Pressurized hydrogen from charged liquid organic hydrogen carrier systems by electrochemical hydrogen compression

We demonstrate that the combination of hydrogen release from a Liquid Organic Hydrogen Carrier (LOHC) system with electrochemical hydrogen compression (EHC) provides three decisive advantages over the state-of-the-art hydrogen provision from such storage system: a) The EHC device produces reduced hydrogen pressure on its suction side connected to the LOHC dehydrogenation unit, thus shifting the thermodynamic equilibrium towards dehydrogenation and accelerating the hydrogen release; b) the EHC device compresses the hydrogen released from the carrier system thus producing high value compressed hydrogen; c) the EHC process is selective for proton transport and thus the process purifies hydrogen from impurities, such as traces of methane. We demonstrate this combination for the production of compressed hydrogen (absolute pressure of 6 bar) from perhydro dibenzyltoluene at dehydrogenation temperatures down to 240 °C in a quality suitable for fuel cell operation, e.g. in a fuel cell vehicle. The presented technology may be highly attractive for providing compressed hydrogen at future hydrogen filling stations that receive and store hydrogen in a LOHC-bound manner.     

Dehydrogenation properties of doped LiAlH4 compacts for hydrogen generator applications

Lithium aluminum hydride (LiAlH₄) is an attractive hydrogen source for fuel cell systems due to its high hydrogen storage capacity and the moderate dehydrogenation conditions. In this contribution, TiCl₃- and ZrCl₄-doped LiAlH₄ powders are prepared and pelletized under different compaction pressures in a uniaxial press. At constant 80 °C and a hydrogen partial pressure of 0.1 MPa, the maximal hydrogen release of suchlike LiAlH₄ compacts amounts to 6.64 wt.%-H₂ (gravimetric capacity) and 53.88 g-H₂ l⁻¹ (volumetric capacity). The hydrogen release properties of the doped LiAlH₄ compacts are studied systematically under variation of the compaction pressure, temperature and hydrogen partial pressure. Furthermore, the volume change of doped LiAlH₄ compacts during dehydrogenation as well as their short-term storability are investigated (shelf life).     

Effects of tank heating on hydrogen release from metal hydride system in VoltaFCEV Fuel Cell Electric Vehicle

Metal hydride (MH) storage is known as a safe storage method because it does not require complex processes like high pressure or very low temperature. However, it is necessary to use a heat exchanger due to the endothermic and exothermic reactions occurring during the charging and discharging processes of the MH tanks. The performance of the MH is adversely affected by the lack of a heat exchanger or a suitable temperature range and it causes non-stable hydrogen supply to the fuel cell systems. In this study, effect of the tank surface temperature on hydrogen flow and hydrogen consumption performance were investigated for the MH hydrogen storage system of a hydrogen Fuel Cell Electric Vehicle (FCEV). Different temperature values were arranged using an external heat circulator device and a heat exchanger inside the MH tank. The fuel cell (FC) was operated at three different power levels (200 W, 400 W, and 600 W) and its performance was determined depending on the temperature and discharge flow rate of the MH tank. When the heat exchanger temperature (HET) was set to 40 °C, the discharge performance of the MH tank increased compared to lower temperatures. For example, when the FC power was set to 200 W and the HET of the system was at 40 °C, 1600 L hydrogen was supplied to the FC and 2000 Wh electrical energy was obtained. The results show that the amount of hydrogen supplied from the MH tank decreases significantly by increasing the flow rate in the system and rapid temperature changes occur in the MH tank.     

Analysis of cooling and heating characteristics of thermal management system for fuel cell bus

Vehicle thermal management system (VTMS) is an important part of the safe operation of fuel cell vehicles (FCVs). In this work, an integrated thermal management system was proposed for a fuel cell bus, with 80 kW fuel cell and 105 kWh battery. Liquid cooling is adopted for fuel cell, battery and motor. The model of VTMS was based on AMESim software. Two modes, including cooling and heating, were simulated for VTMS under different ambient conditions. The simulation is performed under a modified New European Driving Cycle (MNEDC), in which the running time is 1180 s and the distance is 10437 m. Results show that the VTMS could fulfill the temperature requirement for both modes. In cooling mode, ambient temperature of 34 °C, 37 °C and 40 °C are considered. The equivalent hydrogen consumption (EHC) is 505.68 g, 522.93 g and 539.48 g respectively. In heating mode, the ambient temperature is set to be −10 °C, −5 °C, 0 °C, and the corresponding EHC is 840.16 g, 783.64 g and 707.53 g, respectively. Besides, EHC at different heating target temperature for the fuel cell and battery was investigated. Results show that reducing the target heating temperature of fuel cell by 10 °C consumes less hydrogen than reducing the target heating temperature of battery by 5 °C. It is hoped that the results of this work will play a positive role in extending driving range.     

Enhanced hydrogen-storage properties of MgH2 by Fe–Ni catalyst modified three-dimensional graphene

High dehydrogenation temperature and slow dehydrogenation kinetics impede the practical application of magnesium hydride (MgH₂) serving as a potential hydrogen storage medium. In this paper, Fe–Ni catalyst modified three-dimensional graphene was added to MgH₂ by ball milling to optimize the hydrogen storage performance, the impacts and mechanisms of which are systematically investigated based on the thermodynamic and kinetic analysis. The MgH₂+10 wt%Fe–Ni@3DG composite system can absorb 6.35 wt% within 100 s (300 °C, 50 atm H₂ pressure) and release 5.13 wt% within 500 s (300 °C, 0.5 atm H₂ pressure). In addition, it can absorb 6.5 wt% and release 5.7 wt% within 10 min during 7 cycles, exhibiting excellent cycle stability without degradation. The absorption-desorption mechanism of MgH₂ can be changed by the synergistic effects of the two catalyst materials, which significantly promotes the improvement of kinetic performance of dehydrogenation process and reduces the hydrogen desorption temperature.     

Review on studies of the emptying process of compressed hydrogen tanks

Compressed hydrogen tanks are now widely used for onboard hydrogen storage in fuel cell vehicles (FCVs). However, because of the high storage pressure and the low thermal conductivity of carbon fibre reinforced polymer (CFRP), the emptying of such tanks during driving or emergency release can cause a significant temperature decrease and result in an in-tank gas temperature below the low safety temperature limit of ?40 °C even in warm weather. Once the gas temperature within the tank is lower than ?40 °C, the sealing elements at the boss of the tank may fail, and glass transition of the polymer liner of the type IV tank may occur; both can cause hydrogen leakage and severe safety problems. In this paper, the heat transfer correlations, thermodynamic analyses, computational fluid dynamics (CFD) simulations, experimental studies, and thermal management methods associated with the emptying process of compressed hydrogen tanks are comprehensively reviewed. Future research directions on this topic are suggested.     

Experimental and theoretical analysis of a natural gas fuel processor

In this study, a natural gas fuel processor was experimentally and theoretically investigated. The constructed 2.0 kWth fuel processor is suitable for a residential-scale high temperature proton exchange membrane fuel cell. The system consists of an autothermal reformer; gas clean-up units, namely high and low-temperature water-gas shift reactors; and utilities including feeding unit, burner, evaporator and heat exchangers. Commercial monolith catalysts were used in the reactors. The simulation was carried out by using ASPEN HYSYS program. A validated kinetic model and adiabatic equilibrium model were both presented and compared with experimental data. The nominal operating conditions which were determined by the kinetic model were the steam-to-carbon ratio of 3.0, the oxygen-to-carbon ratio of 0.5 and the inlet temperatures of 450 °C for autothermal reformer, 400 °C for high-temperature water-gas shift reactor and 310 °C for low-temperature water-gas shift reactor. Experimental results at the nominal condition showed that the performance criteria of the hydrogen yield, the fuel conversion and the efficiency were 2.53, 93.5% and 82.3% (higher heating value-HHV), respectively. The validated kinetic model was further used for the determination of 2–10kWthermal fuel processor efficiency which was increasing linearly up-to 86.3% (HHV).     

Liquid organic hydrogen carriers (LOHCs) in the thermochemical waste heat recuperation systems: The energy and mass balances

This paper is presented a concept of thermochemical recuperation of waste heat based on hydrogen extraction from liquid organic hydrogen carriers (LOHC), on the example of methylcyclohexane-toluene system. The advantages of this concept is described, for example, a possibility to use a moderate low temperature of waste heat for generation high-exergy “green” hydrogen fuel. To understand the effect of operating parameters on the energy and mass balance, the thermodynamic analysis was performed. The chemical system for hydrogen generation was analyzed via Gibbs free energy minimization method. The thermodynamic analysis was conducted under various operating conditions: temperature of 100–400 °C, pressure of 1–4 bar. Aspen HYSYS software was used for the energy and mass conservation analysis. Sankey diagram for the energy flows is depicted. The results showed that the maximum energy efficiency the thermochemical waste heat recuperation system have in the temperature range above 300–350 °C. In this temperature range, the effect of pressure on the energy balance is negligible and it is recommended for the thermochemical recuperation system to use LOHC with a pressure of 1.5–2 bar. Based on the analysis, it was concluded that the temperature potential of waste heat for about 300–350 °C is enough for the investigated concept. An analysis of a mass balance showed that the decreasing in condensation temperature leads to a significant increasing in the share of condensed toluene from toluene-hydrogen mixture after a reactor. If temperature of a hydrogen-toluene mixture of 20 °C at pressure above 2 bar about 96% of toluene can be condensed after the first condenser.     

Combined dynamic operation of PEM fuel cell and continuous dehydrogenation of perhydro-dibenzyltoluene

Hydrogen storage in liquid organic hydrogen carriers (LOHC) such as the substance system dibenzyltoluene/perhydro-dibenzyltoluene (H0/H18-DBT) offers a promising alternative to conventional methods. In this contribution, we describe the successful demonstration of the dynamic combined operation of a continuously operated LOHC reactor and a PEM (polymer exchange membrane) fuel cell. The fuel cell was operated stable with fluctuating hydrogen release from dehydrogenation of H18-DBT over a total period of 4.5 h, reaching electrical stack powers of 6.6 kW. The contamination with hydrocarbons contained in the hydrogen after activated carbon filtering did not result in any detectable impairment or degradation of the fuel cell. The proposed pressure control algorithm based on a proportional integral (PI) controller proved to be a robust and easy-to-implement approach to enable the dynamic combined operation of LOHC dehydrogenation and PEM fuel cell.     

Dehydrogenation of perhydro-dibenzyltoluene for hydrogen production in a microchannel reactor

A preliminary study regarding the dehydrogenation of perhydro-dibenzyltoluene as a liquid organic hydrogen carrier with switching from a stirred tank reactor to a continuous flow microchannel reactor is presented. The hydrogen production percentage in the case of a continuous flow microchannel reactor was found greater when compared to that of a stirred tank reactor. The hydrogen production was increased from 64.1% to 82.2% with the increase in bottom plate temperature from 260 to 320 °C for 0.01 mL/min flow rate. A maximum of 88% of hydrogen was generated for a 40 hours of operation, at a bottom wall temperature of 290 °C. The kinetic model for the microchannel reactor dehydrogenation was presented with a pre-exponential factor of 3.272 s^?1 and activation energy of 13.79 kJ/mol. The results revealed that a continuous microchannel reactor can be an appropriate technology for the dehydrogenation of perhydro-dibenzyltoluene.     

Excellent catalytic effect of LaNi5 on hydrogen storage properties for aluminium hydride at mild temperature

The catalytic effect of rare-earth hydrogen storage alloy is investigated for dehydrogenation of alane, which shows a significantly reduced onset dehydrogenation temperature (86 °C) with a high-purity hydrogen storage capacity of 8.6 wt% and an improved dehydrogenation kinetics property (6.3 wt% of dehydrogenation at 100 °C within 60 min). The related mechanism is that the catalytic sites on the surface of the hydrogen storage alloy and the hydrogen storage sites of the entire bulk phase of the hydrogen storage reduce the dehydrogenation temperature of AlH₃ and improve the dehydrogenation kinetic performance of AlH₃. This facile and effective method significantly improves the dehydrogenation of AlH₃ and provides a promising strategy for metal hydride modification.     

A parametric study of dehydrogenation of various Liquid Organic Hydrogen Carrier (LOHC) materials and its application to methanation process

Global warming is one of the arch challenges of this era mainly caused by the increasing concentration of carbon dioxide in the atmosphere. Methanation process utilizes carbon dioxide and hydrogen to produce methane gas as an energy-rich fuel. To supply the hydrogen for the methanation process, LOHC could be used as a medium for long-range hydrogen transportation. However, the heat of reaction is needed to recover hydrogen from the LOHC medium. In this study, a new method to utilize the heat from the methanation process for dehydrogenation and optimum conditions are calculated for various LOHC materials. The new process designed uses an Air-Brayton cycle to generate the required high pressure as well as compensate for the LOHC dehydrogenation thermal energy requirement using a proportionate amount of methane produced. Also, the performance of various LOHC materials is compared in the proposed process. The simulation is performed via Aspen Plus® simulator. Dibenzyltoluene is found to be the best selection among the selected LOHC materials for use in this process with a system efficiency of 46.7% with a 100% medium recovery. Pyrrole group LOHC exhibits lower dehydrogenation temperature and energy requirement however are prone to bond scission and generally toxic. Toluene has high volatility resulting in its maximum recovery limited to 96.2% at an elevated pressure of 7 bar decreasing to 84.5% at 1 bar and 30 °C with a system efficiency of 49.08% and a low CVA of 36.74%, while NEC has 63.78% CVA with 55.64% efficiency and DBT has 54.12% CVA with 47.99% efficiency.     

Investigating the stability and degradation of hydrogen PEM fuel cell

The hydrogen proton exchange membrane (PEM) fuel cells are promising to utilize fuel cells in electric vehicle (EV) applications. However, hydrogen PEM fuel cells are still encountering challenges regarding their functionality and degradation mechanism. Therefore, this paper aims to study the performance of a 3.2 kW hydrogen PEM fuel cell under accelerated operation conditions, including varying fuel pressure at a level of 0.1–0.5 bar, variable loading, and short-circuit contingencies. We will also present the results on the degradation estimation mechanism of four fuel cells working at different operational conditions, including high-to-low voltage range and high-to-low temperature variations. These experiments examine over 180 days of continuous fuel cell working cycle. We have observed that the drop in the fuel cells' efficiency is at around 7.2% when varying the stack voltage and up to 14.7% when the fuel cell's temperature is not controlled and remained at 95 °C.     

Benzyltoluene/dibenzyltoluene-based mixtures as suitable liquid organic hydrogen carrier systems for low temperature applications

In this contribution we propose mixtures of the two LOHC systems benzyltoluene (H0-BT)/perhydro benzyltoluene (H12-BT) and dibenzyltoluene (H0-DBT)/perhydro dibenzyltoluene (H18-DBT) as promising hydrogen storage media for technical applications at temperatures below ambient. The mixing of the two LOHC systems provides the advantage of a reduced viscosity of the hydrogen-rich system, for example a 20 wt% addition of H12-BT to H18-DBT reduces the viscosity at 10 °C by 80%. Interestingly, it is also found that the dehydrogenation of such mixture provides a hydrogen release productivity that is 12–16% higher compared to pure H18-DBT dehydrogenation under otherwise identical conditions. This enhanced rate is attributed to a combination of reduced hydrogen partial pressure in the reactor (due to the higher H12-BT vapor pressure), preferred H12-BT dehydrogenation (due to faster H12-BT diffusion) and effective transfer hydrogenation between the two LOHC systems.     

Voltage degradation of high-temperature PEM fuel cells operating at 200 °C under constant load and start-stop conditions

High temperature proton exchange membrane fuel cells (HT-PEM) offer significant advantages over conventional low temperature fuel cells (LT-PEM), including improved fuel impurity tolerance and increased electrode kinetics. These advantages enable use of reformate fuels with potentially lower costs and simplified handling versus ultra-pure hydrogen fuel required for LT-PEM. Although HT-PEM fuel cell operation has been demonstrated at temperatures above 120 °C, relatively few studies have focused on operation at 200 °C or higher where fuel impurity tolerance is maximized, but at the cost of accelerated performance degradation. To help address this research gap, the present study investigated the voltage degradation of HT-PEM fuel cells operating at 200 °C and 0.4 A/cm² under continuous load conditions, and at 200 °C and 0.6 A/cm² during start-stop cycling. Results based on triplicate measurements show an average constant load degradation rate of 102 μV/h, as compared to literature values of 10 μV/h or less at lower temperature and current density. The start-stop experiments showed relatively high degradation rates per cycle up to 50 cycles, with decreasing average degradation rates over 80 and 100 cycles.     

Hydro-catalytic treatment of organoamine boranes for efficient thermal dehydrogenation for hydrogen production

This study aims to present the hydro-catalytic treatment of organoamine boranes for efficient thermal dehydrogenation for hydrogen production. Organoamine boranes, methylamine borane (MeAB), and ethane 1,2 diamine borane (EDAB), known as ammonia borane (AB) carbon derivatives, are synthesized to be used as a solid-state hydrogen storage medium. Thermal dehydrogenation of MeAB and EDAB is performed at 80 °C, 100 °C, and 120 °C under different conditions (self, catalytic, and hydro-catalytic) for hydrogen production and compared with AB. For this purpose, a cobalt-doped activated carbon (Co-AC) catalyst is fabricated. The physicochemical properties of Co-AC catalyst is investigated by well-known techniques such as ATR/FT-IR, XRD, XPS, ICP-MS, BET, and TEM. The synthesized Co-AC catalyst obtained in nano CoOOH structure (20 nm, 12% Co wt) is formed and well-dispersed on the activated carbon support. It has indicated that Co-AC exhibits efficient catalytic activity towards organoamine boranes thermal dehydrogenation. Hydrogen release tests show that hydro-catalytic treatment improves the thermal dehydrogenation kinetics of neat MeAB, EDAB, and AB. Co-AC catalyzed hydro-treatment for thermal dehydrogenation of MeAB and EDAB acceleras the hydrogen release from 0.13 mL H₂/min to 46.12 mL H₂/min, from 0.16 mL H₂/min to 38.06 mL H₂/min, respectively at 80 °C. Moreover, hydro-catalytic treatment significantly lowers the H₂ release barrier of organoamine boranes thermal dehydrogenation, from 110 kJ/mol to 19 kJ/mol for MeAB and 130 kJ/mol to 21 kJ/mol for EDAB. In conclusion, hydro and catalytic treatment presents remarkable synergistic effect in thermal dehydrogenation and improves the hydrogen release kinetics.     

LiBH4–VCl3 and LiAlH4–VCl3 mixtures prepared in soft milling conditions for hydrogen release at low temperature

Mixtures of LiBH₄/VCl₃ and LiAlH₄/VCl₃ in 5:1, 3:1, and 5% mol stoichiometries were prepared and tested for hydrogen release. The mixtures were prepared in 10 min of ball milling at room temperature or with cryogenic (N₂-liquid) cooling. The mixtures demonstrated diverse hydrogen release levels, but all of them started releasing hydrogen at low temperatures (33–66 °C) with a change in the reaction pathway as compared to pure LiBH₄ or LiAlH₄. The driving force for that is the formation of the stable salt LiCl. The best material was the 5% mol VCl₃ + LiAlH₄ cryogenic mixture because of the low-temperature dehydrogenation onset of 34 °C; and the dehydrogenation level of 5.1 wt.%, and 6.4 wt.% that was achieved upon heating at 100 °C and 250 °C, respectively.     

Effect of pilot fuel injection pressure and injection timing on combustion,performance and emission of hydrogen-biodiesel dual fuel engine

The present study highlights the influence of fuel injection pressure (FIP) and fuel injection timing (FIT) of Jatropha biodiesel as pilot fuel on the performance, combustion and emission of a hydrogen dual fuel engine. The hydrogen flow rates used in this study are 5lit/min, 7lit/min, and 9lit/min. The pilot fuel is injected at three FIPs (500, 1000, and 1500 bar) and at three FITs (5°, 11°, and 17?bTDC). The results showed an increase in brake thermal efficiency (B_th)from 25.02% for base diesel operation to 32.15% for hydrogen-biodiesel dual fuel operation with 9lit/min flow rate at a FIP of 1500 bar and a FITof17?bTDC. The cylinder pressure and heat release rate (HRR) are also found to be higher for higher FIPs. Advancement in FIT is found to promote superior HRR for hydrogen dual fuel operations. The unburned hydrocarbon (UHC) and soot emissions are found to reduce by 59.52% and 46.15%, respectively, for hydrogen dual fuel operation with 9lit/min flow rate at a FIP of 1500 bar and a FIT of 11?bTDC. However, it is also observed that the oxides of nitrogen (NO_X) emissions are increased by 20.61% with 9lit/min hydrogen flow rate at a FIP of 1500 bar and a FIT of 17?bTDC. Thus, this study has shown the potential of higher FIP and FIT in improving the performance, combustion and emission of a hydrogen dual fuel engine with Jatropha biodiesel as pilot fuel.     

Connected evaluation of polymer electrolyte membrane fuel cell with dehydrogenation reactor of liquid organic hydrogen carrier

Recently, hydrogen energy technologies attract attention as power systems. To develop hydrogen energy systems, hydrogen storage methods with high storage density and good safety are required. Liquid organic hydrogen carrier (LOHC) is one of the novel hydrogen storage technologies. LOHC has advantages of high storage density, good safety, and easy handling. In this study, a polymer electrolyte membrane fuel cell (PEMFC) stack is operated with hydrogen released from LOHC to evaluate the feasibility of the connected operation of the PEMFC stack and LOHC dehydrogenation reactor. Dibenzyltoluene (H0-DBT) is used as a LOHC material, and the dehydrogenation of perhydro dibenzyltoluene (H18-DBT) is conducted at 240–300 °C. Released hydrogen is purified by adsorbent of activated carbon to remove impurities. However, 100–1400 ppm of methane is observed after the purification, and the PEMFC stack power is reduced from 39.4 W to 39.0 W during the operation by hydrogen dilution and physical adsorption of methane. Then, to evaluate the irreversible damage, pure hydrogen was supplied to the PEMFC stack. The stack power is recovered to 39.4 W. It is concluded that the connected operation of the LOHC dehydrogenation reactor and PEMFC stack is feasible, and the activated carbon adsorbent can be a cost-effective purification method for LOHC.     

Hydrogen storage and heat transfer properties for large-capacity double thin-layered annulus ZrCo bed with secondary containment cavity

Fast heat and mass delivery with high cycling stability of the core component, hydrogen storage bed, in SDS are essential for the operation of the future tritium factory in ITER project. However, the aforementioned properties are still perplexing in large-capacity ZrCo bed, especially for that with secondary containment structure required by the actual tritium operation in the future. Herein, the performance including heating, cycling and cooling with two different size ZrCo beds (loading of ZrCo are 200 g and 2000 g respectively) were systematically studied. The experimental data shows that the maximum heating ability of the middle-size/full-scale storage bed are both about 10 °C/min, and the maximum hydrogen absorption capacity of these ZrCo beds are 44.6 L/405.5 L, respectively. Besides, hydrogen pressure and hydrogen retention during the following desorption can affect the cycling performance of the ZrCo bed. The use of transfer pump can reduce the pressure of the bed during the hydrogen desorption process (operated at 500 °C), which inhibits the disproportionation reaction of the ZrCo alloy. However, the degree of hydrogen pressure reduction in two the types of ZrCo bed are different. As a result, the cycling capacity of the middle-size bed (93.4%, lower hydrogen pressure) is higher than the full-scale bed (68.7%, higher hydrogen pressure) after 10 cycles. When the transfer pump was not used and operated at lower temperature (350 °C), the beds cannot release hydrogen completely, and partial hydrogen atoms are retained in the ZrCo alloy. The middle-size bed still maintains a hydrogen storage capacity of 94.5% after 10 cycles, while 75.9% of the hydrogen storage capacity remained for the full-scale bed. Therefore, the increase of hydrogen surplus in ZrCo alloy is helpful to improve its cycling stability. At last, the cooling performances of the beds under 10 different cooling methods were studied. Among the cooling methods, the best cooling rate was achieved by filling nitrogen in the secondary containment cavity and flowing water passing through the cooling circuit of the bed. This work will provide a crucial reference for the design and optimization of the subsequent operation technology of SDS in ITER.