A Long Cycle-Life High-Voltage Spinel Lithium-Ion Battery Electrode Achieved by Site-Selective Doping

Spinel LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode candidate for the next-generation high energy-density lithium-ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site-selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fd m structure. This site-selective doping not only suppresses unfavorable two-phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg-doped LNMOs exhibit extraordinarily stable electrochemical performance in both half-cells and prototype full-batteries with novel TiNb₂O₇ counter-electrodes. This work pioneers an atomic-doping engineering strategy for electrode materials that could be extended to other energy materials to create high-performance devices.     

Implementation of radiotelemetry in a lab-in-a-pill format

A miniaturised lab-in-a-pill device has been produced incorporating a temperature and pH sensor with wireless communication using the 433.92 MHz ISM band. The device has been designed in order to enable real time in situ measurements in the gastrointestinal (GI) tract, and accordingly, issues concerning the resolution and accuracy of the data, and the lifetime of the device have been considered. The sensors, which will measure two key parameters reflecting the physiological environment in the GI (as indicators for disease) were both controlled by an application specific integrated circuit (ASIC). The data were sampled at 10-bit resolution prior to communication off chip as a single interleaved data stream. This incorporated a power saving serial bitstream data compression algorithm that was found to extend the service lifetime of the pill by 70%. An integrated on-off keying (OOK) radio transmitter was used to send the signal to a local receiver (base station), prior to acquisition on a computer. A permanent magnet was also incorporated in the device to enable non-visual tracking of the system. We report on the implementation of this device, together with an initial study sampling from within the porcine GI tract, showing that measurements from the lab-on-a-pill, in situ, was within 90% of literature values.     

Integral relations for the heat and mass transfer resistivities of the liquid–vapor interface

We derived integral relations for the heat and mass transfer resistivities of the liquid–vapor interface in a one-component system. These relations were obtained assuming the validity of the standard expression for the local entropy production rate as the product of the measurable heat flux times the gradient of the inverse temperature through the surface. The integral relations will be useful to interpret results from nonequilibrium molecular dynamics simulations. We verified in this paper that earlier results obtained using the nonequilibrium van der Waals square gradient model are reproduced. For this case, we calculated the Kapitza length along the coexistence curve.     

Solid-state NMR of endohedral hydrogen-fullerene complexes

We present an overview of solid-state NMR studies of endohedral H(2)-fullerene complexes, including (1)H and (13)C NMR spectra, (1)H and (13)C spin relaxation studies, and the results of (1)H dipole-dipole recoupling experiments. The available data involves three different endohedral H(2)-fullerene complexes, studied over a wide range of temperatures and applied magnetic fields. The symmetry of the cage influences strongly the motionally-averaged nuclear spin interactions of the endohedral H(2) species, as well as its spin relaxation behaviour. In addition, the non-bonding interactions between fullerene cages are influenced by the presence of endohedral hydrogen molecules. The review also presents several pieces of experimental data which are not yet understood, one example being the structured (1)H NMR lineshapes of endohedral H(2) molecules trapped in highly symmetric cages at cryogenic temperatures. This review demonstrates the richness of NMR phenomena displayed by H(2)-fullerene complexes, especially in the cryogenic regime.     

Vibrational circular dichroism spectroscopy of a spin-triplet bis-(biuretato) cobaltate(III) coordination compound with low-lying electronic transitions

Vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy was applied in the analysis of vibrational and low lying electronic transitions of a triplet ground state cobalt(III) coordination compound. The spectroscopic measurements were performed on the tetrabutylammonium salt of (6S,7S)-1,3,5,8,10,12-hexaaza-2,4,9,11-tetraoxo-6,7-diphenyl-dodecanato(4-)cobaltate(III) in DMSO solution and in potassium bromide pellets. The chiral anion exhibits an unusual geometry for cobalt(III), being four-coordinate, planar, and paramagnetic with an intermediate spin state. The spectroscopic results were compared to measurements performed on the free ligand and to theoretical calculations using density functional theory (B3LYP/TZVP). The results of the VCD analysis of the coordination compound identified an electronic, dipole-forbidden, magnetic dipole-allowed low-lying d-d transition located in the mid infrared, as well as several amide stretch transitions located in the fingerprint region (1800-1100 cm(-1)), in both the liquid and solid phase. VCD signals were found to be 5-10 times higher than expected, indicating enhancement of the vibrational CD signals, caused by coupling of the vibrational transitions with the close-lying electronic transition.     

Identification of the hydrogen utilization pathway for the electrocatalytic hydrogenation of phenol

Electrochemical hydrogenation(ECH) of biomass-derived platform molecules is a burgeoning route for the sustainable utilization of hydrogen. However, the noble-metal-catalyzed ECH of phenolic compounds suffers from intense competition with hydrogen evolution reaction. We prepared Pt Rh bimetallic nanoparticles dispersed on highly ordered mesoporous carbon nanospheres, which improves the utilization efficiency of adsorbed hydrogen(Had) to ECH in H–UPD region(0 V vs. RHE).Further analysis reveals(i) the strong overlapping between the d-orbitals of Pt and Rh enhances specific adsorption of phenol;(ii)incorporation of Rh devotes an electronic effect on weakening the alloy–Hadinteraction to increase the FE of ECH. DFT calculations confirm the selectivity difference and the ECH parallel pathways: cyclohexanol and cyclohexanone are formed via hydrogenation/dehydrogenation of the intermediate *C6 H10 OH. These findings deepen our fundamental understanding of the ECH process, and cast new light on exploration of highly efficient electrocatalysts for biomass upgrading.     

Fluid self-diffusion in Scots pine sapwood tracheid cells

The self-diffusion coefficients of water and toluene in Scots pine sapwood was measured using low field pulsed field gradient nuclear magnetic resonance (PFG-NMR). Wood chips of 8 mm diameter were saturated with the respective liquids, and liquid self-diffusion was then traced in one dimension orthogonal to the tracheid cell walls in the wood's radial direction. The experimental echo attenuation curves were exponential, and characteristic self-diffusion coefficients were produced for diffusion times spanning from very short times to times on the order of magnitude of seconds. Observed self-diffusion coefficients were decaying asymptotically as a function of diffusion time, an effect which was ascribed to the cell walls' restriction on confined liquid diffusion. The observed self-diffusion behavior in Scots pine sapwood was compared to self-diffusion coefficients obtained from simulations of diffusion in a square. Principles of molecular displacements in confined geometries were used for elucidating the wood's cellular structure from the observed diffusion coefficients. The results were compared with a mathematical model for diffusion between parallel planes.