Arthur Lovell

Turbostratic graphite nanofibres from electrospun solutions of PAN in dimethylsulphoxide

Homogenous turbostratic graphite nanofibres (TGNFs) have been synthesized by heat treatment of electrospun polyacrylonitrile in dimethylsulphoxide, offering a solution route of low toxicity to manufacture sub-60 nm diameter TGNFs. Characterization techniques including X-ray diffraction, scanning- and transmission electron microscopy have been used to study the graphitization process, and structural morphology of the nanofibres. The TGNFs have an entangled micro-fibril structure with turbostratic ordering of up to 40 graphene layers after heat treatment at 3000 °C.

Ammonia borane–polyethylene oxide composite materials for solid hydrogen storage

Co-electrospinning ammonia borane (AB) and polyethylene oxide (PEO) has created a unique crystal phase that promotes faster hydrogen release from AB below its melting temperature with no incubation time. Integral fibres have been produced containing 75%, 50% and 25% AB by weight. As the PEO content was increased, the onset temperature of dehydrogenation was reduced from 110 °C for pristine AB to 85 °C for the 25% AB fibres. The new phase is characterised by hydrogen bonding between the hydridic hydrogen atoms bonded to the nitrogen atom in AB and the oxygen atom in the PEO backbone. Additionally, the usual foaming of AB during hydrogen release was effectively controlled by the addition of PEO. Some impurities which accompany the hydrogen release – ammonia and diborane – are reduced, however, borazine levels in the gas stream were observed to increase during the loss of the 2nd hydrogen equivalent. Nevertheless, co-electrospun composites of AB and PEO show great promise as a safe, portable and versatile hydrogen storage material.

Probing the binding and spatial arrangement of molecular hydrogen in porous hosts via neutron Compton scattering

The adsorption of molecular hydrogen (H2) in the alkali-graphite intercalate KC24 has been studied using simultaneous neutron diffraction and Compton scattering. Neutron Compton scattering data for the (H2)xKC24 system (x = 0-2.5) were measured at T = 1.5 K as a function of the relative orientation between the neutron beam and the intercalate c-axis. Synchronous with the above proton-recoil measurements, high-resolution diffraction patterns were measured in backscattering geometry. From these diffraction measurements, the intrinsic mosaicity of the Papyex-based intercalate was determined to be approximately 15 degrees half-width-at-half-maximum, in good agreement with previous studies [Finkelstein et al., Physica B, 2000, 291, 213]. Hydrogen uptake by the intercalate leads to a distinct and readily detectable broadening of the isotropic Compton profile compared to bulk H2, indicative of an enhanced interaction of the H2 molecule with the surrounding solid-state environment. Total proton-recoil intensities also scale linearly with the amount of adsorbed hydrogen. Taking as our starting point previous experimental and theoretical results, the isotropic widths of the proton momentum distributions can be explained on the basis of three energy scales, namely, intramolecular H-H vibrations, followed by H-H librations and H2 centre-of-mass translations. From the coverage dependence of these neutron data, we also establish an upper bound of approximately 10 meV for intermolecular hydrogen-hydrogen interactions. Finally, we observe a weak anisotropy of the width of the proton momentum distributions. Comparison of these experimental data with first-principles predictions indicates that subtle quantum mechanical effects associated with particle delocalisation and exchange lie at the heart of the observed behaviour. Overall, these results demonstrate the suitability and largely untapped potential of neutron Compton scattering to explore H2 uptake by solid-state hosts.

Correction: Ammonia borane–polyethylene oxide composite materials for solid hydrogen storage

Correction for ‘Ammonia borane–polyethylene oxide composite materials for solid hydrogen storage’ by A. S. Nathanson et al., J. Mater. Chem. A, 2015, 3, 3683–3691.

The Ammonia-Driven Phase Transition in Bulk and Nanostructured Potassium Graphite KC 24

We report the synthesis of nanostructured stage-2 potassium graphite, KC24, by intercalation of turbostratic graphite nano fibers produced from an electrospun polymer, and compare its properties with exfoliated graphite-based KC24. The nanostructured KC24 sample has low crystalline order and slightly increased interlayer spacing of 8.76 A, compared with 8.65 A in the bulk sample, indicating minimal registration of the graphite planes. Time-resolved time-of-flight neutron diffraction on both nanostructured and bulk KC24 under ammoniation is suggestive of a more homogeneous and faster pressure-modulated phase transition to the ternary ammoniated potassium-graphite in the nanostructured material. Following ammoniation, negligible hydrogen uptake is observed at 50 K.