Do-Hyeong Kim

Facile surface modification of anion-exchange membranes for improvement of diffusion dialysis performance.

In this study, a facile membrane modification method by spin-coating of pyrrole (Py) monomers dissolved in a volatile solvent followed by an interfacial polymerization is proposed. The surface of a commercial anion-exchange membrane (i.e., Neosepta-AFX, Astom Corp., Japan) was successfully modified with polypyrrole (Ppy) to improve the acid recovery performance in diffusion dialysis (DD). The result of DD experiments revealed that both the acid and metal ion transports are significantly influenced by the surface modification. The metal crossover through the membranes was largely reduced while mostly maintaining the acid permeability by introducing a thin Ppy layer with excellent repelling property to cations on the membrane surface. As a result, the anion-exchange membrane modified with the optimum content of Py monomer (5 vol.%) exhibited excellent acid dialysis coefficient (KAcid) and selectivity (KAcid/KMetal) which is approximately twice as high as that of the pristine membrane.

Surface modification and use of polymer complex agents to mitigate metal crossover of anion-exchange membranes

The facile surface modification of a commercial anion-exchange membrane (i.e., Neosepta-AFX, Astom Corp., Japan) was investigated with brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO), which had non-charged polar groups, and its quaternized form (QPPO) to improve the acid recovery efficiency in diffusion dialysis (DD). By coating a thin layer of BPPO on the membrane surface, the significant changes in the surface compactness and charge density were observed while the electrochemical properties were mostly maintained. From the DD experiments, it was revealed that the membrane modified with 1 wt% BPPO exhibited the moderate acid permeability as well as the highest acid selectivity (KAcid/KFe3+=48.81), which is more than double compared with that of the pristine membrane (KAcid/KFe3+=22.48) among the tested membranes. The electron-rich polar groups contained in BPPO are believed to provide moderate proton transport while the reduced swelling property of the membrane surface can effectively mitigate the crossover of metal cations. In addition, the acid selectivity (KAcid/KFe3+=30.69) was largely improved by using small molecular weight poly(ethyleneimine) (PEI, Mn=1800) with a small content (in the range of 1-5 wt%) as a solution additive for the growing size of metal species by the formation of polymer-metal complexes.

Development of Ionomer Binder Solutions Using Polymer Grinding for Solid Alkaline Fuel Cells

In this study, an anion-exchange ionomer solution was prepared by grinding poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) in liquid nitrogen for solid alkaline fuel cells (SAFCs). Type of quaternized PPO (QPPO) solutions was controlled by grinding time. The ionomer binder solutions were characterized in terms of dispersity, particle size, and electrochemical properties. As a result, ionomer binder solutions using grinded polymer showed higher dispersion and smaller particle size distribution than that using non-grinded polymer. The highest ionic conductivity and IEC of the membrane recast by using BPPO-G120s were and , respectively.