Circulative Renewable Energy System for Nighttime Power Supply on the Moon

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

Small‐molecule electrooxidation‐boosted water electrolysis (WE) is an energy‐saving method for hydrogen (H2) production. Herein, PdPt bimetallenes (PdPt BMLs) are obtained through the simple galvanic replacement reaction. PdPt BMLs reveal 2.93‐fold enhancement in intrinsic electroactivity and 4.53‐fold enhancement in mass electroactivity for the formate oxidation reaction (FOR) with respect to Pd metallenes (Pd MLs) at 0.50 V potential due to the synergistic effect. Meanwhile, the introduction of Pt atoms also considerably increases the electroactivity of PdPt BMLs for hydrogen evolution reaction (HER) with respect to Pd MLs in an alkaline medium, which even exceeds that with the use of commercial Pt nanocrystals. Inspired by the outstanding FOR and HER electroactivity of bifunctional PdPt BMLs, a two‐electrode FOR‐boosted WE system (FOR‐WE) is constructed by using PdPt BMLs as the cathode and the anode. The FOR‐WE system only requires an operational voltage of 0.31 V to achieve H2 production, which is 1.48 V lower than that (ca. 1.79 V) with the use of the traditional WE system.

A novel water-splitting electrochemical cycle for hydrogen production using an intermediate electrode

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

Fuel cell systems for space applications in Europe

A great technological advent is the use of renewable energies with the objective of promoting the migration of the world energy matrix. For this, alternatives to generate and store energy are sought. Among them, the use of hydrogen stands out - the most abundant chemical element in our universe - produced from various sources, such as natural gas, biomass and water electrolysis, making it a viable option as a renewable fuel, in addition to being considered a source of clean energy, as its burning does not emit gases such as carbon dioxide (CO2), one of the main responsible for global warming. In addition, hydrogen can be used in a range of applications, including transportation, power generation, heating and industry, making it versatile with fossil fuels. Its intrinsic properties such as its high energy density become advantageous from the perspective of the economy based on hydrogen. When used in fuel cells, it can generate electricity efficiently and without pollutants, after all, the only emission from the fuel cell system is water. The most common way to produce hydrogen is from natural gas, through a process called steam reforming, where methane from natural gas is combined with water vapor to produce hydrogen and carbon dioxide as a by-product. However, this approach still emits CO2, in a smaller amount, when compared to the direct burning of fossil fuels. Another option is the production of hydrogen from biomass, such as agricultural and forestry waste, through gasification processes or anaerobic fermentation, which can be neutral in terms of CO2 emissions, as the carbon released during production is offset by the carbon absorbed. by plants during their growth. In addition, water electrolysis, which uses electricity to split water into hydrogen and oxygen, is another option for producing hydrogen without CO2 emissions when the electricity used comes from renewable sources. With its vast production, hydrogen can be used as a form of renewable energy storage, after all, one of the main limitations of renewable energies, such as solar and wind, is their intermittency, that is, energy generation depends on climatic conditions. Hydrogen can be produced when there is a surplus of renewable energy available, being stored in liquid or gaseous form, in large spoons, facilitating its transport for later use, and also, meeting the growing world energy demand.

Water electrolysis is a crucial technology for large-scale hydrogen generation, that is required for the transition to a fossil fuel-free energy system. Even though water electrolysis systems are already deployed in a limited capacity, the technology is largely constrained to liquid alkaline electrolysis. Proton exchange membrane (PEM) electrolysis could pose an alternative but it is still hindered by high investment costs, in-part due to its reliance on scarce noble-metal catalysts. Alternative structural designs of the anode catalyst layer (CL) could reduce Iridium loading of the whole system and thus accelerate its wide-spread application. In fuel cell research, it was already reported that a multi-layer design with varied ionomer content enhances performance of the CL and in-turn lowers required catalyst loading.[1,2,3]In this study, a gradient design for ionomer content is employed for anode CLs for the application in PEM water electrolysis. CLs are coated in a stacked multi-layer design via ultrasonic spray coating of Iridium/Nafion® suspensions. The target ionomer loadings (10 and 30 wt.%) are confirmed by a combination of thermo-gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The coating process yields homogenously loaded reference CLs as well as through-plane graded CLs with the desired ionomer loading. Additionally, scanning electron microscopy (SEM) in conjunction with energy dispersive spectroscopy (EDS) shows equal CL thickness across all ionomer loadings and spatially differentiated Nafion® content throughout the CLs thickness. Electrochemical characterizations are carried out in an electrolysis-adapted gas diffusion electrode (GDE) half-cell setup to allow for quick examination and prototyping of produced layers. Differences in electrochemical performance of these layers can be observed with one gradient design CL showing reduced overpotential across all current densities compared to the homogenous CLs. In-particular a high ionomer loading near the membrane improves performance, most likely due to increased proton conduction to the membrane and higher available pore volume near the porous transport layer.Further analysis is performed on electrochemical studies to deepen the understanding of the role of ionomer in anodic PEM water electrolysis CLs. Particularly, the investigation of protonic and electric conductivity through the CL is of interest, because this parameter is most influenced by ionomer loading.[4]

The oxygen evolution reaction (OER) plays an important role in many industrial applications like electrolytic water splitting or regenerative fuel cell systems. So far, IrO2 and RuO2 are the benchmark OER catalysts, owing to their high catalytic activity. However, these precious metals are costly and their supply is not sustainable, which makes them unsuitable for large-scale applications. Hence, research efforts have been devoted to the development of low-cost OER catalysts on the basis of first-row transition metals and their oxides. Especially nickel- and cobalt based composites show promising OER catalytic activity. Strategies to further enhance OER activity of the transition metal-based catalysts to levels comparable to the benchmark IrO2 and RuO2 catalysts pursue the design and fabrication of nanoporous catalyst structures and the use of catalyst nanoparticles immobilized on carbon nanomaterial substrates. Porous electrode structures offer high specific surface area available for reaction. However, this increase in surface area comes at the cost of additional transport losses of reactants and products through the porous medium. In this context, gas evolution plays an important role: on the one hand, gas in the pores replaces the electrolyte phase, thus hindering ion transport and reducing the effective ionic conductivity in the porous electrode. Limited ion transport leads to transport losses and defines a reaction penetration depth, beyond which the porous electrode becomes inactive. On the other hand, the gas covers part of the internal surface area, rendering it inactive. In order to maximize the activity of a porous gas evolution electrode, its structure needs to be optimized. To do so, the current work attempts to gain a fundamental understanding of the relationships between structure, properties and performance of the porous electrode. Our approach combines a macro-scale performance model of the electrode with a micro-scale model of gas evolution. At the macro-scale, a classic porous electrode model describes the transport of ions, electrons and produced oxygen using effective medium theory and accounting for the gas phase volume and distribution. The gas phase is modeled by a micro-scale model describing the formation, growth and transport of gas bubbles in the porous medium. The model is applied in practice to a regenerative zinc fuel cell system for energy storage. In this system, energy is released in an alkaline zinc air fuel cell by oxidizing zinc suspended in alkaline solution. The system can be recharged by regenerating the zinc on the cathode of the regenerator unit, as shown in Fig. 1. On the anode of this regenerator unit, the OER takes place, which imposes one of the major losses in the system. The presented work uses this system as a concrete example for the development of a general theory for gas evolving porous electrodes and aims at verifying this theory by targeted experiments on this practical system. The model can then be used to optimize the structure of the electrode in order to optimize the performance of the regenerator. Figure 1

Introduction Water electrolysis is expected a key energy conversion system to introduce large-scale renewable electricity under power grid management. Here, less expensive large system is needed. Alkaline water electrolysis (AWE) systems are well-developed large system to combine hydropower generation, but fluctuated operation with start and stop operation is not considered for conventional systems. Therefore, improvement of durability to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current behavior of bipolar alkaline water electrolyzers and proposes accelerated durability test (ADT) protocol. Theoretical and Experimental Figure 1 shows configuration of bipolar alkaline water electrolyzer, principle of reverse current. An equivalent circuit to analyze reverse current is also shown in the figure. During electrolysis, surface Ni of anode oxidizes to Ni(III) and that of cathode reduces to Ni(0). They electronically connect on a bipolar plate and ionically connect through manifold to distribute electrolyte. In the equivalent circuit, electrochemical potential difference between anode and cathode on a bipolar plate correspond to electromotive force of Uk(t). The R 1 and R 2 correspond ionic resistances of branch and communicating tubes, respectively. Relationship among these parameters can describe as eq. 1 in Fig. 1 based on the Kirchhoff's laws, so reverse current would be estimated. In this study, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using commercially available industrial anode and cathode (De Nora Permelec Ltd). The reverse current was measured ionic current through communicating tube with D. C. clamp meter.As bipolar electrolyzer evaluation, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using the commercially available anode and cathode. Effective electrode size was 27 cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu).As start & stop operation simulated ADT protocol, we propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Results and discussion Figure 2 shows the setup of lab-scale electrolyzer and cell performances in the stacks. All cells showed almost the same performance. Figure 3 shows reverse currents and electrode potentials as a function of time for 2 to 4 cells stack electrolyzer. The longer cell stack had lager reverse current at initial period of stop operation. As the potential difference between anode and cathode decreased, the reverse current decreased. The anode potential significantly decreased certain time, and that for longer cell stack was shorter. For the 4 cells stack, the time for the BP2 was shorter than that for the BP1 and BP3. Simultaneously, the I 2 was larger than the I 1 and I 3. These behaviors could be explained with eq. 1 in the Fig. 1 with the same electromotive force of the U(t=0)s for initial period and time function of U(t)s with same surface condition for all cells at the end of electrolysis. Remarkable point is that the cathode potential of BP2 was higher than the anode, which is impossible with discharge of BP2 itself. This opposite potential of the BP2 would be forced by electromotive force of the BP1 and BP3.Figure 4 shows the anode potential at 10 mAcm-2 (E @10mAcm-2) of oxygen evolution reaction (OER) current during the ADT protocol with various minimum potential: E min. The all anodes significantly degraded for around 3-days test protocol, although DN851 was developed as an active and durable anode for conventional OER electrode. The degradation increased with decreases of the E min. Above 0 V vs. RHE of the E min, The E @10mAcm-2 increased after ca. 800 cycles of introduction period and reached around 1.69 V vs. RHE after 1900 cycles, although it increased from initial period and the increase continued around 2000 cycles for -0.3 V vs. RHE of the E min. From these experimental results, the E min of between 0 to 0.3 V vs. RHE might be suitable for the ADT protocol because of rapid degradation with robustness to the E min. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

The depletion of fossil fuels in the current world has been a major concern due to their role as a primary source of energy for many countries. As non-renewable sources continue to deplete, there is a need for more research and initiatives to reduce reliance on these sources and explore better alternatives, such as renewable energy. Hydrogen is one of the most intriguing energy sources for producing power from fuel cells and heat engines without releasing carbon dioxide or other pollutants. The production of hydrogen via the electrolysis of water using renewable energy sources, such as solar energy, is one of the possible uses for solid oxide electrolysis cells (SOECs). SOECs can be classified as either oxygen-ion conducting or proton-conducting, depending on the electrolyte materials used. This article aims to highlight broad and important aspects of the hybrid SOEC-based solar hydrogen-generating technology, which utilizes a mixed-ion conductor capable of transporting both oxygen ions and protons simultaneously. In addition to providing useful information on the technological efficiency of hydrogen production in SOEC, this review aims to make hydrogen production more efficient than any other water electrolysis system.

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.

The Space Station propulsion system will utilize a water electrolysis system to produce the required eight-to-one ratio of gaseous hydrogen and oxygen propellants. This paper summarizes the state of the art in water electrolysis technologies and the supporting development programs at the NASA Lyndon B. Johnson Space Center. Preliminary proof of concept test data from a fully integrated propulsion testbed are discussed. The technical challenges facing the development of the high-pressure water electrolysis system are discussed.

Efficient water electrolysis is one of the key issues in realizing a clean and renewable energy society based on hydrogen fuel. However, several obstacles remain to be solved for electrochemical water splitting catalysts, which are the high cost of noble metals and the high overpotential of alternative catalysts. Herein, we suggest Ni-based alternative catalysts that have comparable performances with precious metal-based catalysts and could be applied to both cathode and anode by precise phase control of the pristine catalyst. A facile microwave-assisted procedure was used for NiO nanoparticles anchored on reduced graphene oxide (NiO NPs/rGO) with uniform size distribution in ~1.8 nm. Subsequently, the Ni-NiO dual phase of the NPs (A-NiO NPs/rGO) could be obtained via tailored partial reduction of the NiO NPs/rGO. Moreover, we demonstrate from systematic HADDF-EDS and XPS analyses that metallic Ni could be formed in a local area of the NiO NP after the reductive annealing procedure. Indeed, the synergistic catalytic performance of the Ni-NiO phase of the A-NiO NPs/rGO promoted hydrogen evolution reaction activity with an overpotential as 201 mV at 10 mA cm−2, whereas the NiO NPs/rGO showed 353 mV. Meanwhile, the NiO NPs/rGO exhibited the most excellent oxygen evolution reaction performance among all of the Ni-based catalysts, with an overpotential of 369 mV at 10 mA cm−2, indicating that they could be selectively utilized in the overall water splitting. Furthermore, both catalysts retained their activities over 12 h with constant voltage and 1000 cycles under cyclic redox reaction, proving their high durability. Finally, the full cell capability for the overall water electrolysis system was confirmed by observing the generation of hydrogen and oxygen on the surface of the cathode and anode.

Electrochemical fabrication of IrOx nanoarrays with tunable length and morphology for solid polymer electrolyte water electrolysis

Chapter 3 - Hydrogen Production From Water Electrolysis