H2 Uptake Research Articles

Synthesis of activated carbon from high-carbon coal fly ash and its hydrogen storage application

Activated carbons (ACs) have desirable characteristics that make them attractive for many industrial applications. In order to reduce their production cost, there is always a need to find alternative low-cost feedstock precursors. Nowadays zero-waste technologies play an important role in sustainable development, therefore using of coal by-product as source of AC is strongly recommended. In this study, coal fly ash (CFA) sample with a high unburned carbon content was used to synthesize ACs. The effect of acid pre-treatment of the CFA sample using HF and HCl prior to thermochemical activation using KOH was also investigated. The acid washing was found to be effective since it removed most of the inorganic components found in the CFA, as was confirmed by EDS and XRF. The resulting carbon-rich feedstock had relatively high content of meso-/macropores as well as with relative increase in specific surface area (46.19 m2/g - 81.20 m2/g). The obtained AC sample was found to exhibit high specific surface (946.77 m2/g) that was dominated by high microporosity and was tested for hydrogen storage. The H2 uptake (1 bar, 77 K) was found to be 1.35 wt% and with a predictable potential for even higher capacity when measurements are conducted at high pressures.

Facile synthesis of hybrid porous composites and its porous carbon for enhanced H2 and CH4 storage

The anticipated energy crisis due to the extensive use of limited stock fossil fuels forces the scientific society for find prompt solution for commercialization of hydrogen as a clean source of energy. Hence, convenient and efficient solid-state hydrogen storage adsorbents are required. Additionally, the safe commercialization of huge reservoir natural gas (CH4) as an on-board vehicle fuel and alternative to gasoline due to its environmentally friendly combustion is also a vital issue. To this end, in this study we report facile synthesis of polymer-based composites for H2 and CH4 uptake. The cross-linked polymer and its porous composites with activated carbon were developed through in-situ synthesis method. The mass loadings of activated carbon were varied from 7 to 20 wt%. The developed hybrid porous composites achieved high specific surface area (SSA) of 1420 m2/g and total pore volume (TPV) of 0.932 cm3/g as compared to 695 m2/g and 0.857 cm3/g for pristine porous polymer. Additionally, the porous composite was activated converted to a highly porous carbon material achieving SSA and TPV of 2679 m2/g and 1.335 cm3/g, respectively. The H2 adsorption for all developed porous materials was studied at 77 and 298 K and 20 bar achieving excess uptake of 4.4 wt% and 0.17 wt% respectively, which is comparable to the highest reported value for porous carbon. Furthermore, the developed porous materials achieved CH4 uptake of 8.15 mmol/g at 298 K and 20 bar which is also among the top reported values for porous carbon.

Enhancing hydrogen storage by metal substitution in MIL-88A metal-organic framework

MIL-88A metal-organic framework with the unsaturated Fe metal coordination sites has demonstrated to be a promising material for gas storage and capture. However, the hydrogen storage capacity of MIL-88A has to be improved to meet the practical level at the ambient conditions. In this research, we elucidated the effects of transition metal substitution on the hydrogen storage capability of MIL-88A. The trivalent transition metals including Sc, Ti, V, Cr, Mn, and Ni have been selected to substitute for Fe in MIL-88A. Using the van der Waals dispersion-corrected density functional theory calculations, we explored the most favorable adsorption configurations of the hydrogen molecule in M-MIL-88A (M = Sc, Ti, V, Cr, Mn, Ni). We found that the V-MIL-88A has the strongest binding energy of 17 kJ mol−1 with the hydrogen molecule in the side-on configuration on the metal site. Besides, the grand canonical Monte Carlo simulations showed that the metal substitution greatly influences not only the favorable adsorption configuration and energy but also the hydrogen uptake due to the modification of the H2@MIL-88A interaction. Sc-MIL-88A was found to offer the highest gravimetric H2 uptake compared to the other M-MIL-88A. The value is 5.13 wt% at (cryogenic temperature 77 K, 50 bar) and 0.72 wt% at (room temperature 298 K, 100 bar) for the absolute; 4.63 wt% at (77 K, 10 bar) and 0.29 wt% at (298 K, 100 bar) for the excess capacity. Furthermore, Sc-MIL-88A also exhibited the highest volumetric uptake up to 52 g L−1 at 77 K and 7.1 g L−1 at 298 K for the absolute; 46 g L−1 at 77 K and 2.8 g L−1 at 298 K for the excess loading.

Computational Screening of Covalent Organic Frameworks for Hydrogen Storage

Covalent Organic Frameworks (COFs) have been considered as promising materials for gas storage applications due to their highly porous structures and tunable characteristics. In this work, high-throughput molecular simulations were performed to screen the recent Computation-Ready Experimental COF Database (CoRE-COF) for H2 storage a first time in the literature. Predictions for H2 uptakes were first compared with the experimental data of several COFs. Motivated from the good agreement between simulations and experiments, we performed Grand Canonical Monte Carlo (GCMC) simulations to compute volumetric H2 uptakes of 296 COFs at various temperatures and pressures and identified the best candidates which exhibit a superior performance for H2 storage. COFs outperformed several well-known MOFs such as HKUST-1, NU-125, NU-1000 series, NOTT-112 and UiO-67 at 100bar/77K adsorption and 5bar/160K desorption conditions. We also examined the effect of Feynman-Hibbs correction on simulated H2 isotherms and H2 working capacities of COFs to consider quantum effects at low temperatures. Results showed that the Feynman-Hibbs corrections do not affect the ranking of materials based on H2 working capacities, but slightly affect the predictions of H2 adsorption isotherms. We finally examined the structure-performance relations and showed that density and porosity are highly correlated with the volumetric H2 working capacities of COFs. Results of this study will be highly useful in guiding future research and focusing experimental efforts on the best COF adsorbents identified in this study.

Mixed Metal-Organic Framework with Multiple Binding Sites for Efficient C2 H2 /CO2 Separation.

The separation of C2 H2 /CO2 is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal-organic framework (M'MOF), [Fe(pyz)Ni(CN)4 ] (FeNi-M'MOF, pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C2 H2 /CO2 separation. This MOF shows not only a remarkable volumetric C2 H2 uptake of 133 cm3 cm-3 , but also an excellent C2 H2 /CO2 selectivity of 24 under ambient conditions, resulting in the second highest C2 H2 -capture amount of 4.54 mol L-1 , thus outperforming most previous benchmark materials. The separation performance of this material is driven by π-π stacking and multiple intermolecular interactions between C2 H2 molecules and the binding sites of FeNi-M'MOF. This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M'MOF as a promising material for C2 H2 /CO2 separation.

One‐pot Facile Synthesis of Multifunctional Conjugated Microporous Polymers via Suzuki‐Miyaura Coupling Reaction

AbstractA wide set of conjugated microporous polymers (CMPs) are synthesized via a facile Pd‐catalyzed Suzuki‐Miyaura coupling reaction between organo‐boron reagents and organic halides in the presence of K2CO3. According to multiple characterizations, the resulting polymers are thermally stable and fluorescent with large specific surface areas (SSAs) and narrow pore distributions. Especially, polymer synthetized by using 1,3,6,8‐tetrabromopyrene (TBP) and 1,4‐phenylenediboronic acid (PDBA) exhibits the largest apparent SSA up to 1071 m2 g−1, H2 uptake capacity of 152.77 cm3 g−1 (77 K, 1 bar) and CO2 uptake capacity of 58.97 cm3 g−1 (273 K, 1 bar). Furthermore, parallel experiments prove TBP and PDBA are the best building blocks for these series polymers synthesis. Moreover, CMPs feature large SSAs, outstanding thermal and fluorescent performances, and facile preparation, making themselves promising candidates for the future industrial applications.

Metal-Organic Frameworks of Cu(II) Constructed from Functionalized Ligands for High Capacity H2 and CO2 Gas Adsorption and Catalytic Studies.

Two Cu(II)-based metal-organic frameworks (MOFs) having paddle-wheel secondary building units (SBUs), namely, 1Me and 1ipr, were synthesized solvothermally using two new bent di-isophthalate ligands incorporating different substituents. The MOFs showed high porosity (BET surface area, 2191 m2/g for 1Me and 1402 m2/g for 1ipr). For 1Me, very high CO2 adsorption (98.5 wt % at 195 K, 42.9 wt % at 273 K, 23.3 wt % at 298 K) at 1 bar was found, while for 1ipr, it was significantly less (14.3 wt % at 298 K and 1 bar, 54.4 wt % at 298 K at 50 bar). 1Me exhibited H2 uptake of 3.2 wt % at 77 K and 1 bar of pressure, which compares well with other benchmark MOFs. For 1ipr, the H2 uptake was found to be 2.54 wt % under similar experimental conditions. The significant adsorption of H2 and CO2 for 1Me could be due to the presence of micropores as well as unsaturated metal sites in these MOFs besides the presence of substituents that interact with the gas molecules. The experimental adsorption behavior of the MOFs could be justified by theoretical calculations. Additionally, catalytic conversions of CO2 and CS2 into useful chemicals like cyclic carbonates, cyclic trithiocarbonates, and cyclic dithiocarbonates could be achieved.

Synthesis, structure and electrocatalytic H2-evoluting activity of a dinickel model complex related to the active site of [NiFe]-hydrogenases

Structural and functional biomimicking of the active site of [NiFe]-hydrogenases can provide helpful hints for designing bioinspired catalysts to replace the expensive noble metal catalysts for H2 generation and uptake. Treatment of dianion [Ni(phma)]2− [H4phma = N,N'-1,2-phenylenebis(2-mercaptoacetamide)] with [NiCl2(dppp)] (dppp = bis(diphenylphosphino)propane) yielded a dinickel product [Ni(phma)(μ-S,S')Ni(dppp)] (1) as the model complex relevant to the active site of [NiFe]-H2ases. The structure of complex 1 has been characterized by single-crystal X-ray analysis. From cyclic voltammetry and controlled potential electrolysis studies, complex 1 was found to be a moderate electrocatalyst for the H2-evoluting reaction using ClCH2COOH as the proton source.

Elucidating hydrogen storage properties of two-dimensional siligraphene (SiC8) monolayers upon selected metal decoration

DFT investigation of hydrogen (H2) adsorption on pristine and light metal decorated siligraphene SiC8 showed that Ca@SiC8 and Li@SiC8 have promising thermodynamic properties and H2 uptake, which surpasses the U.S. Department of Energy's 2025 goal.

Predicting Hydrogen Storage in Mofs <i>via</i> Machine Learning

The H2 storage capacities of a diverse set of 918,734 metal-organic frameworks (MOFs) sourced from 19 databases is predicted via machine learning (ML). Using only 7 structural features as input, ML identifies 8,282 MOFs with the potential to exceed the capacities of state-of-the-art materials under physisorptive conditions. The identified MOFs are predominantly hypothetical compounds having low densities ( 5,300 m2 g-1), void fractions (~0.90), and pore volumes (>3.3 cm3 g-1). In addition, the relative importance of the input features are characterized, and dependencies on the ML algorithm and training set size are quantified. The single most important features for predicting H2 uptake are pore volume (for gravimetric capacity) and void fraction (for volumetric capacity). The ML models are available for use via the web, allowing for rapid and accurate predictions of usable hydrogen capacities for MOFs with only minimal structural data as input; for the simplest models only a single input feature is required

Gas sorption and supercapacitive properties of hierarchical porous graphitic carbons prepared from the hard-templating of mesoporous ZnO/Zn(OH)2 composite spheres

Three-dimensional (3D) hierarchical porous carbon materials (PCMs) with graphitic carbon walls are facilely prepared through the hard-templating of acid-labile mesoporous ZnO/Zn(OH)2 spheres. Furfuryl alcohol or phloroglucinol is employed as a carbon precursor for two hierarchical porous carbon materials (PCM-F and PCM-P). The basic surfaces of ZnO/Zn(OH)2 are highly suited to the polymerization of the carbon precursors without extra catalysts. After carbonization followed by mild acid etching, hierarchical PCMs are obtained. These PCMs consist of interconnected turbostratic carbon wall structures. Gas sorption analysis indicates the surface areas of PCM-F and PCM-P are 1013 and 1075 m2 g−1, respectively. The corresponding pore volumes are very large, 3.39 and 3.01 cm3 g−1, respectively. The uptake abilities for carbon dioxide and hydrogen are investigated at 196 and 77 K, respectively. The PCM-P reveals higher uptake of H2 (1.19 wt%) and CO2 (282.0 cm3 g−1) than for PCM-F. In contrast, PCM-F shows a high gravimetric specific capacitance of 329.5 F g−1 based on galvanostatic charge/discharge curves at a current density of 0.1 A g−1. The PCM-F exhibits stable capacitance retention after 10,000 cycles at a current density of 5 A g−1.

Hydrogen Uptake Kinetics of 1,4-Bis(phenylethynyl)benzene (DEB) Rubberized Coating on Silicone Foam Substrate.

The hydrogen uptake kinetics of 1,4-bis(phenylethynyl)benzene, or DEB, mixed with palladium (Pd) on activated carbon in a rubber matrix coating on top of a porous silicone foam substrate are investigated. First, isothermal isobaric hydrogenation experiments were performed under different temperatures and H2 pressures to extract the uptake kinetics. The H2 uptake models based on the measured kinetic parameters were then employed to investigate/simulate the performance of the getter under dynamic application environments. The actual hydrogenation characteristics in this type of getter are multifaceted and involve actual H2 concentration in the getter matrix, micrometer-scale diffusion of atomic hydrogen away from Pd sites, precipitation of hydrogenated DEB crystals at the coating surfaces, and mobility of fresh DEB molecules. The kinetic analysis/modeling methodology described in this report can serve as a template for other gas-solid reactions as well. Besides possessing a good hydrogen capacity and excellent performance, this type of rubberized getter also offers some unique advantages over traditional solid getter: flexible structure and protection of the Pd catalyst from exposure to the environment.

Hydrogen Spillover in the Fischer‐Tropsch Synthesis on Carbon‐supported Cobalt Catalysts

AbstractThe Fischer‐Tropsch reaction transforms syngas into high added value products, among which liquid fuels. Numerous parameters determine catalytic activity and selectivity towards the most desired hydrocarbons. The performances of cobalt‐based catalysts used in the reaction are known to depend critically on Co particle size and crystallographic phase. Here, we present a comparative study of Co‐based catalysts supported on three carbon supports: multi‐wall carbon nanotubes, carbon nanofibers and a fibrous material. Our results show that, while the selectivity towards C5+ follows the expected tendency with respect to Co particle size, this is not the case for the TOF. These results can be rationalized considering that the amount of H2 uptake on each catalyst increases with oxygen and defect concentration on the support. The catalyst on the support presenting many edges and oxygen surface groups, necessary for H2 spillover, presents the highest activity. Furthermore, the hydrogen spillover contributes to the enhancement of olefin hydrogenation and methane production.

Triptycene-Based and Amine-Linked Nanoporous Networks for Efficient CO2 Capture and Separation

A set of five nanoporous (pore size <100 nm) amine functionalized and triptycene based organic polymers (TBPALs) were prepared using commercially available phenols (such as quinol and phloroglucinol) and triptycene amines. C−N bonds were formed in the polymerization reactions without employing transitional metal catalysts such as PdII or CuI. TBPALs demonstrated their ability to reversibly capture small gas molecules such as CO2, H2, CH4 and H2. Highest uptake of CO2 and H2 was observed for TBPAL2 at 163.7 mg g-1 (273 K) and 16.2 mg g-1 (77 K) respectively.

In Silico Investigation into H2 Uptake in MOFs: Combined Text/Data Mining and Structural Calculations.

Metal-organic frameworks (MOFs) with high surface areas and adjustable lattice structures are attractive for gas storage and thus have been a great interest in research. Although tremendous amount of data on MOFs have been available in the literature, there are very few studies considering methodological approach for H2 uptake properties of MOFs. In this study, we systematically investigated the H2 uptake capabilities of MOFs by means of text and data mining (TDM) through retrieving data of the surface areas (SA) and pore volumes (PV) from published manuscripts. In addition, we calculated theoretical SA and PV values of all real MOFs available in Cambridge Structural Database (CSD). Prior to calculation, we applied an automated structure analysis algorithm that loads the coordinates of molecules from CSD experimental X-ray single-crystal structure and removes guest/solvent contaminants from the structure. We compared SA, PV, and H2 uptake data from both TDM and structural calculation techniques and unraveled a list of MOFs with H2 uptakes predicted from both experimental and theoretical SA/PV values that may be regarded as the most promising candidates for H2 storage. The extensive and systematic TDM strategy estimates 5975 experimental SA and 7748 experimental PV values (2080 MOFs with SA + PV values) with 78-82% success rate. In addition, structural calculations reveal the theoretical SA and PV values along with a theoretical H2 adsorption limit of MOFs in the absence of guest molecules. Combination of both TDM and structural calculation strategies provides a more comprehensive perspective for the investigation of hydrogen storage capacities in MOFs, which elucidates plausibility of new compounds as candidates for H2 storage materials.

The optimal adsorption pathway of H2 molecules on Ti-Acetylene/ ethylene compounds: A DFT study

Ti-Acetylene/Ethylene complexes were used to be considered as a potential high capacity hydrogen storage media by physisorption. Here, special attentions have been paid to the optimal adsorption pathway of H2 molecules on TiC2H2/TiC2H4 compounds by using CCSD(T) and B3LYP functionals. An interesting result is that some most stable configurations of TiC2H2(nH2)(n = 1–7) complexes are not the structures coordinated by H2 molecules but plausible hydrogenation intermediates. Based on the potential energy profiles and MD simulations, the optimal adsorption pathway is considered as TiC2H2(T) → 1b → 2c → 2b → 2a → 3b → 3a → 4a → 5a → 5b → 6d → C2H6 + Ti(H2)5 for TiC2H2 and TiC2H4(1c) → 2a → 3b → 3a → 4a → 5a → 5b → 6d → C2H6+Ti(H2)5 for TiC2H4. It indicates that the adsorptions of H2 molecules on TiC2H2/TiC2H4 contain chemisorption and physisorption. The product C2H6+Ti(H2)5 exhibits 14 wt% uptake of H2, which is completely consistent with the experimental results.

Ag(I)-benzisothiazolinone complex: synthesis, characterization, H2 storage ability, nano transformation to different Ag nanostructures and Ag nanoflakes antimicrobial activity

A new complex of silver monovalent ions with benzisothiazolinone was reported. This silver coordination polymer was characterized by FTIR, elemental analysis, 1H-NMR and 13C-{1H}-NMR). These measurements show that the bit anion in its silver complex behaves as μ-bridge linking two silver(I) ions as a bidentate ligand through the oxygen and nitrogen atoms. This coordinated polymer was showed non-melting ability, high decomposition and non-solubility in water in addition to all organic solvents except the hot DMSO solvent. Therefore, this polymeric complex had has a high porosity showing thereby that an overall H2 uptake of 5.5 mmol g−1 at 77 K and 10 bar. A new method for the synthesis of a mixture of three different morphological silver nano particles (AgNPs) is reported. The new method includes reduction of the newly prepared silver-benzisothiazolinone complex, [Ag(bit)]n (bit = benzisothiazolinone) with sodium borohydride without using stabilizing agent. The resulting silver nanoparticles Ag NPs were characterized by UV–vis spectra, powder XRD, zeta sizer, zeta potential and scanning electron microscopy (SEM). The results showed that [Ag(bit)]n complex gives three different nano-sized structures spherical, wires and flakes. In order to isolate the larger proportion of the nanostructures, experiments were conducted to control the formation of one form of silver as flakes nanosilver or silver nanowires. The prepared silver nanoparticles were screened for their antibacterial activity against K. pneumonia, P. Aeruginosa, S. aureus and E. coli. Inhibition zone diameter IZD results of 2, 4 and 6 mM Ag NPs was found to be in the range of 7.0–8.4 mm for the selected bacteria.

Lithium and sodium decorated graphdiyne as a candidate for hydrogen storage: First-principles and grand canonical Monte Carlo study

Here through doping Boron element in the aromatic ring of the graphdiyne, we demonstrate that the preferred adsorption site for Li and Na can be changed effectively. For double side Li and Na decorations on the Boron-doped aromatic ring, the binding energies are 2.35 eV and 1.65 eV, which are much larger than their own bulk cohesive energies of1.63 eV and 1.13 eV respectively, indicating that Li and Na atoms will be dispersed evenly on the graphdiyne instead of forming metal clusters. We further investigate H2 storage by using first-principles method. It is found that the average binding energies for Li- and Na-decorated boron-graphdiyne structure with 5 adsorbed H2 molecules per metal, are all in the optimum adsorption energy range (0.2–0.4 eV), which are 0.33, 0.31, 0.29, 0.24 and 0.21 eV for Li-decoration and 0.26, 0.26, 0.26, 0.24 and 0.22 for Na-decoration. Moreover, the molecular dynamics calculations demonstrate our structures are thermodynamic stable under realistic experimental condition. The estimated H2 uptake capacities could reach to 8.81 wt% for Li-decoration and 7.73 wt% for Na-decoration. Finally, we fitted the force field parameters and performed the grand canonical Monte Carlo simulations to address the H2 uptake capacity.

Synthesis, characterization and adsorption studies of a novel triptycene based hydroxyl azo- nanoporous polymer for environmental remediation

Gradual increase in CO2 emission due to energy production from fossils fuels is a major contributor to global warming. Alternatively, “carbon free” nuclear energy generates radioactive and carcinogenic iodine vapors. Thus, the need to develop efficient sorbents for capture of CO2 and I2 is justified. Herein, we report a Triptycene-based-Hydroxyl-Azo-Polymer (TBHAP) derived from relatively inexpensive hydroquinone (one of the two monomers) and using water as a solvent. TBHAP is thermally stable and nanoporous with high surface area (SABET up to 824 m2 g−1). The presence of permanent porosity (due to triptycene), π-rich cavities (from abundant arene rings) and active functional groups [phenolic−OH and azo (NN)] in the polymeric network of TBHAP makes it effective for reversible iodine (188 wt%), H2 (8.9 mg g−1: 77 K, 1 bar) and CO2 (145 mg/g: 273 K, 1 bar) uptake with moderately high CO2/N2 selectivity (84 at 273 K). TBHAP is also an effective and selective adsorbent for toxic cationic dyes [Methylene blue (Qm = 250 mg g−1) and Rhodamine B (Qm = 588 mg g−1)] from an aqueous solution containing binary mixtures of cationic/anionic dyes. Thus, TBHAP is a versatile porous material with various applications in the domain of environmental remediation.

H2 dynamics in the soil of a H2-emitting zone (São Francisco Basin, Brazil): Microbial uptake quantification and reactive transport modelling

Sandy kaolinite-rich soils, collected in a H2-emitting circular depression (ca. 500 m in diameter), located in the São Francisco basin (Brazil), were exposed to H2 gas concentrations in the 500–5000 ppm range for up to eight weeks. The samples were found to consume H2 at a rate of approximately 0.05–0.1 mmol H2/soil kg/day due to the microbial activity. DNA extraction from these soil samples before and after H2 exposure, followed by Ribosomal Intergenic Spacer Analysis (RISA) and 16S rRNA gene amplicon sequencing, indicated that (i) the bacterial community is dominated by phyla that have been previously recognized to scavenge atmospheric H2, and (ii) H2 exposure leads to a significant modification of the bacterial community distribution. Measured H2 uptake rates were fitted to the integrated form of the Michaelis-Menten equation and were further implemented in a 1-D reactive transport model. The model simulates gas-soil interactions in a 1-m vertical soil column, assuming homogeneous distribution of H2-consuming bacteria. The evolution of the H2 concentration in the unsaturated soil porosity along the column was simulated considering two different scenarios: a deep H2 source (Case 1) and a biogenic surface source (Case 2). It was shown that, in the case of diffusion-dominated H2-transport as considered in this study, bacterial activity will control the amplitude of the H2 flux across the column. Moreover, we determined that bacterial activity can dramatically decrease the H2 concentration in the soil porosity, by a factor of two compared to the source concentration. According to the simulation, the time-resolved concentration data collected in the São Francisco depression [Prinzhofer et al., 2019; International Journal of Hydrogen Energy] are consistent with the combination of a deep (Case 1) and a surficial biogenic (Case 2) H2 source in this locality.