Isosteric Heat Of Hydrogen Adsorption Research Articles

Investigation of the densification and heat conducting enhancement measures on MIL-101 and its composite for hydrogen storage by adsorption

Increasing the packing density and enhancing heat conducting of MOFs systems are crucial to their practical applications. For this purpose, MIL-101 was selected and undergone the incorporation of the activated carbon (AC), the densification by mixing expanded graphite (ENG) and employing 3D printing via PVA and bentonite clay. Structural characterizations and adsorption equilibrium tests of hydrogen were conducted. The effect of a honeycomb heat exchanging device (HHED), ENG and 3D printing on the thermal conductivity enhancement was evaluated by the charge/discharge tests of hydrogen on a 0.5 L storage vessel under a flow rate of 20 L/min at 77.15 K. It shows that the specific surface area and micro-pore volume of the sample have the largest values by incorporating AC about 1 wt% but decrease in mixing ENG and 3D printing. The mean limit isosteric heats of hydrogen adsorption on the samples prepared by 3D printing are larger than those on the ENG composites. In comparing with those of addition of ENG, the HEED and 3D printing respectively prolonged the effective charge duration about 3.1%, 11.5% by cutting down the temperature fluctuation about 11.1%, 14.8%. It suggests that 3D printing is more effective on densifying the MOFs by enhancing its thermal conductivity. • Relationship between added AC, ENG, bentonite clay and the structures of the sample. • Relationship between added ENG, bentonite clay and the thermal conductivity of the sample. • 3D printing is a better method for the densification of the MIL-101 than mixing the ENG. • 3D printing performs better on heat conducing enhancement than using heat exchanging devices.

Adsorption-Based Hydrogen Storage in Activated Carbons and Model Carbon Structures

The experimental data on hydrogen adsorption on five nanoporous activated carbons (ACs) of various origins measured over the temperature range of 303–363 K and pressures up to 20 MPa were compared with the predictions of hydrogen density in the slit-like pores of model carbon structures calculated by the Dubinin theory of volume filling of micropores. The highest amount of adsorbed hydrogen was found for the AC sample (ACS) prepared from a polymer mixture by KOH thermochemical activation, characterized by a biporous structure: 11.0 mmol/g at 16 MPa and 303 K. The greatest volumetric capacity over the entire range of temperature and pressure was demonstrated by the densest carbon adsorbent prepared from silicon carbide. The calculations of hydrogen density in the slit-like model pores revealed that the optimal hydrogen storage depended on the pore size, temperature, and pressure. The hydrogen adsorption capacity of the model structures exceeded the US Department of Energy (DOE) target value of 6.5 wt.% starting from 200 K and 20 MPa, whereas the most efficient carbon adsorbent ACS could achieve 7.5 wt.% only at extremely low temperatures. The initial differential molar isosteric heats of hydrogen adsorption in the studied activated carbons were in the range of 2.8–14 kJ/mol and varied during adsorption in a manner specific for each adsorbent.

Evaluation of the effects of heat conducting enhancement measures on MOFs hydrogen storage system for ship's propulsion plant

Experiments were conducted for developing an on board MOFs hydrogen storage system by cryo-adsorption in terms of adsorption equilibrium and charge/discharge characteristic of the adsorbent bed. MIL-101 was synthesized by hydrothermal method, the expanded natural graphite (ENG) and a honeycomb heat exchanging device were then introduced for monolith and heat conducting enhancement. Structural characterization and measurement of thermal conductivity were performed on the MIL-101 and its composites synthesized by mixing ENG with different mass ratios. Adsorption equilibrium data of hydrogen on the MIL-101 and MEI-01 (composite formed by adding ENG with a mass ratio 0.1) were measured at a temperature-pressure range from 77.15K to 87.15 K and 0–6 MPa. Accuracies of results predicted by Langmuirian equations were compared, Toth equation and Henry law were then employed to calculate the isosteric heat of hydrogen adsorption. Charge and discharge tests were conducted under the flow rate 20 L·min−1 on a 3.2 L conformable vessel respectively filled MIL-101, MIL-101+honeycomb heat exchanging device and MEI-01. It shows that the isosteric heats on two samples are similar and are about 3.1kJ·mol−1−7.4kJ·mol−1; the honeycomb heat exchanging device is better on weakening the thermal effect of the adsorbent bed than adding the ENG. It suggests that employing a conformable shape vessel equipped with a honeycomb heat exchanging device is a feasible solution to an on board MOFs hydrogen storage system.

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.

Remarkable isosteric heat of hydrogen adsorption on Cu(I)-exchanged SSZ-39

Hydrogen storage capacity on Cu(I)-exchanged SSZ-39 (AEI), -SSZ-13 (CHA) and Ultra stable-Y (US–Y, FAU) at temperatures between 279 K and 304 K are investigated. The gravimetric hydrogen storage capacity values reaching 83 μmol H2 g−1 (at 279 K and 1 bar) are found to be comparable with the highest adsorption capacity values reported on metal-organic frameworks. The volumetric hydrogen storage capacity values; on the other hand, are found to be more than three times of those reported on metal-organic frameworks (0.57 g/L on Cu(I)-SSZ-39 at 1 bar and 296 K vs. ca. 0.18 g/L on Co2(m-dobdc) at 1 bar and 298 K (Kapelewski MT, Runčevski T, Tarver JD, Jiang HZH, Hurst KE, Parilla PA et al. Record High Hydrogen Storage Capacity in the Metal-Organic Framework Ni2(m-dobdc) at Near-Ambient Temperatures. Chem Mater 2018; 30:8179–89)). The isosteric heat of adsorption values are calculated to be between 80 kJ mol−1 and 49 kJ mol−1 on Cu(I)-SSZ-39 and between 22 kJ mol−1 and 15 kJ mol−1 on Cu(I)-US-Y indicating H2 adsorption mainly at Cu(I) cations located at the eight-membered rings on Cu(I)-SSZ-39 and at six-membered rings on Cu(I)-US-Y. Hydrogen adsorption experiments performed at 77 K showed higher adsorption capacity values for Cu(I)-SSZ-39 at 1 bar, but Cu(I)-US-Y showed potential for hydrogen storage at higher pressure values.

Application of the modified Dubinin-Astakhov equation for a better understanding of high-pressure hydrogen adsorption on activated carbons

Hydrogen storage in activated carbons (ACs) has proven to be a realistic alternative to compression and liquefaction. Adsorption capacities up to 5.8 wt% have indeed been obtained. The amount of adsorbed hydrogen depends on the textural properties of ACs, such as specific surface area and total pore volume. The modified Dubinin-Astakhov (MDA) equation proved to be a good analytical tool for describing hydrogen adsorption in a wide range of pressures and temperatures and for several adsorbents. The parameters of this model have been found to be somehow related to the textural properties of the adsorbent. Thus, we applied this model to understand better hydrogen adsorption on ACs over a wide range of pressures in relation to the textural properties of the ACs.We applied the MDA equation to evaluate also the isosteric heat of hydrogen adsorption, which was found to be in the range of 5–9 kJ mol−1. We compared the results obtained by applying the MDA equation with those obtained by both the sorption isosteric method and the Sips equation. This allowed finding the temperature dependence of the isosteric heat of adsorption, as well as its variation with respect to the textural properties of the ACs.

Adsorption equilibrium of hydrogen adsorption on activated carbon, multi-walled carbon nanotubes and graphene sheets

For obtaining the technical data to develop storage medium with appropriate structure for hydrogen storage system, behavior of hydrogen adsorption on carbon based adsorbents with different micro structures was comparatively studied. Activated carbon (SAC-02), multi-walled carbon nanotubes (MWCNTs) and graphene sheets (GS), which respectively have a specific surface area about 1916 m2/g, 155 m2/g and 221 m2/g, were selected to test adsorption equilibrium at temperature from 77.15 K to 113.15 K and pressure up to 6 MPa. Toth equation was applied to estimate the absolute adsorption amounts, and isosteric heat and limit isosteric heat of hydrogen adsorption were used to investigate the influence of structures variation for hydrogen storage. This study shows that the GS exhibits a higher potential in hydrogen storage though it is a mesoporous adsorbent, and the relative errors of predicted results from Toth equation were less than 2.1%, The value of the isosteric heat of hydrogen adsorption on GS is about 4.01–5.88 kJ/mol, which is higher than 3.67–3.96 kJ/mol for hydrogen adsorption on the SAC-02 and 2.47–4.36 kJ/mol for hydrogen adsorption on the MWCNTs, respectively. It also reveals that adsorbents with fold structure would be more beneficial to adsorbing hydrogen than the adsorbents with pore structure or flat plane, and a higher specific surface area is necessary when the GS was applied to hydrogen storage system.

Oxygen-rich microporous carbons with exceptional hydrogen storage capacity

Porous carbons have been extensively investigated for hydrogen storage but, to date, appear to have an upper limit to their storage capacity. Here, in an effort to circumvent this upper limit, we explore the potential of oxygen-rich activated carbons. We describe cellulose acetate-derived carbons that combine high surface area (3800 m2 g−1) and pore volume (1.8 cm3 g−1) that arise almost entirely (>90%) from micropores, with an oxygen-rich nature. The carbons exhibit enhanced gravimetric hydrogen uptake (8.1 wt% total and 7.0 wt% excess) at −196 °C and 20 bar, rising to a total uptake of 8.9 wt% at 30 bar, and exceptional volumetric uptake of 44 g l−1 at 20 bar, and 48 g l−1 at 30 bar. At room temperature they store up to 0.8 wt% (excess) and 1.2 wt% (total) hydrogen at only 30 bar, and their isosteric heat of hydrogen adsorption is above 10 kJ mol−1.

(Invited) Hydrogen Storage Characterization and Optimization Research Effort, Hyscore

The HySCORE collaboration is a DOE-FCTO funded initiative that brings together internationally recognized leaders in hydrogen storage materials characterization and development from NREL, LBNL, PNNL and NIST. This collaboration is predicated on a synergistic approach to further develop the key core-capabilities necessary for accurate evaluation of hydrogen storage materials capacity, kinetics, and sorption/desorption physio-chemical processes. Furthermore, these experts also conduct a parallel experimental-modeling collaborative approach to utilize the core-capabilities developed in order to rapidly define, model, synthesize and characterize the appropriate materials necessary for achieving the 2020 Hydrogen Storage goals set forth by DOE. The approach is multifaceted to mitigate risk and ensure success as we bridge the gap between physisorption and chemisorption to provide the basis for a new generation of hydrogen storage materials technologies. Our focus is to Develop and Enhance hydrogen storage core capabilities and to Validate claims, concepts, and theories of hydrogen storage materials. The overarching goal is to ascertain pathways and/or new materials that have the possibility to volumetric capacities of greater than 45 g/L and isosteric heats of hydrogen adsorption in the range of 15-20 kJ/mol with the additional caveats of acceptable gravimetric capacities and the ability to deliver on-demand H2 at an appropriate rate and pressure. In order to capture the benefits of reduced system cost and forecourt compression energetics, the maximum overpressure would be <100 bar of hydrogen, with a delivery temperature of greater than 150 K and as close to ambient temperature as possible. This talk will outline the advanced characterization techniques, standardized benchmarking/protocols and capabilities. We will also highlight several new materials sets, the impact of the new characterization tools and how this has acceleratd advances in hydrogen storage materials development.

Improvement of Accuracy for Determination of Isosteric Heat of Hydrogen Adsorption

Improvement of Accuracy for Determination of Isosteric Heat of Hydrogen Adsorption

Hydrogen storage in a layered flexible [Ni2(btc)(en)2]n coordination polymer

[Ni2(btc)(en)2]n coordination polymer exhibits a layered two-dimensional structure with weak interaction between the layers. Correlation of experimental measurements, DFT calculations and molecular simulations demonstrated that its structural features, primarily the inherent flexibility of the layered polymeric structure, lead to improved hydrogen storage performance at room temperature, due to significant enhancement in isosteric heats of hydrogen adsorption. Volumetric measurements of hydrogen adsorption at room temperature show up to 0.3 wt.% hydrogen absorbed at 303 K and 2.63 bar of hydrogen pressure, with isosteric heats of adsorption of about 12.5 kJ mol−1. Predicted performance at room temperature is 1.8 wt.% at 48 bar and 3.5 wt.% at 100 bar, better than both MOF-5 and NU-100, with calculated values of isosteric heats for adsorption of hydrogen in 8–13 kJ mol−1 range at both 77 K and 303 K. Grand canonical Monte Carlo calculations show that this material, at 77 K, exhibits gravimetric hydrogen densities of more than 10 wt.% (up to 8.3 wt.% excess) with the corresponding volumetric density of at least 66 gL−1, which is comparable to MOF-5, but achieved with considerably smaller surface area of about 2500 m2 g−1. This study shows that layered two-dimensional MOFs could be a step towards MOF systems with significantly higher isosteric heats of adsorption, which could provide better room temperature hydrogen storage capabilities.

Erratum to: Isosteric heat of hydrogen adsorption on MOFs: comparison between adsorption calorimetry, sorption isosteric method, and analytical models

Erratum to: Isosteric heat of hydrogen adsorption on MOFs: comparison between adsorption calorimetry, sorption isosteric method, and analytical models

High capacity hydrogen storage at room temperature via physisorption in a coordinatively unsaturated iron complex

Coordinatively unsaturated iron metal sites were introduced in the tris(aminophenyl)bezene-terephthalaldehyde framework to facilitate Kubas type metal–hydrogen binding for ambient temperature hydrogen storage applications. The synthesized compound was characterized via elemental analysis (EA), infrared spectroscopy (IR), thermogravimetric analysis (TGA), nitrogen adsorption-desorption (BET) and X-ray photoelectron spectroscopy (XPS). This complex exhibits a remarkably high gravimetric capacity up to 1.2 wt% at 298 K under 100 atm despite the relatively low BET surface area of 54.6 m2/g. The observed significant isosteric heat of hydrogen adsorption with surface coverage arises from the Kubas type of bonding supported by the results of electron paramagnetic resonance (EPR). Excellent reversibility of hydrogen adsorption was demonstrated.

Isosteric heat of hydrogen adsorption on MOFs: comparison between adsorption calorimetry, sorption isosteric method, and analytical models

Isosteric heat of adsorption is an important parameter required to describe the thermal performance of adsorptive storage systems. It is most frequently calculated from adsorption isotherms measured over wide ranges of pressure and temperature, using the so-called adsorption isosteric method. Direct quantitative estimation of isosteric heats on the other hand is possible using the coupled calorimetric–volumetric method, which involves simultaneous measurement of heat and adsorption. In this work, we compare the isosteric heats of hydrogen adsorption on microporous materials measured by both methods. Furthermore, the experimental data are compared with the isosteric heats obtained using the modified Dubinin–Astakhov, Tóth, and Unilan adsorption analytical models to establish the reliability and limitations of simpler methods and assumptions. To this end, we measure the hydrogen isosteric heats on five prototypical metal–organic frameworks: MOF-5, Cu-BTC, Fe-BTC, MIL-53, and MOF-177 using both experimental methods. For all MOFs, we find a very good agreement between the isosteric heats measured using the calorimetric and isosteric methods throughout the range of loading studied. Models’ prediction on the other hand deviates from both experiments depending on the MOF studied and the range of loading. Under low-loadings of less than 5 mol kg−1, the isosteric heat of hydrogen adsorption decreases in the order Cu-BTC > MIL-53 > MOF-5 > Fe-BTC > MOF-177. The order of isosteric heats is coherent with the strength of hydrogen interaction revealed from previous thermal desorption spectroscopy measurements.

Multiscale Study of Hydrogen Adsorption on Six Designed Covalent Organic Frameworks Based on Porphyrazine, Cyclobutane and Scandium

The first-principles method of hydrogen adsorption is used to investigate the interaction of H2 with the scandium-porphyrazine (Sc-Pz) and porphyrazine (Pz) clusters. The result shows that the interaction of H2 with Sc-Pz is stronger than with Pz. Then grand canonical Monte Carlo simulations are used to investigate hydrogen adsorption in six designed covalent organic frameworks (COFs), which are designed based on porphyrazine, cyclobutane and scandium. When the pressure is from 0.1 to 100 bar and the temperature is 298 K and 77 K, the hydrogen adsorption capacities of the six COFs are calculated. We further study the importance of Sc and fillers to improve the H2 uptake in the modified COFs by analyzing the isosteric heat of hydrogen adsorption.

Adsorption equilibrium of hydrogen on graphene sheets and activated carbon

For obtaining the technical data to evaluate the performance of hydrogen storage by adsorption on graphene sheets (GS), analysis of adsorption equilibrium of hydrogen on the GS and the activated carbon were carried out based on the hydrogen adsorption data covering a wide temperature range. The GS and SAC-02 activated carbon, which respectively had a specific surface area about 300m2/g and 2074m2/g, were selected as adsorbents. Six adsorption isotherms of excess amounts of high purity hydrogen were measured at temperature from 77.15K to 293.15K and pressure up to 6MPa. Parameters of Langmuir, Langmuir–Freundlich and Toth equations were set by non-linear fit against adsorption data, predicting accuracy of the equations was then evaluated by the accumulated relative errors between experimental data and those from the equations under different pressure regions. Absolute adsorption amounts determined by the modified equation were used to calculate the isosteric heat of adsorption.It shows that both adsorption isotherms of hydrogen on the GS and the activated carbon have the features of Type I, but the trend of isotherms varying over the pressure is different within the lower temperature region. Results from Langmuir equation have the largest error. Toth equation can much accurately predict the adsorption data with an overall accumulated relative error less than 4%. The value of the isosteric heat of hydrogen adsorption on the GS is about 5.06–6.37kJ/mol, which is much higher than 4.05–5.52kJ/mol for hydrogen on the SAC-02 activated carbon under the whole experimental condition. It reveals that interaction between hydrogen molecules and the graphene layer is stronger than that of hydrogen and carbon surface, and Toth equation could be appropriate to analyzing adsorption equilibrium for hydrogen on carbon based adsorbents.

Copper-based coordination polymers from thiophene and furan dicarboxylates with high isosteric heats of hydrogen adsorption

Cu-based coordination polymers containing thiophene (TDC) and furan (FDC) dicarboxylates were prepared and their hydrogen uptake characteristics were investigated.

Analysis of adsorption equilibrium of hydrogen on graphene sheets

The adsorption equilibrium of hydrogen on graphene sheets (GS) was studied based on a sample of GS with SBET = 300 m2/g at the temperatures of 77.15 K–293.15 K and the pressures of 0 MPa–6 MPa. In the meantime, the adsorptions (Excess adsorption measurements) of hydrogen on granular coconut shell SAC-02 activated carbon (SBET = 2074 m2/g) and carbon nanofiber (CNFs, SBET = 205 m2/g) were investigated at the pressures of 0–8 MPa and the temperature of 77.15 K. The outcomes from experiments were used to determine the parameters in Toth equation by way of Non-linear fit. The absolute adsorption amounts of hydrogen on the GS, which were calculated from the equation, were used to calculate the isosteric heat of hydrogen adsorption by use of adsorption isosteres.It shows that, under the experimental conditions, the excess adsorption amount of hydrogen on the GS increases monotonically and correlatively as pressure increases, and the mean relative deviation between the experimental data and those predicted from Toth equation is less than 1%. The result also shows that the storage density of hydrogen on the GS is 1.75 wt% and 0.168 gH2/L at pressure 5.4 MPa and temperature 77.15 K, which is lower than that of hydrogen on the activated carbon but is higher than that of hydrogen on the CNFs. The isosteric heat of hydrogen adsorption on the GS falls within 5.14 kJ/mol–6.37 kJ/mol, which is comparable to that of hydrogen adsorption on the activated carbon. It suggests that interaction between hydrogen molecules and the graphene layer is stronger than that between hydrogen and carbon surface, and the hydrogen storage capacity of GS is closely related to its physical properties.

The hydrogen storage capacity of mono-substituted MOF-5 derivatives: An experimental and computational approach

Herein we report the synthesis and hydrogen storage capability of four simple MOF-5 modifications, i.e. CH3-MOF-5, OCH3-MOF-5, Br-MOF-5 and Cl-MOF-5. The mono-substituted MOF-5s, with the exception of OCH3-MOF-5, exhibit the same topology as that of unsubstituted MOF-5. The BET surface areas are in the range of 680–2750m2g−1 for this series. Introducing these functional groups appears to have a significant effect on the thermal stability of the resulting frameworks. The thermal stability of CH3-MOF-5 is comparable to that of MOF-5 after heat-treatment, i.e. vacuum dried at 200°C for 40h, whereas the structure of Cl-MOF-5 collapses under the same conditions. Activated MOF-5, CH3-MOF-5, Br-MOF-5 and Cl-MOF-5 show 1.44wt.%, 1.47wt.%, 1.08wt.% and 0.99wt.% of hydrogen uptake capacities at 77K and 1bar, respectively. Experimental and computational results reveal that the introduction of –CH3, –Br and –Cl has only a minor effect on the isosteric heat of hydrogen adsorption for MOF-5 and the experimental values are in the range of 2.8 – 3.0kJmol−1 for all derivatives. This explains the similar hydrogen adsorption capacities of MOF-5 and CH3-MOF-5. The poor porous structures of Br-MOF-5 and Cl-MOF-5, however, result in lower hydrogen adsorption capacities compared to MOF-5 despite their similar isosteric heat of hydrogen adsorption. At high pressures (>20bar), the excess hydrogen capacity appears to be a strong function of the specific surface area.

Preparation of sulfur-doped microporous carbons for the storage of hydrogen and carbon dioxide

Structurally well ordered, sulfur-doped microporous carbon materials have been successfully prepared by a nanocasting method using zeolite EMC-2 as a hard template. The carbon materials exhibited well-resolved diffraction peaks in powder XRD patterns and ordered micropore channels in TEM images. Adjusting the synthesis conditions, carbons possess a tunable sulfur content in the range of 1.3–6.6wt.%, a surface area of 729–1627m2g−1 and a pore volume of 0.60–0.90cm3g−1. A significant proportion of the porosity in the carbons (up to 82% and 63% for surface area and pore volume, respectively) is contributed by micropores. The sulfur-doped microporous carbons exhibit isosteric heat of hydrogen adsorption up to 9.2kJmol−1 and a high hydrogen uptake density of 14.3×10−3mmolm−2 at −196°C and 20bar, one of the highest ever observed for nanoporous carbons. They also show a high CO2 adsorption energy up to 59kJmol−1 at lower coverages (with 22kJmol−1 at higher CO2 coverages), the highest ever reported for any porous carbon materials and one of the highest amongst all the porous materials. These findings suggest that S-doped microporous carbons are potential promising adsorbents for hydrogen and CO2.