The density and dimensional changes of Nafion 117 H have been measured as a function of the water content. Swelling of Nafion commences at N (= mol ratio water to hydrogen ion) -1.9. Some anisotropy of dimensional changes was observed. Water-sorption isotherms obey Henry's Law with a nonzero intercept indicating some water retention. The diffusion coefficient of water in Nafion and the electrical conductivity of Nafion are strong functions of the water content. The latter is exploited for the development of a humidity sensor.
The sluggish hydrogen oxidation reaction (HOR) under alkaline conditions has hindered the commercialization of hydroxide-exchange membrane hydrogen fuel cells.Alowcost Ni/NiO/C catalyst with abundant Ni/NiO interfacial sites was developed as acompetent HOR electrocatalyst in alkaline media. Ni/NiO/C exhibits an HOR activity one order of magnitude higher than that of its parent Ni/C counterpart. Moreover,N i/NiO/C also shows better stability and CO tolerance than commercial Pt/C in alkaline media, which renders it av ery promising HOR electrocatalyst for hydrogen fuel cell applications.D ensity functional theory (DFT) calculations were also performed to shed light on the enhanced HOR performance of Ni/NiO/C;the DFT results indicate that both hydrogen and hydroxideachieveoptimal binding energies at the Ni/NiO interface,resulting from the balanced electronic and oxophilic effects at the Ni/NiO interface.Along with the rapid progress in the generation of clean hydrogen from water with renewable energy sources such as solar and wind energies,i ncreasing attention has been devoted to the efficient utilization of hydrogen directly as agreen fuel, in that the sole product of hydrogen combustion is water. Within this context, the hydrogen fuel cell is one of the most promising technologies for hydrogen utilization. [1] Even though commercial hydrogen fuel cells employing proton exchange membranes exhibit high power output, [2]
Carbon-carbon bond-forming reductive elimination from elusive organocopper(III) complexes has been considered the key step in many copper-catalyzed and organocuprate reactions. However, organocopper(III) complexes with well-defined structures that can undergo reductive elimination are extremely rare, especially for the formation of Csp 3-Csp 3 bonds. We report herein a general method for the synthesis of a series [alkyl-Cu III-(CF 3) 3 ]complexes, the structures of which have been unequivocally characterized by NMR, mass spectrometry and X-ray crystal diffraction. At elevated temperature, these complexes undergo reductive elimination following first-order kinetics, forming alky-CF 3 products with good yields (up to 91%). Both Kinetic studies and DFT calculations indicate that the reductive elimination to form Csp 3-CF 3 bonds proceeds through a concerted transition state, with a ΔH ‡ =20 kcal/mol barrier.
With the utilization of a "bifunctional liganddirected strategy", three isostructural indium−organic frameworks based on dual secondary building units (SBUs) were successfully constructed with targeted structures. In their frameworks, two types of unsaturated monomeric indium SBUs[In(OOC-) 2 (-N-)X(H 2 O)] and [In(OOC-) 2 (-N-)X 2 ] − (X = Cl, Br, and I)assemble to form 1D tubular channels with both open metal sites and weak base polarizing substituents. The trimeric indium SBUs [In 3 O(OOC-) 6 (DMA) 3 ] + serve as robust external linkers to extend into a 3D honeycomb double-walled framework with nanoscale channels. By changing the polarizing substituents in situ with different halogens (Cl − , Br − , and I − ), three obtained isostructural MOFs show different channel characteristics, such as alkalinity of the polarizing substituents, acidity of the polarized open indium sites, extended channel sizes, and increased pore volumes (from -I to -Cl). Subsequently, we took the three MOFs collectively as a platform to investigate the impact of the different coordinated halide ions on channel functions, especially on CO 2 adsorption and chemical conversion. Accordingly, the three nanochannel MOF catalysts exhibited highly effective performances in catalyzing cycloaddition of CO 2 with large-sized epoxides, particularly styrene oxide, into value-added productsstyrene carbonates with yields of 91−93% and high selectivity of 95−98%under mild conditions. We speculated that the superior catalytic efficiencies of the three MOF catalysts could be ascribed to the synergistic effect of open indium sites as Lewis acid with different halide ions as weak base sites, which might enhance the catalytic selectivity through polarizing and activating CO 2 molecules during the reaction process.
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