Current status of combined systems using alkaline fuel cells and ammonia as a hydrogen carrier

In order to solve the hydrogen storage problem ammonia is considered as a storage compound. Hydrogen is supplied by a cracking process. According to equilibrium conditions traces of ammonia are expected, which are known to negatively affect PEM-based fuel cells. Experiments with alkaline fuel cells were carried out. No negative effects on the cell performance were found, when the feed gas contained low concentrations of ammonia.     

Forced ventilation for sensing-based risk mitigation of leaking hydrogen in a partially open space

This study performs the numerical simulation of hydrogen dispersion in a partially open space with a single roof vent. The effects of various roof vent positions, leak positions, leak flow rates and exhaust flow rates on the forced ventilation of leaking hydrogen, are shown and discussed. Based on the results, a proper roof vent position and the disadvantage of ventilation with constant exhaust flow rates are established. To overcome the disadvantage, a new control strategy to change exhaust flow rates with the roof vent fixed at the proper position is proposed. First a plot is constructed to show acceptable exhaust flow rates to various inflow rates and leak positions. Assuming real-time sensing of hydrogen concentration and height-direction velocity, volume flow rates of leaking hydrogen are then estimated. Based on the estimated leak flow rates and hydrogen sensor information near the roof, control is conducted considering the plot of acceptable exhaust flow rates to various inflow rates and leak positions. The proposed method is validated against various leak positions, leak flow rates and leak modes. This paper proposes an innovative approach to sensing-based risk mitigation control of hydrogen dispersion and accumulation in a partially open space by forced ventilation.     

Palladium-polyelectrolyte hybrid nanoparticles for hydrogen sensor in fuel cells

We prepared palladium-polyelectrolyte hybrid nanoparticles by using a metallization of polyelectrolyte. In this study, we selected polyacrylic acid (PAA) as a polyelectrolyte and reduced the palladium ions on the PAA by using ascorbic acids in order to form a unique spherically shaped mosslike hybrid nanoparticle. Palladium (Pd) can absorb hydrogen to become PdH_x, and the storage of hydrogen increases the electrical resistance and volume of Pd materials. The use of this material is attracting growing interest as a reliable, cheap, ultracompact, and safe hydrogen sensor for use in fuel cells. We showed the utilization of the Pd-PAA hybrid nanoparticles as a highly sensitive hydrogen sensor that exhibited a switch response depending on volume expansion in a cyclic atmosphere exchange.     

A self-regulating hydrogen generator for micro fuel cells

The ever-increasing power demands and miniaturization of portable electronics, micro-sensors and actuators, and emerging technologies such as cognitive arthropods have created a significant interest in development of micro fuel cells. One of the major challenges in development of hydrogen micro fuel cells is the fabrication and integration of auxiliary systems for generating, regulating, and delivering hydrogen gas to the membrane electrode assembly (MEA). In this paper, we report the development of a hydrogen gas generator with a micro-scale control system that does not consume any power. The hydrogen generator consists of a hydride reactor and a water reservoir, with a regulating valve separating them. The regulating valve consists of a port from the water reservoir and a movable membrane with via holes that permit water to flow from the reservoir to the hydride reactor. Water flows towards the hydride reactor, but stops within the membrane via holes due to capillary forces. Water vapor then diffuses from the via holes into the hydride reactor resulting in generation of hydrogen gas. When the rate of hydrogen consumed by the MEA is lower than the generation rate, gas pressure builds up inside the hydride reactor, deflecting the membrane, closing the water regulator valve, until the pressure drops, whereby the valve reopens. We have integrated the self-regulating micro hydrogen generator to a MEA and successfully conducted fuel cell tests under varying load conditions.     

A mini-type hydrogen generator from aluminum for proton exchange membrane fuel cells

A safe and simple hydrogen generator, which produced hydrogen by chemical reaction of aluminum and sodium hydroxide solution, was proposed for proton exchange membrane fuel cells. The effects of concentration, dropping rate and initial temperature of sodium hydroxide solution on hydrogen generation rate were investigated. The results showed that about 38 ml min⁻¹ of hydrogen generation rate was obtained with 25 wt.% concentration and 0.01 ml s⁻¹ dropping rate of sodium hydroxide solution. The cell fueled by hydrogen from the generator exhibited performance improvement at low current densities, which was mainly due to the humidified hydrogen reduced the protonic resistivity of the proton exchange membrane. The hydrogen generator could stably operate a single cell under 500 mA for nearly 5 h with about 77% hydrogen utilization ratio.     

Electrochemical analysis of hydrogen membrane fuel cells

An electrochemical analysis was conducted with respect to a hydrogen membrane fuel cell with SrZr_0.8In_0.2O_3−δ electrolyte, which is a new type of fuel cell featuring an ultra-thin proton conductor supported on a dense metal anode. Most of the voltage loss derives from the cathode and the electrolyte, and a small amount of anode polarization was observed only in regions with high current density. The cathode polarization was approximately an order of magnitude lower than that of SOFCs. Furthermore, the conductivity of the film electrolyte was almost identical to that of the sinter at 600 °C; however, it was several times as large at 400 °C. A TEM micrograph revealed that the film electrolyte consists mainly of long columnar crystals, and this crystal structure can be related to the conductivity enhancement below 600 °C.     

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.     

Comparative risk assessment with focus on hydrogen and selected fuel cells: Application to Europe

In this study, a first-of-its-kind comparative risk assessment is presented for accidents in the energy sector in EU28 with focus on hydrogen (H₂) and selected fuel cells, namely proton exchange membrane (PEM), phosphoric acid (PAFC), alkaline (AFC) and molten carbonate (MCFC) fuel cells. The analysis is based on PSI's well-established framework for comparative risk assessment, using available historical experience from its ENergy-related Severe Accident Database (ENSAD). For H₂, the technological risks are first identified and characterized to set up the so-called H₂ ENSAD, a subset of ENSAD including historical observations related only to H₂ accidents only. Afterwards risk indicators, namely fatality rate and maximum consequence, have been estimated for H₂ and selected fuel cells, and then compared to fossil fuels, hydro-power and selected new renewable technologies. H₂ and selected fuel cells showed fatality rates lower than natural gas, whereas maximum consequences were similar to other new renewables.     

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.     

Development of a high-efficiency hydrogen generator for fuel cells for distributed power generation

A collaborative effort between Intelligent Energy and Cal Poly Pomona has developed an adsorption enhanced reformer (AER) for hydrogen generation for use in conjunction with fuel cells in small sizes. The AER operates at a lower temperature (about 500 °C) and has a higher hydrogen yield and purity than those in the conventional steam reforming. It employs ceria supported rhodium as the catalyst and potassium-promoted hydrotalcites to remove carbon dioxide from the products. A novel pulsing feed concept is developed for the AER operation to allow a deeper conversion of the feedstock to hydrogen. Continuous production of near fuel-cell grade hydrogen is demonstrated in the AER with four packed beds running alternately. In the best case of methane reforming, the overall conversion to hydrogen is 92% while the carbon dioxide and carbon monoxide concentrations in the production stream are on the ppm level. The ratio of carbon dioxide in the regeneration exhaust to the one in the product stream is on the order of 10³.     

Design of fuel cell systems laboratory for hydrogen,carbon monoxide and hydrocarbon safety

As research and development efforts in the area of fuel cells and hydrogen based energy accelerate, a large number of accidents have occurred in research laboratories. In this context, a design methodology for a simple, scaleable, modular and human-independent system for hydrogen, carbon monoxide and hydrocarbon safety in research laboratories is valuable. We have designed, developed and operationalized such a system in a pre-existing generic laboratory space. In this paper, we provide details of the mechanical, electrical and control aspects of this laboratory. We use CFD analysis to design a ventilation system, and to locate gas detectors for optimum detection time. The gas detectors, actuators, a real-time controller and other electrical components are part of a safety monitoring system that continuously gathers information, processes this information and takes appropriate action to safeguard personnel and equipment in real time. This fully operational safety laboratory is now a University-level research hub for all fuel cell (and other energy related) research activities, and is also one of a kind in the region. We also expect that the experience gained in this endeavor will be useful to other researchers in building a safe workplace.     

Electrochemical hydrogen storage: Opportunities for fuel storage,batteries, fuel cells,and supercapacitors

Solid-state storage of hydrogen is a possible breakthrough to realise the unique futures of hydrogen as a green fuel. Among possible methods, electrochemical hydrogen storage is very promising, as can be conducted at low temperature and pressure with a simple device reversibly. However, it has been overshadowed by the physical hydrogen storage in the literature, and thus, research efforts are not adequately connected to lead us in the right direction. On the other hand, electrochemical hydrogen storage is the basis of some other electrochemical power sources such as batteries, fuel cells, and supercapacitors. For instance, available hydrogen storage materials can build supercapacitors with exceptionally high specific capacitance in order of 4000 F g^?1. In general, electrochemical hydrogen storage plays a substantial role in the future of not only hydrogen storage but also electrochemical power sources. There are some vague points which have obscured our understanding of the corresponding system to be developed practically. This review aims to portray the entire field and detect those ambiguous points which are indeed the key obstacles. It is clarified that different materials have somehow similar mechanisms for electrochemical hydrogen storage, which is initiated by hydrogen dissociation, surface adsorption and probably diffusing deep within the bulk material. This mechanism is different from the insertion/extraction of alkali metals, though battery materials look similar. Based on the available reports, it seems that the most promising material design for the future of electrochemical hydrogen storage is a class of subtly designed nanocomposites of Mg-based alloys and mesoporous carbons.     

Diagnosis of hydrogen crossover and emission in proton exchange membrane fuel cells

When hydrogen leaks through holes in membrane-electrode assemblies (MEAs) in proton exchange membrane (PEM) fuel cells, it recombines directly with air. This recombination results in a reduction in oxygen concentration on the cathode side of the MEA. In this paper, the signatures of electrochemical impedance spectroscopy (EIS) are analyzed in different multi-cell stack configurations to show the relation between hydrogen leak rate and reduced oxygen concentrations. The reduction in concentration was made by mixing oxygen with nitrogen at different rates, and the increase in hydrogen leak rate was made by controlling the differential pressure (dP) between anode and cathode. To analyze the impedance signatures, we fit the data of oxygen concentration and dP with the parameters of a Randles circuit. The correlation between the parameters of the two data sets allows us to understand the change in impedance signatures with respect to reduction of oxygen in the cathode side. To have a better insight on the effect of insufficient oxygen at the cathode, a model that establishes a relationship between impedance and voltage was considered. Using this model along with the impedance signatures we were able to detect the reduction of oxygen concentrations at the cathode with the help of fuzzy rule-base. However, resolution of detection was reduced with the reduction of leak rate and/or increases in the stack cell count.     

Diagnosis of hydrogen crossover and emission in proton exchange membrane fuel cells

When hydrogen leaks through holes or cracks in membrane-electrode assemblies (MEAs) in Proton Exchange Membrane (PEM) fuel cells, it recombines directly with air. This recombination results in a reduction in oxygen concentration on the cathode side of the MEA. In this paper, the signatures of electrochemical impedance spectroscopy (EIS) are analyzed in different multi-cell stack configurations to show the relation between hydrogen leak rate and reduced oxygen concentrations. The reduction in concentration was made by mixing oxygen with nitrogen at different rates, and the increase in hydrogen leak rate was made by controlling the differential pressure (dP) between anode and cathode. To analyze the impedance signatures, we fit the data of oxygen concentration and dP with the parameters of a Randles circuit. The correlation between the parameters of the two data sets allows us to understand the change in impedance signatures with respect to reduction of oxygen in the cathode side. To have a better insight on the effect of insufficient oxygen at the cathode, a model that establishes a relationship between impedance and voltage was considered. Using this model along with the impedance signatures we were able to detect the reduction of oxygen concentrations at the cathode with the help of fuzzy rule-base. However, resolution of detection was reduced with the reduction of leak rate and/or increases in the stack cell count.     

Projections of the price of hydrogen fuel

The concept of remote solar plant giving piped hydrogen fuel is gaining strength with the likelihood of realization. Electricity (in 1977 U.S. $) for use in electrolysis with a 50 per cent load factor at the producing plant would be 1 cent/kWh now, and 1.5 cents (still 1977$) in 1985. Potential will be 1.5 V. Cost of 1 MBTU will be in the region of $5 (electrolysis). Photovoltaic electricity using Fresnel concentration and heat exchangers should cost 1 cent/kWh. H₂ transport costs should be some 1 mill/1000 km. Examination of ten approaches gives a maximum hydrogen cost of $9/MBTU, a likely value of $5, and speculative laboratory possibilities which could give $1/MBTU.     

Optimization of hydrogen feeding procedure in PEM fuel cell systems for transportation

The hydrogen feeding sub-system is one of balance of plant (BOP) components necessary for the correct operation of a fuel cell system (FCS). In this paper the performance of a 6 kW PEM (Proton Exchange Membrane) FCS, able to work with two fuel feeding procedures (dead-end or flow-through), was experimentally evaluated with the aim to highlight the effect of the anode operation mode on stack efficiency and durability. The FCS operated at low reactant pressure (<50 kPa) and temperature (<330 K), without external humidification. The experiments were performed in both steady state and dynamic conditions. The performance of some cells in dead-end mode worsened during transient phases, while a more stable working was observed with fuel recirculation. This behavior evidenced the positive role of the flow-through procedure in controlling flooding phenomena, with the additional advantage to simplify the management issues related to hydrogen purge and air stoichiometric ratio. The flow-through modality resulted a useful way to optimize the stack efficiency and to reduce the risks of fast degradation due to reactant starvation during transient operative phases.     

Analysis of Ontario's hydrogen economy demands from hydrogen fuel cell vehicles

The ‘Hydrogen Economy’ is a proposed system where hydrogen is produced from carbon dioxide free energy sources and is used as an alternative fuel for transportation. The utilization of hydrogen to power fuel cell vehicles (FCVs) can significantly decrease air pollutants and greenhouse gases emission from the transportation sector. In order to build the future hydrogen economy, there must be a significant development in the hydrogen infrastructure, and huge investments will be needed for the development of hydrogen production, storage, and distribution technologies. This paper focuses on the analysis of hydrogen demand from hydrogen FCVs in Ontario, Canada, and the related cost of hydrogen. Three potential hydrogen demand scenarios over a long period of time were projected to estimate hydrogen FCVs market penetration, and the costs associated with the hydrogen production, storage and distribution were also calculated. A sensitivity analysis was implemented to investigate the uncertainties of some parameters on the design of the future hydrogen infrastructure. It was found that the cost of hydrogen is very sensitive to electricity price, but other factors such as water price, energy efficiency of electrolysis, and plant life have insignificant impact on the total cost of hydrogen produced.     

Hydrolysis reaction of ball-milled Mg-metal chlorides composite for hydrogen generation for fuel cells

In this paper, the hydrolysis properties for hydrogen generation by Mg-metal chlorides composites in pure water are investigated. The composites were prepared by high energy ball milling. It is found that the Mg-metal chlorides composites are very promising for hydrogen generation by hydrolysis reaction. The micro-galvanic cell formed by Mg and the other metal which produced by replacement reaction occurred during the ball-milling process is very effective for improving the hydrolysis reactivity. Based on the investigations of different kinds of chlorides additives, it is found that the Mg-10 wt% FeCl₃ composite ball-milled for 30 min has the best hydrolysis properties with an initial hydrogen generation rate of 1479.1 ml*g⁻¹ min⁻¹ and a theoretical hydrogen production yield of 98% in 2 min.