Mechanochemical reactions and hydrogen storage capacities in MBH4–SiS2 systems (M=Li or Na)

The hydrogen storage properties, and phase compositions of mechanochemically prepared mixtures of xMBH4-SiS2 (x = 2–8), where M = Li or Na, were investigated using gas sorption analysis, powder X-ray diffraction, and infrared and solid-state NMR spectroscopic methods. The 2LiBH4:1SiS2 system forms an amorphous product that releases ca. 4.3 wt % of H2 below 385 °C with a Tonset of 88 °C without detectable diborane emission. The dehydrogenated sample reversibly absorbs 1.5 wt % of H2 at 385 °C under 160 bar pressure. The H2 release from materials with varying LiBH4:SiS2 ratios peaks at 8.2 wt % for the 6LiBH4:1SiS2 composition, with a reversible hydrogen storage capacity of 2.4 wt %. The H2 desorption capacities of the Li-containing systems surpass those of Na-containing systems. Solid-state NMR studies indicate that products of mechanochemical reactions in the LiBH4SiS2 system consist of one-dimensional chains of edge-sharing SiS4/2 tetrahedra in which the non-bridging S-ends are terminated with Li+, which are further coordinated to the [BH4]− anions. A variety of possible polymorphs in the LiSiS-(BH4) composition space have been identified using first principles and thermodynamic modeling that supports the likelihood of formation of such novel complexes

Probing the unusual anion mobility of LiBH_4 confined in highly ordered nanoporous carbon frameworks via solid state NMR and quasielastic neutron scattering

Particle size and particle–framework interactions have profound effects on the kinetics, reaction pathways, and even thermodynamics of complex hydrides incorporated in frameworks possessing nanoscale features. Tuning these properties may hold the key to the utilization of complex hydrides in practical applications for hydrogen storage. Using carefully synthesized, highly-ordered, nanoporous carbons (NPCs), we have previously shown quantitative differences in the kinetics and reaction pathways of LiBH_4 when incorporated into the frameworks. In this paper, we probe the anion mobility of LiBH_4 confined in NPC frameworks by a combination of solid state NMR and quasielastic neutron scattering (QENS) and present some new insights into the nanoconfinement effect. NMR and QENS spectra of LiBH_4 confined in a 4 nm pore NPC suggest that the BH_4− anions nearer the LiBH_4–carbon pore interface exhibit much more rapid translational and reorientational motions compared to those in the LiBH_4 interior. Moreover, an overly broadened BH_4− torsional vibration band reveals a disorder-induced array of BH_4− rotational potentials. XRD results are consistent with a lack of LiBH_4 long-range order in the pores. Consistent with differential scanning calorimetry measurements, neither NMR nor QENS detects a clear solid–solid phase transition as observed in the bulk, indicating that borohydride–framework interactions and/or nanosize effects have large roles in confined LiBH_4

Getting Ahead: A Resident Led Quality Improvement Project to Increase Diabetic Nephropathy Screening in an Underserved Hispanic-Predominant Population

Introduction: Diabetes is the leading cause of end-stage renal disease (ESRD) in the United States (US), with 37 million having chronic kidney disease. Despite national guidelines recommendations for diabetic nephropathy screening with urine albumin-to-creatinine ratio (UACR), less than 50% receive full screening. Our Internal Medicine residents led a quality improvement project to increase diabetic nephropathy screening rate with UACR in our resident clinic by 50% in one academic year. Methods: We conducted the resident-led quality improvement project from July 2021 to April 2022. We reviewed the electronic medical records (EMR) from our clinic pre-intervention July 2020 to June 2021 and compared this to post intervention July 2021 to March 2022 determining the nephropathy screening rates in patients with diabetes. Our interventions included resident education, pre and post surveys to test foundational knowledge, adding UACR in the affordable laboratory order form and establishing normal reference range of UACR in the EMR. Results: We collected 217 patients with diabetes, 27% were uninsured, 38% had Medicare/Medicaid and 90% identified as Hispanic. Comparing pre to post intervention, there was a significant change of 45 (20.7%) vs 71 (32.7%) patients screened for diabetic nephropathy with a UACR. The correct average score of knowledge-based questions was 82% on the pre survey, which increased to 88% in the post survey. Conclusion: Our study showed promising results on improving diabetic nephropathy screening. The comprehensive approach including resident education about diabetic nephropathy screening with UACR and more so facilitating the order set in the EMR were key to achieve this goal

Desalination utilizing clathrate hydrates (LDRD final report).

Advances are reported in several aspects of clathrate hydrate desalination fundamentals necessary to develop an economical means to produce municipal quantities of potable water from seawater or brackish feedstock. These aspects include the following, (1) advances in defining the most promising systems design based on new types of hydrate guest molecules, (2) selection of optimal multi-phase reactors and separation arrangements, and, (3) applicability of an inert heat exchange fluid to moderate hydrate growth, control the morphology of the solid hydrate material formed, and facilitate separation of hydrate solids from concentrated brine. The rate of R141b hydrate formation was determined and found to depend only on the degree of supercooling. The rate of R141b hydrate formation in the presence of a heat exchange fluid depended on the degree of supercooling according to the same rate equation as pure R141b with secondary dependence on salinity. Experiments demonstrated that a perfluorocarbon heat exchange fluid assisted separation of R141b hydrates from brine. Preliminary experiments using the guest species, difluoromethane, showed that hydrate formation rates were substantial at temperatures up to at least 12 C and demonstrated partial separation of water from brine. We present a detailed molecular picture of the structure and dynamics of R141b guest molecules within water cages, obtained from ab initio calculations, molecular dynamics simulations, and Raman spectroscopy. Density functional theory calculations were used to provide an energetic and molecular orbital description of R141b stability in both large and small cages in a structure II hydrate. Additionally, the hydrate of an isomer, 1,2-dichloro-1-fluoroethane, does not form at ambient conditions because of extensive overlap of electron density between guest and host. Classical molecular dynamics simulations and laboratory trials support the results for the isomer hydrate. Molecular dynamics simulations show that R141b hydrate is stable at temperatures up to 265K, while the isomer hydrate is only stable up to 150K. Despite hydrogen bonding between guest and host, R141b molecules rotated freely within the water cage. The Raman spectrum of R141b in both the pure and hydrate phases was also compared with vibrational analysis from both computational methods. In particular, the frequency of the C-Cl stretch mode (585 cm{sup -1}) undergoes a shift to higher frequency in the hydrate phase. Raman spectra also indicate that this peak undergoes splitting and intensity variation as the temperature is decreased from 4 C to -4 C

First-Principles Calculated Decomposition Pathways for LiBH4 Nanoclusters

We analyze thermodynamic stability and decomposition pathways of LiBH4 nanoclusters using grand-canonical free-energy minimization based on total energies and vibrational frequencies obtained from density-functional theory (DFT) calculations. We consider (LiBH4)n nanoclusters with n = 2 to 12 as reactants, while the possible products include (Li)n, (B)n, (LiB)n, (LiH)n, and Li2BnHn; off-stoichiometric LinBnHm (m ≤ 4n) clusters were considered for n = 2, 3, and 6. Cluster ground-state configurations have been predicted using prototype electrostatic ground-state (PEGS) and genetic algorithm (GA) based structural optimizations. Free-energy calculations show hydrogen release pathways markedly differ from those in bulk LiBH4. While experiments have found that the bulk material decomposes into LiH and B, with Li2B12H12 as a kinetically inhibited intermediate phase, (LiBH4)n nanoclusters with n ≤ 12 are predicted to decompose into mixed LinBn clusters via a series of intermediate clusters of LinBnHm (m ≤ 4n). The calculated pressure-composition isotherms and temperature-pressure isobars exhibit sloping plateaus due to finite size effects on reaction thermodynamics. Generally, decomposition temperatures of free-standing clusters are found to increase with decreasing cluster size due to thermodynamic destabilization of reaction products

Mechanochemical reactions and hydrogen storage capacities in MBH4–SiS2 systems (M=Li or Na)

The hydrogen storage properties, and phase compositions of mechanochemically prepared mixtures of xMBH4-SiS2 (x = 2–8), where M = Li or Na, were investigated using gas sorption analysis, powder X-ray diffraction, and infrared and solid-state NMR spectroscopic methods. The 2LiBH4:1SiS2 system forms an amorphous product that releases ca. 4.3 wt % of H2 below 385 °C with a Tonset of 88 °C without detectable diborane emission. The dehydrogenated sample reversibly absorbs 1.5 wt % of H2 at 385 °C under 160 bar pressure. The H2 release from materials with varying LiBH4:SiS2 ratios peaks at 8.2 wt % for the 6LiBH4:1SiS2 composition, with a reversible hydrogen storage capacity of 2.4 wt %. The H2 desorption capacities of the Li-containing systems surpass those of Na-containing systems. Solid-state NMR studies indicate that products of mechanochemical reactions in the LiBH4SiS2 system consist of one-dimensional chains of edge-sharing SiS4/2 tetrahedra in which the non-bridging S-ends are terminated with Li+, which are further coordinated to the [BH4]− anions. A variety of possible polymorphs in the LiSiS-(BH4) composition space have been identified using first principles and thermodynamic modeling that supports the likelihood of formation of such novel complexes.</p

Interstital-atom-induced phase transformation upon hydrogenation in vanadium

We investigated the effect of interstitial atoms on hydrogen storage properties in vanadium. When the nitrogen concentration was below 0.4 wt%, the plateau pressures of the pressure-composition-isotherm curve increased with increasing nitrogen concentration during hydrogen absorption and desorption and vanadium samples with a body-centered cubic (BCC) transformed to VH0.5 with a body-centered tetragonal (BCT) of c/a=1.1, and then VH2 with a face-centered cubic (FCC). When the nitrogen concentration exceeded 0.6 wt%, a new single-phase region appeared in the pressure-composition isotherm The X-ray diffraction data indicated that this new hydride phase was VH1.0 with a BCT structure and c/a = 1.24, and the phase transformation took place as V became VH0.5, followed by VH1.0 and then VH2. Density functional theory calculations indicated that the BCT structure model with hydrogen atoms fully occupying the octahedral sites (denoted as the Oz site) can explain the experimentally obtained crystal structure for VH1.0; they also indicated that the VH1.0 phase was stabilized by the addition of nitrogen. In addition, the nitrogen occupation site changed from the Oz site in VH0.5 and VH1.0 to the tetrahedral site in VH2 in coordination with hydrogen during hydrogen absorption. A similar phenomenon was observed in carbon-containing vanadium. It can thus be concluded that the phase transformation pathway and stability of the hydride phases in the V–H system are highly sensitive to the addition of interstitial carbon and nitrogen atoms

Clathrate hydrates for production of potable water

Clathrate hydrates are crystalline inclusion compounds of water and a guest molecule that can form at temperatures above the freezing point of water. Such inclusion compounds exclude dissolved solutes, e.g., sodium chloride present in the aqueous phase, and thereby provide a basis for desalination. Clathrate hydrate formation experiments were performed using several guest molecules, including R141b (CFClH), a commercial refrigerant, and ethylene. Ethylene, a gaseous hydrate guest, readily formed hydrates with saline water at up to 5°C and 20 atm. of pressure. Hydrates of R141b, in the liquid state, were formed at temperatures from 2°C to 6°C and atmospheric pressure from deionized water and 2% - 7% NaCl solutions. Significant reductions in saline content were obtained with both forming agents in a batch reactor without additional separation equipment. Samples of the R141b hydrates were characterized by cold-stage x-ray diffraction and Raman spectroscopy and determined to be structure II. Proof-of-concept experiments were performed to demonstrate a novel technique of desalination using R141b as the hydrate forming agent and an inert secondary fluid