Deliverable Capacity Research Articles

HiGee Strategy toward Rapid Mass Production of Porous Covalent Organic Polymers with Superior Methane Deliverable Capacity

AbstractHigh porosity with well‐defined molecular reticulation along with strong stability is desired for natural gas delivery. The catalyzed Yamamoto‐type Ullmann cross‐coupling route with efficient terminal halogen removal capability is currently used to prepare porous organic materials with high specific surface area as well as ultrahigh hydrothermal stability. As a typical fast coupling reaction, the traditional stirred solvothermal approach shows the limitation of macroscopic reaction kinetics due to the increasing viscosity of the reaction mixture with the molecular network growth until it turns to a jelly‐like consistency. Herein, a high‐gravity chemical synthetic strategy to achieve rapid and economical preparation of a class of, but not limited to, covalent organic polymers (COPs) with high hydrothermal stability using the Ullman cross‐coupling route is described. The viscous fluid is vigorously split into homogeneous microdroplets through the rotating packed bed (RPB) under the HiGee environment. The HiGee approach shortens the traditional reaction time from 600 to 15 min as well as reduces the usage of high‐cost nickel (0) catalyst by 40 wt%. Specially, the COP‐10 obtained with the HiGee approach displays an excellent deliverable methane capacity of 415 cm3 STP g−1 at 298 K with working pressures 5–65 bar, which is higher than that of most reported porous organic materials.

Design principles for the ultimate gas deliverable capacity material: nonporous to porous deformations without volume change

A rotating slit pore motif yields a non-porous to porous structural transition without a change in unit cell volume.

Near-Fastest Battery Balancing by Cell/Module Reconfiguration

Charge imbalance is a very common issue in multi-cell /module/pack battery systems due to manufacturing variations, inconsistent charging/discharging, and uneven thermal distribution. As a consequence, the deliverable charge capacity, battery lifespan, and system reliability may all decrease over time. To tackle this issue, various external circuit designs can be attached for charge balance, and the internal battery cell/module/pack connection can also significantly affect the charge balance performance. This paper focuses on minimizing the battery charge equalization (BCE) time by battery cell/module reconfiguration. Specifically, for the reconfigurable module-based BCE system, we propose reconfiguration algorithms for fast charge equalization under different levels of system reconfigurability. For battery systems allowing module reconfiguration and intra-module cell reconfiguration, the proposed module-based bounded reconfiguration algorithm can reach or get very close to the minimum BCE times obtained by exhaustive search. When the reconfigurability level is extended by allowing inter-module cell reconfiguration, the proposed module-based complete reconfiguration algorithm can achieve similar optimality to that of the genetic algorithm (GA). Moreover, as compared to the circuit experiments, exhaustive search, and GA, the proposed algorithms take much less computational time. The optimality and computational efficiency of the proposed algorithms are demonstrated by both circuit and numerical experiments.

Simulating Enhanced Methane Deliverable Capacity of Guest Responsive Pores in Intrinsically Flexible MOFs.

A novel computational procedure, based on the principles of flat-histogram Monte Carlo, is developed for facile prediction of the adsorption thermodynamics of intrinsically flexible adsorbents. We then demonstrate how an accurate prediction of methane deliverable capacity in a metal-organic framework (MOF) with significant intrinsic flexibility requires use of such a method. Dynamic side chains in the framework respond to methane adsorbates and reorganize to exhibit a more conducive pore space at high adsorbate densities while simultaneously providing a less conducive pore space at low adsorbate densities. This "responsive pore" MOF achieves ∼20% higher deliverable capacity than if the framework were rigid and elucidates a strategy for designing high deliverable capacity MOFs in the future.

Prediction of hydrogen adsorption in nanoporous materials from the energy distribution of adsorption sites

We present a fast and accurate, semi-analytical method for predicting hydrogen adsorption in nanoporous materials. For any temperature and pressure, the adsorbed amount is calculated as an integral over the energy density of adsorption sites (guest-host interactions) plus an average guest-guest term. The guest-host interaction energy is calculated using a classical force field with hydrogen modelled as a single-site probe. The guest-guest interaction energy is approximated using an average coordination number, which is regressed using Gaussian Process Regression (GPR). Local adsorption at each site is then modelled using a Langmuir isotherm, which when weighted with its probability density gives an accurate description of hydrogen adsorption. The method is tested on 933 metal-organic frameworks (MOFs) from the Computation-Ready Experimental (CoRE) MOF database at 77 K from to 100 bar, and the results are compared against GCMC predictions. To demonstrate the utility of the method, we calculated hydrogen adsorption isotherms for 12,914 existing MOF structures, at two different temperatures at a speed about 100 times that of GCMC simulations and analyzed the results. We found 13 MOFs with predicted deliverable capacities exceeding the DOE target of 50 g/L for adsorption at 100 bar, 77 K and desorption at 5 bar, 160 K.

Electrochemical performance of porous CaFe2O4 as a promising anode material for lithium-ion batteries

Abstract The performance of existing lithium-ion batteries (LIBs) is greatly hindered by the low specific capacity of graphite-based anodes (372 mAh g−1). Therefore, development of suitable anode materials that exhibit higher and stable capacity is necessary to improve performance. Transition metal oxides have attracted tremendous attention as next-generation anode materials for LIBs due to their high theoretical capacity. Herein, we report the synthesis of a porous CaFe2O4 by a facile and time efficient solution combustion synthesis technique for use in an anode for LIBs. The as-prepared material exhibited improved electrochemical performance with specific discharge capacities of 441 mAh g−1, 518 mAh g−1, and 516 mAh g−1 for the initial three cycles. It achieved stability with a deliverable specific discharge capacity of 551 mAh g−1 after 150 cycles at a current density of 200 mA g−1. The porous CaFe2O4 exhibits improved cyclic performance and rate capability. These improvements are attributed to the porous nature of active material and, more importantly, the presence of CaO, which effectively alleviates the volume changes by acting as a buffer matrix.

Challenges and opportunities for using formate to store, transport, and use hydrogen

Abstract In this perspective article, the synthesis and thermodynamic properties of aqueous solutions of formate salts (FS, HCO2−) are described in relationship to the concept of H2 carriers. The physiochemical properties of solid FS, aqueous formate solutions, and aqueous bicarbonate solutions set the limitations for storage capacity, deliverable capacity, and usable H2 capacity of these H2 carriers, respectively. These parameters will help in the design of systems that use H2 carriers for storage and transport of H2 for fuel cell power applications. FS, as well as admixtures with formic acid (FA, H2CO2), have potential to address the goals outlined in the U.S. Department of Energy's H2@scale initiative to store in chemical bonds a significant quantity of energy (hundreds of megawatts) obtained from large scale renewable resources.

Computational screening carbon-based adsorbents for CH4 delivery capacity

To put adsorbed natural gas for applicable vehicle fuel use, one has to achieve adequate delivery capacities of CH4 (the main component of natural gas) in porous adsorbent materials. A computational screen has been performed to investigate factors that influence the deliverable capacity of CH4 in carbon-based porous adsorbents, including unique textural properties (volumetric specific surface area, porosity, pore size distribution, surface chemical properties) and adsorption operation condition (temperature and pressure) using Monte Carlo simulations. By a systematic study of 580 models with unique textural properties at different adsorption operation conditions, general trends of improving CH4 deliverable capacity have been identified. Also, structural property thresholds were obtained assuming the target of U.S. department of energy's Advanced Research Projects Agency. The suggested method and results obtained from this work can facilitate a fast screening and guide the development of new synthesis routes for carbonaceous materials targeted at effective deliveries of natural gas for vehicle fuel.

Exceptionally Highly Stable Cycling Performance and Facile Oxygen-Redox of Manganese-Based Cathode Materials for Rechargeable Sodium Batteries

Recent finding on oxygen redox is considered as a brand-new chemistry in rechargeable battery systems using monovalent charge carries such as lithium and sodium. This kind of redox species can generate extra electron in addition to transition-metal redox. This combination enables achievement of high capacity, so that this chemistry becomes more important to provide sustainable electrode materials for lithium- and sodium-ion batteries. These interests have been applied towards in sodium-ion batteries; however, most of the compounds are employing expensive transition metals such as Ru, Ir, etc. In this study we introduce a new system, P2-Na2/3[Mn0.7Zn0.3]O2 and its derivatives, of which a hybridized chemistry stemming from oxygen-redox and transition-metal redox that are highly reversible over cycles. The composites were synthesized by combustion method. The aqueous solution of stoichiometric values of sodium nitrate (98%), manganese (II) nitrate hexahydrate (97%), and zinc (II) nitrate hexahydrate (98%) were added to aqueous citric acid solution (nitrates : citric acid, 1 : 0.5 in weight). The solution was heated on a hot plate at 100 °C for overnight under constant stirring to evaporate the solvent. Then dried powder was further heated to 200 °C for auto combustion of citric acid. Burnt powder further heated at 500 °C for 3 h to decompose the nitrates and yield a homogeneously mixed amorphous powder containing carbon residues. The obtained decomposition product was pelletized and heated in a tube furnace at 700 °C (heating rate – 5 °C / min) for 10 h in air atmosphere and then slowly cooled to room temperature. The obtained powder was transferred to Ar-filled glove box to avoid the contact with moisture in the air. X-ray diffraction (XRD, Xpert, PANalytical) using Cu-Kα radiation was employed to characterize the crystal structure of the synthesized powders. XRD measurement was carried out in the 2θ range of 10−80° with a step size of 0.03°. The FULLPROF Rietveld program was used to analyze the observed powder diffraction patterns. Structural studies during cycle were examined by means of operando X-ray diffraction (XRD) and ex situ X-ray Absorption Spectroscopy (XAS). The ex situ XAS measurements were performed at the 7D beamline and 4D beamline of the Pohang Accelerator Laboratory (PAL), Pohang, South Korea, respectively. Electrochemical properties were studied in an half-cell configuration assembling a R2032 coin-type cell using sodium metal as the negative electrode in an Ar-filled glove box. The electrolyte solution comprised 0.5 M NaPF6 in propylene carbonate and fluorinated ethylene carbonate (PC:FEC, 98:2 in volume). The cells were charged and discharged between 1.5 V and 4.6 V at a rate of 0.1C at 25 °C. The calculated XRD pattern of the sample was obtained by Rietveld refinement using the FullProf software, as shown in Figure 1a. The result was well matched with the P2-type structure (Figure 1a) with P63/mmc space group, with an acceptable reliability factor (Rwp) of approximately 10%. The initial charge-discharge profiles of P2-Na2/3[Mn0.7Zn0.3]O2 electrode are presented in Figure 1b. During initial charge, the electrode exhibited a long plateau above 4 V delivering a capacity of 120 mAh g−1. The average oxidation state of Mn for the electrode was 3.9+, such that the deliverable capacity is theoretically expected to be 26 mAh g−1 in the voltage range. However, the delivered capacity is over than theoretical value. The explanation for the unexpected capacity is the oxygen redox. So, at higher voltage the delivered capacity is driven by O2-/O1- redox and lower by Mn3+/Mn4+ redox. More detailed experimental and theoretical studies will be presented at the meeting. Figure 1. (a) Rietveld refinement and crystal structure of P2-Na2/3[Mn0.7Zn0.3]O2; (b) Initial charge-discharge profiles of P2-Na2/3[Mn0.7Zn0.3]O2 electrode. Figure 1

Fabrication and Investigation of MCMB–LiNi0.5Mn1.5O4Pouch Cells for High Energy Density Lithium-Ion Batteries: Indigenous Efforts and Challenges for Realization

In the present work, we have fabricated indigenous 300 mAh lithium-ion rechargeable pouch cells using laboratory made LiMn1.5Ni0.5O4 cathode and commercial meso carbon micro-beads anode. Required mass balancing was performed to yield pouch cell of 300 mAh capacity at C/4 rate. When charged and discharged at C/4 and C/3 rates the fabricated pouch cells retained ~ 79% of their capacities after 50 cycles. Post-mortem analysis of the cycled pouch cell indicated the dissolution of Mn and Ni from cathode and deposition of the same at anode and separator. The observed bulging of the cycled pouch cell could be due to evolution of gases through chemical decomposition of conventional organic electrolyte. Though active material dissolution and gas evolution might reduce deliverable capacity and operating voltage of the fabricated pouch cells, yet the reported electrochemical characteristics were far superior to many of the existing literature reports.

Functionalization-Induced Breathing Control in Metal–Organic Frameworks for Methane Storage with High Deliverable Capacity

Metal–organic frameworks (MOFs) that can undergo structural flexibility upon gas sorption cycle bear enormous potential particularly as adsorbents for methane storage. A molecular level control over such flexibility can be advantageous for the development of smart adsorbents with increased deliverable capacity. Herein, we report the flexible and stable MIL-53(Al) type MOFs, whose breathing behavior can be controlled by systematic installation of hydrogen bonding sites into the frameworks. Such a control has been fine-tuned to induce high deliverable capacity in MOFs by changing gas pressure, temperature, and density. The establishment of a structure–property relationship for methane storage and successful pelletization of MOFs pave the way for MOF-based onboard natural gas storage.

Extraordinarily large and stable methane delivery of MIL-53(Al) under LNG-ANG conditions

Natural gas (NG) is the most eco-friendly hydrocarbon fuel. However, due to its low energy density at ambient temperature and pressure, it is currently used restrictively. Recently, the coupling of liquefied natural gas (LNG) regasification and the adsorbed natural gas (ANG) charging processes has been suggested as a possible solution for expanding the uses of NG. Although metal-organic frameworks (MOFs) have been widely studied for ANG systems, few studies have been conducted on LNG-ANG systems. We evaluated the potential of MIL-53(Al) for LNG-ANG and compared it with HKUST-1 and Norit RB3. MIL-53(Al) exhibited a significantly larger deliverable capacity (262.3 v(STP)/v), which is almost close to the deliverable methane capacity target. GCMC simulations suggest that MIL-53(Al) may be transformed to a more favorable structure for methane adsorption at 159 K. Even with this flexible behavior, MIL-53(Al) was stable under repeated temperature swings between cryogenic and room temperatures. We believe that this flexible behavior of MIL-53(Al) could be applied to other gas storage and separations.

Spray-Printed and Self-Assembled Honeycomb Electrodes of Silicon-Decorated Carbon Nanofibers for Li-Ion Batteries.

Directional, micron-scale honeycomb pores in Li-ion battery electrodes were fabricated using a layer-by-layer, self-assembly approach based on spray-printing of carbon nanofibers. By controlling the drying behavior of each printed electrode layer through optimization of (i) the volume ratio of fugitive bisolvent carriers in the suspension and (ii) the substrate temperature during printing, self-assembled, honeycomb pore channels through the electrode were created spontaneously and reliably on current collector areas larger than 20 cm × 15 cm. The honeycomb pore structure promoted efficient Li-ion dynamics at high charge/discharge current densities. Incorporating an optimum fraction (2.5 wt %) of high-energy-density Si particulate into the honeycomb electrodes provided a 4-fold increase in deliverable discharge capacity at 8000 mA/g. The spray-printed, honeycomb pore electrodes were then investigated as negative electrodes coupled with similar spray-printed LiFePO4 positive electrodes in a full Li-ion cell configuration, providing an approximately 50% improvement in rate capacity retention over half-cell configurations of identical electrodes at 4000 mA/g.

Idealized Carbon-Based Materials Exhibiting Record Deliverable Capacities for Vehicular Methane Storage

Materials for vehicular methane storage have been extensively studied, although no suitable material has been found. In this work, we use molecular simulation to investigate three types of carbon-b...

Critical Factors in Computational Characterization of Hydrogen Storage in Metal–Organic Frameworks

Inconsistencies in high-pressure H2 adsorption data and a lack of comparative experiment–theory studies have made the evaluation of both new and existing metal–organic frameworks (MOFs) challenging in the context of hydrogen storage applications. In this work, we performed grand canonical Monte Carlo (GCMC) simulations in nearly 500 experimentally refined MOF structures to examine the variance in simulation results because of the equation of state, H2 potential, and the effect of density functional theory structural optimization. We find that hydrogen capacity at 77 K and 100 bar, as well as hydrogen 100-to-5 bar deliverable capacity, is correlated more strongly with the MOF pore volume than with the MOF surface area (the latter correlation is known as the Chahine’s rule). The tested methodologies provide consistent rankings of materials. In addition, four prototypical MOFs (MOF-74, CuBTC, ZIF-8, and MOF-5) with a range of surface areas, pore structures, and surface chemistries, representative of promisin...

In Silico Screening of Metal-Organic Frameworks for Adsorption-Driven Heat Pumps and Chillers.

A computational screening of 2930 experimentally synthesized metal–organic frameworks (MOFs) is carried out to find the best-performing structures for adsorption-driven cooling (AC) applications with methanol and ethanol as working fluids. The screening methodology consists of four subsequent screening steps for each adsorbate. At the end of each step, the most promising MOFs for AC application are selected for further investigation. In the first step, the structures are selected on the basis of physical properties (pore limiting diameter). In each following step, points of the adsorption isotherms of the selected structures are calculated from Monte Carlo simulations in the grand-canonical ensemble. The most promising MOFs are selected on the basis of the working capacity of the structures and the location of the adsorption step (if present), which can be related to the applicable operational conditions in AC. Because of the possibility of reversible pore condensation (first-order phase transition), the mid-density scheme is used to efficiently and accurately determine the location of the adsorption step. At the end of the screening procedure, six MOFs with high deliverable working capacities (∼0.6 mL working fluid in 1 mL structure) and diverse adsorption step locations are selected for both adsorbates from the original 2930 structures. Because the highest experimentally measured deliverable working capacity to date for MOFs with methanol is ca. 0.45 mL mL–1, the selected six structures show the potential to improve the efficiency of ACs.

Hierarchical micro/nanostructured WO3 with structural water for high-performance pseudocapacitors

Exploring electrode materials with high energy density is crucial for the application of electrochemical energy storage. Herein, we innovatively synthesized frisbee-shaped architecture of h-WO3·nH2O by a simple hydrothermal method, which is assembled by nanorods of ∼80 nm in diameter, with structural water storing in the open hexagonal tunnels via a template-free strategy for supercapacitor application. This electrode material possesses high specific capacitance of 391 F g−1 at 0.5 A g−1, superior rate capacity of 298 F g−1 at 10 A g−1, and almost 100% capacitance retention after 2000 cycles at 10 A g−1, which can be ascribed to its unique hierarchical micro/nanostructure and water chains within the channels of crystalline h-WO3. The unique self-assembled frisbee-shaped micro/nanostructure can avoid further aggregation of nanosized building blocks and allow sufficient ions accessible surface, beneficial to increasing deliverable capacity. Notably, the presence of structural water also offers fast hydrated protons transport pathway, resulting in high capacity and good stability at high rate.

Computation-Ready, Experimental Covalent Organic Framework for Methane Delivery: Screening and Material Design

CH4 storage associated with adsorbed natural gas technology attracts considerable researches on finding porous materials with remarkable CH4 delivery performance. In this work, we update the online accessible computation-ready, experimental (CoRE) covalent organic frameworks (COFs) database with 280 COFs in 12 topologies. All framework structures are constructed and compiled from the respective experimental studies and are further evaluated for CH4 delivery. The highest deliverable capacity (DC) between 65 and 5.8 bar among the CoRE COFs is 190 v(STP)/v at 298 K achieved by 3D PI-COF-4. Structure–property relationships show that large volumetric surface area generally benefits CH4 delivery. 2D-COFs can also be top performing materials if constructing their pore channels is passable in three dimensions, as the volumetric surface area will be increased accordingly. This idea can be realized by enlarging the interlayer spacings of 2D-COFs. We also evaluate the DC of CoRE COFs under conditions of 233 K, 65 ba...

Green synthesis and characterization of aluminium fumarate metal-organic framework for heat transformation applications

Microporous materials with higher uptake – offtake difference per adsorption – desorption cycle have great potential to design adsorption assisted chillers, heat pumps and thermal batteries. In this context, we report a green reaction method for synthesizing aluminium fumarate (AlFum) metal-organic framework (MOF). The water uptake on AlFum shows S-shape isotherm curve with sharp increase in uptake – offtake difference in a narrow pressure range. The proposed green synthesized AlFum exhibits higher deliverable energy capacity as compared to that of conventional (dimethylformamide based synthesis) AlFum for adsorptive cooling applications.

Capacity Retention for (De)lithiation of Silver Containing α-MnO2: Impact of Structural Distortion and Transition Metal Dissolution

Crystallite size reduction is a strategy utilized to increase deliverable capacity by decreasing the path length for lithium ion diffusion. However, reduction in crystallite size may also exacerbate unfavorable reactions within a battery limiting cycle life. Here, differences in capacity retention are observed for silver containing α-MnO2 (silver hollandite, AgHol), with two crystallite sizes. Under 30 mA/g discharge, the smaller crystallite size material (AgHol-S, 5 nm) delivers 266 mAh/g initial capacity with 91% capacity decrease from cycles 2–50. In contrast, the larger crystallite size material (AgHol-L, 14 nm) has an initial capacity of 129 mAh/g and only 9% decrease from cycles 2–50. A second electrochemical test was conducted using a capacity limit rather than a voltage limit. Under those test conditions, the structural distortion for the two materials observed by X-ray absorption spectroscopy (XAS) was similar, yet the terminal voltage decrease was more significant for the small crystallite sized sample. Determination of Mn dissolution revealed Mn solubility 5.4X higher for AgHol-S than AgHol-L with accompanying higher Mn deposition on the negative electrode and increased cell impedance. This study provides quantitative determination of capacity fade as related to structural distortion and transition metal dissolution as related to crystallite size.