Cross-Linked Benzoxazine–Benzimidazole Copolymer Electrolyte Membranes for Fuel Cells at Elevated Temperature

Here we report new H₃PO₄-doped cross-linked benzoxazine–benzimidazole copolymer membranes showing high proton conductivity and long-term durability for use in proton-exchange membrane fuel cells at elevated temperatures (>100 °C). The cross-linked copolymer membranes were prepared by mixing of poly­[2,2′-(<i>m</i>-phenylene)-5,5′-bibenzimidazole] (PBI) with 3-phenyl-3,4-dihydro-6-<i>tert</i>-butyl-2<i>H</i>-1,3-benzoxazine (<i>p</i>BUa) in <i><i>N,N</i></i>-dimethylacetamide, with subsequent stepwise heating to 220 °C, and even large-sized films (30 cm × 140 m) could be easily prepared. The membranes showed high proton conductivities of up to 0.12 S cm^–1 at 150 °C under anhydrous conditions. Membrane–electrode assemblies (MEAs) employing the membranes showed operating voltages of 0.71 V at 0.2 A cm^–2. Furthermore, the MEAs displayed long-term durability up to 1999 cycles, with much slower performance decay, −0.03 mV h^–1, than those prepared using the PBI membrane in <i>in situ</i> accelerated lifetime mode (load cycling testing)

CO₂ Enhanced Chemical Vapor Deposition Growth of Few-Layer Graphene over NiO_<i>x</i>

The use of mild oxidants in chemical vapor deposition (CVD) reactions has proven enormously useful. This was also true for the CVD growth of carbon nanotubes. As yet though, the use of mild oxidants in the CVD of graphene has remained unexplored. Here we explore the use of CO₂ as a mild oxidant during the growth of graphene over Ni with CH₄ as the feedstock. Both our experimental and theoretical findings provide in-depth insight into the growth mechanisms and point to the mild oxidants playing multiple roles. Mild oxidants lead to the formation of a suboxide in the Ni, which suppresses the bulk diffusion of C species suggesting a surface growth mechanism. Moreover, the formation of a suboxide leads to enhanced catalytic activity at the substrate surface, which allows reduced synthesis temperatures, even as low as 700 °C. Even at these low temperatures, the quality of the graphene is exceedingly high as indicated by a negligible D mode in the Raman spectra. These findings suggest the use of mild oxidants in the CVD fabrication as a whole could have a positive impact

Dendrite-Free Lithium Deposition for Lithium Metal Anodes with Interconnected Microsphere Protection

A lithium (Li) metal anode is required to achieve a high-energy-density battery, but because of an undesirable growth of Li dendrites, it still has safety and cyclability issues. In this study, we have developed a microsphere-protected (MSP) Li metal anode to suppress the growth of Li dendrites. Microspheres could guide Li ions to selective areas and pressurize dendrites during their growth. Interconnections between microspheres improved the pressurization. By using an MSP Li metal anode in a 200 mAh pouch-type Li/NCA full cell at 4.2 V, dendrite-free Li deposits with a density of 0.4 g/cm³, which is 3 times greater than that in the case of bare Li metal, were obtained after charging at 2.9 mAh/cm². The MSP Li metal enhanced the cyclability to 190 cycles with a criterion of 90% capacity retention of the initial discharge capacity at a current density of 1.45 mA/cm²

To Do or Not to Do; Dilemma of Intra-Arterial Revascularization in Acute Ischemic Stroke

<div><p>Background</p><p>There has still been lack of evidence for definite imaging criteria of intra-arterial revascularization (IAR). Therefore, IAR selection is left largely to individual clinicians. In this study, we sought to investigate the overall agreement of IAR selection among different stroke clinicians and factors associated with good agreement of IAR selection.</p><p>Methods</p><p>From the prospectively registered data base of a tertiary hospital, we identified consecutive patients with acute ischemic stroke. IAR selection based on the provided magnetic resonance imaging (MRI) results and clinical information were independently performed by 5 independent stroke physicians currently working at 4 different university hospitals. MRI results were also reviewed by 2 independent experienced neurologists blinded to clinical data and physicians' IAR selection. The Alberta Stroke Program Early Computed Tomography Score (ASPECTS) was calculated on initial DWI and MTT. We arbitrarily used ASPECTS differences between DWI and MTT (D-M ASPECTS) to quantitatively evaluate mismatch.</p><p>Results</p><p>The overall interobserver agreement of IAR selection was fair (kappa = 0.398). In patients with DWI-ASPECTS >6, interobserver agreement was moderate to substantial (0.398–0.620). In patients with D-M ASPECTS >4, interobserver agreement was moderate to almost perfect (0.532–1.000). Patients with higher DWI or D-M ASPECTS had better agreement of IAR selection.</p><p>Conclusion</p><p>Our study showed that DWI-ASPSECTS >6 and D-M ASPECTS >4 had moderate to substantial agreement of IAR selection among different stroke physicians. However, there is still poor agreement as to whether IAR should not be performed in patients with lower DWI and D-M ASPECTS.</p></div

The general characteristics of the 3 groups according to the proportion of physicians who selected IAR.

<p>Abbreviations: FAT; first known abnormal time, FLAIR; Fluid-attenuated inversion recovery, PVWMH; periventricular white matter hyperintensity, M2; M2 segment of middle cerebral artery. ICA; internal carotid artery, dICA; distal ICA, M1; M1 segment of middle cerebral artery, M2; M2 segment of middle cerebral artery, DWI; diffusion-weighted imaging, ASPECTS; Alberta Stroke Program Early Computed Tomography Score, MTT; mean transit time, D-M ASPECTS; ASPECTS differences between DWI and MTT.</p

Comparisons of outcomes according to IAR treatment in patients of each group.

<p>Abbreviations: IVT, Intravenous thrombolysis; HT, hemorrhagic transformation; HI, hemorrhagic infarction; PH, parenchymal hemorrhage; mRS, modified Rankin Scale.</p><p>*P<0.05 (OR, 6.059; 95% CI, 1.003–36.583) by multivariate logistic regression analysis, adjusted by age and initial NIHSS.</p

The general characteristics of the subjects.

<p>Abbreviations: ICA; internal carotid artery, M1; M1 segment of middle cerebral artery, M2; M2 segment of middle cerebral artery, FAT; first known abnormal time, IVT; intravenous thrombolysis, IAR; intra-arterial revascularization.</p

Representative cases of lesion patterns of poor agreements for IAR (A, group B) and lesion patterns with good agreement for IAR decision (B, group C).

<p>(A) The figures show moderate sized lesions of right hemisphere on DWI, occlusion of right distal internal carotid artery, and large perfusion deficit on PWI. (B) The figures show small lesion of basal ganglia on DWI, occlusion of right internal carotid artery, and large hemispheric perfusion deficit on PWI.</p

Interobserver agreement of IAR selection between 5 clinicians for 125 stroke patients.

<p>The level of agreement is represented by kappa (κ) value calculated using DWI, MTT, and D-M ASPECTS.</p><p>Abbreviations: DWI; diffusion-weighted imaging, ASPECTS; Alberta Stroke Program Early Computed Tomography Score, MTT; mean transit time, D-M ASPECTS; ASPECTS differences between DWI and MTT.</p

Si/Ge Double-Layered Nanotube Array as a Lithium Ion Battery Anode

Problems related to tremendous volume changes associated with cycling and the low electron conductivity and ion diffusivity of Si represent major obstacles to its use in high-capacity anodes for lithium ion batteries. We have developed a group IVA based nanotube heterostructure array, consisting of a high-capacity Si inner layer and a highly conductive Ge outer layer, to yield both favorable mechanics and kinetics in battery applications. This type of Si/Ge double-layered nanotube array electrode exhibits improved electrochemical performances over the analogous homogeneous Si system, including stable capacity retention (85% after 50 cycles) and doubled capacity at a 3<i>C</i> rate. These results stem from reduced maximum hoop strain in the nanotubes, supported by theoretical mechanics modeling, and lowered activation energy barrier for Li diffusion. This electrode technology creates opportunities in the development of group IVA nanotube heterostructures for next generation lithium ion batteries