Polyacrylonitrile-based highly porous carbon materials for exceptional hydrogen storage

In this paper, a common low-cost chemical material-polyacrylonitrile (PAN) is transformed into porous carbon with excellent specific surface area (2564.6–3048.8 m² g⁻¹) and highly concentrated micropore size distribution (0.7–2.0 nm). Benefit to the unique structure, the as-prepared materials show appealing hydrogen adsorption capacity (4.70–5.94 wt % at 20 bar, 7.15–10.14 wt % at 50 bar), demonstrating a promising prospect of practical application. This work also confirmed that the narrow and deep ultramicropore (<0.7 nm) could facilitate adsorption of hydrogen molecules significantly at atmospheric pressure, and the volume increase of supermicropore (0.7–2.0 nm) could lead to hydrogen capacity promotion at relative high pressure (>20 bar), which provides valuable guidance for the construction of ideal porous adsorbent for efficiency hydrogen storage.     

Copper-doped activated carbon from amorphous cellulose for hydrogen,methane and carbon dioxide storage

The transition away from fossil fuel and ultimately to a carbon-neutral energy sector requires new storage materials for hydrogen and methane as well as new solutions for carbon capture and storage. Among the investigated adsorbents, activated carbons are considered especially promising because they have a high specific surface area, are lightweight, thermally and chemically stable, and easy to produce. Moreover, their porosity can be tuned and they can be produced from inexpensive and environmentally friendly raw materials. This study reports on the development and characterization of activated carbons synthesized starting from amorphous cellulose with and without the inclusion of copper nanoparticles. The aim was to investigate how the presence of different concentrations of metal nanoparticles affects porosity and gas storage properties. Therefore, the research work focused on synthesis and characterization of physical and chemical properties of pristine and metal-doped activated carbons materials and on further investigation to analyze their hydrogen, methane and carbon dioxide adsorption capacity. For an optimized Cu content the microporosity is improved, resulting in a specific surface area increase of 25%, which leads to a H₂ uptake (at 77 K) higher than the theoretical value predicted by the Chahine Rule. For CH₄, the storage capacity is improved by the addition of Cu but less importantly because the size of the molecule hampers easy access of the smaller pores. For CO₂ a 26% increase in adsorption capacity compared to pure activated carbon was achieved, which translated with an absolute value of over 48 wt% at 298 K and 15 bar of pressure.     

Nitrogen-incorporated carbon nanotube derived from polystyrene and polypyrrole as hydrogen storage material

“Synthesis of nitrogen-doped carbon nanotubes from polymeric precursors (polystyrene and polypyrrole) by poly-condensation followed by carbonization under an inert atmosphere is reported. Three different carbonization temperatures (500 °C, 700 °C and 900 °C) were employed to synthesize three different carbon nanostructures with different morphologies. These were designated as NCNR-500 (nitrogen-doped carbon nanorods), NCBCT-700 (nitrogen-doped fused bead carbon nanotubes), and NCNT-900 (nitrogen-doped carbon nanotubes) according to morphology and carbonization temperature. Microstructure, morphology, porosity, and nitrogen content were characterized by several different techniques. The effects of carbonization temperature and the role of functional groups were also investigated. Total and excess hydrogen storage capacities of 2.0 wt% and 1.8 wt%, respectively, were measured at 298 K and 100 bar for the NCNT-900 material. This is higher than the capacities of the NCNR-500 and NCBCT-700 materials. NCNT-900 exhibited a porous structure with high specific surface area and total pore volume of 870 m/g and 0.62 cm³/g, respectively.     

Enhanced electrochemical hydrogen storage capacity of activated mesoporous carbon materials containing nickel inclusions

Electrochemical properties of activated ordered mesoporous carbon (OMC) containing nickel inclusions are investigated using cyclic voltammetry and galvanostatic charge/discharge techniques. The hard-template-route prepared OMC is of structurally well-ordered two-dimensional hexagonal structure with a high specific surface area of 1896.95 cm² g⁻¹, a pore volume of 1.781 cm³ g⁻¹ and a pore size of 5.1 nm, respectively. It is shown that OMC/0.3Ni electrode displays the highest specific capacitance of 186.1 Fg⁻¹, almost 1.4 times higher than that of pure OMC electrode. The hydrogen storage capacity of pure OMC electrode is 87 mAh g⁻¹ and there exists no discharge platform. With the amount of nickel addition increasing, there appears a relatively stable discharge platform, and the discharge capacity reaches a maximum of 170 mAh g⁻¹ as the molar ratio of Ni:OMC is 0.3, almost two times higher than that of pure OMC electrode. The electrochemical properties of OMC can be greatly improved with incorporation of nickel powders. The Ni activated OMC electrodes display a high capacity retainability with strong resistance against oxidation and corrosion.     

Theoretical study of hydrogen storage by spillover on porous carbon materials

Hydrogen storage by spillover in porous carbon material (PCM) has achieved great success in experiments. During the past 20 years, a large number of theoretical works have been performed to explore the hydrogen spillover mechanism, look for high-performance hydrogen storage materials and high-efficiency catalysts. In this paper, we summarize and analyze the results of the past researches, and draw the following conclusions: (1) In PCM surface, the stability of chemisorbed H can be reached through phase nucleation process, which can be initiated in the vicinity of surface impurities or defects. (2) To achieve the 2020 U.S. Department of Energy (DOE) target, the PCM material used for hydrogen storage by spillover should have a sp² carbon ratio greater than 0.43 and a surface area less than 3500 m²/g, which gives us an inspiration for exploring hydrogen spillover materials. (3) Due to a high barrier, the hydrogen spillover almost can not be initiated on pure PCM substrate at room temperature. By introducing the defects or impurities (e.g. holes, carbon bridges, oxygen functional groups, boron atoms and fluorine atoms), the spillover barriers can be reduced to a reasonable range. In addition, hydrogen atoms may also migrate in a gas phase. (4) According to our previous results of kinetic Monte Carlo simulations, there is a linear relationship between the reaction temperature and the migration barrier. The optimal barrier for the hydrogen spillover should be in the range of 0.60–0.88 eV. (5) Once the hydrogen atoms are chemically adsorbed on the carbon substrate, it is difficult to diffuse again due to the strong strength of C–H bond. Several theoretical diffusion mechanisms have been proposed. For example, the H atoms in physisorption state can diffuse freely on carbon surfaces with high mobility, using the shuttle gases (e.g. BH⁻₄, H₂O, HF and NH₃) to make the migration thermodynamically possible and decrease the migration barrier, the H atoms diffuse inside the interlayer space of the bi- and tetralayer graphene, and introducing the impurities on the surface to facilitate the hydrogen diffusion. (6) The H desorption through the directly recombination or the reverse spillover is unlikely to occur at normal temperature. The Eley-Rideal reaction may be the only possible mechanism for desorption of the adsorbed H atoms in carbon substrate. Finally, we have made a prospect for further research works on hydrogen storage by spillover.     

High hydrogen storage capacity of rice hull based porous carbon

A kind of porous carbon with high specific surface area (approximately 4000 m²/g) was prepared from rice hull through carbonization and sodium hydroxide activation. The effects of preparation parameters on the characteristics of the porous carbon were studied. The properties of these porous carbon samples were investigated by X-ray diffraction and scanning electron microscope (SEM) and Fourier transform infrared spectroscopy. The rice hull based porous carbon exhibits high hydrogen storage capacity of 7.7 wt% at 77 K and 1.2 MPa.     

A study on the hydrogen storage capacity of Ni-plated porous carbon nanofibers

In this study, we prepared highly porous carbon-nanofiber-supported nickel nanoparticles as a promising material for hydrogen storage. The porous carbons were activated at 1050 °C, and the nickel nanoparticles were loaded by an electroless metal-plating method. The textural properties of the porous carbon nanofibers were analyzed using N₂/77 K adsorption isotherms. The hydrogen storage capacity of the carbons was evaluated at 298 K and 100 bar. It was found that the amount of hydrogen stored was enhanced by increasing nickel content, showing 2.2 wt.% in the PCNF-Ni-40 sample (5.1 wt.% and 6.4% of nickel content and dispersion rate, respectively) owing to the effects of the spill-over of hydrogen molecules onto the metal–carbon interfaces. This result clearly indicates that the presence of highly dispersed nickel particles can enhance high-capacity hydrogen storage.     

Investigation of hydrogen storage capacity of various carbon materials

Hydrogen storage capacity of various carbon materials, including activated carbon (AC), single-walled carbon nanohorn, single-walled carbon nanotubes, and graphitic carbon nanofibers, was investigated at 303 and 77 K, respectively. The results showed that hydrogen storage capacity of carbon materials was less than 1 wt% at 303 K, and a super activated carbon, Maxsorb, had the highest capacity (0.67 wt%). By lowering adsorption temperature to 77 K, hydrogen storage capacity of carbon materials increased significantly and Maxsorb could store a large amount of hydrogen (5.7 wt%) at a relatively low pressure of 3 MPa. Hydrogen storage capacity of carbon materials was proportional to their specific surface area and the volume of micropores, and the narrow micropores was preferred to adsorption of hydrogen, indicating that all carbon materials adsorbed hydrogen gas through physical adsorption on the surface.     

Degradation of biomass components to prepare porous carbon for exceptional hydrogen storage capacity

Porous carbon has been constructed in various strategies for hydrogen storage. In this work, a simple-effective strategy was proposed to transform sustainable biomass into porous carbon by degrade partial lignin and hemicellulose with Na₂SO₃ and NaOH aqueous mixture. This method collapses the biomass structure to provide more active sites, and also avoid the generation and accumulation of non-porous carbon nanosheets. As a result, the as-prepared sample possesses high specific surface area (2849 m² g^?1) and large pore volume (1.08 cm³ g^?1) concentrating almost completely on micropore. Benefit to these characteristics, the as-prepared sample exhibits appealing hydrogen storage capacity of 3.01 wt% at 77 K, 1 bar and 0.85 wt% at 298 K, 50 bar. The isosteric heat of hydrogen adsorption is as high as 8.0 kJ mol^?1, which is superior to the most biochars. This strategy is of great significance to the conversion of biomass and the preparation of high-performance hydrogen storage materials.     

Synthesis and hydrogen storage capacity of exfoliated turbostratic carbon nanofibers

Turbostratic carbon nanofibers (CNFs) with a rough surface, open pore walls, and a defect structure were continuously produced by the thermal decomposition of alcohol in the presence of an iron catalyst and a sulfur promoter at 1100 °C under a nitrogen atmosphere in a vertical chemical vapor deposition reactor. A graphite exfoliation technique using intercalation and thermal shock was employed to expand the graphene layers of the as-produced turbostratic CNFs. The hydrogen storage capacity of the turbostratic CNF samples was measured using the volumetric method with a pressure of up to 1 MPa at 77 K. The hydrogen storage capacities of the as-produced and exfoliated turbostratic CNFs were 1.5 and 5 wt%, respectively. The defects on the surface and expandable graphitic structure are considered important keys to increasing the hydrogen uptake in turbostratic CNFs.     

Posidonia Oceanica and Wood chips activated carbon as interesting materials for hydrogen storage

The goal is to investigate the feasibility to use a local biomass (Posidonia Oceanica and Wood chips), as a raw precursor, to the production of activated carbons (AC) with a high surface area and remarkable hydrogen (H₂) adsorption properties.Biomasses (particle size of 0.3–0.4 mm) were pyrolyzed at 600 °C with a heating rate of 5 °C/min under an argon atmosphere. The biochar obtained from the carbonization step was chemically activated with KOH. The activation methodology induces a considerable improvement of the properties of the porous carbon in terms of carbon content (from 58 to 69 wt% to 93–96 wt%), surface area (from 41 to 425 m²/g to 2810–2835 m²/g) and H₂ adsorption in cryogenic condition (from 0,1 wt% to over 5 wt%).All porous carbons were characterized in terms of elemental analysis (CHNS–O), textural properties and H₂ adsorption measurements.     

Nitrogen doped porous carbon derived from EDTA: Effect of pores on hydrogen storage properties

N doped carbon samples have been prepared from commonly available precursor EDTA and thoroughly characterised using a variety of techniques. It has been found that with increase in annealing temperature graphitic character increases along with decrease in nitrogen content. During chemical activation by treatment with H₃PO₄, C atoms from the network structure get oxidised preferentially giving rise to larger pores, as confirmed by TEM and SAXS analysis. Possible mechanism of activation has been proposed based on NMR and XPS results. From NMR it is established that the activated samples consist of both orthophosphate (Q^o) and pyrophosphate (Q¹) structural units and are weakly linked to carbon network. Pore size has been correlated with hydrogen storage capacity and it has been found that the presence of large number of pores with lower diameter is preferable for getting better hydrogen storage capacity in porous carbon based materials.     

SANS characterization of porous magnesium for hydrogen storage

Porous magnesium was produced through the thermal decomposition of various additives in an effort to increase hydrogen storage capacity. Samples were characterized using SANS and different theoretical models were applied to the results and discussed. The polydisperse self-assembled (PSA) model was found to best represent the scattering from these materials as this model incorporates the polydispersity of the pores and allows for variations in structure factor. Pure magnesium produced using the same thermal method absorbed a negligible amount of hydrogen, and hydrogen uptake was found to increase with increasing porosity as determined using the PSA model. Maximum hydrogen uptake (1.3%) was found when 0.3% Cs₂CO₃ and 0.5% Ni were combined as an additive during thermal treatment. In addition, the development of porosity was found to promote hydrogen desorption at lower temperatures. SANS represents an indispensible method by which to characterize materials and the PSA model described in this work has the potential to be extremely useful in the characterisation of porous metallic systems.     

Automotive hydrogen storage system using cryo-adsorption on activated carbon

An integrated model of a sorbent-based cryogenic compressed hydrogen system is used to assess the prospect of meeting the near-term targets of 36 kg-H₂/m³ volumetric and 4.5 wt% gravimetric capacity for hydrogen-fueled vehicles. The model includes the thermodynamics of H₂ sorption, heat transfer during adsorption and desorption, sorption dynamics, energetics of cryogenic tank cooling, and containment of H₂ in geodesically wound carbon fiber tanks. The results from the model show that recoverable hydrogen, rather than excess or absolute adsorption, is a determining measure of whether a sorbent is a good candidate material for on-board storage of H₂. A temperature swing is needed to recover >80% of the sorption capacity of the superactivated carbon sorbent at 100 K and 100 bar as the tank is depressurized to 3–8 bar. The storage pressure at which the system needs to operate in order to approach the system capacity targets has been determined and compared with the breakeven pressure above which the storage tank is more compact if H₂ is stored only as a cryo-compressed gas. The amount of liquid N₂ needed to cool the hydrogen dispensed to the vehicle to 100 K and to remove the heat of adsorption during refueling has been estimated. The electrical energy needed to produce the requisite liquid N₂ by air liquefaction is compared with the electrical energy needed to liquefy the same amount of H₂ at a central plant. The alternate option of adiabatically refueling the sorbent tank with liquid H₂ has been evaluated to determine the relationship between the storage temperature and the sustainable temperature swing. Finally, simulations have been run to estimate the increase in specific surface area and bulk density of medium needed to satisfy the system capacity targets with H₂ storage at 100 bar.     

Divulging the electrochemical hydrogen storage of ternary BNP-doped carbon derived from biomass scaled to a pouch cell supercapacitor

Activated carbon materials have been studied extensively as electrode materials for supercapacitors (SCs), but their poor capacitance and energy density have hampered their growth. We present a one-step synthesis of a ternary boron-nitrogen-phosphorous-doped carbon (BNPC) from biomass hemp fibre to determine its electrochemical hydrogen storage ability using SC applications. FESEM micrographs reveal mixed morphologies like square, diamond and cylindrical-shaped nanosheets, confirming the hetero-atom doping into the carbon skeleton. The optimized BNPC electrode delivers a half-cell specific capacitance and hydrogen-storage capacity of 520 Fg^-1 (1 Ag^-1) and 360 mAhg⁻¹ (10 mVs⁻¹), respectively. To demonstrate the practicability of the as-prepared BNPC electrode, a symmetric pouch-cell supercapacitor device was assembled which exhibits a full-cell specific capacitance of 262.56 Fg^-1 at 1 Ag^-1 and a specific energy of ~118 Wh kg⁻¹ at a specific power of ~5759 Wkg^-1 with an operating potential window of 1.8 V and 99.7% capacitance retention over 10,000 cycles. This excellent electrochemical performance can be ascribed to the synergetic properties of fast-electrolyte-ion diffusion due to the doping of heteroatoms into the carbon matrix, high conductivity and high specific surface area and effective microporosity of BNPC (1555.5 m²g^-1). Also, the chemical stability of the BNPC materials, was investigated with density functional theory (DFT)-single point calculations, where the least molecular orbital energy gap was obtained by the BNPC, which confirms its structural stability. Thus, the prepared ternary BNP-doped carbon derived from biomass has provided a new direction to enhance the electrochemical energy storage potential.     

Catenated metal-organic frameworks: Promising hydrogen purification materials and high hydrogen storage medium with further lithium doping

Based on the first-principles derived force fields and grand canonical Monte Carlo simulations, we find that the catenated metal-organic frameworks outperform the noncatenated structures, in terms of H₂ separation from other gases (CH₄, CO and CO₂) and H₂ adsorption by Li doping. A system utilizing IRMOF-11 (or IRMOF-13) for hydrogen separation and Li-doped IRMOF-9 for hydrogen storage is therefore proposed, with hydrogen uptake of 4.91 wt% and 36.6 g/L at 243 K and 100 bar for Li-doped IRMOF-9, which is close to the 2017 DOE target. It is promising to find appropriate microporous materials for hydrogen purification and storage at ambient conditions with structure catenated.     

Preparation and characterization of mica glass-ceramics as hydrogen storage materials

This work is an attempt to study storing hydrogen in safe, reliable, compact, and cost-effective glass-ceramics materials for the first time. The effect of replacing K⁺ by Na⁺ or Li⁺ in the fluorophlogopite formula KMg₃AlSi₃O₁₀F₂ was studied using DTA, XRD and SEM. Also the effect of the crystallized phases within glass-ceramics on the surface area and capacity of storing hydrogen under different pressures were studied. Replacement of K⁺ by Na⁺ or Li⁺ leads to increase the temperature of crystallization in the same order. XRD revealed crystallization of spodumene (LiAlSi₂O₆) and forsterite (Mg₂SiO₄) in GLi and Na-fluorophlogopite (NaMg₃AlSi₃O₁₀F₂) and Na-mica (NaAl₃Si₃O₁₁) in GNa while Lucite (KAlSi₂O₆) and forsterite in GK. Surface area measurements for optimum samples showed low values in the range 0.48–0.58 m²/g; also total pore volumes have low values 9.4 × 10^?4–6.99 × 10^?3 cm³/g. The hydrogen adsorption content reached 1.25, 2.5, 1.34 sand 1.9 wt% for GLi, GNa, GK and GK samples heated for 2 h at 770,1100, 1000 and 1100 °C, respectively. The results obtained that, Na-bearing samples are the proper for hydrogen storage wherein sodium mica and phlogopite with characteristic sheet structure were crystallized.     

Acetic acid catalysed carbon xerogels derived from resorcinol-furfural for hydrogen storage

Carbon xerogels were prepared from the sol-gel polymerisation of resorcinol with furfural followed by carbonisation and activation, and their hydrogen storage properties were studied. Acetic acid was used as a catalyst to adjust the initial pH value of the resorcinol-furfural solution. The acetic acid facilitates the condensation reaction by reducing the gelation time dramatically from a few days to several hours. The effect of precursor acidity on the final gels are chemically distinguishable (by 13C CPMAS NMR) from the acetic acid catalysed organic gels compared with uncatalysed gel. The connectivity of the primary carbon particles and particle size are related to the degree of acidity, as were found from SEM photographs. The pore structures were studied by small angle X-ray scattering and nitrogen adsorption techniques after carbonisation and activation in order to determine the effect of precursor pH variables on the resulting samples. A catalysed carbon xerogel prepared with pH ∼ 4.8 has a surface area of 1924 ± 26 m² g⁻¹, a micropore volume of 0.86 ± 0.08 cm³ g⁻¹ and a hydrogen uptake of 4.65 wt.% at 77 K and 3.9 MPa, showing it to be a promising material for hydrogen storage.     

A simple method for the production of highly ordered porous carbon materials with increased hydrogen uptake capacities

The synthesis, characterization and hydrogen uptake of porous carbons generated by heat treatment was investigated using various zeolites and mesoporous silicas as hard templates. The effect of heat treatment on the structural order, textural properties and hydrogen uptake capacities of porous carbons templated from the model zeolite EMC-2 in a temperature range of 600–800 °C during chemical vapour deposition were studied in details. The heat treatment improved the structural order of replicated microporous carbons, significantly increased both total and microporous surface area and pore volume, and remarkably increased the hydrogen uptake capacity. The optimized heat treatment conditions were at 900 °C for 3 h. The heat treatment at high temperatures was found to be a simple and general approach to synthesize well-ordered microporous carbons from different zeolite templates, using various carbon precursors and through different synthesis methods. The microporous carbons possessed a high surface area and pore volume with increased microporosity and therefore exhibited improved hydrogen storage capacities up to 5.85 wt% at 20 bar and −196 °C. The heat treatment, however, has no obvious effect on the textural properties and hydrogen uptake capacities for mesoporous carbons templated from mesoporous silicas.     

Investigations of AB5-type hydrogen storage materials with enhanced hydrogen storage capacity

The present study deals with investigations on synthesis, characterization and hydrogenation behavior of the MmNi₅-type hydrogen storage alloys Mm_0.9Ca_0.1Ni_4.9−xFe_xAl_0.1 (x = 0, 0.1, 0.2 and 0.3). All the alloys are synthesized by radio frequency induction melting following the composite pellet route. The X-ray diffraction pattern of dehydrogenated alloy without iron, detects peaks corresponding to calcium hydride, which are absent in the XRD pattern of the alloy with iron. The hydrogenation behavior is monitored by means of activation curves, absorption-desorption pressure-composition isotherms, hysteresis factors and desorption kinetic curves. The substitution of Iron at the place of nickel in the alloys Mm_0.9Ca_0.1Ni_4.9−xFe_xAl_0.1 (x = 0, 0.1, 0.2 and 0.3) gives an increase in the hydrogen storage capacity as 1.82, 1.90, 2.2 and 1.95 wt% corresponding to x = 0, 0.1, 0.2 and 0.3 respectively. The correlation between structural characteristics and hydrogenation behavior is described and discussed.