Active magnetic regenerators (AMRs) for hydrogen liquefaction represent a promising alternative to conventional Joule-Thomson and turbine-based technologies. However, quantitative evaluation of the mechanical work associated with magnetic forces remains essential for improving system efficiency. At the National Institute for Materials Science (NIMS), a tandem-type AMR system packed with HoAl2 magnetocaloric material and magnetized using a conduction-cooled NbTi superconducting magnet was developed. The effect of magnetic-force cancellation on mechanical input work and system efficiency is investigated and compared with a conventional single-bed AMR. Numerical analysis shows that the mechanical work obtained by integrating the axial magnetic force agrees well with the thermodynamic work evaluated from the T-S diagram, confirming the validity of force-based work estimation. For the single-bed AMR, a substantial portion of the input work is identified as magnetization-related work that is theoretically recoverable through an external regenerative mechanism, leading to an increased second-law efficiency ηII under ideal recovery conditions. However, the effectiveness of such recovery is strongly limited when a realistic reciprocating efficiency is considered. In contrast, the tandem configuration directly reduces the required actuator input work through partial cancellation of opposing magnetic forces, without relying on any energy recovery mechanism. As a result, numerical analysis shows that the tandem-type AMR achieves a second-law efficiency of 0.67 solely through magnetic-force cancellation. This corresponds to an approximately 43% improvement compared to the second-law efficiency of 0.47 for the single-bed AMR when a realistic reciprocating efficiency is considered. Furthermore, experimental results indicate that the tandem configuration effectively reduces magnetic forces compared with the single-bed AMR. At a magnetic field of 2 T, the tandem-type AMR exhibits a higher system efficiency ηII=0.28 than the single-bed AMR equipped with a practical regenerative mechanism ηII=0.18 under comparable conditions, corresponding to a 55.6% improvement in second-law efficiency. These results suggest that the tandem-type AMR configuration offers an effective and structurally simple approach to improving the efficiency of high-field magnetic refrigeration systems for hydrogen liquefaction.

Anion Exchange Membrane (AEM) water electrolyzer is expected to be the next generation water electrolyzer that can realize low cost and high performance. Because the ionic conductivity of AEM and catalytic activity cannot be sufficiently maintained if DI water is supplied to the anode in the current AEM water electrolyzer, a dilute solution of KOH or K 2 CO 3 ( We compared the performance of AEM water electrolysis when using K 2 CO 3 and KOH solution as the anode electrolyte, adjusted to a pH of around 12, and confirmed that K 2 CO 3 solution provides higher performance at this pH level [1]. On the other hand, many previous studies have shown that using a high pH electrolyte is useful for improving electrolysis performance. In this study, we conducted an electrolysis test by supplying a higher concentration of KOH solution to the anode, and re-examined the effects of the electrolyte solute and pH on electrolysis behavior. In the AEM water electrolysis tests, 1wt.%-KOH solution (pH=13.2) and 10wt.%-K 2 CO 3 solution (pH=11.8) were used as the anode electrolytes. Two types of cells were used in the AEM water electrolysis tests. One was Cell-1, with an electrode area of 25 cm 2 , and the other was Cell-2, with an electrode area of 1 cm 2 . In both cell tests, the electrolyte was supplied only to the anode, and the cathode was maintained in a dry state, and all tests were carried out at a cell temperature of 50ºC. In the test using Cell-1, current-voltage characteristics and dew point of the generated hydrogen were measured, and in the test using Cell-2, a reference electrode was inserted, and in addition to the current-voltage characteristics, overpotential separation of the anode and cathode was performed. The test results for both cells were examined, and the effects of the electrolyte solute and pH on the electrolysis behavior were considered. References [1] H. Ito et al., Int. J. Hydrog. Energy , 43, 17030 (2018).

Recently, anion exchange membrane water electrolyzers have been attracting attention as a low-cost, high-performance water electrolysis system. In AEM water electrolysis, although water as fuel is consumed at the cathode, “cathode dry operation”, in which electrolyte solution is supplied only to the anode, can be applied. This operation scheme enables relatively dry hydrogen to be extracted from the cathode and has the advantages of simplifying the hydrogen purification line and facilitating pressurized operation. However, our previous study [1] has shown that cathode dry operation also has the problem of significant mass transfer overpotential due to water transport through the membrane. In this study, both the bilateral electrolyte supply operation, in which the electrolyte solution is also supplied to the cathode, and the cathode dry operation were applied to the same cell, and the effects of the electrolyte supply scheme on the electrolysis performance were compared and examined. Acknowledgement This work was supported partly by the New Energy and Industrial Development Organization (NEDO) through the Advancement of Hydrogen Technologies and Utilization Project (P 14021). The authors wish to express their gratitude to Tokuyama Corporation for their support and helpful advice. Reference [1] R. Wang et al., Int. J. Hydrog. Energy, 47, 40835 (2022).

Solid Oxide Fuel Cells (SOFCs) generate electricity efficiently for high reaction activity and internal reforming of hydrocarbons at high temperatures, which consequently have the potential to replace conventional thermal power generations. It is expected to adjust the output with voltage whenever possible when the scale of SOFC enlarges more than the megawatt-class to reduce transmission loss. Our group aims to establish the design guideline for high-voltage insulation in high-temperature oxidizing and reducing atmospheres. This paper describes the creepage distance dependency of DC breakdown voltage in hydrogen assumed an anode environment. The authors measured the characteristics of alumina at 700 - 900°C and compared them to that in air assumed a cathode environment, which was clarified in a previous report. In both atmospheres, the results show that the breakdown mechanism follows Townsend ’s theory in a wide range; however, it affected by space charge in a region of specific creepage distances. Moreover, creepage distance to obtain the same breakdown voltage and the mechanism transition in hydrogen is approximately twice that in air. It is suggested that the mean free path and ionization index for impact ionization could govern the relationship between creepage distance and breakdown strength, regardless of the gas type, hydrogen or air.

The scale of hydrogen production from renewable energy sources is expected to increase worldwide in the future. Water electrolysis is a practical way to produce hydrogen from renewable energy sources. Water electrolyzers that use an anion exchange membrane (AEM) are expected to be new devices for hydrogen (H2) production that achieve high performance at low capital cost. In AEM water electrolysis, “cathode dry operation” is sometimes applied. In this operation mode, water (electrolyte solution) is supplied only to the anode, not to the cathode where water is consumed in the reaction, keeping the cathode dry. In this way, relatively dry hydrogen can be extracted directly from the cathode, simplifying the hydrogen drying process. When water electrolyzers are installed in large quantities (over 1000 units), the cost of balance of plants (BOPs) is expected to account for the majority of system costs [1], and simplifying the BOPs are important for reducing system costs. However, it was observed that cathode dry operation would cause concentration overpotentials due to water diffusion through the membrane [2], which may limit the current density and membrane thickness to prevent cathode dry-out. In this study, the effects of electrolyte composition and concentration on the water behavior in the membrane during cathodic dry operation on the electrolysis performance were quantitatively investigated. AcknowledgementThis work was supported partly by the New Energy and Industrial Development Organization (NEDO) through the Advancement of Hydrogen Technologies and Utilization Project (P 14021). The authors wish to express their gratitude to Tokuyama Corporation for their support and helpful advice. References [1] Mayyas et al. Manufacturing cost analysis for proton exchange membrane water electrolyzers, NREL Technical report, NREL/TP-6A20-72740 (2019). [2] R. Wang et al, Int. J. Hydrog. Energy, 47, 40835 (2022).

The net water drag coefficient (αNWD) is supposedly an essential index in water management, and must be negative for system operation for polymer electrolyte fuel cell (PEFC) systems. In this study, αNWD is carefully examined by measurement of the water content in the gases supplied to and those discharged from the cell/stack under gas supply conditions similar to those in a real PEFC system. We focus on the effect of anode hydrogen (H2) flow conditions (i.e., flow rate and relative humidity) on αNWD under a constant flow condition of cathode air. Measured characteristics of current density (i) - αNWD in which the relative humidity of discharged H2 from the anode is constant at around 100%, show that αNWD is stable when i exceeds a certain threshold. The value of αNWD in this stable region is particularly sensitive to changes in the stoichiometric ratio of H2. These measurements also suggest that in the αNWD stable region, almost the entire area of the membrane is fully hydrated, and the effect of back diffusion on αNWD becomes negligible. Analysis of the observed relationships between αNWD and several variables indicate that increasing the H2 circulation flow rate effectively prevents anode dry-out.

The effect of water diffusion through an anion exchange membrane (AEM) on the concentration overpotential (ηconc) during cathode dry operation of AEM water electrolysis was experimentally examined using electrolytic cells with different membrane electrode assemblies (MEAs). The specially designed MEAs were used in the cells to obtain reliable and reproducible data to clarify the influence of membrane thickness (tmem) and porosity of cathode catalyst layer (CL). The relative humidity of generated hydrogen (ϕH2) during electrolysis was also measured based on dew point measurements of the hydrogen. The ηconc analysis for cells with single- and double-AEM MEAs revealed that water diffusion through the membrane was the main contributor to ηconc. The quantitative agreement between ϕH2 data and ηconc revealed that the difference in ηconc between the two types of MEAs is explained by the water concentration difference between anode and cathode via the Nernst equation. The effect of the porosity of the cathode CL on cell performance and on water transport was also examined experimentally. The results revealed that a high-porosity cathode CL tended to keep the cathode in a drier state during electrolysis compared with a low-porosity cathode CL. When ϕH2 is lower than a threshold value in the range from 0.5 to 0.6, the ion conductivity of AEM and ionomer would decrease, and the cell performance would deteriorate due to an increase in cell resistance (Rcell) and/or activation overpotential (ηact).

Solid Oxide Fuel Cells (SOFCs), which work at 600 ∼ 1000°C and have efficiencies of over 60%, are expected to be larger capacity. However, expanding SOFCs will rise operating voltage and increase the risk of insulation failure. Extending creepage distance is one of the ways to reduce the risk. In order to clarify the effect of extending creepage distance on dielectric strength, it is indispensable to elucidate the mechanism of creepage distance dependency for electrical breakdown in high temperature and non-uniform electric field.

Anion exchange membrane (AEM) water electrolyzers are expected to be novel devices for hydrogen (H2) production that achieve high performance at low capital cost. The effect of catalyst distribution in anode porous transport electrodes (PTEs) on the performance of AEM water electrolysis is experimentally examined. Based on the analysis of the correlation between the PTE structure and the electrolysis performance, it was revealed that the surface catalyst coverage is related to the activation overpotential, and that the location and compactness of the catalyst layer (CL) affects the concentration overpotential. This suggests that the water diffusion through the membrane is related to the concentration overpotential, and that denser CLs can promote water diffusion and thus mitigate the concentration overpotential. Based on the electrolysis data with PTEs of different thickness, it was also revealed that decreasing the thickness of the anode PTE enables good performance with low catalyst loading.

Power grids require more flexibility to adapt to the integration of variable renewable energy sources, which naturally produce inconsistent supply. Distributed energy resources installed at consumer sites can provide flexibility from the demand side. The aim of this study is to evaluate the potential of providing grid flexibility using combined heat and power (CHP) systems. A model that reproduces the operation of power sources was used to analyze the predicted lack of grid flexibility in the power system for the year 2030, and the model was used for the greater Tokyo area. We then scrutinized flexibility provision by the CHPs of four types of business facilities by tracking their operational changes in response to electricity time-of-use rates that reflect flexibility insufficiency. The nationwide potential of flexibility supply was calculated from the simulation result as well as nationwide CHP penetration data. The results show that the introduction of time-of-use rates as an economic incentive leads to a sizeable reduction in consumers’ energy costs, and the provision of flexibility depends substantially on the facilities’ heat-to-electricity ratios. We concluded that the aggregation of CHPs and sundry components, along with integrated working of various types of facilities, offers the most effective grid flexibility support.

CO2 tolerance of hydrogen storage alloys of AB(2)-type (C14 Laves phase) Ti0.515Zr0.485Mn1.2Cr0.8M0.1 (AB(2)-M, M = none, Fe, Co, Ni, and Cu) depends on dopant M. Since our goal is to clarify this mechanism, we determined the elemental analysis using X-ray absorption spectroscopy (XAS), scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), and neutron powder diffraction (NPD) with Rietveld refinement in this study. As a result of XAS analysis, a strong evidence of all doped elements occupying B site in AB(2) was obtained. SEM-EDX showed inhomogeneous composition with vacancy in B site and linear correlation of Ti/Zr and Mn/Cr ratio. The peak width in XRD patterns of AB(2)-M depends on the magnitude of homogeneity, therefore the Rietveld analysis using NPD patterns could not be well refined. Thus, homogeneity is not important but element of B site would be important for CO2 tolerance as well as AB(5) type alloys.

Due to the high penetration of renewable energy systems (RES), power system requires more flexibility to respond to the fluctuation of variable renewable energy sources. A viable economic measure that can be used to achieve greater flexibility is using distributed energy resources (DERs) installed on the demand side. Electricity time-of-use (TOU) rates can be used as an incentive to encourage prosumers to provide more flexibility by controlling the DERs. We propose TOU pricing that ensures every prosumer saves on energy costs. An aggregator procures flexibility from residential prosumers and provides this flexibility to a power system operator in exchange for a reward. A simulation model that reflects the power system's flexibility requirements and the assignment of TOU pricing to satisfy the cost minimization requirements of the DERs of prosumers is described. Numerical simulations were performed for three scenarios with different flexibility requirements. The results indicate that the proposed TOU pricing is economically efficient and enables the aggregator to procure flexibility from its prosumers while increasing its own profit and reducing the energy cost of its prosumers.

As global warming and the exhaustion of fossil fuels deepen, major countries are trying to promote the spread of renewable energy such as solar and wind power. Hydrogen with high energy density, no harmful emissions and various transportation, storage methods is regarded as the optimal energy carrier for renewable energy. Water electrolysis technology is usually used for the transformation of renewable resources to hydrogen. In the development of water electrolysis technology, proton exchange membrane (PEM) water electrolysis used a PEM with high mechanical/chemical stability and a membrane electrode assembly (MEA) with a zero-gap structure of electrodes has excellent variability to power fluctuation and a better electrolysis efficiency. However, due to the acidic electrolyte, cell components materials of PEM water electrolysis are limited to precious metal such as iridium (Ir) based catalysts on anode and platinum-group metals (PGMs) catalyst on cathode. In contrast, in the anion exchange membrane (AEM) water electrolysis, alkaline membrane can be used as electrolyte which means, compared with PEM water electrolysis, widely available non-precious metal catalysts and stainless components can be used. However, different from proton exchange ionomer (PEI), typical models of anion exchange ionomer (AEI) tend to lack mechanical and chemical stabilities and are difficult to apply to the binder for anode catalyst layer [1]. Therefore, we have adopted a different electrode structure for each of the two electrodes in the MEA, that is, catalyst-coated-membrane (CCM) for the cathode and porous transport electrode (PTE) for the anode. In this study, various types of PTE were fabricated and applied for the anode. The effect of each property of PTE (catalyst lading, porosity, thickness, and pore diameter) on the electrolysis performance was examined experimentally. Acknowledgement Part of the experiments reported here are supported by the New Energy and Industrial Technology Development Organization (NEDO). Reference [1] H. Ito et al. J. Appl. Electrochem., 48, 305 (2018)

Li-rich oxide cathodes are of prime importance for the development of high-energy lithium-ion batteries (LIBs). Li-rich layered oxides, however, always undergo irreversible structural evolution, leading to inevitable capacity and voltage decay during cycling. Meanwhile, Li-rich cation-disordered rock-salt oxides usually exhibit sluggish kinetics and inferior cycling stability, despite their firm structure and stable voltage output. Herein, a new Li-rich rock-salt oxide Li2Ni1/3Ru2/3O3 with Fd-3m space group, where partial cation-ordering arrangement exists in cationic sites, is reported. Results demonstrate that a cathode fabricated from Li2Ni1/3Ru2/3O3 delivers a large capacity, outstanding rate capability as well as good cycling performance with negligible voltage decay, in contrast to the common cations disordered oxides with space group Fm-3m. First principle calculations also indicate that rock-salt oxide with space group Fd-3m possesses oxygen activity potential at the state of delithiation, and good kinetics with more 0-TM (TM = transition metals) percolation networks. In situ Raman results confirm the reversible anionic redox chemistry, confirming O2-/O- evolution during cycles in Li-rich rock-salt cathode for the first time. These findings open up the opportunity to design high-performance oxide cathodes and promote the development of high-energy LIBs.

The authors proposed grid flexibility dispatch by controlling distributed energy resources (DER) of prosumers to respond to high penetration of variable renewable energy sources. DER are interconnected via DC link and can be controlled flexibly by an energy management system (EMS), which is installed to a prosumer. The prosumers buy/sell electricity and supply flexibility to markets via an aggregator. An operational simulation was performed to evaluate possibility of flexibility dispatch by DER responding to incentives.

This article reports the electrochemical performance of hybridized Li-ion conductive membranes consisting of a monolayer of Li-ion-conducting particles uniformly embedded in an insulating polymer matrix. The prepared hybridized Li-ion conductive membranes with the Li1.3Al0.3Ti1.7P3O12 (LATP) solid electrolyte and a cycloolefin polymer were studied via AC impedance spectroscopy and typical battery testing. The conductivities of the hybridized Li-ion conductive membranes were 0.53 mS cm(-1) at 20 degrees C and 0.22 mS cm(-1) at -10 degrees C, approximately 6 and 15 times higher, respectively, than those of the commercial LATP sintered disc. In addition, the activation energy (17.2 kJ mol(-1)) was in agreement with that of the bulk of LATP and approximately half that of the commercial LATP sintered disc. The membranes were used in batteries and the possibility of further improvement was referred from the results of their overpotentials and surface analyses.

A suitable Mn doping (x = 0.1) enhances the kinetics and structural stability of Na2RuO3, generating a superior electrochemical performance.

For polymer electrolyte fuel cell (PEFC) systems in vehicle applications, removal of external humidifiers from the cathode is desirable to reduce system efficiency, cost, space and weight, and thus PEFCs should achieve continuous self-humidification operation under cathode-dry conditions. A critical index to judge the success or failure of self-humidification is net water drag coefficient (alpha(NWD)). Self-humidification operation requires alpha(NWD)to be negative. Here, alpha(NWD) is experimentally evaluated using cells with different configurations of gas diffusion layer (GDL), membrane, and flow channel geometry. Experimental results confirmed that alpha(NWD) remains negative under cathode-dry conditions at a cell temperature of 60 degrees C, and that current density - net water drag coefficient (i - alpha(NWD)) characteristics are immune to configurations compared with the cell performance, when the flow rate of air at the cathode is low enough to keep alpha(NWD) low. In addition, under these conditions, the effect of flow velocity and pressure on the i - alpha(NWD) characteristics was limited. On the other hand, as expected, a thinner membrane promotes back-diffusion of water to the anode. In conclusion, the flow rate of air should be determined carefully so that the cell performance is maintained while self-humidification is achieved. (c) 2019 The Electrochemical Society.

This study presents newly designed and produced solid Li-ion conductive composite layers based on polymer electrolytes and Li-ion-conducting particles. The composite layers are studied using AC impedance spectroscopy. The conductivity of the composite layers is 0.14mS/cm at room temperature. We discuss the Li-ion transfer mechanism via a characteristic frequency of impedance analysis and show that the interior of Li-ion-conducting particles is the major Li-ion path. The activation energy is less than that of polymer electrolytes while being greater than that of the grain boundary of Li-ion–conducting particles. The newly designed composite layers could be utilized in solid-state Li-ion batteries and solid-state Li-air batteries.