Hydrogen Pump Research Articles

A Comparative Study on the Prediction of Hydrogen, Nitrogen, and Water Vapor of Regenerative Hydrogen Pump With Different Turbulence Models

Abstract The flow in a regenerative hydrogen pump used in a proton exchange membrane (PEM) fuel cell system is complex, including velocity mixing, streamline distortion, swirling flow, corner flow, and possible boundary separation. Experimental measurement and computational fluid dynamics (CFD) prediction are the main methods used to evaluate such performance. In this work, regenerative hydrogen designed for fuel cell electric vehicles with an impeller diameter of 91 mm and a shaft speed of 22,000 rpm is tested with a mixture of nitrogen, hydrogen, and water vapor. During the test, the flowrate and shaft speed ranges are 151–881 L/min and 8000–22,000 rpm, respectively. The inlet pressure and temperature are 171 kPa and 66 °C, respectively. Then, the flow is predicted by the k − ε model, the renormalization group (RNG) k − ε model, the explicit algebraic Reynolds stress models (EARSM) and the shear-stress transport (SST) detached eddy simulation (DES) model. The differences between the tested and predicted performances are compared. With these results, the velocity distribution in the side channel, the radial force of the impeller and casting, and the changes in the downstream pressure and velocity are analyzed in consideration of the ability of the turbulence models to simulate each characteristic flow. On this basis, the differences and abilities of the turbulence models for predicting the flow in regenerative hydrogen pumps are summarized.

FeNiCu-based composite catalyst for hydrogen storage in MgH2

FeNiCu-based composite catalysis proves to be an effective strategy for enhancing the hydrogen storage performance of MgH2. Two catalysts, (Cu0.2Ni0.8) O/NiFe2O4 and FeNi3/Fe4Cu3, are successfully synthesized and doped into MgH2 to improve its hydrogen storage capability. Experimental results demonstrate that MgH2 + 5 wt% (Cu0.2Ni0.8)O/NiFe2O4 (MgH2 + 5 A) and MgH2 + 5 wt% FeNi3/Fe4Cu3 (MgH2 + 5B) composites desorption at 171 ℃ and 178 ℃, respectively, which is 100 ℃ lower than that of ball-milled MgH2. Under conditions of 150 ℃ and 3 MPa, MgH2 + 5 A can absorb 6.02 wt% H2 in just one minute. MgH2 + 5B, at 225/325 ℃, exhibits hydrogen absorption/desorption exceeding 7 wt% H2 for 1 h. The synergistic effect of in situ formed Mg2Ni and Fe positively impacts the hydrogen storage behavior of MgH2. The introduced interface offers numerous low-energy barrier H-diffusion channels, resulting in accelerated release and hydrogen absorption. Additionally, Cu4O3 dispersed on the surface of the matrix particles maintains its valence during the process of hydrogen absorption/desorption. This property can facilitate the conversion of Mg2Ni/Mg2NiH4 into a “hydrogen pump”. This study provides an experimental basis and new insights for designing highly efficient catalysts for Mg-based hydrogen storage materials.

Effect of Carbon-Supported Rare Earth Oxide Catalysts on the Microstructure, Hydrogen Storage Kinetics, and Thermodynamics of Mg-La-Ni Alloys

In this study, using an improved chemical vapor deposition carbonization method, Eu2O3@C, PrO1.83@C, and La2O3@C composite catalysts were successfully synthesized and incorporated into Mg96La3Ni alloys via ball milling. These catalysts significantly enhanced the hydrogen storage properties of the alloys, particularly in terms of hydrogenation kinetics. Among the catalysts, PrO1.83@C demonstrated the most significant improvement. At 360 °C, the Mg96La3Ni alloy containing 3 wt.% PrO1.83@C achieved a 75.1% hydrogenation saturation ratio within 2 minutes and released 3 wt.% H2 in 3.1 minutes. While the catalysts did not significantly alter the alloy's thermodynamics, they substantially reduced the dehydrogenation activation energy. The addition of 3 wt.% Eu2O3@C, PrO1.83@C, and La2O3@C lowered the activation energy barriers to 116.6, 101.4, and 114.8 kJ/mol H2, respectively, compared to 121.67 kJ/mol H2 for the pristine Mg96La3Ni alloy. This enhancement is attributed to the synergistic effects of the "hydrogen pump" mechanism of rare earth hydrides and the abundant active sites provided by the carbon component, which collectively promote faster hydrogen diffusion and nucleation reactions.

MOF-derived Ni3Fe/Ni/NiFe2O4@C for enhanced hydrogen storage performance of MgH2

Magnesium hydride (MgH2) is an important material for hydrogen (H2) storage and transportation owing to its high capacity and reversibility. However, its intrinsic properties have considerably limited its industrial application. In this study, the NiFe-800 catalyst as metal-organic framework (MOF) derivative was first utilized to promote the intrinsic properties of MgH2. Compared to pure MgH2, which releases 1.24 wt% H2 in 60 min at 275 °C, the MgH2-10 NiFe-800 composite releases 5.85 wt% H2 in the same time. Even at a lower temperature of 250 °C, the MgH2-10 NiFe-800 composite releases 3.57 wt% H2, surpassing the performance of pure MgH2 at 275 °C. Correspondingly, while pure MgH2 absorbs 2.08 wt% H2 in 60 min at 125 °C, the MgH2-10 NiFe-800 composite absorbs 5.35 wt% H2 in just 1 min. Remarkably, the MgH2-10 NiFe-800 composite absorbs 2.27 wt% H2 in 60 min at 50 °C and 4.64 wt% H2 at 75 °C. This indicates that MgH2-10 NiFe-800 exhibits optimum performance with excellent kinetics at low temperatures. Furthermore, the capacity of the MgH2-10 NiFe-800 composite remains largely stable after 10 cycles. Moreover, the Mg2Ni/Mg2NiH4 acts as a “hydrogen pump”, providing effective diffusion channels that enhance the kinetic process of the composite during cycling. Additionally, Fe0 facilitates electron transfer and creates hydrogen diffusion channels and catalytic sites. Finally, carbon (C) effectively prevents particle agglomeration and maintains the cyclic stability of the composites. Consequently, the synergistic effects of Mg2Ni/Mg2NiH4, Fe0, and C considerably improve the kinetic properties and cycling stability of MgH2. This work offers an effective and valuable approach to improving the hydrogen storage efficiency in the commercial application of MgH2.

Investigation of microstructure, hydrogen storage performance of Re-Mg-based alloy modified by RE2O3 (RE = Dy, Er, Yb)

In order to further study the hydrogen storage mechanism of Mg-based hydrogen storage materials, Mg90Ce5Y5 alloy was used as the basis, and three kinds of heavy rare earth oxides were doped into the alloy by ball milling technology. The microstructure and hydrogen storage properties were characterized by XRD, SEM, TEM and PCI. The results show that the hydrogen absorption rate and discharge rate of modified Mg90Ce5Y5 alloy are significantly increased, and the performance is Er2O3 > Dy2O3 > Yb2O3. The hydrogen storage capacity of Er2O3 catalyzed samples is 5.02 wt%, which is higher than 4.82 wt% and 4.80 wt% of Dy2O3 and Yb2O3 catalyzed samples. The hydrogen absorption saturation rate of the sample catalyzed by Er2O3 for 2 min is ∼90 %, the complete release of hydrogen only takes 50 min at 573 K, and the dehydrogenation activation energy is 76.9 kJ/mol. The hydrogen absorption and emission rate is fast, and the dehydrogenation activation energy is slightly lower than that of the other two catalysts. In the process of hydrogen absorption and desorption, the three catalysts exhibit different phase transitions, namely DyH2↔DyH3, ErH2↔ErH3 and irreversible YbH2. DyH2↔DyH3, ErH2↔ErH3 phase transitions have the "hydrogen pump" effect, which can effectively improve the hydrogen absorption and desorption kinetic rate of Mg90Ce5Y5 alloy. Some nano-rare earth compounds and phase transformation significantly improve the kinetic properties of the alloy. However, the enthalpy change of all three catalytic alloys is around 76 kJ/mol H2, which is considered only a slight improvement in thermodynamic properties.

The effect of irradiation for Nafion membrane electrode rapid separation of hydrogen-methane by electrochemical hydrogen pumps

Designing an efficient and reliable tritium plant has become a major challenge to developing nuclear fusion, which focuses on efficient and safe hydrogen isotope separation and purification. The electrochemical hydrogen pump (EHP) developed in recent years can be used to separate and compress hydrogen. Herein, we used the commercial Nafion membrane electrode in the EHP, which has excellent H2/CH4 separation performance. When the cell voltage is at 0.8 V, the current density is 2.04 A/cm2, the hydrogen separation rate can reach 14.2 mL/ (min ·cm2), and the hydrogen purity is more than 99.99 %. The damage mechanism of electron beam irradiation on the membrane electrode was revealed. It was found that irradiation caused Nafion’s main chain and branch chain to break, producing hydroxyl and carboxyl functional groups. The degree of chain fracture increased with the radiation dose, perforation and cracks occurred in the proton exchange membrane (PEM). Under the electron beam irradiation dose of 10 kGy, the membrane electrode can still maintain excellent H2/CH4 separation performance, and the hydrogen permeability caused by cracks and perforations is at a very low level. This study reveals the change of macroscopic performance caused by the microscopic mechanism of membrane electrode irradiation damage, provides a promising way to separate hydrogen isotope gases and is expected to promote the development of tritium plants in fusion engineering.

Design and multi-objective optimization of hybrid process of membrane separation and electrochemical hydrogen pump for hydrogen production from biogas

A new hybrid process for hydrogen (H2) production that including membrane separation, electrochemical hydrogen pump (EHP) and steam methane reforming (SMR) was proposed. Firstly, the combination of two different membranes (PEO-CA) is applied to upgrade the biogas and capture CO2. Secondly, to avoid the toxic effect of CO on the EHP catalyst and, more importantly, to improve the H2 purity, the reforming reaction module is supplemented with water gas shift after the SMR. Finally, EHP is used to achieve high purity hydrogen. Simultaneously, the heat and power integration are considered to improve system efficiency. Sensitivity analysis, maximal information coefficient method and response surface methodology are applied to establish the correlation between objectives and parameters. Then, the second generation multi-objective non-dominated genetic algorithm (NSGA-II) is utilized to achieve minimum levelized cost of hydrogen (LCoH) and carbon emission per unit of hydrogen (ECO2). The optimized LCoH is 2.72 $/kgH2, and the ECO2 is 3.24 kgCO2e. Multi-stage membrane carbon capture process enhances CH4 conversion in SMR. The application of EHP reduces energy consumption and enhances hydrogen yield compared to PSA. The innovative use of membrane is hybridized with EHP to achieve the system intensification. The new hybrid process has a significant advantage in terms of ECO2 (37.45% reduction), although the price is higher compared to conventional biogas-to-hydrogen processes. Thus the new process is a promising low-carbon hydrogen production process from biogas.

Ultralow degradation cold start of proton exchange membrane fuel cell with alternating hydrogen pump method

Cold start impedes widespread diffusion of fuel cell vehicles (FCVs) in regions with temperatures below zero. Alternating hydrogen pump (AHP) method, distinguished by its unlimited ohmic heating capability without generating water, has been shown to be a quick and efficient method of cold starts in both single cell and short stacks. In this paper, we continue to examine possible degradation with this novel method. For this purpose, we carefully designed three experiments with different levels of stress, aimed to separate the contribution to any degradation from major factors. It was found there was no significant difference among the three cases. AHP method incurred minimal degradation after 3600 times of equivalent −30 °C cold starts. This study concludes that AHP method is not only quick and efficient, but also highly durable, hence AHP is a promising alternative cold start strategy with great potential to facilitate the diffusion of FCVs.

Improvement of Reversal-Tolerance of Pt/Ti4O7-C Catalysts by the Addition of Oxygen Evolution Catalysts

When hydrogen is depleted in a polymer electrolyte fuel cell, the anode potential increases (cell reversal), which involves the oxidation of supported carbon (COR) and causes the growth of Pt particles, resulting in the deactivation of the anode catalyst. The addition of the oxygen evolution (OER) catalysts has been reported to suppress the degradation1. Though it has also been reported that the combination of Ti4O7 with Ir catalysts increased the reversal tolerance2, the combination of Pt/Ti4O7 and Ti4O7-supported OER catalysts has not been reported. We have reported that Pt catalysts supported on Ti4O7-C synthesized by the carbothermal process showed excellent performance3. In order to investigate how the distribution of the OER catalyst in the catalyst layer affects the reversal-tolerance, we compared the performance of the physical mixture of Pt/Ti4O7-C and Ti4O7-supported OER catalysts with the composite catalysts (Pt and OER catalyst supported on Ti4O7-C) in this study. The hydrogen starvation was carried out during the hydrogen pump tests in order to clarify the degradation on HOR. Experimental Preparation of catalysts: 20 wt% Pt/Ti4O7-C (11 wt% C) was prepared as previously reported3. RuO2 catalysts Ti4O7-C or Pt/Ti4O7-C was impregnated with RuCl3 solution, and precipitated at pH 8 with NaOH solution. The residue was washed, and dried at 150°C. 21 wt% RuO2/Ti4O7-C and 19 wt% Pt-2.0 wt% RuO2/Ti4O7-C were used for the physical mixture (abbreviated to catalyst-M) and for the composite catalyst, respectively. IrO2 catalysts Ti4O7-C or Pt/Ti4O7-C was impregnated in IrCl3 solution, and hydrothermally treated at 180°C. Afterwards, the solution was washed and dried at 80°C. 3.8 wt% IrO2 and 8 wt% Pt-3.7 wt% IrO2/Ti4O7-C were used for the physical mixture and the composite catalyst, respectively. Electrochemical measurement: The MEA was composed of Nafion NRE211 as the electrolyte membrane, a commercial heat-treated c-Pt/C (Pt loading: 0.5 mg-Pt/cm2) as the cathode, and the above-mentioned catalyst or a commercially available c-Pt/C (Pt loading: 0.2 mg-Pt/cm2) as the anode. The RuO2 and IrO2 loadings were 0.021- 0.042 mg/cm2 and are indicated in parentheses. The performance was evaluated with IV curves, the hydrogen pump, CV and LSV by flowing H2 gas to the cathode under 80°C fully humidified condition. The hydrogen starvation was performed by switching the anode supply gas to N2 (RH 100%) while the hydrogen pump was carried out at 0.2 A/cm2 for 10 minutes at a cutoff voltage of 2.7 V. After the test, a hydrogen pump, CV, LSV, and an IV test were performed. The second hydrogen starvation test was repeated in the same manner. Results and Discussion As shown in Table 1, the voltage of c-Pt/C quickly increased above 1.7 V, however, a plateau was observed at 1.8 V after the rapid voltage increase during the second hydrogen starvation, which indicated COR. After the second hydrogen starvation, the current at 0.4 V for the LSV increased from 7.1 mA/cm2 before the second test to 47.9 mA/cm2, indicating the damage of the membrane. The HOR activity also deteriorated after the hydrogen starvation. No improvement was observed for Pt/Ti4O7-C and Pt/Ti4O7-C+RuO2/Ti4O7-M (0.025) under this condition, however, the voltage rise to 1.7 V on the RuO2 composite catalyst was suppressed for the first starvation, due to the OER. This effect disappeared for the second hydrogen starvation. On the other hand, the catalyst physically mixed with IrO2/Ti4O7-C showed a voltage plateau from 1.50 to 1.75 V during the hydrogen starvation, indicating a significant improvement, and the increase in the IrO2 loading improved the reversal-tolerance. Furthermore, for the IrO2 composite catalyst, a plateau due to the OER was observed at 1.5 - 1.7 V for the two hydrogen starvation tests. The voltage increase of the hydrogen pump after the tests was also slight and the change in ECSA was small. Since the difference from the physical mixture was clearly observed, it was deduced that the OER catalyst in the vicinity of the Pt catalyst improved the reversal-tolerance.Acknowledgments: This work was supported by NEDO.(1) T. R. Ralph et al., Platinum Metals Rev. , 46, 117 (2002). (2) T. Ioroi et al., J. Power Sources, 450, 227656 (2020). (3) M. Chisaka et al., Chem. Comm. , 57, 12772 (2021). Figure 1

Hydrogen Contaminant Detectors for Ensuring Hydrogen Fuel Quality

The California Energy Commission tracks Hydrogen Refueling Station (HRSs) installations within California and states that there are 66 light duty retail stations open within the State with another 34 in the planning stages.1 The hydrogen dispensed in these stations is expected to meet SAE J2719 standards for the maximum allowable concentration of various impurities.2 Currently HRSs have their fuel analyzed periodically to verify that they meet fuel specifications. However, this implies that any anomaly in the purification system resulting in contaminated hydrogen can result in significant damage to fuel cell vehicles before being detected. Therefore, the development of hydrogen contaminant detectors that can continuously monitor the hydrogen for impurities like Carbon monoxide (CO) and hydrogen Sulfide (H2S) is of great interest. LANL has developed a hydrogen contaminant detector based on a hydrogen pumping cell that is sensitive to < 200 ppb CO and < 4 ppb H2S.3,4 In this talk we will present details of the working mechanism of this hydrogen contaminant detector and present results from the field testing of the detector at a HRS. Acknowledgements This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Safety, Codes & Standards (SCS) sub-program (Project Manager: Laura Hill).REFERENCES: https://www.energy.ca.gov/data-reports/energy-almanac/zero-emission-vehicle-and-infrastructure-statistics/hydrogen-refueling.San Marchi, E. S. Hecht, I. W. Ekoto, K. M. Groth, C. LaFleur, B. P. Somerday, R. Mukundan, T. Rockward, T; J. Keller, C. W. James, Int. J. Hydrogen Energy, 42(11), 7263-7274 (2017)Brosha, T. Rockward, C. J. Romero, M. S. Wilson, C. Kreller and R. Mukundan, U.S Patent # 10,490,833 (2019).R. Mukundan, E. L. Brosha, C. J. Romero, D. Poppe, T. Rockward, “Development of an electrochemical hydrogen contaminant detector”, Journal of The Electrochemical Society, 167(14), 147507 (2020)

Overcoming Challenges in Ion-Pair Membrane Technology: Advancements in Fuel Cells and Electrochemical Hydrogen Pumps

The Membrane Electrode Assembly (MEA) stands as the pivotal element in electrochemical devices such as fuel cells and electrochemical hydrogen pumps (EHP). Notably, ion-pair High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFCs) with reduced phosphoric acid concentrations within the MEA have been innovatively designed, allowing for the integration of diverse ion-conducting binders, known as ionomers, into both the cathode and anode electrodes [1]. This study delineates initial distinctions in MEA configurations among different device types (HT-Fuel cell and EHP), conducting a comprehensive analysis of performance disparities between traditional polybenzimidazole-based systems and various ion-pair proton exchange membranes [2].Subsequently, a detailed exploration unfolds, focusing on the utilization of ion-pair membranes and different ionomer types for the three aforementioned devices. This comprehensive examination offers a unified comparative analysis encompassing ionomer type, membrane thickness, catalyst:ionomer ratio, and phosphoric acid doping levels, particularly in the context of performance at intermediate temperatures (160℃). Conclusions are drawn based on results derived from both half-cell and single-cell evaluations. Finally, overarching guidelines are presented to inform the formulation of high-performance MEA configurations tailored for ion-pair HT-PEMFCs and EHPs.

Comparing Effects of Back Diffusion and Membrane Resistance on the Performance of a Low Temperature Electrochemical Hydrogen Pump

“Green” hydrogen produced via electrolysis using electricity from renewable energy sources is seen as a promising energy carrier to aid in the transition from fossil fuels because its production emits no carbon and consumes only water as a reactant. However, the high energy demand required to compress hydrogen to higher energy densities required for efficient transport and storage remains a bottleneck for its deployment1-4. Electrochemical hydrogen pumps (EHPs) are an attractive solution since they operate via isothermal compression and are thus more efficient than typical mechanical compressors which operate adiabatically1,2,5. EHPs also have the advantage of low noise, absence of moving parts, and ability to simultaneously purify hydrogen during compression1-4.In this study, an in-house built EHP test cell with an active geometric area of 25 cm2 was constructed using membrane electrode assemblies (MEA) based on a proton exchange membrane (PEM) and a platinum catalyst. The cell was used to pressurize hydrogen from atmospheric pressure to 10 barg. The net performance of EHPs is a result of the tradeoff between the two major losses that is, back diffusion of H2 and membrane resistance3-5. Thus, we compared the effect of varying temperature, in the range of 30-75°C, on cell performance. Current densities reaching 1.0 A cm-2 (corresponding to a specific hydrogen flow rate of 7.45 mLs min-1 cm-²) were achieved during testing. Linear sweep voltammetry was used to quantify the back diffusion of hydrogen with temperature, see Figure 1(a). Electrochemical impedance spectroscopy was used to determine the series resistance of the EHP. Figure 1(b) shows the increase in voltage with increasing high frequency resistance, whose largest contribution comes from the membrane, with reducing cell temperatures. Stepped chronopotentiometry measurements were used to characterize the overall cell performance. Figure 1 (c) and (d) show the effect of temperature on the polarization curves at a cathode pressure of 5 and 10 barg, respectively, of the EHP operating with an Aquivion E98-09S membrane with 0.25 mg cm-2 Pt per electrode. At 0.5 A cm-2, an applied voltage of 195 mV was required to compress hydrogen at atmospheric pressure in one step to 10 barg operating at 30°C, corresponding to an overall efficiency of 16%. When the cell temperature is raised to 75°C, a lower voltage of 132 mV is required at 0.5 A cm-2 due to the stronger effect of the reduced series resistance that leads to a higher cell efficiency of 27%. This work shows that membrane resistance has a greater effect than back diffusion on the overall EHP performance to pressures of 10 barg.Future work is focused on coupling this EHP with a photovoltaic driven electrolyser and further decreasing the energy demand required to compress hydrogen. References J. Zou, N. Han, J. Yan, Q. Feng, Y. Wang, Z. Zhai, J. Fan, L. Zeng, H. Li, H. Wang., Electrochemical Energy Reviews 2020, 3, 690–729.G. Sdanghi, J. Dillet, S. Didierjean, V. Fierro, G. Maranzana., Fuel Cells 2020, 3, 370-380Y. Hao, H. Nakajima, H. Yoshizumi, A. Inada, K. Sasaki, K. Ito., International Journal of Hydrogen Energy 2016, 41, 13879-13887.M. Ivanova, R. Peters, M. Müller, S. Haas, M. Seidler, G. Mutschke, K. Eckert, P. Röse, S. Calnan, R. Bagacki, R. Schlatmann, C. Grosselindemann, L. Schäfer, N. Menzler, A. Weber, R. Van de Krol, F. Liang, F. Abdi, S. Brendelberger, N. Neumann, J. Grobbel, M. Roeb, C. Sattler, I. Duran, B. Dietrich, C. Hofberger, L. Stoppel, N. Uhlenbruck, T. Wetzel, D. Rauner, A. Hecimovic, U. Fantz, N. Kulyk, J. Harting, O. Guillon., Angewandte Chemie, 2023, 62, e202218850B. Kee, D. Curran, H. Zhu, R. Braun, S. DeCaluwe, R. Kee, S. Ricote., Membranes 2019, 9,77. Figure 1

Y and Ni microalloying on Mg/MgH2 for enhancing the hydrogenation and dehydrogenation performance

Magnesium microalloying is an effective approach to reduce MgH2 stability and further improve the hydrogen storage performance. Here, we fabricated Mg-10Y and Mg-10Y-5Ni via mechanical alloying, and investigated the effect of Y and Ni microalloying on the hydrogenation and dehydrogenation performances. It was shown that the synergistic of Mg2NiH4/MgH2 can effectively reduce the hydrogen release energy barrier, playing an important role in thermodynamics. Besides, compared with pure Mg, a significant kinetics improvement of Mg-10Y was observed with 90% of the theoretical hydrogen storage capacity at only 5 min, which can be assigned to the "hydrogen pumping" effect of the dispersed YH2/YH3 phase. Furthermore, the introduction of Ni can effectively improve the hydrogen absorption/release of Mg-10Y, and the activation energy jumps from 117.76 to 59.97 kJ/mol H2. Note that the hydrogenation/dehydrogenation kinetics remained unchanged after 20 cycles, with a hydrogen uptake of 6.05 wt.% and release of 5.9 wt.%, suggesting that these alloys can be industrialized at a certain industrial level.

Vermiform Ni@CNT derived from one-pot calcination of Ni-MOF precursor for improving hydrogen storage of MgH2

The Ni-coated carbon nanotubes (Ni@CNT) composite was synthesized by the facile “filtration + calcination” of Ni-based metal−organic framework (MOF) precursor and the obtained composite was used as a catalyst for MgH2. MgH2 was mixed evenly with different amounts of Ni@CNT (2.5, 5.0 and 7.5, wt.%) through ball milling. The MgH2−5wt.%Ni@CNT can absorb 5.2 wt.% H2 at 423 K in 200 s and release about 3.75 wt.% H2 at 573 K in 1000 s. And its dehydrogenation and rehydrogenation activation energies are reduced to 87.63 and 45.28 kJ/mol (H2). The in-situ generated Mg2Ni/Mg2NiH4 exhibits a good catalytic effect due to the provided more diffusion channels that can be used as “hydrogen pump”. And the presence of carbon nanotubes improves the properties of MgH2 to some extent.

Graphene-loaded nickel−vanadium bimetal oxides as hydrogen pumps to boost solid-state hydrogen storage kinetic performance of magnesium hydride

To modify the thermodynamics and kinetic performance of magnesium hydride (MgH2) for solid-state hydrogen storage, Ni3V2O8-rGO (rGO represents reduced graphene oxide) and Ni3V2O8 nanocomposites were prepared by hydrothermal and subsequent heat treatment. The beginning hydrogen desorption temperature of 7 wt.% Ni3V2O8-rGO modified MgH2 was reduced to 208 °C, while the additive-free MgH2 and 7 wt.% Ni3V2O8 doped MgH2 appeared to discharge hydrogen at 340 and 226 °C, respectively. A charging capacity of about 4.7 wt.% H2 for MgH2 + 7 wt.% Ni3V2O8-rGO was achieved at 125 °C in 10 min, while the dehydrogenated MgH2 took 60 min to absorb only 4.6 wt.% H2 at 215 °C. The microstructure analysis confirmed that the in-situ generated Mg2Ni/Mg2NiH4 and metallic V contributed significantly to the enhanced performance of MgH2. In addition, the presence of rGO in the MgH2 + 7 wt.% Ni3V2O8-rGO composite reduced particle aggregation tendency of Mg/MgH2, leading to improving the cyclic stability of MgH2 during 20 cycles.

Mxene-supported NbVH nanoparticles as efficient catalysts for reversible hydrogen storage in magnesium borohydride

Bimetallic niobium vanadium hydride nanoparticles (NbVH NPs) anchored on Ti3C2 were synthesized using a facile ball milling method as an effective catalyst for the dehydrogenation kinetics and reversibility of Mg(BH4)2. It was found that the onset dehydrogenation temperature of the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite was 105.7 °C and released 9.07 wt% of hydrogen at 330 °C, while undoped Mg(BH4)2 only released 4.2 wt% of H2 from 248 °C to 330 °C. Additionally, the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite achieved remarkable hydrogen release of over 9.44 wt% at a temperature as low as 230 °C, indicating unexpected dehydrogenation kinetics. In the reversible hydrogen desorption tests, Mg(BH4)2 + 30NbVH NPs@Ti3C2 released 5.98 wt% of H2 in the 2nd cycle at 250 °C and maintained a reversible capacity of 4.35 wt% after 10 cycles, demonstrating a remarkable enhancement in reversibility. The enhancement in the dehydrogenation kinetics of Mg(BH4)2 could be attributed to the greatly reduced activation energies from 343 kJ·mol−1 and 138.3 kJ·mol−1 to 103.7 kJ·mol−1 and 124 kJ·mol−1. Investigations on the evaluation of catalyst and Mg(BH4)2 during reversible hydrogen storage have revealed that NbVH NPs actually acted as a “bidirectional hydrogen pump”, facilitating both the hydrogen release and uptake from Mg(BH4)2. This strategy of multi-component hydrides may show a new way to design effective catalysts for solid-state hydrogen storage materials.

Hydrogen extraction from 0.1 % H2–He mixture: The interplay phenomena of electrode, temperature, and voltage in BZYN & BZCYYb

Hydrogen pumps, crafted from proton-conductive ceramic electrolyte and paired with either oxide or metallic electrodes, have been designed for the extraction of hydrogen isotopes from helium gas mixtures containing 0.1 % hydrogen isotopes, particularly within the context of TES for nuclear fusion reactors. This study presents the electrochemical hydrogen permeation research conducted on the perovskite proton conductor materials BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and BaZr0.8Y0.16Ni0.04O3-δ (BZYN) under these operational conditions. It was observed that nickel electrodes provided superior performance over SrFe0.8Mo0.2O3-δ (SFM) electrodes in terms of hydrogen extraction efficiency. Hydrogen pumps that integrated BZCYYb as the electrolyte with nickel electrodes showed enhanced efficiency, while those utilizing BZYN as the electrolyte coupled with nickel electrodes demonstrated greater stability. Furthermore, the study explored the voltammetric nonlinearity at low hydrogen concentrations and the dependency of concentration polarization efficiency on both voltage and temperature, aiming to establish optimal conditions that balance stability and efficiency for both types of hydrogen pumps.

Technical evaluation of electrochemical separation of hydrogen from a natural gas/hydrogen mixture

In this work, we investigate the electrochemical separation of hydrogen from a 10% H2/methane natural gas blend using a single cell experimental setup for electrochemical hydrogen pumping (EHP). Results show that the overall efficiency for hydrogen separation is high, ranging from about 87% at 0.2 A/cm2 to 75% at 0.6 A/cm2. In addition, we develop a zero-dimensional model for the hydrogen separation process including the membrane permeation of H2 as well as CH4, N2, and CO2 as the main components in natural gas. We derive analytical expressions for the permeability of these gases as a function of temperature and membrane humidity using available permeability data. Although the presence of dilutive inert gases poses a challenge, the modelled data indicate that it should be possible to produce fuel cell quality hydrogen using a single hydrogen separation stage. Importantly, this indicates technological feasibility of distributing hydrogen for use in fuel cells through existing natural gas infrastructure. Extension of this research to combined hydrogen separation and compression within the same EHP unit is recommended as future work.

A 10 × 10 cm2 protonic ceramic electrochemical hydrogen pump for efficient and durable hydrogen purification

Protonic ceramic electrochemical hydrogen pumps (PCEHPs) have garnered notice as a promising technology for the hydrogen separation. However, the practical application of PCEHPs has been limited by the insufficient performance and stability. In this work, a 10 × 10 cm2 PCEHP with the symmetrical configuration of “porous Ni-BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb) supporting layer | porous Ni-BCZYYb functional layer | dense BCZYYb electrolyte layer | porous Ni-BCZYYb functional layer | porous Ni-BCZYYb supporting layer” is fabricated by the tape-casting, hot-pressing lamination, and co-sintering process. The PCEHP with an active area of 1.13cm2 shows an impressive hydrogen separation rate of 7.93 mL min−1 cm−2 under 0.3 V with a Faradaic efficiency of 88 % at 650 °C. Furthermore, it exhibits excellent stability for over 500 h in both the electrolysis and thermal cycling modes. Notably, a 10 × 10 cm2 PCEHP with a large active area of 81 cm2 was fabricated and demonstrated a remarkable H2 flux of 153.32 mL min−1 at 650 °C under 0.3 V. The results indicate that the developed PCEHPs have great potential for hydrogen purification.

Synergistic Effect of the Hydrogen Pump and Heterostructure Enables Superior Hydrogen Storage Performance of MgH2

Synergistic Effect of the Hydrogen Pump and Heterostructure Enables Superior Hydrogen Storage Performance of MgH₂