Tae-hoon Lim - Academia.edu (original) (raw)

Papers by Tae-hoon Lim

ECS Meeting Abstracts, 2013

ECS Meeting Abstracts, 2010

Effectiveness factor which was defined as the ratio of the current produced by the electrode unde... more Effectiveness factor which was defined as the ratio of the current produced by the electrode under diffusional resistance to that produced by the electrode without diffusional resistance was investigated for porous gas diffusion electrode described by agglomerate model. System variables including reaction rate, diffusion coefficient, and agglomerate size were combined into three dimensionless parameters, and their effects on effectiveness factor were studied. Effectiveness factor reaches a maximum value with a critical electrode thickness.

Studies in surface science and catalysis

The effect of Gd 2 O 3 doping on the catalyst Ni/MgO was studied. The Gd doping suppressed coke f... more The effect of Gd 2 O 3 doping on the catalyst Ni/MgO was studied. The Gd doping suppressed coke formation, and enhanced catalytic activity for steam reforming reaction. The Gd doping seemed to activate the dissociative adsorption of water to increase OH concentration on the catalyst as if steam feed was increased. BET surface area and Ni dispersion were increased with the increase of Gd addition till 10wt% referenced to Ni weight, and then decreased due to the segregation of Gd 2 O 3 from the mixed compound of Gd and MgO. The increase of Ni dispersion was one of the reasons to suppress coke formation.

Key Engineering Materials, 2005

Page 1. Journal Citation (to be inserted by the publisher) Copyright by Trans Tech Publications F... more Page 1. Journal Citation (to be inserted by the publisher) Copyright by Trans Tech Publications Fabrication of an Anode-Supported Sofc with a Sol-Gel Coating Method for a Mixed-Gas Fuel Cell Nguyen Xuan Phuong Vo, Sung ...

The Journal of Physical Chemistry C, 2009

We present the role of Pd ensembles in the selective direct synthesis of H 2 O 2 from H 2 and O 2... more We present the role of Pd ensembles in the selective direct synthesis of H 2 O 2 from H 2 and O 2 on a PdAu alloy surface based on periodic density functional theory calculations. Our calculations demonstrate that H 2 O 2 formation is strongly affected by the spatial arrangement of Pd and Au surface atoms. In particular, Pd monomers surrounded by less active Au atoms that suppress O-O bond scission are primarily responsible for the significantly enhanced selectivity toward H 2 O 2 formation on PdAu alloys compared to that on the monometallic Pd and Au counterparts.

Polymer Degradation and Stability, 2012

ABSTRACT Thermogravimetric analysis (TGA) has been proposed as a new post-analysis tool of membra... more ABSTRACT Thermogravimetric analysis (TGA) has been proposed as a new post-analysis tool of membrane electrode assembly (MEA) for polymer electrolyte membrane fuel (PEMFC). Analysis of catalyst layer (CL) samples with various Nafion ionomer contents quantitatively confirmed that the Nafion ionomer decomposed first at around 320 °C and the support carbon at around 410 °C. For the degradation analysis of MEAs, the amount variation of components, including platinum (Pt) and attached gas diffusion layer (GDL), and the degree of Pt agglomeration could be evaluated from weight changes and DTG peak shifts (the platinum activation effect), respectively. For an MEA degraded by start-up/shut-down cycling, Pt agglomeration and significant GDL attachment, as well as invariant Pt amount and slight weight decrease of Nafion and supporting carbon, could be analyzed by a single TGA measurement. Similar degradation analysis was also possible for stack-operated MEAs. This TGA analysis technique is expected to be effectively utilized as a preliminary diagnosis tool in a routine characterization of degraded PEMFC MEAs.

Korean Journal of Chemical Engineering, 2006

Korean Journal of Chemical Engineering, 2008

LPG has good infrastructure and is anticipated to be used for production of hydrogen, and n-butan... more LPG has good infrastructure and is anticipated to be used for production of hydrogen, and n-butane which constitutes a main component of LPG for vehicles. Partial oxidation (POX) of n-butane is investigated in this research by employing ceria-promoted Ni/calcium hydroxyapatite catalysts (Ce x Ni 2.5 /Ca 10 (OH) 2 (PO 4) 6 x=0.1-0.3) which have recently been reported to exhibit good catalytic performance in POX of methane and propane. The experiments were carried out with changing ceria content, O 2 /n-C 4 H 10 ratio and reaction temperature. As the O 2 /n-C 4 H 10 ratio increased up to 2.75, the n-C 4 H 10 conversion and H 2 yield increased and the selectivity of methane and other hydrocarbons decreased. But with O 2 /n-C 4 H 10 =3.0, the n-C 4 H 10 conversion and H 2 yield decreased. Ce 0.1 Ni 2.5 /Ca 10 (OH) 2 (PO 4) 6 showed the highest n-C 4 H 10 conversion and H 2 yield on the whole. In durability tests, higher hydrogen yield and better catalyst stability were obtained with the O 2 /n-C 4 H 10 ratio of 2.75 than with the ratio of 2.5.

Journal of the American Chemical Society, 2012

Journal of Materials Chemistry, 2012

ABSTRACT Different shapes of various nickel structures, including dendrite, particle and film are... more ABSTRACT Different shapes of various nickel structures, including dendrite, particle and film are fabricated by electrodeposition under various conditions. The shape of nickel structures is definitely dependent on the deposition potential, leading to different electrochemical surface area and edge facets. The nickel particle which has a polycrystalline center and edge is obtained at high negative potential. On the other hand, the nickel dendrite deposited by relatively low negative potential exhibits large electrochemical surface area and a particularly active facet for hydrogen evolution reaction (HER) in alkaline water electrolysis. In fact the nickel dendrite shows the highest catalytic activity and stability for HER among the various nickel structures.

Journal of Materials Chemistry, 2012

ABSTRACT ortho-Dichlorobenzene (ODB) was investigated as a pore modifier for both Nafion membrane... more ABSTRACT ortho-Dichlorobenzene (ODB) was investigated as a pore modifier for both Nafion membranes and proton exchange membrane fuel cell (PEMFC) catalyst layers. When ODB containing Nafion dispersions are cast into a film, evaporation leads to dense membranes with one highly porous surface layer occupying 20–30% of the overall thickness. Dense Nafion membranes with a porous top layer are interesting for use in membrane humidifiers, for increasing the electrode–membrane interface areas in electrochemical devices like fuel cells or electrolysers, and other applications. Fuel cell membrane electrode assemblies were obtained by spray coating commercial Nafion 212 membranes with ODB containing catalyst inks. ODB does not poison the catalyst, and 54–120% higher potentials in comparison to the 217 mV obtained with an ODB free ink were achieved at 1.5 stoic air flow, 100% rh and a current density of 1 A cm−2. This shows that the porous catalyst electrode structure is changed, resulting in a reduced contribution of mass transport limited overpotentials. Furthermore, MEAs prepared with ODB in the catalyst ink are less sensitive towards changes in the air flow rate and the cathode relative humidity (between 50% rh and 100% rh: 217–292 mV at 1 A cm−2 without ODB and 439–478 mV with ODB).

International Journal of Hydrogen Energy, 2014

Herein we report the spatially uneven degradation of a polymer electrolyte membrane fuel cell (PE... more Herein we report the spatially uneven degradation of a polymer electrolyte membrane fuel cell (PEMFC) stack operated under load variation. Fifteen sub-membrane electrode assemblies (sub-MEAs) at various cell positions and various points within each cell were obtained from the original MEAs employed in the fuel cell stack. Polarization curves and the voltammetric charge of these MEAs were measured in order to correlate localized performances with the redistributed electrochemically active surface on Pt using the polarization technique and cyclic voltammetry. Several ex situ characterizations including electron probe microanalysis, environmental scanning electron microscopy, and X-ray diffraction were also performed to find evidence, supporting the inhomogeneous degradation of the fuel cell stack. Possible routes and processes for the non-uniform stack degradation during the PEMFC stack operation will also be discussed.

ECS Meeting Abstracts, 2013

ECS Meeting Abstracts, 2010

Effectiveness factor which was defined as the ratio of the current produced by the electrode unde... more Effectiveness factor which was defined as the ratio of the current produced by the electrode under diffusional resistance to that produced by the electrode without diffusional resistance was investigated for porous gas diffusion electrode described by agglomerate model. System variables including reaction rate, diffusion coefficient, and agglomerate size were combined into three dimensionless parameters, and their effects on effectiveness factor were studied. Effectiveness factor reaches a maximum value with a critical electrode thickness.

Studies in surface science and catalysis

The effect of Gd 2 O 3 doping on the catalyst Ni/MgO was studied. The Gd doping suppressed coke f... more The effect of Gd 2 O 3 doping on the catalyst Ni/MgO was studied. The Gd doping suppressed coke formation, and enhanced catalytic activity for steam reforming reaction. The Gd doping seemed to activate the dissociative adsorption of water to increase OH concentration on the catalyst as if steam feed was increased. BET surface area and Ni dispersion were increased with the increase of Gd addition till 10wt% referenced to Ni weight, and then decreased due to the segregation of Gd 2 O 3 from the mixed compound of Gd and MgO. The increase of Ni dispersion was one of the reasons to suppress coke formation.

Key Engineering Materials, 2005

Page 1. Journal Citation (to be inserted by the publisher) Copyright by Trans Tech Publications F... more Page 1. Journal Citation (to be inserted by the publisher) Copyright by Trans Tech Publications Fabrication of an Anode-Supported Sofc with a Sol-Gel Coating Method for a Mixed-Gas Fuel Cell Nguyen Xuan Phuong Vo, Sung ...

The Journal of Physical Chemistry C, 2009

We present the role of Pd ensembles in the selective direct synthesis of H 2 O 2 from H 2 and O 2... more We present the role of Pd ensembles in the selective direct synthesis of H 2 O 2 from H 2 and O 2 on a PdAu alloy surface based on periodic density functional theory calculations. Our calculations demonstrate that H 2 O 2 formation is strongly affected by the spatial arrangement of Pd and Au surface atoms. In particular, Pd monomers surrounded by less active Au atoms that suppress O-O bond scission are primarily responsible for the significantly enhanced selectivity toward H 2 O 2 formation on PdAu alloys compared to that on the monometallic Pd and Au counterparts.

Polymer Degradation and Stability, 2012

ABSTRACT Thermogravimetric analysis (TGA) has been proposed as a new post-analysis tool of membra... more ABSTRACT Thermogravimetric analysis (TGA) has been proposed as a new post-analysis tool of membrane electrode assembly (MEA) for polymer electrolyte membrane fuel (PEMFC). Analysis of catalyst layer (CL) samples with various Nafion ionomer contents quantitatively confirmed that the Nafion ionomer decomposed first at around 320 °C and the support carbon at around 410 °C. For the degradation analysis of MEAs, the amount variation of components, including platinum (Pt) and attached gas diffusion layer (GDL), and the degree of Pt agglomeration could be evaluated from weight changes and DTG peak shifts (the platinum activation effect), respectively. For an MEA degraded by start-up/shut-down cycling, Pt agglomeration and significant GDL attachment, as well as invariant Pt amount and slight weight decrease of Nafion and supporting carbon, could be analyzed by a single TGA measurement. Similar degradation analysis was also possible for stack-operated MEAs. This TGA analysis technique is expected to be effectively utilized as a preliminary diagnosis tool in a routine characterization of degraded PEMFC MEAs.

Korean Journal of Chemical Engineering, 2006

Korean Journal of Chemical Engineering, 2008

LPG has good infrastructure and is anticipated to be used for production of hydrogen, and n-butan... more LPG has good infrastructure and is anticipated to be used for production of hydrogen, and n-butane which constitutes a main component of LPG for vehicles. Partial oxidation (POX) of n-butane is investigated in this research by employing ceria-promoted Ni/calcium hydroxyapatite catalysts (Ce x Ni 2.5 /Ca 10 (OH) 2 (PO 4) 6 x=0.1-0.3) which have recently been reported to exhibit good catalytic performance in POX of methane and propane. The experiments were carried out with changing ceria content, O 2 /n-C 4 H 10 ratio and reaction temperature. As the O 2 /n-C 4 H 10 ratio increased up to 2.75, the n-C 4 H 10 conversion and H 2 yield increased and the selectivity of methane and other hydrocarbons decreased. But with O 2 /n-C 4 H 10 =3.0, the n-C 4 H 10 conversion and H 2 yield decreased. Ce 0.1 Ni 2.5 /Ca 10 (OH) 2 (PO 4) 6 showed the highest n-C 4 H 10 conversion and H 2 yield on the whole. In durability tests, higher hydrogen yield and better catalyst stability were obtained with the O 2 /n-C 4 H 10 ratio of 2.75 than with the ratio of 2.5.

Journal of the American Chemical Society, 2012

Journal of Materials Chemistry, 2012

ABSTRACT Different shapes of various nickel structures, including dendrite, particle and film are... more ABSTRACT Different shapes of various nickel structures, including dendrite, particle and film are fabricated by electrodeposition under various conditions. The shape of nickel structures is definitely dependent on the deposition potential, leading to different electrochemical surface area and edge facets. The nickel particle which has a polycrystalline center and edge is obtained at high negative potential. On the other hand, the nickel dendrite deposited by relatively low negative potential exhibits large electrochemical surface area and a particularly active facet for hydrogen evolution reaction (HER) in alkaline water electrolysis. In fact the nickel dendrite shows the highest catalytic activity and stability for HER among the various nickel structures.

Journal of Materials Chemistry, 2012

ABSTRACT ortho-Dichlorobenzene (ODB) was investigated as a pore modifier for both Nafion membrane... more ABSTRACT ortho-Dichlorobenzene (ODB) was investigated as a pore modifier for both Nafion membranes and proton exchange membrane fuel cell (PEMFC) catalyst layers. When ODB containing Nafion dispersions are cast into a film, evaporation leads to dense membranes with one highly porous surface layer occupying 20–30% of the overall thickness. Dense Nafion membranes with a porous top layer are interesting for use in membrane humidifiers, for increasing the electrode–membrane interface areas in electrochemical devices like fuel cells or electrolysers, and other applications. Fuel cell membrane electrode assemblies were obtained by spray coating commercial Nafion 212 membranes with ODB containing catalyst inks. ODB does not poison the catalyst, and 54–120% higher potentials in comparison to the 217 mV obtained with an ODB free ink were achieved at 1.5 stoic air flow, 100% rh and a current density of 1 A cm−2. This shows that the porous catalyst electrode structure is changed, resulting in a reduced contribution of mass transport limited overpotentials. Furthermore, MEAs prepared with ODB in the catalyst ink are less sensitive towards changes in the air flow rate and the cathode relative humidity (between 50% rh and 100% rh: 217–292 mV at 1 A cm−2 without ODB and 439–478 mV with ODB).

International Journal of Hydrogen Energy, 2014

Herein we report the spatially uneven degradation of a polymer electrolyte membrane fuel cell (PE... more Herein we report the spatially uneven degradation of a polymer electrolyte membrane fuel cell (PEMFC) stack operated under load variation. Fifteen sub-membrane electrode assemblies (sub-MEAs) at various cell positions and various points within each cell were obtained from the original MEAs employed in the fuel cell stack. Polarization curves and the voltammetric charge of these MEAs were measured in order to correlate localized performances with the redistributed electrochemically active surface on Pt using the polarization technique and cyclic voltammetry. Several ex situ characterizations including electron probe microanalysis, environmental scanning electron microscopy, and X-ray diffraction were also performed to find evidence, supporting the inhomogeneous degradation of the fuel cell stack. Possible routes and processes for the non-uniform stack degradation during the PEMFC stack operation will also be discussed.