either as a compressed or as a refrigerated liquefied gas. Since the beginning of the last century, hydrogen is stored in seamless steel cylinders. At the end of the 60 s, tubes also made of seamless steels were used; specific attention was paid to hydrogen embrittlement in the 70 s. Aluminum cylinders were also used for hydrogen storage since the end of the 60 s, but their cost was higher compared to steel cylinders and smaller water capacity. To further increase the service pressure of hydrogen tanks or to slightly decrease the weight, metallic cylinders can be hoop-wrapped. Then, with specific developments for space or military applications, fully-wrapped tanks started to be developed in the 80 s. Because of their low weight, they started to be used in for portable applications: for vehicles (on-board storages of natural gas), for leisure applications (paint-ball) etc… These fully-wrapped composite tanks, named types III and IV are now developed for hydrogen energy storage; the requested pressure is very high (from 700 to 850 bar) leads to specific issues which are discussed. Each technology is described in term of materials, manufacturing technologies and approval tests. The specific issues due to very high pressure are depicted.