Regenerative Fuel Cell System Research Articles

(Invited) Regenerative Fuel Cell System Utilizing a High Differential Pressure Water Electrolysis Technology

The expansion of manned activities in space requires energy system technology that utilizes sunlight, and hydrogen fuel cells are one such means. By electrolyzing water with sunlight, energy is stored with oxygen and hydrogen, and electricity is generated by fuel cells. The generated water can be recycled, and energy can be stored and supplied without external replenishment. This is commonly called a regenerative fuel cell. In the space domain, such energy systems must be compact and lightweight, and gas must be stored under high pressure. However, mechanical compressors that are generally used for compressing are heavy, and there are also issues of vibration and noise.Since the 1990s, Honda has worked on the development of high-differential-pressure water electrolysis technology that generate hydrogen from renewable energy and compress without a mechanical compressor, in parallel with the development of fuel cell technology. High-differential-pressure water electrolysis is a technology that generates high pressure hydrogen by moving the protons generated by electrolysis to the cathode through the Proton exchange membrane (PEM) . The energy required is only the potential generated by the difference in hydrogen concentration, which is superior to small mechanical compressors whose efficiency is reduced by friction loss. However, a large differential pressure is generated across the PEM because only one side is at a high pressure. Honda has achieved a maximum pressure increase of 70 MPa by using its own structure. Moreover, this principle can be applied not only to the generation and pressurization of hydrogen, but also to oxygen. Honda is working on the development of RFC technology that integrates these hydrogen technologies with the aim of applying them not only to sustainability on Earth, but also to the space domain. Currently, we are undertaking a JAXA project and are promoting the production of a breadboard model.The feature of Honda's RFC technology is that it applies high-differential-pressure water electrolysis technology, not only to generate oxygen and hydrogen, but also to pressurize each gas. By not using a mechanical compressor, it is possible to downsize the system, and it is also no vibration or noise. Utilizing the characteristics of this technology, we are planning to build an energy system that can store energy at high density and apply it to various manned missions.Honda's RFC consists of the high-differential-pressure water electrolysis system that simultaneously electrolyzes water and pressurizes oxygen, a Electrochemical hydrogen compressor system (EHC system) that electrochemically pressurizes the hydrogen and a fuel cell system. In the electrolysis stack, oxygen is generated and compressed to the target pressure by the differential pressure water electrolysis. The generated hydrogen is sent to the EHC stack that also applies the technology of high-differential pressure water electrolysis, where the hydrogen is pressurized. As a result, both oxygen and hydrogen gases were generated and compressed without a mechanical compressor. For the fuel cell system, the compact and highly efficient fuel cell technology that has been developed for FCVs is applied. When the fuel cell is used on the ground, oxygen is supplied from the atmosphere, but in space RFC it is necessary to generate electricity using pure oxygen and to circulate the system. A dedicated circulating FC system was constructed to achieve stable power generation. The water produced by power generation is used in the next water electrolysis cycle, and the proof of principle as RFC has been completed. In addition to these basic functions, for space application, we must address issues not found on Earth, such as heat management in a vacuum, radiation, and vibrations during launch. Starting with the lunar exploration mission scheduled for 2030, Honda will develop this technology for the spread of manned activities. Figure 1

Characterization of bipolar plates manufactured with various Pb/C ratios for unitized regenerative fuel cell system.

The weight reduction of the bipolar plate (BP) is essential for commercializing unitized regenerative fuel cells (URFCs). In order to lighten the weight of the bipolar plate, we have used Pb/C composite powder as a cost-effective primary material, which is a mixture of low-density graphite and lead. Further, varied lead-carbon weight ratios (1: 8, 1:4, 1:1, 4:1, and 8:1) were investigated for fabricating the bipolar plate by hot-pressing process adding styrene-butadiene rubber (SBR) as a binder. The specific surface area, porosity, and microstructure characteristics corresponding to the varied lead-graphite ratio of the prepared bipolar plates were studied. The relative difference in conductivity upon the compressibility of the plates is also examined. Finally, the wettability and electrochemical properties of the prepared bipolar plates were evaluated through water contact angle and cyclic voltammetry analysis.

Application of Fuel Cells in Energy Storage

Based on a technology that separates power conversion and energy storage, fuel cell energy storage enables each function to be separately tuned for performance, cost, or other key variables. This capacity to tune every component of an energy storage system might provide considerable advantages for many uses. Here, different fuel cell-based energy storage systems are discovered that use hydrogen as the energy storage medium. Electrolyzes are fully regenerative fuel cell systems that are relevant for Polymer Electrolyte Membrane (PEM) fuel cells. The technological and product development status of these systems and the state of various hydrogen storage technology choices will be discussed.

Exergy Analysis of Electrochemical Systems for Space Exploration

Human exploration of space, facilitated by electrochemical systems, will require integration of many seemingly disparate systems including but not limited to power systems, in situ resource utilization (ISRU), and environmental control and life support (ECLS). Through combining expressions of the First and Second Laws of Thermodynamics exergy quantifies the useful work that can be obtained from a system, subject to environmental limitations. This approach provides a means of integrating diverse systems and components based on one consistent and physically meaningful property: exergy. Using this property as a basis, diverse systems can be analyzed and integrated effectively based on the exergy destruction and exergy efficiency. Here, the applicability of exergy analysis to systems design and integration is demonstrated through two examples involving electrochemical systems that support human space exploration.First, analysis of the ECLS system aboard the International Space Station (ISS) is conducted to assess its overall performance in terms of exergy destruction rates and exergy efficiency. The ECLS system is divided into constituent subsystems which are further divided into key components. Based on this system decomposition, exergy balances are derived for each component and subsystem. Special focus is given to the Oxygen Generation Assembly (OGA) within the ECLS Atmospheric Revitalization Subsystem. The results of parametric studies of the OGA proton exchange membrane electrolyzer performance are presented with an emphasis on the impacts of operational conditions on exergy efficiency. This electrolyzer is a significant contributor to system exergy destruction and exhibits a low exergetic efficiency. It therefore presents an opportunity for improving overall ECLS system performance.Following the example of ECLS exergy analysis, the application of exergy analysis to the integration of power and ISRU systems for lunar exploration is presented through system level models. Exergy destruction and efficiency are quantified over the lunar diurnal cycle for power and ISRU systems. The power systems analysis focuses on photovoltaic arrays paired with battery and regenerative fuel cell systems. The ISRU system analysis focuses on production of oxygen from lunar regolith through the reduction of ilmenite combined with water electrolysis. Here the application of exergy analysis identifies key opportunities for the use of byproduct heat and the optimal sizing of system components.The studies presented demonstrate the capability of exergy analysis to support the design and integration of electrochemical systems within larger power, ISRU, and ECLS systems supporting space exploration. This approach can enable the full and efficient use of a system’s available work potential based on a consistent, physically meaningful property. Therefore, exergy analysis is shown to be a key tool for the future design and integration of electrochemical systems for space exploration.

A new strategy of carbon – Pb composite as a bipolar plate material for unitized regenerative fuel cell system

In this study, we investigated the possibilities and combination of cost-effective materials of carbon (C) and lead (Pb) with polypropylene (PP) polymer as a new kind of bipolar plate for unitized regenerative fuel cell and polymer electrolyte membrane fuel cell systems. The homogeneous composite structure of C:Pb developed through facile mechanical milling process, and optimized. The new bipolar plate was fabricated with PP using compression molding process with hot pressing techniques. A dense and smooth surface morphology of C:Pb bipolar plate was acquired with the uniform thickness of 1.33 (±0.17) mm. Compared to C, an improved electrical properties (~20%) obtained to the powdered C:Pb composite materials because of homogeneous composition of Pb metal particles with large surface area of C. The C:Pb bipolar plate revealed an efficient water contact angle behavior than the C bipolar plate, where the water contact angle for C and C:Pb bipolar plates are 82.4° and 93.1°, respectively. A sophisticated electrochemical stability performance has obtained to the C:Pb bipolar plate in acidic condition. According to Tafel plots analysis, higher corrosion resistance has observed to the C:Pb bipolar plate than the C bipolar plate. The fabricated new kind of C:Pb bipolar plate provides the many advantageous, thus it proves the insights for further developments and applicability in the practical application. In the perspective view, the performances of C:Pb bipolar plate can be further altered through modification of different carbon structures together with impregnation of Pb nanostructured materials into the pores and/or embedded throughout the surface, and efficient conductive polymers.

(Invited) Highly Stable Nanocarbon Catalysts for Reversible Energy Storage and Conversion Via Oxygen Electrocatalysis

Energy conversion and storage via direct electrochemical oxidation and reduction processes, such as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), can provide a clean, efficient, and economically viable means of meeting this sustainability challenge, by allowing stored renewable energy to be reliably delivered where and when it is needed. During the development of the highly demanded nonprecious metal catalysts to replace precious metals for these applications, carbon catalysts have many advantages over metal oxides, including excellent electrical conductivity, high surface area, and easy functionalization. However, most carbon-based catalysts suffer from poor activity and stability for the more challenging OER under a highly oxidative conditions. This represents one of grand challenges in energy conversion research societies.For the first time, this work demonstrated that a new class of large-diameter tubular nanocarbon (>500 nm in diameter) catalyst is capable of catalyzing both the ORR and the OER with activity comparable to Pt and exceeding Ir, respectively, for these two reactions. Most importantly, the tube catalyst exhibited good stability upon cycling across a wide potential window (0 to 1.9 V vs RHE) in 0.1 M NaOH electrolyte. The high OER activity was verified using well-designed electrochemical tests, demonstrating that the current generated during the OER arose solely from oxygen evolution, rather than carbon oxidation. This is the first example of such excellent OER activity and durability of a nanostructured carbon-based electrocatalyst across the complete ORR-OER potential window. The newly developed carbon tubes were synthesized via a one-step template-free graphitization process using inexpensive dicyandiamide (DCDA) precursor as carbon/nitrogen source and a ternary FeCoNi alloy as a catalyst. Generation of a mixed metal catalyst, i.e., FeCoNi during the graphitization process is the key factor to yield the largest tube size for maximum electrochemically accessible surface areas, dominant graphitic nitrogen doping, and thicker tube walls, which are associated with the significantly improved activity and durability. The cost effective, easily scalable, single step and environmentally benign synthesis procedure further favors this nanocarbon’s application as a practical bifunctional electrocatalyst for the ORR and OER, with potential to advance the development and commercialization of regenerative fuel cell systems and rechargeable metal-air batteries. The use of nanostructured carbon as bifunctional ORR/OER catalysts will open up new research direction in this field and further advance the role of carbon nanomaterials in oxygen electrocatalysis for energy conversion and storage.

System analysis of a Moon base at the south pole: Considering landing sites, ECLSS and ISRU

The objective of this paper is to perform an in-depth feasibility analysis and dimensioning of a potential Environmental Control and Life Support System (ECLSS) and power system for a crewed lunar base at the lunar south pole. The analyzed ECLSS includes an In-Situ Resource Utilization (ISRU) reactor for oxygen resupply and a Regenerative Fuel Cell System (RFCS) as power supply during shadow phases. The co-dependencies and interactions between the ECLSS sub-systems themselves and with the environment are incorporated to achieve a holistic system analysis. We used a fixed ECLSS configuration based on the current NASA plans for a Moon base ECLSS with a fixed function-to-subsystem allocation. The performed trade-offs are then restricted within the design space, to e.g. resize tanks and individual subsystems instead of considering other possible subsystems. We chose this approach because the aim of this paper is to perform an in-depth system analysis of all related subsystems and their interaction with the environment instead of a top-level trade-off.The first step is the selection of a suitable landing site and the dynamic simulation of its lighting conditions over the investigated period of 1 year. We use a slope map with a resolution of 120 m per pixel, a Permanently Shaded Region (PSR) map with a resolution of 240 m per pixel and a digital elevation model with a resolution of 240 m per point, which is interpolated from a source with a resolution of 60 m per pixel and meshed with triangles by the Thermal Moon Simulator (TherMoS) tool in order to calculate illumination values. The requirements chosen for the candidate landing sites are a slope of less than 5° over a diameter of at least 1 km and having both a PSR and a Peak of Light (POL) in less than 10 km distance. We discuss the four most promising candidate sites in this paper and calculate initial energy storage system estimates to select two landing sites for further analysis.We derive a reaction kinetics model for the ilmenite hydrogen reduction ISRU process from literature data and incorporate it into a dynamic model with simulated lighting and thermal conditions to calculate heat losses to the environment and the required electrical energy for its operation. In addition, we use the derived model to analyze and compare different design options of the ISRU reactor with an Equivalent System Mass (ESM) based optimization approach to identify the optimal operating conditions. Using this approach, we found operating temperatures above 1150 K resulted in higher ESM values for the reactor than lower temperatures.For the Moon base, we combine an ISS ECLSS model and the ISRU reactor model. The state-of-the-art urine and water processing technologies achieve recovery rates of up to 98%. Hence, we expect the overall ECLSS including the ISRU reactor to have a water surplus when combined with a Sabatier reactor to process metabolic CO2 from the crew into methane and water. Therefore, the Sabatier reactor combined with an electrolyzer can potentially generate methane and oxygen as fuel for resupply missions. The system can achieve a theoretic fuel production of 4100 kg per year using this approach. Although the dynamic analysis showed that only 2588 kg could be produced per year because of the lean operating conditions of the Sabatier and its efficiency of below 100%. The produced oxygen and methane could reduce operating costs for the base by reducing the required fuel resupply. Based on the power demands of the other subsystems and the available solar power and shadow duration at the selected landing site, we dimensioned the RFCS and estimate the required mass for it to 19,500 kg. Which is less than half the mass required if lithium batteries are used. The overall system requires resupply of approximately 6580 kg per year for a crew of six. The dynamic analysis of the system showed that the initial mostly steady state sizing approach can be optimized and relevant system parameters can be reduced by more than 15%.

Experimental analysis of the performance characteristics of the regenerative fuel cell system based on serpentine flow-field design

The energy demand has recently been increasing dramatically; thus, it is evident that scientists worldwide need to find out the solution to solve the above problem. Among these technologies, solar and wind power energy are the most potential source as alternatives to fossil fuels. However, these energy sources are not continuous and are therefore considered as additional sources. A regenerative fuel cell (RFC) is a type of fuel cell that can function as an electrolyzer and fuel cell; therefore, this system is an independent power source and overcome the drawbacks of the original fuel cell system. This research has built a system to control the entire regenerative fuel cell system’s flow, temperature, and energy. The system uses electricity to produce hydrogen and oxygen for storage; when the electrical power is insufficient, the system can automatically reverse the operation using hydrogen and oxygen to create electrical energy. The result showed that the power density in fuel cell mode ranges from 0.1 to 0.69W/cm2 in the fuel cell mode, and the flow rate of hydrogen and oxygen reaches a stable value of 1100 and 2200 ml/min after 10 minutes, respectively.

(Invited) Nanocarbon Catalysts for Reversible Energy Storage and Conversion Via Oxygen Electrocatalysis

Energy conversion and storage via direct electrochemical oxidation and reduction processes, such as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), can provide a clean, efficient, and economically viable means of meeting this sustainability challenge, by allowing stored renewable energy to be reliably delivered where and when it is needed. During the development of the highly demanded nonprecious metal catalysts to replace precious metals for these applications, carbon catalysts have many advantages over metal oxides, including excellent electrical conductivity, high surface area, and easy functionalization. However, most carbon-based catalysts suffer from poor activity and stability for the more challenging OER under a highly oxidative conditions. This represents one of grand challenges in energy conversion research societies.For the first time, this work demonstrated that a new class of large-diameter tubular nanocarbon (>500 nm in diameter) catalyst is capable of catalyzing both the ORR and the OER with activity comparable to Pt and exceeding Ir, respectively, for these two reactions. Most importantly, the tube catalyst exhibited good stability upon cycling across a wide potential window (0 to 1.9 V vs RHE) in 0.1 M NaOH electrolyte. The high OER activity was verified using well-designed electrochemical tests, demonstrating that the current generated during the OER arose solely from oxygen evolution, rather than carbon oxidation. This is the first example of such excellent OER activity and durability of a nanostructured carbon-based electrocatalyst across the complete ORR-OER potential window. The newly developed carbon tubes were synthesized via a one-step template-free graphitization process using inexpensive dicyandiamide (DCDA) precursor as carbon/nitrogen source and a ternary FeCoNi alloy as a catalyst. Generation of a mixed metal catalyst, i.e., FeCoNi during the graphitization process is the key factor to yield the largest tube size for maximum electrochemically accessible surface areas, dominant graphitic nitrogen doping, and thicker tube walls, which are associated with the significantly improved activity and durability. The cost effective, easily scalable, single step and environmentally benign synthesis procedure further favors this nanocarbon’s application as a practical bifunctional electrocatalyst for the ORR and OER, with potential to advance the development and commercialization of regenerative fuel cell systems and rechargeable metal-air batteries. The use of nanostructured carbon as bifunctional ORR/OER catalysts will open up new research direction in this field and further advance the role of carbon nanomaterials in oxygen electrocatalysis for energy conversion and storage.

Regenerative Solid Oxide Fuel Cells for Venus Interior Probe Energy Storage

A novel variable altitude Venus interior probe is currently under development that uses in-situ power and propulsion to lower a balloon down into Venus’s atmosphere, approximately 20 km from the surface, and then bring it back up above the clouds and hover at approximately 60 km from the surface. One of the biggest challenges is finding an energy storage solution that can withstand Venus’s harsh atmosphere. At 20 km the probe will experience temperatures close to 325°C, pressures around 20 atm, and an atmosphere composed of CO2, with trace amounts of sulfur containing compounds. Conventional energy storage technologies, like batteries, are not an option under these conditions. The only technology that can survive under these conditions are solid oxide fuel cells (SOFCs), which operate in a temperature range between 600 – 1000 °C. Fuel cells are devices that convert chemical energy, in this case from hydrogen and oxygen, into electricity with the only byproducts being heat and water. Solid oxide fuel cells can be run reversibly as an electrolyzer, taking the byproduct water and splitting it into hydrogen and oxygen that can then be used to run the fuel cell. A regenerative fuel cell system may therefore be built around a single SOFC stack. The goal is to run the SOFC to power the probe at 20 km and then reverse the SOFC to an electrolyzer when the probe is back above the clouds and use solar power to produce hydrogen and oxygen. The data presented in this work shows the successful operation of a regenerative SOFC. Figure 1A shows a SOFC that was run in H2/O2 as an electrolyzer. Figure 1B shows a SOFC run as a fuel cell in different conditions including H2/O2 (red line) and H2/Air at different flow rates (blue lines). The goal of this work is to pinpoint the exact conditions a SOFC would need to operate at in order to successfully store energy for an interior probe in the Venus atmosphere. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and NASA’s Innovative Concepts (NIAC) Program: “Venus Interior Probe Using In-situ Power and Propulsion (VIP-INSPR). Figure 1

Improving the electric performance of a unitized regenerative fuel cell during mode switching through mass transfer enhancement

Mode switching is essential in a unitized regenerative fuel cell system. The switching of electricity, reactants, and reversible electrochemical reactions occurs, thereby affecting cell performance. During model switching, insufficient reactant supply may cause severe concentration, especially along the width of the catalyst layer which is not currently considered in a low-dimensional model. To fill this gap, a three-dimensional simulation in a proton exchange membrane unitized regenerative fuel cell is performed and validated to investigate the dynamic responses of current density and mass transfer. Results certify that reductions on current density and hydrogen generation are severe, as the cell is switched to a high electrolysis voltage. The analysis of species transfer along the width of the porous layers indicates that the deterioration is attributed to the occurrence of serious concentration polarization which is caused by the severe local water starvation on the catalyst layer, especially below the rib. A high inlet velocity for reactant and low fuel cell voltage are conducive for remitting local water starvation to improve cell performance effectively. However, a slight deterioration cannot be avoided completely before the water supply arrives, which is limited by the high rates of electrochemical reactions at a high electrolysis voltage.

La0.1Ca0.9MnO3/Co3O4 for oxygen reduction and evolution reactions (ORER) in alkaline electrolyte

Non-precious metal bifunctional catalysts are of great interest for metal–air batteries, electrolysis, and regenerative fuel cell systems due to their performance and cost benefits compared to the Pt group metals (PGM). In this work, metal oxides of La0.1Ca0.9MnO3 and nano Co3O47 catalyst as bifunctional catalysts were used in oxygen reduction and evolution reactions (ORER). The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption isotherms. The electrocatalytic activity of the perovskite-type La0.1Ca0.9MnO3 and Co3O4 catalysts both as single and mixtures of both were assessed in alkaline solutions at room temperature. Electrocatalyst activity, stability, and electrode kinetics were studied using cyclic voltammetry (CV) and rotating disk electrode (RDE). This study shows that the bifunctional performance of the mixed La0.1Ca0.9MnO3 and nano Co3O4 was superior in comparison to either La0.1Ca0.9MnO3 or nano Co3O4 alone for ORER. The improved activity is due to the synergistic effect between the La0.1Ca0.9MnO3 and nano Co3O4 structural and surface properties. This work illustrates that hybridization between these two metal oxides results in the excellent bifunctional oxygen redox activity, stability, and cyclability, leading to a cost-effective application in energy conversion and storage, albeit to the cost of higher catalyst loadings.

Metal Loading Effect on the Activity of Co3O4/N‐Doped Reduced Graphene Oxide Nanocomposites as Bifunctional Oxygen Reduction/Evolution Catalysts

AbstractThe development of effective and stable reversible oxygen electrodes is of upmost importance for bringing regenerative energy storage and conversion systems to a commercial reality. However, realization of such electrodes is motivated by low activity and instability of the current electrocatalysts working for both water splitting and oxygen reduction. Herein, we report a series of Co3O4/graphene‐based catalysts with different Co mass loadings prepared by using a facile one‐step hydrothermal route. N‐doped reduced graphene oxide (NRGO) was utilized as a substrate for the deposition of oxide particles. The structural properties and surface composition of the different materials were investigated by powder X‐ray diffraction, transmission electron microscopy, and X‐ray photoelectron spectroscopy measurements. The effect of Co mass loading on the morphostructural properties of oxide nanoparticles and also on their electroactivity towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) was addressed. This study revealed the optimum range for metal loading on the graphene substrate. Co3O4/NRGO with a Co mass loading of 30 wt.% exhibits the highest activity towards ORR and OER, with a reversibility criterion of 763 mV. This work is very helpful for the electrocatalysis community, and will allow effective catalysts to be developed for high‐power metal/air battery or regenerative fuel cell systems, based on earth‐abundant and scalable electrocatalysts.

9-5-1 1kW級一体化再生形燃料電池システムを用いたエネルギー変換効率の評価(Session 9-5 水素製造・貯蔵・利用V)

9-5-1 1kW級一体化再生形燃料電池システムを用いたエネルギー変換効率の評価(Session 9-5 水素製造・貯蔵・利用V)

Optimized High Temperature PEM Fuel Cell & High Pressure PEM Electrolyser for Regenerative Fuel Cell Systems in GEO Telecommunication Satellites

Next generation telecommunication satellites will demand increasingly more power. Power levels up to 50 kW are foreseen for the next decades. Battery technology that can sustain up to 50 kW for eclipse lengths of up to 72 minutes will represent a major impact on the total mass of the satellite, even with new Li-ion battery technologies. Regenerative fuel cell systems (RFCS) were identified years ago as a possible alternative to rechargeable batteries. CMR Prototech has investigated this technology in a series of projects initiated by ESA focusing on both the essential fuel cell technology, demonstration of cycle performance of a RFCS, corresponding to 15 years in orbit, as well as the very important reactants storage systems. In the last two years the development has been focused towards optimising the key elements of the RFCS; the HTPEM fuel cell and the High Pressure PEM electrolyser. In these ESA activities the main target has been to optimise the design by reducing the mass and at the same time improve the performance, thus increasing the specific energy. This paper will present the latest development, including the main results, showing that significant steps have been taken to increase TRL on these key components.

Investigation of Advanced Components in a High Pressure Single-Cell Electrolyser for the Development of a HP-PEM-ELY Stack as Part of a Regenerative Fuel Cell System

The objective of the presented work, done under current ESA activity (Contract No. 4000109578/13/NL/SC), is the performance and tolerance evaluation of selected components and materials for the development of a High Pressure, Polymer Electrolyte Membrane (PEM) Electrolyser (HP-PEM-ELY) Stack, aiming to operate at 80 bar with a performance output of 0.3 A/cm 2 at 1.6 V. An extensive study was performed on a single-cell high pressure PEM electrolyser manifold, leading to a list of materials with suitable properties and engineering solutions towards operation in space environment. This investigation provided the necessary feedback for the design of a HP-PEM-ELY stack, which is also discussed. The ultimate target of the current ESA activity is to implement research findings, develop and operate a complete regenerative fuel cell system, comprising of a High Temperature Fuel Cell Stack and the HP-PEM-ELY stack. System aspects are briefly discussed.

Flight paths for a regenerative fuel cell based high altitude long endurance unmanned aerial vehicle

Unmanned aerial vehicles (UAVs) are being developed worldwide for the purpose of communications or military activities. We considered a Regenerative fuel cell (RFC)-based High altitude long endurance (HALE) UAVs because it can regenerate hydrogen and oxygen by using power of photovoltaic arrays during the day. To make an RFC-based HALE UAVs fly continuously, the study of flight paths is essential and an easy approach using the current technologies. We introduced the four cases of flight paths and determined their required energies. It is concluded that climb-after-glide flight is best feasible flight path among four flight paths for RFC system-based HALE UAVs due to air density and time of operating motor. In addition to climb-after-glide flight other flight strategies enable the aircraft to continuously conduct missions in limited range of an altitude, which validated that the RFC system is suitable for use in a HALE UAVs.

A Feasibility Study for a Stratospheric Long-endurance Hybrid Unmanned Aerial Vehicle using a Regenerative Fuel Cell System

In the stratosphere, the air is stable and a photovoltaic (PV) system can produce more solar energy compared to in the atmosphere. If unmanned aerial vehicles (UAVs) fly in the stratosphere, the flight stability and efficiency of the mission are improved. On the other hand, the weakened lift force of the UAV due to the rarefied atmosphere can require more power for lift according to the weight and/or wing area of the UAV. To solve this problem, it is necessary to minimize the weight of the aircraft and improve the performance of the power system. A regenerative fuel cell (RFC) consisting of a fuel cell (FC) and water electrolysis (WE) combined PV power system has been investigated as a good alterative because of its higher specific energy. The WE system produces hydrogen and oxygen, providing extra energy beyond the energy generated by the PV system in the daytime, and then saves the gases in tanks. The FC system supplies the required power to the UAV at night, so the additional fuel supply to the UAV is not needed anymore. The specific energy of RFC systems is higher than that of Li-ion battery systems, so they have less weight than batteries that supply the same energy to the UAV. In this paper, for a stratospheric long-endurance hybrid UAV based on an RFC system, three major design factors (UAV weight, wing area and performance of WE) affecting the ability of long-term flight were determined and a simulation-based feasibility study was performed. The effects of the three design factors were analyzed as the flight time increased, and acceptable values of the factors for long endurance were found. As a result, the long-endurance of the target UAV was possible when the values were under 350 kg, above 150 m2 and under 80 kWh/kg H2. Keywords: Polymer Electrolyte Membrane Fuel Cell, Regenerative Fuel Cell, Unmanned Aerial Vehicle, Hybrid System, Stratospheric Long Endurance

A Feasibility Study for a Stratospheric Long-endurance Hybrid Unmanned Aerial Vehicle using a Regenerative Fuel Cell System

In the stratosphere, the air is stable and a photovoltaic (PV) system can produce more solar energy compared to in the atmosphere. If unmanned aerial vehicles (UAVs) fly in the stratosphere, the flight stability and efficiency of the mission are improved. On the other hand, the weakened lift force of the UAV due to the rarefied atmosphere can require more power for lift according to the weight and/or wing area of the UAV. To solve this problem, it is necessary to minimize the weight of the aircraft and improve the performance of the power system. A regenerative fuel cell (RFC) consisting of a fuel cell (FC) and water electrolysis (WE) combined PV power system has been investigated as a good alterative because of its higher specific energy. The WE system produces hydrogen and oxygen, providing extra energy beyond the energy generated by the PV system in the daytime, and then saves the gases in tanks. The FC system supplies the required power to the UAV at night, so the additional fuel supply to the UAV is not needed anymore. The specific energy of RFC systems is higher than that of Li-ion battery systems, so they have less weight than batteries that supply the same energy to the UAV. In this paper, for a stratospheric long-endurance hybrid UAV based on an RFC system, three major design factors (UAV weight, wing area and performance of WE) affecting the ability of long-term flight were determined and a simulation-based feasibility study was performed. The effects of the three design factors were analyzed as the flight time increased, and acceptable values of the factors for long endurance were found. As a result, the long-endurance of the target UAV was possible when the values were under 350 kg, above 150 m 2 and under 80 kWh/kg H2.

Investigation of an integrated hydrogen production system based on nuclear and renewable energy sources: Comparative evaluation of hydrogen production options with a regenerative fuel cell system

Hydrogen has risen as a sustainable and efficient energy carrier option in reducing environmental pollution, and is seen as a potential solution for the current energy crisis. Hydrogen production via water decomposition is a potential process for direct utilization of nuclear thermal energy to increase efficiency and thereby facilitate energy savings. While many of the available renewable energy resources are limited due to their reliability, quality, quantity and density, nuclear energy has the potential to contribute a significant share of energy supply with very limited impacts to climate change. The proposed model in this study is an integrated hydrogen production system combining both nuclear and solar energy sources. This integrated system includes storage of hydrogen and its conversion to electricity by a regenerative fuel cell system when needed. There are many matured water splitting processes that can be linked with the nuclear and solar energy sources to decompose water to its constituents, among which is hydrogen. In this regard, a comparative study is carried out to evaluate an optimal and feasible hydrogen production/storage process with a regenerative fuel cell that can be linked to this integrated system. Studies conducted here on hydrogen production processes show the thermochemical water decomposition to be the better option for producing hydrogen, comparing to electrolysis, due to its high efficiencies and low costs. Energy and exergy efficiencies of various hydrogen production processes, and fuel cell systems are evaluated and compared. Also, a parametric study is conducted on these efficiencies to see the effect of various operating conditions.