Dong-Cheol Jeong

Growth kinetics of plasma-polymerized films

The growth kinetics of polymer thin films prepared by plasma-based deposition method were explored using atomic force microscopy. The growth behavior of the first layer of the polythiophene somewhat differs from that of the other layers because the first layer is directly deposited on the substrate, whereas the other layers are deposited on the polymer itself. After the deposition of the first layer, each layer is formed with a cycle of 15 s. The present work represents the growth kinetics of the plasma-polymerized films and could be helpful for further studies on growth kinetics in other material systems as well as for applications of plasma-polymerized thin films.

Synthesis and electronic properties of N-heterocyclic carbene-containing conducting polymers with coinage metals

Following the recent development of functional materials based on metal-containing conducting polymers, we designed and synthesized a series of bithiophene based N-heterocyclic carbene (NHC) conducting polymers containing coinage metals (Cu, Ag, and Au). Absorption spectroscopy, NMR spectroscopy, cyclic voltammetry, and X-ray photoelectron spectroscopy (XPS) were used to analyze the monomers and the polymer thin films. The peak currents of the electrodeposited films on Pt-button electrodes increased proportionally with the scan rate, exhibiting the stability of the polymer thin films. Remarkably, in the electrochemical studies of the coinage metal complexes, the redox potential of Cu+/Cu2+ perfectly matched with the redox wave of quaterthiophene moieties of the polymer backbone. However, the redox potential of Ag/Ag+ did not match with the redox potential of the polymer backbone. During the oxidation process in the spectroelectrochemical studies, the conducting coinage metallopolymers exhibited a drastic color change from orange (reduced form) to dark green (oxidized form), and they can be envisioned in the applications of electrochromic materials.

Repairable photoactive polymer systems via metal–terpyridine-based self-assembly

The development of sustainable polymeric photo-catalytic systems for the conversion of solar energy is an important issue. In this perspective, efficient photo-catalytic systems have been developed by many research groups; however, their long-term stability or sustainability is still challenging and need to be resolved. In order to realize sustainable polymeric photoactive systems, we developed terpyridine (tpy)-based polymers and their ruthenium complexes, which were reversibly assembled and disassembled through metal ion–ligand interactions. In the presence of metal ions, Ru-based photoactive polymers were assembled on tpy-coated ITO substrates, generating visible-light induced photocurrents. Subsequently, when disassembled by the introduction of tetra-n-butylammonium fluoride, the assembled polymeric complex decomposed, decreasing the photocurrent. However, the photocurrent efficiency of this system was recovered through re-assembly and repeated several times without a significant decrease in its efficiency. In addition, a sustainable photo-catalyst system was achieved by photo-oxidative coupling with benzylamine. The initial active photo-catalytic system became inactive after disassembly; however, its activity was restored through assembly again, and this process was repeated successfully several times. The self-assembly via reversible metal ion–ligand interaction would enable photo-catalytic systems to be self-repairable and sustainable.

Binaphthyl-Containing Electroactive Polymer Networks by Ring-Opening Metathesis Polymerization

Abstract

Binaphthyl-based molecular barrier materials for phosphoric acid poisoning in high-temperature proton exchange membrane fuel cells

In this study, thiol-functionalized binaphthyl barrier molecules were designed and synthesized for eliminating phosphoric acid (PA)-poisoning on Pt catalysts in oxygen reduction reactions (ORRs). In high-temperature proton exchange membrane fuel cell, the ORR activity of Pt catalysts significantly decreases because of the PA poisoning. The binaphthyl thiol (BNSH) molecules with a tweezer-like structure can self-assemble on the Pt surface, thereby blocking the adsorption of PA, while permitting the approach of smaller oxygen molecules. After the treatment of Pt surfaces with BNSHs, the ORR activities were tested in the presence of PA, and the results were compared with respect to the molecular structures of BNSHs. Even in the presence of PA, the ORR activity of BNSH-treated Pt catalysts appeared to restore significantly up to the level of the pristine Pt without PA (kinetic current density at 0.8 V from 12 to 20.4 mA cm−2). This enhanced activity was attributed to the physical blocking of PA molecules on Pt surface and was affected by the molecular structures such as tweezer backbone, length of alkyl chains, and the type and number of functional groups.