Pt/CeO2 catalyst synthesized by combustion method for dehydrogenation of perhydro-dibenzyltoluene as liquid organic hydrogen carrier: Effect of pore size and metal dispersion

Liquid organic hydrogen carrier (LOHC) is a chemical hydrogen storage method that stores hydrogen in the form of liquid organics. Dibenzyltoluene (DBT) is a promising LOHC material due to its high storage density, low ignitability, and low cost. In this study, Pt/Al₂O₃ and Pt/CeO₂ catalysts are synthesized using a combustion nanocatalyst synthesis method called the glycine nitrate process (GNP) to obtain high catalytic activity for the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT). Pt/CeO₂ exhibits much faster dehydrogenation than Pt/Al₂O₃, 80.5%/2.5 h versus 3.5%/2.5 h. To investigate the causes of the difference in the dehydrogenation rates, microstructural characterization by N₂ physisorption, CO chemisorption and transmission electron microscopy analysis are conducted, and the catalytic activities are evaluated at various liquid hourly space velocities (LHSVs). The differences in dehydrogenation can be attributed to the mass transport of liquid H18-DBT into the catalyst pores being slow due to the small pores in Pt/Al₂O₃, which is a rarely addressed issue for other LOHC materials. This is because many LOHC materials are dehydrogenated at the gas phase, which has higher diffusivity than that of the liquid phase. Pt/CeO₂ synthesized by the GNP is also compared with a commercial Pt/Al₂O₃ catalyst. The commercial Pt/Al₂O₃ catalyst shows a dehydrogenation of 17.8%/2.5 h, which is much slower than that of Pt/CeO₂ synthesized by the GNP, at 80.5%/2.5 h.     

Viscosity,surface tension,and density of the liquid organic hydrogen carrier system based on diphenylmethane,biphenyl, and benzophenone

Liquid organic hydrogen carriers (LOHCs) relying on eutectic diphenylmethane-biphenyl mixtures feature advantageous characteristics such as low melting points and large hydrogen storage capacities. For contributing to a reliable database of process-relevant thermophysical properties, the present study investigates the viscosity, surface tension, and density of the LOHC-system based on diphenylmethane, biphenyl, and benzophenone between (278 and 573) K. General agreement between the viscosity and surface tension results from surface light scattering and the data from capillary viscometry and pendant-drop tensiometry is found. Larger surface tension differences beyond 10% for systems containing benzophenone seem to originate from surface orientation effects. For the eutectic diphenylmethane-biphenyl mixture including its hydrogenated dicyclohexylmethane-bicyclohexyl analog, the densities, surface tensions, and viscosities are not significantly different from those of the corresponding pure compounds. By gradually replacing diphenylmethane by its oxidized form benzophenone in mixtures with biphenyl, an increase in density, surface tension, and especially viscosity is observed.     

Efficiency analysis of depressurization process and pressure control strategies for liquid hydrogen storage system in microgravity

In order to investigate dynamic characteristics of pressure fluctuation and thermal efficiency of a liquid hydrogen (LH₂) storage system during depressurization process under microgravity condition, a transient CFD model of LH₂ tank is established. Based on the assumption of lumped vapor, a UDF code is developed to solve phase change and heat transfer between liquid phase and vapor one. The thermal efficiency is provided for assessing the performance of different pressure control methods. Results show that raising the injection velocity and decreasing the temperature of the injection liquid can enhance the effect of fluid mixing and shorten the depressurization time. Increasing the pressure lower limit can also improve the efficiency of depressurization process. The model can predict the tendency of pressure changes in the tank, and provide theoretical guide to design LH₂ tank and optimize its parameters for space application.     

Dehydrogenation of ethylene diamine monoborane adducts and their cyclic products (monomers,dimers, and trimers): Potential liquid organic hydrogen carriers

The dehydrogenation mechanisms of ethylene diamine monoborane (EDMB) adducts and its derivatives having CH₃, Cl, F, NH₂, OCH₃, CN, and H substituents at two sites on the ethylene backbone were investigated to explore their potential as liquid organic hydrogen carriers (LOHCs). Using density functional theory calculations, the thermodynamic parameters of the EDMB adducts and dehydrogenation reactions to form cyclic monomers, dimers, and trimers were calculated. In particular, we focused on the free energy barriers of EDMB adducts substituted with Cl/CN, Cl/OCH₃, F/CN, F/OCH₃, F/F, and NH₂/H for cyclic monomer formation, H/CH₃, H/CN, Cl/H, and NH₂/H for cyclic dimer formation, and H/Cl, H/F, and NH₂/H for cyclic trimer formation, which are promising candidates for chemical hydrogen storage. We also explored the formation of cyclic trimers from the selected cyclic monomers with CH₃/CH₃, H/CH₃, and NH₂/H substituents. As a result, the dehydrogenation pathways and transition states of the various adducts for the formation for the various cycles were identified, and electrostatic potential surfaces and frontier molecular orbitals calculations were calculated to understand the reaction further. The results obtained indicate the potential of these materials for hydrogen storage, and we hope that this work will encourage the experimental investigation of these materials.     

Tuning the alloy degree for Pd-M/Al2O3 (M=Co/ Ni /Cu) bimetallic catalysts to enhance the activity and selectivity of dodecahydro-N-ethylcarbazole dehydrogenation

Hydrogen is a promising candidate to substitute the fossil fuels. However, the efficient hydrogen storage technologies restrict the commercial applications. Developing new catalysts with high activity and selectivity is important for the dehydrogenation reaction in N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NECZ/12H-NECZ) hydrogen storage system. In this work, a series of Pd-M/Al₂O₃ (M = Co, Ni and Cu) bimetallic catalysts are synthesized successfully and show good performance in the dehydrogenation reaction of 12H-NECZ than the commercial Pd/Al₂O₃ catalyst. The Pd₁Co₁/Al₂O₃ catalyst (Practical Pd content = 2.4136 wt%) showed the highest catalytic performance with 95.34% H₂ release amount, TOF of 230.5 min⁻¹ and 85.4% selectivity of NECZ. Combined with the characterization analysis, it can be proposed that the dehydrogenation performance of 12H-NECZ is dependent on the alloy phases, reasonable electronic structures and nanoparticle size of catalysts. The fine-tuned alloy degree and appropriate nanoparticle size of Pd₁Co₁/Al₂O₃ bring the 17.7% increase of H₂ release amount and 99.5% increase of NECZ selectivity than those of Pd/Al₂O₃. For the bimetallic catalysts, the enhancement of selectivity of NECZ is mainly from the increase of the kinetic constant of rate-limiting step.     

Thermodynamic analysis and assessment of novel ORC- DEC integrated PEMFC system for liquid hydrogen fueled ship application

Proton-exchange membrane fuel cell (PEMFC) and liquid hydrogen are gaining attention as a power generation system and alternative fuel of ship. This study proposes a novel PEMFC system, integrated with the organic Rankine cycle–direct expansion cycle (ORC-DEC), which exploits cold exergy from liquid hydrogen and low temperature waste heat generated by the PEMFC for application in a liquid hydrogen fueled ship. A thermodynamic model of each subsystem was established and analyzed from the economic, energy, and exergy viewpoints. Moreover, parametric analysis was performed to identify the effects of certain key parameters, such as the working fluid in the ORC, pressure exerted by the fuel pump, cooling water temperature of the PEMFC, and the stack current density on the system performance. The results showed that the proposed system could generate 221 kW of additional power. The overall system achieved an exergy and energy efficiency of 43.52 and 40.45%, respectively. The PEMFC system had the largest exergy destruction, followed by the cryogenic heat exchanger. Propane showed the best performance among the several investigated ORC working fluids and the system performance improved with the increase in the cooling water temperature of the PEMFC. The economic analysis showed that the average payback time of ORC-DEC was 11.2 years and the average net present value (NPV) was $295,268 at liquid hydrogen costing $3 to $7, showing the potential viability of the system.     

Balancing molecular level influences of intermolecular frustrated Lewis pairs (FLP) for successful design of FLP catalysts for hydrogen storage applications

The rise in energy demands and the deleterious environmental issues related to fossil fuels has led to a surge of interest in hydrogen as a “green” alternative. Hydrogen's extraordinary energy density makes it a potential energy and economic “power”-house. Significant research has been dedicated to materials-based hydrogen storage. One area, liquid organic hydrogen carriers (LOHC) is of substantial interest for the reversible transportation of hydrogen from production to end-use facilities. There are challenges associated with this technology including the dependency on precious metal-based catalysts. Recent work in frustrated Lewis pair (FLP) catalysis demonstrates promise for addressing these challenges. This review is focused on assessing recent literature on the utilization of intermolecular FLP main group catalysts for improved hydrogenation/dehydrogenation of various substrates including potential LOHC complexes. This review will present an overview of FLPs, highlight potential hydrogen storage applications, and propose areas where knowledge gaps exist that require further investigations.     

Modeling and optimization of composite thermal insulation system with HGMs and VDMLI for liquid hydrogen on orbit storage

The passive thermal insulation system for liquid hydrogen (LH₂) on orbit storage mainly consists of foam and variable density multilayer insulation (VDMLI) which have been considered as the most efficient and reliable thermal insulation system. The foam provides main heat leak protection on launch stage and the VDMLI plays a major role on orbit stage. However, compared with the extremely low thermal conductivity of VDMLI (1 × 10⁻⁵ W/(m·K)) at high vacuum, the foam was almost useless. Recently, based on hollow glass microspheres (HGMs) we have proposed the HGMs-VDMLI system which performs better than foam-VDMLI system. In order to improve insulation performance and balance weigh and environmental adaptability of passive insulation system, the HGMs-VDMLI insulation system should be configured optimally. In this paper, the thickness of HGMs and the number and arrangement of spacers of VDMLI were configured optimally by the “layer by layer” model. The effective thicknesses of HGMs were 25 mm for 60 layers MLI and 20 mm for 45 layers VDMLI. Compared with 35 mm foam and 45 layers VDMLI system, the heat flux of 20 mm HGMs and 45 layers VDMLI system was reduced by 11.97% with the same weight, or the weight of which was reduced by 9.91% with the same heat flux. Moreover, the effects of warm boundary temperature (WBT) and vacuum pressure on thermal insulation performance of the system were also discussed.     

Catalyst development for viability of electrochemical hydrogen purifier and compressor (EHPC) technology

Considering the disadvantages of conventional compressors, which are widely used in the world, it is thought that the electrochemical hydrogen purifier and compressor system (EHPC) to be developed will provide great advantages in hydrogen technologies. The electrocatalyst, which is one of the main components of the EHPC system, is critical for both the performance and applicability of the system. In this study, commercial carbon black supported Pt and Pd containing catalysts were prepared for the EHPC system by using microwave heating method. The synthesized catalysts were mono and bimetallic and were named as Pt/C, Pd/C and PtPd/C, respectively. By characterizing the prepared catalysts with ICP-MS, SEM-EDS, TEM, XRD and XPS, information about the distribution, amount, morphology and composition of metal nanoparticles on the support material was obtained. In addition, electrochemical properties of the catalysts were determined by CV analysis. The physical characterization results revealed that the catalysts were successfully synthesized by microwave method and that different ratios of metals and bimetallic could be loaded on the support material. It was also seen that the electrochemical activity of the PtPd/C bimetallic catalyst was better than the others.     

Development and performance evaluation of Proton Exchange Membrane (PEM) based hydrogen generator for portable applications

This paper presents the development of key components, specifications, configuration and operation characteristics of an 80 l/h Proton Exchange Membrane (PEM) water electrolyzer system for portable application. The developed PEM water electrolyzer can produce 80 l/h hydrogen (purity > 99.99%) with moderate pressure range up to 500 kPa (73 psi) at an operating current of 100 A with energy efficiency of 77.48%. The reliability in operation of developed PEM water electrolyzer system is tested for running the stack about 3000 h with 100 A current. The results indicate the reasonable stability of MEA fabrication and cell design method.     

Analysis and assessment of partial re-liquefaction system for liquefied hydrogen tankers using liquefied natural gas (LNG) and H2 hybrid propulsion

Boil-off gas (BOG) is inevitable on board liquefied hydrogen tankers and must be managed effectively, by using it as fuel, re-liquefying it or burning it, to avoid cargo tank pressure issues. This study aims to develop a BOG re-liquefaction system optimized for l60,000 m³ liquefied hydrogen tankers with an LNG and hydrogen hybrid propulsion system. The proposed system comprises hydrogen compression and helium refrigerant sections with 2 J–Brayton cascade cycles. Cold energy recovery from the fuels and feed BOG exiting the cargo tanks was used. The system exhibits a coefficient of performance (COP) of 0.07, a specific energy consumption (SEC) of 3.30 kWh/kg_LH2, and exergy efficiency of 74.9%, with the hydrogen BOG entering the re-liquefaction system at a feed temperature of −220 °C. The theoretical COP and SEC values at ideal conditions were 0.09 and 2.47 kWh/kg_LH2, respectively. The effects of varying the hydrogen compression pressure, inlet temperature of the hydrogen expander, feed hydrogen temperature and helium compression pressure were investigated. Additionally, the LNG-to-hydrogen fuel ratio was adjusted to satisfy the Energy Efficiency Design Index (EEDI) Phase 2 and 3 emission requirements.     

Synthesis and characterization of crosslinked sulfonated poly(arylene ether sulfone) membranes for high temperature PEMFC applications

Sulfonated poly(arylene ether sulfone) copolymers containing carboxyl groups are prepared by an aromatic substitution polymerization reaction using phenolphthalin, 3,3′-disulfonated-4,4′-dichlorodiphenyl sulfone, 4,4′-dichlorodiphenyl sulfone and 4,4′-bisphenol A as polymer electrolyte membranes for the development of high temperature polymer electrolyte membrane fuel cells. Thin, ductile films are fabricated by the solution casting method, which resulted in membranes with a thickness of approximately 50 μm. Hydroquinone is used to crosslink the prepared copolymer in the presence of the catalyst, sodium hypophosphite. The synthesized copolymers and membranes are characterized by ¹H NMR, FT-IR, TGA, ion exchange capacity, water uptake and proton conductivity measurements. The water uptake and proton conductivity of the membranes are decreased with increasing the degree of crosslinking which is determined by phenolphthalin content in the copolymer (0-15 mol%). The prepared membranes are tested in a 9 cm² commercial single cell at 80 °C and 120 °C in humidified H₂/air under different relative humidity conditions. The uncrosslinked membrane is found to perform better than the crosslinked membranes at 80 °C; however, the crosslinked membranes perform better at 120 °C. The crosslinked membrane containing 10 mol% of phenolphthalin (CPS-PP10) shows the best performance of 600 mA cm⁻² at 0.6 V and better performance than the commercial Nafion^® 112 (540 mA cm⁻² at 0.6 V) at 120 °C and 30 % RH.     

Measurements and predictive models of high-pressure H2 solubility in brine (H2O+NaCl) for underground hydrogen storage application

In the context of Underground Hydrogen Storage (UHS), the stored gas is in direct contact with brine (residual brine from the cavern or formation water of deep aquifers). Therefore, knowledge of the phase equilibria (solubility of hydrogen in brine and water content in the hydrogen-rich phase) in the geological reservoir is necessary for the study of hydrogen mobility and reactivity, as well as the control, monitoring and optimization of the storage. The absence of measured data of high-pressure H₂ solubility in brine has recently led scientists to develop predictive models or to generate pseudo-data using molecular simulation. However, experimental measurements are needed for model evaluation and validation. In this work, an experimental apparatus based on the “static-analytic” method developed and used in our previous work for the measurement of gas solubility in brine was used. New solubility data of H₂ in H₂O+NaCl were measured more or less under the geological conditions of the storage, at temperatures between 323 and 373 K, NaCl molalities between 0 and 5m, and pressures up to 230 bar. These data were used to parameterize and evaluate three models (Geochemical, SW, and e-PR-CPA models) tested in this work. Solubility and water content tables were generated by the e-PR-CPA model, as well as a simple formulation (Setschenow-type relationship) for quick and accurate calculations (in the fitting range) of H₂ solubility in water and brine was proposed. Finally, the developed models estimate very well the water content in hydrogen-rich phase and capture and calculate precisely the salting-out effect on H₂ solubility.     

Hydrolysis characteristics of calcium hydride (CaH2) powder in the presence of ethylene glycol,methanol, and ethanol for controllable hydrogen production

Calcium hydride (CaH₂) reacts vigorously with water, liberating hydrogen gas. For the development of an effective hydrogen storage system, it is an absolute necessity to control the rate of hydrogen production. In the present study, the effects of different solvent, ethylene glycol, methanol, and ethanol, on the hydrolysis of CaH₂ for controllable hydrogen production were investigated. Reactions were performed at different temperatures (20, 40, and 60°C) in order to calculate the kinetic parameters. The Arrhenius equation was used to calculate the activation energies. The activation of energy of the hydrolysis reaction of CaH₂ in an ethanol solution (E_a = 20.03 kJ/mol) was found to be less than the other reactions.     

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m² PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m² evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between ?0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.     

Effect of O2 and temperature on the catalytic performance of Ni/Al2O3 and Ni/MgAl2O4 for the dry reforming of methane (DRM)

Al₂O₃ and MgAl₂O₄ supported 10% (w/w) Ni catalysts having a dispersion of 1.5 and 2.0% are active for DRM at 600 and 750 °C. High temperature reduction of both the calcined catalysts resulted in metallic Ni being formed, suggesting strong support metal interactions. The CH₄ and CO₂ conversion during DRM are relatively constant with time-on-stream, and are higher for Ni/MgAl₂O₄ than Ni/Al₂O₃. Carbon-whiskers are also detected on both catalysts. O₂ co-feed of 2.6% (v/v) and increasing reaction temperature to 750 °C helped in decreasing the amount of carbon deposited, except for Ni/MgAl₂O₄ at 600 °C. Furthermore, higher conversions and H₂/CO ratios are achieved. It appears that on spent Ni/MgAl₂O₄ a different type of carbon species was formed, and this carbon species was difficult to remove by oxygen at 600 °C. Thus, co-feeding O₂, using an appropriate temperature, and choosing a suitable support can reduce the carbon present on the nickel catalysts during DRM.     

Influence of reduction temperature on Ni particle size and catalytic performance of Ni/Mg(Al)O catalyst for CO2 reforming of CH4

Hydrotalcite-derived Ni/Mg(Al)O is promising for CH₄–CO₂ reforming. However, the catalysts reported so far suffer from sever coking at low temperatures. In this work, we demonstrate that a significant improvement of coke-resistance of Ni/Mg(Al)O can be achieved by fine tuning the Ni particle size through adjusting the reduction condition of catalyst. Ni particles having average size within 4.0–7.1 nm are in situ generated by reducing the catalyst at a selected temperature within 923–1073 K. Controllability of Ni particle size is related to the formation of Mg(Ni,Al)O solid solution upon hydrotalcite decomposition. It is found that the catalyst reduced at 973 K exhibits high activity, stability, and coke-resistance even at reaction temperature as low as 773 K. In contrast, the catalyst reduced at 923 K has low activity and deactivates due to Ni oxidation, while those reduced at 1023 and 1073 K suffer from sintering and severe coking. STEM and O₂-TPO reveal that coke deposition is directly proportional to the Ni particle size but becomes negligible at a size below 6.2 nm. It is evidenced that a critical size of about 6 nm is required to inhibit coking effectively. CO₂ temperature-programmed surface reaction indicates that the deposited carbon on small Ni particles can be easily removed by the CO₂ activated at the Ni–Mg(Al)O interfaces, accounting for the better resistance to coking.