Pervaporation removal of water from ionic liquid solutions using Nafion membranes

<p>We report a pervaporation process to remove water from a solution containing ionic liquid (IL) + solvent + water. Specifically, Nafion-based membranes were employed for the separation, and tributylmethylammonium dimethylphosphate and N-methyl-2-pyrrolidone (NMP) were the IL and solvent, respectively. Membrane swelling in contact with the IL–NMP–H₂O solution was accommodated by judicious use of gaskets and membrane supports. The pervaporation fluxes of water and NMP increased with temperature and flow rate of the permeate sweep gas. Among the membranes examined, a commercially available Nafion membrane (XL, Ion Power) provided the highest water (10 mg h⁻¹ cm⁻²) and NMP (182 mg h⁻¹ cm⁻²) fluxes. The results show that pervaporation separation is a technologically feasible method to decrease the water content of an IL–NMP–H₂O solution from 1 to 0.5 wt%.</p

Electrocatalytic Activity and Stability of Titania-Supported Platinum–Palladium Electrocatalysts for Polymer Electrolyte Membrane Fuel Cell

Titania-supported platinum–palladium electrocatalysts (PtPd/TiO₂) were synthesized and investigated as alternative catalysts for the oxygen reduction reaction (ORR). Transmission electron microscope images revealed a uniform distribution of metal nanoparticles (<i>d</i>_M = 3–5 nm) on the TiO₂ support. An increase in ORR activity has been observed with an increase in the Pd content of the bimetallic alloy up to 30%, and beyond this composition, the decrease in catalytic activity has been found to be due to the blocking of Pt active sites by a large amount of Pd in the catalyst. The PtPd/TiO₂ electrocatalyst with a Pt/Pd composition of 70:30 shows activity comparable to that of a commercial Pt/C catalyst (TKK) in rotating ring-disk electrode studies. The accelerated durability test results show good stability for the PtPd/TiO₂ electrocatalysts at high potentials in terms of minimum loss in the Pt electrochemical surface area. The high stability of the PtPd/TiO₂ electrocatalyst synthesized in this investigation offers a new approach to improve the reliability and durability of polymer electrolyte membrane-based fuel cell cathode catalysts

Layer-Dependent Electrocatalysis of MoS₂ for Hydrogen Evolution

The quantitative correlation of the catalytic activity with the microscopic structure of heterogeneous catalysts is a major challenge for the field of catalysis science. It requests synergistic capabilities to tailor the structure with atomic scale precision and to control the catalytic reaction to proceed through well-defined pathways. Here we leverage on the controlled growth of MoS₂ atomically thin films to demonstrate that the catalytic activity of MoS₂ for the hydrogen evolution reaction decreases by a factor of ∼4.47 for the addition of every one more layer. Similar layer dependence is also found in edge-riched MoS₂ pyramid platelets. This layer-dependent electrocatalysis can be correlated to the hopping of electrons in the vertical direction of MoS₂ layers over an interlayer potential barrier. Our experimental results suggest the potential barrier to be 0.119 V, consistent with theoretical calculations. Different from the conventional wisdom, which states that the number of edge sites is important, our results suggest that increasing the hopping efficiency of electrons in the vertical direction is a key for the development of high-efficiency two-dimensional material catalysts