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Enhanced charge transfer with Ag grids at electrolyte/electrode interfaces in solid oxide fuel cells
Choi, Mingi,Hwang, Sangyeon,Byun, Doyoung,Lee, Wonyoung The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.12
<▼1><P>This paper demonstrated the effect of Ag grids at the electrolyte/electrode interfaces on the electrochemical performance of solid oxide fuel cells (SOFCs).</P></▼1><▼2><P>We systematically investigated the effect of Ag grids at the electrolyte/electrode interfaces on the electrochemical performance of solid oxide fuel cells (SOFCs). Electrohydrodynamic jet printing was employed to fabricate Ag grids with a precise control of the geometry. A substantial reduction in the polarization resistance was observed when the pitch of the Ag grids decreased from 400 to 50 μm, indicating enhanced charge transfer through efficient supply and distribution of electrons along the Ag grids at the electrolyte/electrode interfaces. Our results demonstrate the possibility of engineering interfaces with metallic grids to achieve enhanced electrochemical performances for SOFCs operating at intermediate temperatures.</P></▼2>
Choi, Mingi,Yong, Kijung The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.22
<P>Vertically aligned high-quality single crystalline brookite TiO2 nanoarrays were synthesized for the first time using an environmentally benign one-step hydrothermal reaction. They have a unique bullet-shaped structure which has a length of 700-1000 nm and a width of 150-250 nm with a sharpened tip structure. By adjusting the concentration of NaOH in hydrothermal reaction, we could also synthesize other types of TiO2 nanostructures including anatase TiO2 nanotubes/nanowires. The morphologies and crystal structures of the products were confirmed by scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. Their vertically aligned structures facilitate their application as photoanodes in photoelectrochemical cells, and the photoelectrochemical properties such as photocurrent density and open circuit voltage were measured in a three-electrode electrochemical cell with TiO2 nanoarrays, Ag/AgCl and a Pt flag as the working, reference and counter electrodes, respectively, incorporating a 0.1 M NaOH electrolyte solution. The fabricated brookite TiO2 nanoarrays exhibited a highly enhanced photocurrent density and a longer electron lifetime compared with anatase TiO2 nanoarrays with similar lengths.</P>
Choi, Mingi,Hwang, Sangyeon,Byun, Doyoung,Lee, Wonyoung The Korean Ceramic Society 2015 한국세라믹학회지 Vol.52 No.5
The specific role of current collectors was investigated at the electrolyte/electrode interface of solid oxide fuel cells (SOFCs). Ag grids were fabricated as current collectors using electrohydrodynamic (EHD) jet printing for precise control of the grid geometry. The Ag grids reduced both the ohmic and polarization resistances as the pitch of the Ag grids decreased from $400{\mu}m$ to $100{\mu}m$. The effective electron distribution along the Ag grids improved the charge transport and transfer at the interface, extending the active reaction sites. Our results demonstrate the applicability of EHD jet printing to the fabrication of efficient current collectors for performance enhancement of SOFCs.
Nano-film coated cathode functional layers towards high performance solid oxide fuel cells
Choi, Mingi,Lee, Jongseo,Lee, Wonyoung The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.25
<P>Nano-structured composite electrodes, from a carefully conducted infiltration process, are one of the most promising electrode structures for intermediate temperature solid oxide fuel cells (IT-SOFCs), due to their ability to promote the oxygen reduction reaction (ORR) and enlarge triple phase boundaries (TPBs). Here, we demonstrate rational design of infiltrated nano-structures for IT-SOFCs with enhanced ORR kinetics and excellent stability. We systematically designed a nano-structured cathode functional layer (CFL) from the infiltration of Sm0.5Sr0.5CoO3−δ (SSC) into porous Gd0.2Ce0.8O2−δ (GDC). By controlling the drying process during the infiltration process, two distinct nano-structures of SSC, discrete coating and film-like coating, were fabricated on the GDC scaffolds. The CFL with the film-like coating showed ∼30% reduction in polarization resistance (<I>R</I>p) and ∼15% increase in peak power density at 650 °C compared to the CFL with the discrete coating in spite of ∼12-fold lower loading of infiltration materials. Furthermore, the CFL with the film-like coating showed an excellent stability, maintaining an <I>R</I>p of 0.029 Ω cm<SUP>2</SUP> for 100 h at 650 °C. Our results demonstrated that the high performance and stability of composite electrodes for IT-SOFCs can be achieved through a thin-film coated CFL.</P>
Choi, Mingi,Lim, Jonghun,Baek, Minki,Choi, Wonyong,Kim, Wooyul,Yong, Kijung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.19
<P>Among three polymorphs of TiO2, the brookite is the least known phase in many aspects of its properties and photoactivities (especially comparable to anatase and rutile) because it is the rarest phase to be synthesized in the standard environment among the TiO2 polymorphs. In this study, we address the unrevealed photocatalytic properties of pure brookite TiO2 film as an environmental photocatalyst. Highly crystalline brookite nanostructures were synthesized on titanium foil using a well-designed hydrothermal reaction, without harmful precursors and selective etching of anatase, to afford pure brookite. The photocatalytic degradation of rhodamine B, tetramethylammonium chloride, and 4-chlorophenol on UV-illuminated pure brookite were investigated and compared with those on anatase and ruffle TiO2. The present research explores the generation of OH radicals as main oxidants on brookite. In addition, tetramethylammonium, as a mobile OH radical indicator, was degraded over both pure anatase and brookite phases, but not rutile. The brookite phase showed much higher photoactivity among TiO2 polymorphs, despite its smaller surface area compared with anatase. This result can be ascribed to the following properties of the brookite TiO2 film: (i) the higher driving force with more negative flat-band potential, (ii) the efficient charge transfer kinetics with low resistance, and (iii) the generation of more hydroxyl radicals, including mobile OH radicals. The brookite-nanostructured TiO2 electrode facilitates photocatalyst collection and recycling with excellent stability, and readily controls photocatalytic degradation rates with facile input of additional potential.</P>
흡기가열을 이용한 가솔린 압축착화 엔진의 연소 및 배기특성 모델링
최민기(Mingi Choi),오윤중(Yunjung Oh),류봉우(Bong Woo Ryu),이창식(Chang Sik Lee),박성욱(Sungwook Park) 한국연소학회 2011 KOSCOSYMPOSIUM논문집 Vol.- No.43
This paper presents numerical study on combustion and emissions characteristics of GDICI(gasoline Direct Injection Compression Ignition) engine using intake preheating. Numerical modeling was conducted by using the KIVA-3V Release2 code. In addition, Chemkin Chemistry solver was integrated into KIVA code to simulate the ignition and combustion precesses in order to predict combustion and exhaust emissions characteristics. The fuel was modeled using PRF mechanims to simulate the fuel oxidation process. To achieve gas pressure in cylinder and emissions characteristics, the experiments were performed on a single-cylinder engine. The simulation results agreed well with the experimental data.