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•The features and utilization of diverse hydrogen storage technologies are compared.•Various systems for Liquid Organic Hydrogen Carriers (LOHCs) are investigated.•The catalysts, ...reactors, and projects of LOHCs technology are discussed.•Concept and roadmap to prepare LOHCs by the conversion of biomass are proposed.•The feasibility and challenges for biomass-based LOHCs are analyzed.
Hydrogen has attracted widespread attention as a carbon-neutral energy source, but developing efficient and safe hydrogen storage technologies remains a huge challenge. Recently, liquid organic hydrogen carriers (LOHCs) technology has shown great potential for efficient and stable hydrogen storage and transport. This technology allows for safe and economical large-scale transoceanic transportation and long-cycle hydrogen storage. In particular, traditional organic hydrogen storage liquids are derived from nonrenewable fossil fuels through costly refining procedures, resulting in unavoidable environmental contamination. Biomass holds great promise for the preparation of LOHCs due to its unique carbon-balance properties and feasibility to manufacture aromatic and nitrogen-doped compounds. According to recent studies, almost 100% conversion and 92% yield of benzene could be obtained through advanced biomass conversion technologies, showing great potential in preparing biomass-based LOHCs. Overall, the present LOHCs systems and their unique applications are introduced in this review, and the technical paths are summarized. Furthermore, this paper provides an outlook on the future development of LOHCs technology, focusing on biomass-derived aromatic and N-doped compounds and their applications in hydrogen storage.
Hydrogen, as a primary carbon-free energy carrier is confronted by challenges in storage and transportation. However, liquid organic hydrogen carriers (LOHCs) present a promising solution for storing ...and transporting hydrogen at ambient temperature and atmospheric pressure. Unlike circular energy carriers such as methanol, ammonia, and synthetic natural gas, LOHCs do not produce by-products during hydrogen recovery. LOHCs only act as hydrogen carriers and the carriers can also be recycled for reuse. Although there are considerable advantages to LOHCs, there are also some drawbacks, especially relative to the energy consumption during the dehydrogenation step of the LOHC recycling. This review summarizes the recent progresses in LOHC technologies, focusing on catalyst developments, process and reactor designs, applications, and techno-economic assessments (TEA). LOHC technologies can potentially offer significant benefits to Australia, especially in terms of hydrogen as an export commodity. LOHCs can help avoid capital costs associated with infrastructure, such as transportation vessels, while reducing hydrogen loss during transportation, such as in the case of liquid hydrogen (LH2). Additionally, it minimises CO2 emissions, as observed in methane and methanol reforming. Thus, it is essential to dedicate more efforts to explore and develop LOHC technologies in the Australian context.
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•Recent progresses in liquid organic hydrogen carrier (LOHC) technology were reviewed,•Energy consumption in different segments of LOHC were compared to other technologies,•Techno-economic analysis results were summarised,•Essentiality to develop LOHC technology were highlighted from the Australian context.
As a compound for liquid organic hydrogen carrier (LOHC) applications, 1-(3-cyclohexylpropyl)-3-ethylcyclohexane was designed and its dehydrogenation reaction was investigated using density ...functional theory calculations. To check how this compound could be stable, vibrational frequency analysis and formation energy calculations were conducted. Our findings revealed that this LOHC compound was dynamically and chemically stable. Using Mulliken population analysis, the dehydrogenation process was clearly explained. To reduce the dehydrogenation energy, different substituents, such as N, Cl, and Br were used. Our results suggested that N-substitution could be potentially suitable to lower the dehydrogenation energy. Reaction barriers of pristine and N-substituted systems for dehydrogenation reactions were investigated through nudged elastic band methods. In addition, the gap between HOMO and LUMO was calculated to check chemical reactivity.
•LOHC was designed using by-products produced in petrochemical plants.•The hydrogen storage capacity (wt%) for the designed system was 6.82%.•Substitution of N-atom with C-atom lowered the dehydrogenation energy.•Energy barriers for all dehydrogenation steps were investigated.•This study will be useful for identifying cost effective LOHC materials.
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•RuCo catalyst for efficient hydrogen storage of various LOHCs was prepared by SEA-UR.•Higher dispersion and antioxidant capacity of RuCo alloy increase the active sites.•Ultrafine ...particles and electron transfer between Ru and Co improve catalytic activity.•Strong coordination effect between RuCo alloy and Si-OH improves catalytic stability.•RuxCoy/S15-SU can efficiently catalyze hydrogen storage in NEC, DBT, MBT and acenaphthene.
SBA-15-loaded RuCo alloy nanoparticle catalysts (RuxCoy/S15-SU) for the efficient catalysis of hydrogen storage by various liquid organic hydrogen carriers (LOHCs) were prepared via strong electrostatic adsorption (SEA)-ultrasonic in-situ reduction (UR) technology. The above prepared catalysts were subjected to a series of characterization, such as XPS, H2-TPD/TPR, N2 adsorption–desorption, ICP, CO-chemisorption, FT-IR, XRD and TEM. Ru3+ and Co2+ were evenly anchored on the surface of SBA-15 by SEA, and ultrafine RuCo alloy nanoparticles were formed by UR without any chemical reducing or stabilizing agents. The addition of Co enhanced the dispersion and antioxidant capacity of the RuCo alloy NPs with an average particle size of 2.07 nm and increased the number of catalytically active sites. The synergistic effect of ultrafine particle size and electron transfer between Co and Ru improved the catalytic performance of monobenzyltoluene (MBT) for hydrogen storage. SEA-UR technology strengthened the coordination effect between RuCo alloy NPs and Si-OH, which enhanced the catalytic stability. H2-TPD and H2-TPR indicated that the addition of Co led to more activated H2 to produce hydrogen overflow. For the hydrogenation of MBT, the produced Ru2Co1/S15-SU showed excellent catalytic performance. The hydrogen storage efficiency of MBT was 99.98 % under 110 °C and 6 MPa H2 for 26 min, and the TOF was 145 min−1, which is significantly superior to that of Ru/S15-SU catalyst and that reported in the literature. The hydrogen storage efficiency was still as high as 99.7 % after ten cycles, which was much better than that of Ru/S15-SU and commercial 5 wt% Ru/Al2O3. Ru2Co1/S15-SU is also suitable for efficiently catalyzing hydrogen storage of N-ethylcarbazole, dibenzyltoluene and acenaphthene.
Strategies to decrease the dehydrogenation enthalpy (ΔHd) of dibenzyl toluene (DBT) were examined by density functional theory (DFT) modeling. The stronger electron-donating substituent showed higher ...hydrogen-releasing properties. The sequences of the dehydrogenation process of perhydro-dibenzyl toluene (18H-DBT) and perhydro-lithium 3,5-dibenzyl phenolate (18H-DBT-OLi), which is the compound of modified DBT with the highest potential, were the same. The energy required to release hydrogen from 18H-DBT-OLi (11.514 kcal/mol) was smaller than that from 18H-DBT (12.574 kcal/mol). In the hydrogen-releasing process, the rate-determining steps for the dehydrogenation of 18H-DBT and 18H-DBT-OLi were the 12H-DBT → 10H-DBT + H2 and 12H-DBT-OLi → 10H-DBT-OLi + H2 steps, respectively. Furthermore, the charge distribution of 18H-DBT and 18H-DBT-OLi was also explored.
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•Electron-donating groups promoted the dehydrogenation reaction of DBT.•The sequence of dehydrogenation of 18H-DBT and 18H-DBT-OLi was the same.•The rate-determining step (RDS) for dehydrogenation of 18H-DBT was 12H-DBT. → 10H-DBT + H2.•The RDS for dehydrogenation of modified 18H-DBT was 12H-DBT-OLi. → 10H-DBT-OLi + H2.•The interaction of electron-donating groups with adjacent carbons induced changes in charge distribution of modified DBT.
The resurgence of interest in the hydrogen economy could hinge on the distribution of hydrogen in a safe and efficient manner. Whilst great progress has been made with cryogenic hydrogen storage or ...liquefied ammonia, liquid organic hydrogen carriers (LOHCs) remain attractive due to their lack of need for cryogenic temperatures or high pressures, most commonly a cycle between methylcyclohexane and toluene. Oxidation of methylcyclohexane to release hydrogen will be more efficient if the equilibrium limitations can be removed by separating the mixture. This report describes a family of six ternary and quaternary multicomponent metal–organic frameworks (MOFs) that contain the three‐dimensional cubane‐1,4‐dicarboxylate (cdc) ligand. Of these MOFs, the most promising is a quaternary MOF (CUB‐30), comprising cdc, 4,4′‐biphenyldicarboxylate (bpdc) and tritopic truxene linkers. Contrary to conventional wisdom that adsorptive interactions with larger, hydrocarbon guests are dominated by π–π interactions, here we report that contoured aliphatic pore environments can exhibit high selectivity and capacity for LOHC separations at low pressures. This is the first time, to the best of our knowledge, where selective adsorption for cyclohexane over benzene is witnessed, underlining the unique adsorptive behavior afforded by the unconventional cubane moiety.
The hydrocarbon adsorption behavior of multicomponent MOFs with contoured pore environments is explored. Contrary to conventional wisdom, i.e., that adsorptive interactions with larger hydrocarbon guests are dominated by π–π interactions, it is found that contoured aliphatic pore environments can exhibit high selectivity and capacity at low pressures.
Estimates on the costs of renewable energy supply by hydrogen and hydrogen-based derivatives such as ammonia or organic compounds (e.g., synthetic methane, methanol, Fischer-Tropsch fuels) vary ...substantially among current publications. Hence, comprehensive analyses of each stage of the renewable energy supply chain are necessary, with ship transportation as the focus of this work. Shipping cost projections for various hydrogen-based derivatives from a wide range of recent international publications are compared, identifying uncertainties and research gaps in the shipping of Power-to-X energy carriers. While transportation costs in literature reveal a consistent picture for liquid ammonia, projections for liquid hydrogen, LOHCs, and, surprisingly, also for methanol, Fischer-Tropsch fuels and liquid methane differ significantly. Technological and economic assumptions contributing to the discrepancies are discussed. A sensitivity analysis is provided to quantify the effects of divergent assumptions for different parameters on shipping costs.
•Projections of future ammonia shipping costs are quite consistent.•Cost projections for hydrogen diverge as large-scale shipping is not established.•Cost projections for hydrocarbon energy carriers reveal significant inconsistencies.•Discrepancies mainly attribute to ship's speed, lifetime and CAPEX assumptions.
Methylcyclohexane is an appealing liquid organic hydrogen carrier produced from toluene hydrogenation. The direct toluene electro-hydrogenation technique in proton exchange membrane electrolyzers ...avoids heat losses and reduces the electricity consumption concerning the conventional methods. However, this technology faces a critical issue. The water dragged by electro-osmosis from the anode side blocks the toluene supply to the cathode reaction site. This paper presents the experimental visualization, for the first time, of water droplets and generated hydrogen bubbles inside the cathode porous transport layer of a direct toluene electro-hydrogenation cell. Experiments were conducted under different current densities and using not only pure water but also dilute sulfuric acid as anode reactant. The visualizations revealed that the bubbling grew sharply as the electric current increased between 20 and 100 mA/cm2. It was also observed that water droplets got stuck inside the cell. As for hydrogen, small bubbles left the cell rapidly while larger ones stayed inside for longer. Finally, the experimental visualizations confirmed that the water dragging phenomenon was mitigated by using dilute sulfuric acid as anode reactant instead of pure water. Indeed, the hydrogen generation was halved at 200 mA/cm2 and the methylcyclohexane Faraday efficiency was boosted by 15%–22% points.
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•Mass transport was studied in a direct toluene electro-hydrogenation electrolyzer.•First visualization of dragged water and generated hydrogen inside an operating cell.•More liquid water droplets and H2 bubbles were observed as the current rises.•Dragged water increases H2 generation and hampers toluene hydrogenation.•Sulfuric acid minimizes the water flux and boosts the Faraday efficiency.
Liquid organic hydrogen carriers (LOHC) are unsaturated organic compounds used for chemical hydrogen storage. Using an equilibrium model of the LOHC N-ethylcarbazole, we discuss potential efficiency ...increases of hydrogen storage systems based on N-ethylcarbazole by the integration of low-temperature waste heat. N-ethylcarbazole is well suited for pressure swing operation with heat exchange between hydrogenation and dehydrogenation. We present and discuss kinetic data of the dehydrogenation reaction gathered in a tubular reactor that was mounted in different orientations and flow configurations. Similar maximum values of power density are reached in vertical and in horizontal orientation. Vertical orientation allows the favorable operation with counter-flow of the liquid carrier and the evolved hydrogen gas and radial heat transfer is significantly better than in horizontal orientation. In vertical reactor configurations, catalyst efficiency and operational stability are impaired at high void fractions. This issue can be reduced by dehydrogenation at elevated pressure and intermediate gas separation from the catalyst bed.
•Chemical hydrogen storage using N-ethylcarbazole as liquid organic hydrogen carrier.•N-ethylcarbazole is well suited for integration of low-temperature waste heat.•Power density of vertical dehydrogenation reactors is similar to horizontal orientation.•High void fractions cause catalyst dewetting in vertical dehydrogenation reactors.•Catalyst dewetting is reduced by increased pressure and intermediate gas separation.
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