Influence of the ratio of resin to polymeric binder on the heterogeneity of cation-exchange membranes

<div><p></p><p>In this study, heterogeneous cation-exchange membranes were prepared by a casting method using mixtures of cation exchange resin and polymeric binder for the application of desalination and water treatment. The influence of the ratio of cation-exchange resin to polymeric binder on the electrochemical properties, such as the characteristic values in the current–voltage relationship, electrical conductivity, and chronopotentiometric values, was investigated and the preparation method was optimized based on the characterized properties of the heterogeneous cation-exchange membranes. The heterogeneity, determined by their ion-exchange resin content, was estimated based on the characterized electrochemical properties, which is related to the inter-gel phase fraction and the conducting phase. It was observed that the heterogeneity of the prepared cation-exchange membranes increased with transition time and limiting current density. In electrodialytic experiments, the heterogeneous cation-exchange membranes showed reasonably good desalination performance compared to commercial heterogeneous membranes, which is related to the heterogeneity as well as the membrane properties.</p></div

Nitrogen-Deficient ORR Active Sites Formation by Iron-Assisted Water Vapor Activation of Electrospun Carbon Nanofibers

Fe- and N-modified carbon nanofibers (Fe–CNF) were synthesized via electrospinning and pyrolysis as electrocatalysts for oxygen reduction reaction (ORR). In order to increase the exposed surface area with the active sites buried inside Fe–CNF, we attempted water vapor activation for Fe–CNF and observed a substantial improvement of ORR activity up to the comparable level with Pt/C. Unlike what was expected, however, water vapor activation did not significantly increase the specific surface area of Fe–CNF; instead, it induced a depletion of surface N content, which makes it difficult to explain the improved ORR activity with the increase of surface area with N-based active sites. In water vapor activation, the chemical phase of embedded particles is changed from Fe₃C to Fe₃O₄ and nitrogen-free Fe- and C-based ORR active sites were exposed, which seemed to be related with hierarchical macro/mesopore structure and graphitic edge defects. This study demonstrates a facile activation method for better ORR activity of Fe-modified CNF and suggests a potential relationship of surface carbon structure with the catalytic activity toward ORR rather than the type and concentration of N in Fe–CNF, which should be investigated further