PEFC stacks as power sources for hybrid propulsion systems

In this paper the performance of two polymeric electrolyte fuel cell systems (FCS) for hybrid power trains are presented and discussed. In particular, an experimental analysis was effected on 2.4 and 20 kW stacks with the aim to investigate the energy management issues of the two FCSs for utilization as power sources in electric power trains for scooter and minibus, respectively. The stack characterizations permitted the effect of the main operative variables (temperature, pressure and stoichiometric ratio) on mean power density of cells to be evaluated. The FCS efficiency was evaluated and compared for the two traction systems, individuating the optimal operative conditions for automotive application and specifying the energy losses of the auxiliary components. The efficiency of both fuel cell systems resulted higher than 40% in a wide range of loads (100–600 mA/cm²), with maximum values close to 50%. The experimental characterization of the two power trains was carried out on dynamic test benches, able to simulate the behaviour of the two vehicles on the European R40 driving cycle. The characterization of the two propulsion systems on R40 driving cycle evidenced that the overall efficiency was not affected significantly by the hybrid configuration adopted, as the efficiency values ranged from 27 to 29% in the different procedures analyzed.     

Transmission electron microscopic observations of the decomposition process of lithium alanate

The thermal decomposition process of lithium alanate (LiAlH₄) was investigated by TEM, TG-DTA and XRD. It was shown that LiAlH₄ decomposes through a two-step reaction: a liquid-to-solid phase transition in the first step of the decomposition and a solid-to-solid reaction in the second step of the decomposition, both steps accompanied by hydrogen release. The particle size of the aluminum (Al), which formed in the first decomposition step, was much larger than that in the second decomposition step. In addition, Al particles formed in the liquid phase of LiAlH₄ in the first decomposition step, while, they form in solid phase of Li₃AlH₆ in the second decomposition step, resulting in the kinetics of the first decomposition step being faster than that of the second decomposition step. The investigation clearly demonstrated the reaction model of the decomposition of LiAlH₄ in the nano-scale, showing different diffusion processes of Al in each of the decomposition steps.     

Efficiencies of hydrogen storage systems onboard fuel cell vehicles

Energy efficiency, vehicle weight, driving range, and fuel economy are compared among fuel cell vehicles (FCV) with different types of fuel storage and battery-powered electric vehicles. Three options for onboard fuel storage are examined and compared in order to evaluate the most energy efficient option of storing fuel in fuel cell vehicles: compressed hydrogen gas storage, metal hydride storage, and onboard reformer of methanol. Solar energy is considered the primary source for fair comparison of efficiencies for true zero emission vehicles. Component efficiencies are from the literature. The battery powered electric vehicle has the highest efficiency of conversion from solar energy for a driving range of 300 miles. Among the fuel cell vehicles, the most efficient is the vehicle with onboard compressed hydrogen storage. The compressed gas FCV is also the leader in four other categories: vehicle weight for a given range, driving range for a given weight, efficiency starting with fossil fuels, and miles per gallon equivalent (about equal to a hybrid electric) on urban and highway driving cycles.     

An experimental study of a PEM fuel cell power train for urban bus application

An experimental study was carried out on a fuel cell propulsion system for minibus application with the aim to investigate the main issues of energy management within the system in dynamic conditions. The fuel cell system (FCS), based on a 20 kW PEM stack, was integrated into the power train comprising DC–DC converter, Pb batteries as energy storage systems and asynchronous electric drive of 30 kW. As reference vehicle a minibus for public transportation in historical centres was adopted. A preliminary experimental analysis was conducted on the FCS connected to a resistive load through a DC–DC converter, in order to verify the stack dynamic performance varying its power acceleration from 0.5 kW s⁻¹ to about 4 kW s⁻¹. The experiments on the power train were conducted on a test bench able to simulate the vehicle parameters and road characteristics on specific driving cycles, in particular the European R40 cycle was adopted as reference. The “soft hybrid” configuration, which permitted the utilization of a minimum size energy storage system and implied the use of FCS mainly in dynamic operation, was compared with the “hard hybrid” solution, characterized by FCS operation at limited power in stationary conditions. Different control strategies of power flows between fuel cells, electric energy storage system and electric drive were adopted in order to verify the two above hybrid approaches during the vehicle mission, in terms of efficiencies of individual components and of the overall power train.     

Metal hydride hydrogen storage tank for fuel cell utility vehicles

The “low-temperature” intermetallic hydrides with hydrogen storage capacities below 2 wt% can provide compact H₂ storage simultaneously serving as a ballast. Thus, their low weight capacity, which is usually considered as a major disadvantage to their use in vehicular H₂ storage applications, is an advantage for the heavy duty utility vehicles. Here, we present new engineering solutions of a MH hydrogen storage tank for fuel cell utility vehicles which combines compactness, adjustable high weight, as well as good dynamics of hydrogen charge/discharge. The tank is an assembly of several MH cassettes each comprising several MH containers made of stainless steel tube with embedded (pressed-in) perforated copper fins and filled with a powder of a composite MH material which contains AB₂- and AB₅-type hydride forming alloys and expanded natural graphite. The assembly of the MH containers staggered together with heating/cooling tubes in the cassette is encased in molten lead followed by the solidification of the latter. The tank can provide >2 h long H₂ supply to the fuel cell stack operated at 11 kWe (H₂ flow rate of 120 NL/min). The refuelling time of the MH tank (T = 15–20 °C, P(H₂) = 100–150 bar) is about 15–20 min.     

The fuel cell electric vehicles: The highlight review

Transportation sector is the important sector and consumed the most fossil fuel in the world. Since COVID-19 started in 2019, this sector had become the world connector because every country relies on logistics. The transportation sector does not only deal with the human transportation but also relates to logistics. Research in every country has searched for alternative transportation to replace internal combustion engines using fossil fuel, one of the most prominent choices is fuel cells. Fuel cells can use hydrogen as fuel. Hydrogen can be fed to the fuel cells to provide electric power to drive vehicles, no greenhouse gas emission and no direct combustion required. The fuel cells have been developed widely as the 21st century energy-conservation devices for mobile, stationary, and especially vehicles. The fuel cell electric vehicles using hydrogen as fuel were also called hydrogen fuel cell vehicles or hydrogen electric vehicles. The fuel cells were misconceived by several people that they were batteries, but the fuel cells could provide electric power continuously if their fuel was provided continuously. The batteries could provide electric power as their only capacities, when all ions are released, no power could be provided. Because the fuel cell vehicles play important roles for our future transportation, the overall review for these vehicles is significantly interesting. This overall review can provide general and technical information, variety of readers; vehicle users, manufacturers, and scientists, can perceive and understand the fuel cell vehicles within this review. The readers can realize how important the fuel cell technologies are and support research around the world to drive the fuel cell vehicles to be the leading vehicles in our sustainable developing world.     

Electrochemical reaction of lithium alanate dissolved in diethyl ether and tetrahydrofuran

We present electrochemical properties of lithium alanate (LiAlH₄) dissolved in aprotic ethers – diethyl ether (Et₂O) and tetrahydrofuran (THF) – under an Ar atmosphere of 1 atm at 298 K. Specific conductivities of both LiAlH₄–THF and LiAlH₄–Et₂O solutions are measured by AC four-terminal method. Cyclic voltammetry is performed with using a beaker-type electrochemical cell consisted of a Ni wire, Ni mesh and Li wire as a working, counter and reference electrode, respectively. In order to clarify the electrochemical behavior, anodic polarization of LiAlH₄–THF solution is measured. The current density of 1.0 M LiAlH₄–THF solution reaches to 1 A cm⁻², which is higher than the LiAlH₄–Et₂O solution. Quantitative analysis of H₂ gas generated on the working electrode during the potentiostatic electrolysis tells that the number of electrons involved in the anodic reaction at the limiting current is one in case of the LiAlH₄–THF solution. We propose conceivable electrochemical reactions of LiAlH₄ in the non-aqueous ethereal solutions.     

Recent challenges of hydrogen storage technologies for fuel cell vehicles

Fuel cell vehicles have a high potential to reduce both energy consumption and carbon dioxide emissions. However, due to the low density, hydrogen gas limits the amount of hydrogen stored on board. This restriction also prevents wide penetration of fuel cells. Hydrogen storage is the key technology towards the hydrogen society. Currently high-pressure tanks and liquid hydrogen tanks are used for road tests, but both technologies do not meet all the requirements of future fuel cell vehicles. This paper briefly explains the current status of conventional technologies (simple containment) such as high-pressure tank systems and cryogenic storage. Another method, hydrogen-absorbing alloy has been long investigated but it has several difficulties for the vehicle applications such as low temperature discharge characteristics and quick charge capability due to its reaction heat. We tested a new idea of combining metal hydride and high pressure. It will solve some difficulties and improve performance such as gravimetric density. This paper describes the latest material and system development.     

Design of a hybrid electric fuel cell power train for an urban bus

With the requirements for reducing emissions and improving fuel economy, new markets have become attractive for automotive companies that are developing electric, hybrid, and plug-in vehicles using new technologies candidates to be implemented in the next generations of vehicles. Most of all, hybrid vehicles are attracting interest due to great potential to achieve higher fuel economy and a longer range with respect to pure electric mode but often this solution is not petroleum free. Within a national project CNR TAE Institute is involved in the development of a zero emission hybrid electric city bus based on PEM fuel cell technology able to increase the range at least 30% with respect to the same vehicle in pure electric configuration. Design, control and preliminary results are reported in this paper.     

Hydrogen fuel cell electric vehicle performance and user-response assessment: Results of an extended driver study

This study examined driver acceptance and performance of hydrogen fuel cell electric vehicles as tested in real-world conditions over a two-year period. The study sample was a volunteer group of “n = 54” drivers who drove the vehicle for a month-long trial period. Each driver took ‘before’ and ‘after’ surveys regarding their driving experience. Drivers drove an average of 1400 miles per month, and either witnessed and/or performed vehicle refueling 3–10 times during their test period.Key findings from the study include that: 1) 80% of study participant drivers found that the fuel cell vehicle (FCV) performance “exceeded” or “greatly exceeded” their expectations; 2) 98% of study participant drivers view hydrogen as a fuel for vehicles as being “as safe” or “safer” than gasoline as a fuel for vehicles; and 3) 94% of participants view the process of fueling a vehicle with hydrogen to be “as safe” or “safer” than gasoline fueling. Other findings include that 85% of study participants who performed their own fueling described hydrogen fueling to be “somewhat” or “very” simple. Of the participants, 62% percent had to forgo at least one trip due to lack of hydrogen fuel, although vehicle range was rated by 75% of participants as entirely or mostly adequate. If fueling infrastructure availability was not an issue, and fuel cost per-mile was at parity with gasoline, 75% of participants would be willing to pay $40,000 or less for an FCV.     

Comments on solid state hydrogen storage systems design for fuel cell vehicles

In recent years, significant research and development efforts were spent on hydrogen storage technologies with the goal of realizing a breakthrough for fuel cell vehicle applications. This article scrutinizes design targets and material screening criteria for solid state hydrogen storage. Adopting an automotive engineering point of view, four important, but often neglected, issues are discussed: 1) volumetric storage capacity, 2) heat transfer for desorption, 3) recharging at low temperatures and 4) cold start of the vehicle. The article shall help to understand the requirements and support the research community when screening new materials.     

Method to release hydrogen from ammonia borane for portable fuel cell applications

Ammonia borane (AB, NH₃BH₃) is considered to be a promising hydrogen storage material as it contains 19.6 wt% hydrogen. It is difficult, however, to release hydrogen from AB. Thermolysis, catalytic hydrolysis and heat generated by additional reactive mixtures are usually employed, but these methods have disadvantages that limit their use for portable applications. In this paper, we demonstrate a new approach to release hydrogen, which does not require any catalyst and produces relatively high hydrogen yield and environmentally benign byproducts. It involves nano-aluminum (nAl)/water combustion reaction, which provides heat for AB dehydrogenation and releases additional hydrogen from water. To facilitate higher H₂ yield from thermolysis, as compared to hydrolysis, AB is spatially separated from the nAl/water mixture using a concentric cylindrical container. The effect of the container design on hydrogen generation is studied and optimized. This study also includes transient temperature and pressure measurements, and product characterization using mass spectrometer and ¹¹B NMR. This approach provides H₂ yield up to 9.5 wt% on material basis. Our experimental results and analysis show that a proposed power source based on this method is promising for portable electronic devices.     

Hydrogen from aluminium in a flow reactor for fuel cell applications

Aluminium appears to be a promising material for on-board hydrogen generation in fuel cell applications given the comparatively large amount of hydrogen produced per gram of aluminium in a safe system. A microfuel processor with aluminium and water as reactants is developed in a flow reactor for application in portable power sources. Two types of reactor are used. One reactor permits the direct feeding of liquid water in channels containing aluminium pellets, whereas the other utilizes the heat produced from the reaction to vapourize liquid water before entry into the reactor. Two additives, namely, calcium oxide (CaO) and sodium hydroxide (NaOH), are used to enhance the reaction rate. A maximum conversion of 78.6% with respect to aluminium is achieved when the water entering in the reactor is vapourized partially. In the case of liquid water entering the reactor, the conversion is 74.4%.     

Cycling and engineering properties of highly compacted sodium alanate pellets

Sodium alanate powder comprised of NaH and Al was doped with 3 mol% titanium chloride (TiCl₃) and pelletized into highly compacted cylindrical pellets. The pelletization process was performed to improve thermal conductivity and volumetric hydrogen capacity of the metal hydride, compared to loose or tapped powder, which are vital requirements for on-board hydrogen storage applications. The pelletization process was performed over a range of 69–345 MPa (10–50 kPSI) with a 95% increase in density and improvement in thermal conductivity 18 times greater compared to powder at the maximum pelletization pressure (1.60 g/cm³ and 0.82 g/cm³; 9.09 W/m K and 0.50 W/m K, respectively). Hydrogen cycling capacities and kinetics were not adversely affected by the pelletization process although 10 cycles are required to obtain full hydrogen capacity. Pellet cycling capacity maintained a stable 4 wt% H₂ over 50 cycles. Ti-doped NaH + Al pellets exhibited similar thermal cycling expansion as with the loose powder; within 30 cycles there was a 50% loss in pellet density and by 50 cycles the loss in pellet structural integrity made handling problematic.     

Experimental investigation of a liquid cooled high temperature proton exchange membrane (HT-PEM) fuel cell coupled to a sodium alanate tank

In high temperature proton exchange membrane (HT-PEM) fuel cells, waste heat at approximately 160 °C is produced, which can be used for thermal integration of solid state hydrogen storage systems. In the present study, an HT-PEM fuel cell stack (400 W) with direct liquid cooling is characterized and coupled to a separately characterized sodium alanate storage tank (300 g material). The coupled system is studied in steady state for 20 min operation and all relevant heat flows are determined. Even though heat losses at that specific power and temperature level cannot be completely avoided, it is demonstrated that the amount of heat transferred from the fuel cell stack to the cooling liquid circuit is sufficient to desorb the necessary amount of hydrogen from the storage tank. Furthermore, it is shown that the reaction rate of the sodium alanate at 160 °C and 1.7 bar is adequate to provide the hydrogen to the fuel cell stack. Based on these experimental investigations, a set of recommendations is given for the future design and layout of similar coupled systems.     

Modelization of hybrid systems with hydrogen and renewable energy oriented to electric propulsion in sailboats

This paper presents a conceptual model of a hybrid electric sailboat in which energy from electric grid is stored in batteries and energy from renewable energies (eolic, solar and hydro) is stored as hydrogen. The main objective of this model is to study the viability of electrifying traditional sailboats with internal combustion engines into hybrid systems with batteries and fuel cell. The most important advantage of this design is the possibility to reduce up to zero emissions of traditional sailboat. Conversion of renewable energy to hydrogen is performed through an electrolyzer and post conversion to energy is carried out by a fuel cell. The fuel cell with the batteries forms the hybrid system (batteries-fuel cell) for propulsion electrical energy supply. In order to model the boat dynamic and energy systems, modular mathematical models were developed under Matlab^®-Simulink^®, using a fixed-step solver for the simulation of global model. A simulated logic controller manages the global model. In this paper, many models have been used: some of them are based in literature models and others were developed from experimental data. A control strategy has also been developed to manage energy flows and then it has been embedded to Matlab^® language. The global model permits test the performance of the sailboat.     

Experimental evaluation of a passive fuel cell/battery hybrid power system for an unmanned ground vehicle

Unmanned vehicles are increasing the performance of monitoring and surveillance in several applications. Endurance is a key issue in these systems, in particular in electric vehicles, powered at present mainly by batteries. Hybrid power systems based on batteries and fuel cells have the potential to achieve high energy density and specific energy, increasing also the life time and safe operating conditions of the power system. The objective of this research is to analyze the performance of a passive hybrid power system, designed and developed to be integrated into an existing Unmanned Ground Vehicle (UGV). The proposed solution is based on six LiPo cells, connected in series, and a 200 W PEM fuel cell stack, directly connected in parallel to the battery without any limitation to its charge. The paper presents the characterization of the system behavior, and shows the main results in terms of performance and energy management.     

Off-grid solar powered charging station for electric and hydrogen vehicles including fuel cell and hydrogen storage

This paper designs an off-grid charging station for electric and hydrogen vehicles. Both the electric and hydrogen vehicles are charged at the same time. They appear as two electrical and hydrogen load demand on the charging station and the charging station is powered by solar panels. The output power of solar system is separated into two parts. On part of solar power is used to supply the electrical load demand (to charge the electric vehicles) and rest runs water electrolyzer and it will be converted to the hydrogen. The hydrogen is stored and it supplies the hydrogen load demand (to charge the hydrogen-burning vehicles). The uncertainty of parameters (solar energy, consumed power by electrical vehicles, and consumed power by hydrogen vehicles) is included and modeled. The fuel cell is added to the charging station to deal with such uncertainty. The fuel cell runs on hydrogen and produces electrical energy to supply electrical loading under uncertainties. The diesel generator is also added to the charging station as a supplementary generation. The problem is modeled as stochastic optimization programming and minimizes the investment and operational costs of solar and diesel systems. The introduced planning finds optimal rated powers of solar system and diesel generator, operation pattern for diesel generator and fuel cell, and the stored hydrogen. The results confirm that the cost of changing station is covered by investment cost of solar system (95%), operational cost of diesel generator (4.5%), and investment cost of diesel generator (0.5%). The fuel cell and diesel generator supply the load demand when the solar energy is zero. About 97% of solar energy will be converted to hydrogen and stored. The optimal operation of diesel generator reduces the cost approximately 15%.