Chanmin Lee

Synthesis of silica aerogels from waterglass via new modified ambient drying

A new modified ambient drying process for synthesizing silica aerogels cost-effectively from waterglass has been developed. Crack-free silica aerogels were obtained via solvent exchange/surface modification of wet gels using IPA/TMCS/n-Hexane solution. Silica aerogels were heated at different temperatures. The effects of heating temperature on chemical bonding state of aerogels were investigated by means of DTA and FTIR. The surface characteristic of the aerogel was hydrophobic when heat-treated under 350°C. The porosities, densities, and specific surface areas of the silica aerogels were in the range of 93–94%, 0.12–0.15 g/cm3, and ∼630 m2/g, respectively. Distinct spring back phenomena were observed in surface modified wet gels during drying.

Direct spun aligned carbon nanotube web-reinforced proton exchange membranes for fuel cells

A new method combining electrospinning of SPEEK and direct spinning of CNT forests has been used to prepare sulfonated poly(ether ether ketone) (SPEEK)/directly spinnable carbon nanotube (dsCNT) composite proton exchange membranes. The SPEEK/dsCNT membrane is more robust than SPEEK alone, and in a fuel cell significantly outperforms both SPEEK and the commercial Nafion 212 membranes.

Catalytic Properties of CeO2-Supported LaMnO3 for NO Oxidation

CeO2-supported LaMnO3 perovskite oxides were prepared to study their catalytic properties in the oxidation of NO to NO2. To prepare the catalyst and investigate the interaction between LaMnO3 and CeO2, two deposition methods were used. Extended X-ray absorption fine structure studies confirmed that perovskite oxide phases were formed on the CeO2 support. Moreover, X-ray photoelectron spectroscopy and temperature-programmed reduction with H2 studies revealed that the reduction temperatures for perovskite oxides and CeO2 support decreased by the deposition followed by calcination at 650 °C, and that the interaction between the LaMnO3 and CeO2 support can be controlled by changing the preparation method. The LaMnO3/CeO2 catalyst in which LaMnO3 was highly dispersed on CeO2 exhibited higher NO oxidation activity than either LaMnO3 or CeO2. The thermal stability of the LaMnO3/CeO2 catalyst was compared with that of alumina-supported LaMnO3 catalysts over 850–1050 °C.Graphical Abstract

Oxide–Carbon Nanofibrous Composite Support for a Highly Active and Stable Polymer Electrolyte Membrane Fuel-Cell Catalyst

Well-designed electronic configurations and structural properties of electrocatalyst alter the activity, stability, and mass transport for enhanced catalytic reactions. We introduce a nanofibrous oxide-carbon composite by an in situ method of carbon nanofiber (CNF) growth by highly dispersed Ni nanoparticles that are exsoluted from a NiTiO3 surface. The nanofibrous feature has a 3D web structure with improved mass-transfer properties at the electrode. In addition, the design of the CNF/TiO2 support allows for complex properties for excellent stability and activity from the TiO2 oxide support and high electric conductivity through the connected CNF, respectively. Developed CNF/TiO2-Pt nanofibrous catalyst displays exemplary oxygen-reduction reaction (ORR) activity with significant improvement of the electrochemical surface area. Moreover, exceptional resistance to carbon corrosion and Pt dissolution is proven by durability-test protocols based on the Department of Energy. These results are well-reflected to the single-cell tests with even-better performance at the kinetic zone compared to the commercial Pt/C under different operation conditions. CNF/TiO2-Pt displays an enhanced active state due to the strong synergetic interactions, which decrease the Pt d-band vacancy by electron transfer from the oxide-carbon support. A distinct reaction mechanism is also proposed and eventually demonstrates a promising example of an ORR electrocatalyst design.