Design and computational analysis of a metal hydride hydrogen storage system with hexagonal honeycomb based heat transfer enhancements-part A

In this study, design and performance analysis is carried out for a 10 kWh metal hydride based hydrogen storage system. The system is equipped with distinctive aluminium hexagonal honeycomb based heat transfer enhancements (HTE) having higher surface area to volume ratio for effective heat transfer combined with low system weight addition. The system performance was studied under different operating conditions. The optimum absorption condition was achieved at 35 bar with water at room temperature as heat transfer fluid where up to 90% absorption was completed in 7200 s. The performance of the reactor was observed to significantly improve upon the addition of the HTE network at a minimal system weight penalty.     

Studies on 10kg alloy mass metal hydride based reactor for hydrogen storage

A 10 kg alloy mass metal hydride reactor, with LaNi₅ alloy was designed. Heat transfer enhacement in the reactor was achieved by including embedded cooling tubes and an external water jacket. Detailed parametric study has been carried to understand the performance of the system. The effect of both geometrical and operational parameters was studied in simulations. The optimized geometrical parameters were used for fabricating the reactor. Experimental studies were carried on the fabricated reactor. Absorption studies were carried out for different supply pressure and different cooling fluid temperatures. Storage capacity of 1.13 wt% was found in 1620 s at a supply pressure of 25 bar and with a flow rate of 20 LPM. Similarily, desorption studies were carried out for varying heat transfer fluid temperatures. Complete and fastest desorption was observed at 80 °C with the reaction completion time of 2700 s.     

Computational study on metal hydride based three-stage hydrogen compressor

A mathematical model for predicting the performances of a three-stage metal hydride based hydrogen compressor (MHHC) is presented. The performance of the MHHC is predicted by solving the unsteady heat and mass transfer characteristics of the coupled metal hydride beds of cylindrical configuration. The governing equations for energy, momentum and mass conservations, and reaction kinetic equations are solved simultaneously using the finite volume method. Metal hydrides chosen for a three-stage MHHC are LaNi₅, MmNi_4.6Al_0.4 and Ti_0.99Zr_0.01V_0.43Fe_0.99Cr_0.05Mn_1.5. Numerical results obtained for a single-stage MHHC using MmNi_4.6Al_0.4 are in good agreement with the experimental data reported in the literature. Using three-stage compression, a maximum pressure ratio of 28 is achieved for the supply conditions of 20 °C absorption temperature and 2.5 bar supply pressure. A maximum delivery pressure of 100 bar is obtained for the operating conditions of 20 °C absorption temperature and 120 °C desorption temperature.     

Refueling-station costs for metal hydride storage tanks on board hydrogen fuel cell vehicles

Refueling costs account for much of the fuel cost for light-duty hydrogen fuel-cell electric vehicles. We estimate cost savings for hydrogen dispensing if metal hydride (MH) storage tanks are used on board instead of 700-bar tanks. We consider a low-temperature, low-enthalpy scenario and a high-temperature, high-enthalpy scenario to bracket the design space. The refueling costs are insensitive to most uncertainties. Uncertainties associated with the cooling duty, coolant pump pressure, heat exchanger (HX) fan, and HX operating time have little effect on cost. The largest sensitivities are to tank pressure and station labor. The cost of a full-service attendant, if the refueling interconnect were to prevent self-service, is the single largest cost uncertainty. MH scenarios achieve $0.71–$0.75/kg-H₂ savings by reducing compressor costs without incurring the cryogenics costs associated with cold-storage alternatives. Practical refueling station considerations are likely to affect the choice of the MH and tank design.     

Study on performance comparison of different fin combinations of catalyst filled plate fin heat exchanger for hydrogen liquefaction

A mathematical model of catalyst filled plate fin heat exchanger (CFPFHE) is established to compare different fin models and analyze fin performance of different fin combinations. The results show that the single-layer fin model inadequately reflects the double-layers fin model from flow distribution and fin performance. The indexes of ortho-para hydrogen conversion (YY_pH2) of different fin combinations are all about 0.95, meeting the requirement of the CFPFHE. The plain_serrated fin has the best fin performance among four fin combinations. Compared with the plain_plain, the Colburn heat transfer factor (j factor) and thermal enhancement factor (TEF) of cool and hot sides of the plain_serrated fin are increased by 68.0～51.0% and 28.5～13.6%, 8.5～6.1% and 8.4%～6.1% at Re_hot = 500～1500, respectively. Further, the fin combinations of high-efficiency fin and plain respectively used in cool and hot sides have excellent overall fin performance, which provides a theoretical guidance for fin selection of the CFPFHE.     

Enhanced hydrogen storage performance of Cu3(BTC)2 in situ inserted with few-layer silicon-based nanosheets

Silicon-based nanosheets (SNS) were synthesised via a mild (60 °C) and time-saving (8 h) modified topochemical method. Then, Cu₃(BTC)₂ and SNS@Cu₃(BTC)₂ were successfully synthesised by microwave irradiation, and their characteristics and hydrogen storage performance were analysed by multiple techniques. The accordion-like SNS exhibited void spaces, a unique low buckled structure, and ultrathin, almost transparent, loosely stacked layers with a high specific surface area (362 m²/g). After in-situ synthesis with Cu₃(BTC)₂, the SNS compound achieved a high specific surface area (1526 m²/g), outstanding hydrogen storage performance (5.6 wt%), and a desirable hydrogen diffusion coefficient (10^?7). Thus, SNS doping improved the hydrogen storage performance of Cu₃(BTC)₂ by 64% through electron transfer reactions with Cu enabled by the unique composite nanostructure of SNS@Cu₃(BTC)₂. This study presents a promising method of synthesising SNS and porous composite materials for hydrogen storage.     

Performance analysis of a novel solar PTC integrated system for multi-generation with hydrogen production

The performance analysis of a novel multi-generation (MG) system that is developed for electricity, cooling, hot water and hydrogen production is presented in this study. MG systems in literature are predominantly built on a gas cycle, integrated with other thermodynamic cycles. The aim of this study is to achieve better thermodynamic (energy and exergy) performance using a MG system (without a gas cycle) that produces hydrogen. A proton exchange membrane (PEM) utilizes some of the electricity generated by the MG system to produce hydrogen. Two Rankine cycles with regeneration and reheat principles are used in the MG configuration. Double effect and single effect absorption cycles are also used to produce cooling. The electricity, hot water, cooling effect, and hydrogen production from the multi-generation are 1027 kW, 188.5 kW, 11.23 kg/s and 0.9785 kg/h respectively. An overall energy and exergy efficiency of 71.6% and 24.5% respectively is achieved considering the solar parabolic trough collector (PTC) input and this can increase to 93.3% and 31.9% if the input source is 100% efficient. The greenhouse gas emission reduction of this MG system is also analyzed.     

A strategy of mid-temperature natural gas based chemical looping reforming for hydrogen production

Steam methane reforming (SMR) needs the reaction heat at a temperature above 800 °C provided by the combustion of natural gas and suffers from adverse environmental impact and the hydrogen separated from other chemicals needs extra energy penalty. In order to avoid the expensive cost and high power consumption caused by capturing CO₂ after combustion in SMR, natural gas Chemical Looping Reforming (CLR) is proposed, where the chemical looping combustion of metal oxides replaced the direct combustion of NG to convert natural gas to hydrogen and carbon dioxide. Although CO₂ can be separated with less energy penalty when combustion, CLR still require higher temperature heat for the hydrogen production and cause the poor sintering of oxygen carriers (OC). Here, we report a high-rate hydrogen production and low-energy penalty of strategy by natural gas chemical-looping process with both metallic oxide reduction and metal oxidation coupled with steam. Fe₃O₄ is employed as an oxygen carrier. Different from the common chemical looping reforming, the double side reactions of both the reduction and oxidization enable to provide the hydrogen in the range of 500–600 °C under the atmospheric pressure. Furthermore, the CO₂ is absorbed and captured with reduction reaction simultaneously.Through the thermodynamic analysis and irreversibility analysis of hydrogen production by natural gas via chemical looping reforming at atmospheric pressure, we provide a possibility of hydrogen production from methane at moderate temperature. The reported results in this paper should be viewed as optimistic due to several idealized assumptions: Considering that the chemical looping reaction is carried out at the equilibrium temperature of 500 °C, and complete CO₂ capture can be achieved. It is assumed that the unreacted methane and hydrogen are completely separated by physical adsorption. This paper may have the potential of saving the natural gas consumption required to produce 1 m³ H₂ and reducing the cost of hydrogen production.     

Thermodynamic and heat-hydrogen transfer analyses of novel multistage hydrogen-alloy sorption heat pump

The requirement of simultaneous heating and cooling effects at different zones of a building demands for the development of an energy-efficient air-conditioning system for heating and cooling outputs. In order to fulfil this requirement, a novel multistage hydrogen-alloy–based sorption heat pump (H-A SHP) for space air-conditioning is proposed in the present work. The proposed system produces multiple cooling and heating outputs at 20°C and 45°C, respectively, with single heat input at 160°C. A set of MmNi₅, La_0.8Ce_0.2Ni₅, MmNi_4.4Al_0.6, and LaNi_4.6Al_0.4 metal hydrides (MHs) is chosen to operate at the above-mentioned temperature range with hydrogen as working fluid. The proposed system can completely eliminate the requirement of conventional compressor because it operates using waste heat, and useful outputs (cooling-heating) result from reaction enthalpies (MH + H₂ interaction). The thermodynamic and heat-hydrogen transfer analyses of H-A SHP are carried out through finite volume approach, in which heat and mass transfer equations are solved to foresee the variations in MH bed temperature, hydrogen concentration, and heat interactions during cycle operation as well as the amount of cooling and heating outputs delivered to the air-conditioning space. The numerical code is validated with experimental pressure-concentration isotherms (PCIs) measured through Sievert's apparatus. The maximum heat exchange during the cooling and heating processes, at a particular instant of time, is observed as 257.5 and 286.1 W with cooling temperature of 10°C and heating temperature of 53°C, respectively. The thermodynamic performance is estimated as 178.5 kJ of cooling effect, 265.5 kJ of upgraded heat with overall coefficient of performance (COP) of 6.8, and overall specific alloy output of 396.5 W/0.34 kg of alloy.     

Effect of B-site Al substitution on hydrogen production of La0.4Sr0.6Mn1-xAlx (x=0.4, 0.5 and 0.6) perovskite oxides

Thermochemical water splitting using perovskite oxides as redox materials is one of the important way to use solar energy to produce green hydrogen. Thus, it is hence important to discover new materials that can be used for this purpose. In this regard, we focused on Al-substituted La_0.4Sr_0.6Mn_1-xAl_xO₃ (x = 0.4, 0.5 and 0.6) perovskite oxides, namely as La_0.4Sr_0.6Mn_0.6Al_0.4 (LSMA4664), La_0.4Sr_0.6Mn_0.5Al_0.5 (LSMA4655), and La_0.4Sr_0.6Mn_0.4Al_0.6 (LSMA4646) which have been successfully synthesized. Herein, synthesized LSMA4664, LSMA4655, and LSMA4646 were subjected to three consecutive thermochemical cycles in order to determine their oxygen capacity, hydrogen capacity, re-oxidation capability and structural stability following three cycles. Thermochemical cycles were carried out at 1400 °C for reduction and 800 °C for the oxidation reaction. LSMA4646 exhibited the highest O₂ production capacity with 275 μmol/g among the other perovskites employed in the study. Moreover, LSMA4646 has also the highest H₂ production, 144 μmol/g, with 90% of re-oxidation capability by the end of three thermochemical water splitting cycles. On the other hand, LSMA4664 has the lowest H₂ production and only kept approximately one-third of its hydrogen production capacity by the end of cycles. Thus, the current study provides insight that the increase in the Al-substitution enhances both oxygen and hydrogen production capacity. Besides, increasing the Al amount increases the structural stability during the redox reactions, the re-oxidation capability was also increased from 38% to 89% after thermochemical cycles.     

Reaction paths via a new transient phase in non-equilibrium hydrogen absorption of LaNi2Co3

This study investigated the non-equilibrium hydrogen absorption reaction paths of the AB₅-type LaNi₂Co₃ alloy using time-resolved in situ synchrotron X-ray diffraction. Diffraction data were collected every second for reactions under two hydrogen loading pressures. Hydrogen absorption with a hydrogen loading of 1 MPa rapidly transformed α phase to a transient phase (estimated to be LaNi₂Co₃H_3.1–3.6, named γ1); this has not previously been observed under equilibrium processes. The γ1 phase continuously transformed into the γ phase (LaNi₂Co₃H_4.5–5.0), and the β phase (LaNi₂Co₃H_~3.6) was not formed. When 0.18 MPa of hydrogen was loaded, initially, the γ1 phase appeared, followed by the formation of the β phase, finally transforming into the γ phase. These results indicate that a higher loading pressure promotes the formation of the γ1 phase and assists its continuous transformation into the γ phase by enhancing the dissolution of hydrogen into the α and γ1 phases.     

Hydrogen production using chemical looping technology: A review with emphasis on H2 yield of various oxygen carriers

Natural H₂ in useful quantities is negligible, which makes hydrogen unsuitable as an energy resource compared to other fuels. H₂ production by solar, biological, or electrical sources needs more energy than obtained by combusting it. Lower generation of pollutants and better energy efficiency makes hydrogen a potential energy carrier. Hydrogen finds potential applications in automobile and energy production. However, the cost of producing hydrogen is extremely high. Chemical-looping technology for H₂ generation has caught widespread attention in recent years. This work, presents some recent findings and provides a comprehensive overview of different chemical looping techniques such as chemical looping reforming, syngas chemical looping, coal direct chemical looping, and chemical looping hydrogen generation method for H₂ generation. The above processes are discussed in terms of the relevant chemical reactions and the associated heat of reactions to ascertain the overall endothermicity or exothermicity of the H₂ production. We have compared the H₂ yield data of different Fe/Ni, spinel and perovskites-based oxygen carriers (OC) reported in previous literature. This review is the first comprehensive study to compare the H₂ yield data of all the previously reported oxygen carriers as a function of temperature and redox cycles. In addition, the article summarizes the characteristics and reaction mechanisms of various oxygen carrier materials used for H₂ generation. Lastly, we have reviewed the application of Density Function Theory (DFT) to study the effect of various dopant addition on the efficiency of H₂ production of the oxygen carriers and discussed ASPEN simulations of different chemical looping techniques.     

Effect of introducing manganese as additive on microstructure,hydrogen storage properties and rate limiting step of Ti–Cr alloy

TiCr₂ with adding different amount of Mn (0, 2, 4 and 8 wt.%) alloys have been investigated. All alloys have C14-type main phase (gray color in SEM) and Ti minor phase (dark gray color in SEM). Rietveld fitting results proved that the lattice parameter a and cell volume of C14-type phase decreased with increasing Mn content. The first hydrogenation measurement manifest that all alloys have best activation properties and could be activated without any prior heat treatment and hydrogen exposure. However, introducing Mn led to the decrease of the first hydrogen absorption rate of TiCr₂ alloy, which may be due to the decrease of cell volume of C14-type main phase. The first hydrogenation properties at low temperature and effect of air exposure of the alloy were discussed. The results showed that the maximum hydrogen absorption capacity at 0 °C was obviously higher than that at room temperature. In addition, TiCr₂ alloy doped with minor amounts of Mn after long-time air exposure showed better hydrogenation performance. This may be due to the Mn additive acting as a deoxidizer. Finally, the first hydrogenation kinetic mechanisms of all alloys at different temperature were also studied by using the rate limiting step.     

Modulating Fischer-Tropsch synthesis performance on the Co3O4@SixAly catalysts by tuning metal-support interaction and acidity

ZIF-67 derived catalysts for Fischer-Tropsch synthesis have attracted much attention in recent years, while there is still a potential to improve their activity and selectivity. In this work, we prepared Si/Al co-immobilized Co₃O₄@Si_xAl_y catalysts by in-situ doping tetraethylorthosilicate and aluminum nitrate during the synthesis of ZIF-67. The effects of different Si/Al ratios on the metal-support interaction, acidity and FTS performance were explored. Results indicated that the Co₃O₄@Si₀Al₄ catalyst exhibited the best FTS performance with the CO conversion as high as 79.9% and CTY (cobalt time yield) value of 19.5 × 10^?5 mol_CO·g_Co^?1·s^?1, which was ascribed to the moderate metal-support interaction and the most active Co sites. Meanwhile, the Co₃O₄@Si₃Al₁ and Co₃O₄@Si₂Al₂ catalysts exhibited higher iso-paraffin and olefin selectivity due to more acidic sites.     

Density-functional quantum computations on bandgap engineering and tuning of optoelectronic properties of MgH2 via Mo doping: Prospects and potential for clean energy hydrogen-storage fuel and optoelectronic applications

With the increasing depletion of conventional energy sources and their detrimental environmental hazards, it is imperative to search for sustainable alternative clean energy sources. In the recent decades, hydrogen has emerged as potential source of clean energy. One of the potential alternatives to achieve the objective is the designing and characterization of materials for hydrogen-storage energy applications. In this regard, metal-bearing hydrides are the most promising candidates. For instance, magnesium-bearing hydrides are the focus of current research work owing to high hydrogen capacity of 7.6 wt%. In this paper, we first time report density functional-based quantum theoretical analysis to explore the potential of Mo-doped magnesium hydrides MgH₂:Mo for optoelectronic and hydrogen-storage applications. For the quantum computations of the required optoelectronics and energy storage properties, we employed all-electron methods within generalized gradient approximation (GGA). Besides applying GGA approximation to account for the electronic correlated effects, we employed the Hubbard potential U (= 4 eV) for onsite repulsive Coulomb force. We predict that 10% doping by weight of Mo into MgH₂ suppresses its insulating band gap of 4.9 eV to semiconducting band gap of order 3.15 eV for spin up and 0.15 eV for spin down. As such the doping of Mo can tune the the bandgap, structural, electronic and optoelectronic properties of MgH₂ considerably for potential applications.     

Analysis of a novel metal hydride cycle for simultaneous heating and cooling

Out of the many promising applications of metal hydrides, refrigeration, heat pumping and heat transformation are important. In order to achieve improved performance, a novel three-alloy cycle is proposed in which, for heat input at an intermediate temperature, heat outputs at high temperature and also at warm temperature are obtained in addition to refrigeration. The performance of this cycle using the alloys LaNi_4.6Sn_0.4, LaNi_4.7Al_0.3 and MmNi_4.5Al_0.5 is studied based on thermodynamics and reaction kinetics. Coefficients of performance, half-cycle times and specific alloy outputs are evaluated.     

Hydrogen sulphide to hydrogen via H2S methane reformation: Thermodynamics and process scheme assessment

Hydrogen Sulphide Methane Reformation (HSMR) represents a valid alternative for the simultaneous H₂S valorisation and hydrogen production at the industrial scale, without direct CO₂ emissions. The major concerns about the process commercialization are the possible coke formation in the reaction zone and the lack of active and selective catalysts. The study of the thermodynamics is the essential preliminary step for the reaction phenomena understanding. In this work, a deep thermodynamic analysis is performed to explore the system behaviour as a function of temperature, pressure, and inlet feed composition, using the Aspen Plus RGibbs module. In this way, the optimal process operating conditions to avoid carbon lay down can be identified.Assessed the system's thermodynamics, a preliminary process scheme is developed and simulated in Aspen Plus V11.0®, considering hydrogen production and its distribution in pipeline with methane. The process performances are discussed in terms of products' purity and process energy consumptions.     

Enhancement of bio-hydrogen generation by spirulina via an electrochemical photo-bioreactor (EPBR)

The biological production of hydrogen by microalgae is considered as an advantageous process. However, its yields are sometimes limited. To go beyond this limit, the improvement of the H₂ generation rate by Spirulina was studied via an electrochemical photo-bioreactor (EPBR). This EPBR led to hydrogen evolution rates of up to 27.49 and 13.37 mol of H₂.d⁻¹.m⁻³ for the anode and cathode chambers, respectively, under 0.3 V voltage and ~2.5 mA current. These results represent about a 4-fold increase compared to the H₂ production rate recorded without the application of a voltage. This increase in bio-hydrogen production is correlated with a drop in the concentration of NADPH. The Electrochemical Sequential Batch Reactor (ESRB) provided a more interesting total production rate which was 2.65 m³ m⁻³ d⁻¹, compared to the batch mode, which gave 1.2 m³ m⁻³.d⁻¹. The results show, for the first time, the boosting effect of the voltage on the metabolism of H₂ production by the Spirulina strain.     

Demonstration of a single-stage metal hydride hydrogen compressor composed of BCC V40TiCr alloy

In this study, demonstration of a one-stage metal hydride hydrogen compressor (MH compressor) by using a BCC alloy was performed. It was estimated that V₄₀Ti₂₂Cr₃₈ could compress approximately 1.6 wt% of hydrogen from 1.0 to 10 MPa in 20–140 °C temperature range from equilibrium theory via pressure-composition-isotherm measurements. For demonstration of an actual MH compressor, a kg-scale experimental system was set up; V₄₀Ti₂₂Cr₃₈ (1.4 kg) was introduced into a 1-inch cylindrical vessel with a heat-medium flow tube outside. As a result, 1.0 MPa of hydrogen can be compressed into the hydrogen cylinder at >10 MPa by hydrogen absorption at 10 °C and desorption at 160 °C for 30 min each (1 cycle/h) to achieve a compression rate of 0.23 Nm³/h and indicate the potential of the practical MH compressors by using BCC alloy.