• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.497-505
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• 2019

Lanthanum-based transition metal cations containing perovskites have emerged as potential catalysts for the intermediate-temperature (600-800℃) oxygen reduction reaction (ORR). Here, we report a facile acetylacetone-assisted combustion route for the synthesis of nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The as-prepared powder was analyzed by thermogravimetry analysis-differential scanning calorimetry. The powder calcined at 800℃ was characterized by X-ray diffraction, scanning electrode microscopy, energy dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area measurements. It was found that the porosity of the air electrode significantly increased by utilizing the nanostructured LSCF6428 instead of commercial powder. The performance of a single cell fabricated with the nanostructured LSCF6428 cathode increased by 112%, from 0.4 to 0.85 W cm^-2, at 700℃. Electrochemical impedance spectroscopy showed a considerable reduction in the area-specific resistance and activation energy from 133.5 to 61.5 kJ/mol, resulting in enhanced electrocatalytic activity toward ORR and overall cell performance.

• Journal of the Korean Chemical Society
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• v.41 no.8
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• pp.385-391
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• 1997

Diffusion Coefficient$(D_0)$ and electrode reaction rate Constant$(K_0)$ of Co$(dimethyl bipyridine)_3(ClO_4)_2$ were determined by cyclic voltammetry and chronoamperometry. It was also investigated that the effects of solvent, concentration, and scan rate, etc. on the diffusion coefficient and the temperature effect on the rate constant. The peak currents and diffusion coefficients were dcreased as increasing the viscosity of solvent. Diffusion coefficient was $5.54{\times}10^{-6 }cm^2/sec$ and the reaction rate constant was $2.39{\times}10^{-3 }/s$ at 25$^{\circ}C$. The thermodynamic parameters such as ${\Delta}G^{\neq},\;{\Delta}H^{\neq},\;and\;{\Delta}S$ were calculated from plotting the reaction rate constants versus the solution temperatures. This compound was shown the catalytic effect on the oxygen reduction that the reduction peak current of oxygen was greatly enhanced and the peak potential was shifted to +0.2 volt.

• Korean Journal of Materials Research
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• v.19 no.12
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• pp.667-673
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• 2009

The electrocatalytic characteristics of oxygen reduction reaction of the $PtxM_{(1-x)}$ (M = Co, Cu, Ni) supported on multi-walled carbon nanotubes (MWNTs) have been evaluated in a Polymer Electrolyte Membrane Fuel Cell (PEMFC). The $Pt_xM_{(1-x)}$/MWNTs catalysts with a Pt : M atomic ratio of about 3 : 1 were synthesized and applied to the cathode of PEMFC. The crystalline structure and morphology images of the $Pt_xM_{(1-x)}$ particles were characterized by X-ray diffraction and transmission electron microscopy, respectively. The results showed that the crystalline structure of the Pt alloy particles in Pt/MWNTs and $Pt_xM_{(1-x)}$/MWNTs catalysts are seen as FCC, and synthesized $Pt_xM_{(1-x)}$ crystals have lattice parameters smaller than the pure Pt crystal. According to the electrochemical surface area (ESA) calculated with cyclic voltammetry analysis, $Pt_{0.77}Co_{0.23}$/MWNTs catalyst has higher ESA than the other catalysts. The evaluation of a unit cell test using Pt/MWNTs or $Pt_xM_{(1-x)}$/MWNTs as the cathode catalysts demonstrated higher cell performance than did a commercial Pt/C catalyst. Among the MWNTs-supported Pt and $Pt_xM_{(1-x)}$ (M = Co, Cu, Ni) catalysts, the $Pt_{0.77}Co_{0.23}$/MWNTs shows the highest performance with the cathode catalyst of PEMFC because they had the largest ESA.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.151-158
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• 2022

Iron and nitrogen coordinated carbon catalyst (Fe-N-C) is the most promising non-precious metal catalyst (NPMC) studied to alternate the Pt-group oxygen reduction reaction (ORR) catalyst. In this work, Fe/N/C type catalysts are prepared by four different nitrogen precursors; N, N, N', N'-tetramethylethylenediamine (TMEDA), 1,2-ethylenediamine (EDA), m-dicyanobenzene (DCB), dicyandiamide (DCDA) which can chelate a transition metal; In addition, the catalysts conducted the pyrolysis process at four different temperatures of 700, 800, 900, 1000 ℃ to investigate the ORR activities depend on pyrolysis temperature and to find an appropriate temperature. The characterizations of catalysts were investigated by scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDS), X-ray diffraction (XRD), and element analysis (EA). The electrocatalytic activity was measured by ORR polarization, also the electron transfer number was calculated from the slope of the K-L plot. The FeNC-EDA-800 which were prepared at pyrolysis temperature of 800 ℃ with EDA showed better ORR activity than the other catalysts.

• Journal of Electrochemical Science and Technology
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• v.8 no.4
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• pp.274-281
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• 2017

This paper describes the simple fabrication of an electrode modified with electrochemically reduced graphene oxide (ERGO) for the simultaneous electrocatalytic detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA). ERGO was formed on a glassy carbon (GC) electrode by the reduction of graphene oxide (GO) using linear sweep voltammetry. The ERGO/GC electrode was formed by subjecting a GO solution ($1mg\;mL^{-1}$ in 0.25 M NaCl) to a linear scan from 0 V to -1.4 V at a scan rate of $20mVs^{-1}$. The ERGO/GC electrode was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy, contact angle measurements, electrochemical impedance spectroscopy, and cyclic voltammetry. The electrochemical performance of the ERGO/GC electrode with respect to the detection of DA, AA, and UA in 0.1 M PBS (pH 7.4) was investigated by differential pulse voltammetry (DPV) and amperometry. The ERGO/GC electrode exhibited three well-separated voltammetric peaks and increased oxidation currents during the DPV measurements, thus allowing for the simultaneous and individual detection of DA, AA, and UA. The detection limits for DA, AA, and UA were found to be 0.46, 77, and $0.31{\mu}M$ respectively, using the amperometric i-t curve technique, with the S/N ratio being 3.

• Journal of the Korean Electrochemical Society
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• v.12 no.2
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• pp.131-141
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• 2009

The conversion of carbon dioxide to value-added compounds has been attracted to solve the environmental problems due to the climate change caused by greenhouse effect in addition to recycle the abundant and renewable carbon source. For utilizing carbon dioxide to useful compounds, the development of catalysts and optimization of experimental conditions are indispensable since carbon dioxide is the most stable one among carbon compounds and the a certain amount of energy is required for the carbon dioxide conversion. The technologies developed for the electrochemical carbon dioxide conversion were reviewed in terms of electrocatalyst which can be electrode material, inorganic complex, and enzyme. This field should be developed further since no good catalyst having selectivity, efficiency, and stability all together.

• Journal of the Korean Ceramic Society
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• v.51 no.4
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• pp.278-282
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• 2014

Due to high ionic conductivity and favorable oxygen electrocatalysis, doped $Bi_2O_3$ systems are promising candidates as solid oxide fuel cell cathode materials. Recently, several researchers reported reasonably low cathode polarization resistance by adding electronically conducting materials such as (La,Sr)$MnO_3$ (LSM) or Ag to doped $Bi_2O_3$ compositions. Despite extensive research efforts toward maximizing cathode performance, however, the inherent catalytic activity and electrochemical reaction pathways of these promising materials remain largely unknown. Here, we prepare a symmetrical structure with identically sized $Y_{0.5}Bi_{1.5}O_3$/LSM composite electrodes on both sides of a YSZ electrolyte substrate. AC impedance spectroscopy (ACIS) measurements of electrochemical cells with varied cathode compositions reveal the important role of bismuth oxide phase for oxygen electrocatalysis. These observations aid in directing future research into the reaction pathways and the site-specific electrocatalytic activity as well as giving improved guidance for optimizing SOFC cathode structures with doped $Bi_2O_3$ compositions.

• Journal of Electrochemical Science and Technology
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• v.2 no.3
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• pp.163-167
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• 2011

Nicotinamide adenine dinucleotide, $NAD^+$, and its reduced form, NADH, play important roles as coenzymes in many enzymatic reactions. Electrochemical methods for $NAD^+$ or NADH detection or generation are drawn attention because it can provide the simple and low cost platform with fairly good sensitivity. In this study, the polysiloxane viologen polymer/diaphorase/hydrophilic polyurethane (PSV/DI/HPU) modified electrodes were simply prepared and demonstrated for bio-electrocatalytic $NAD^+$ sensors. The electrodes were co-immobilized with diaphorase and polysiloxane viologen polymer as an electron mediator followed by the overcoating with HPU membrane. The mixture of the enzyme and the electron mediator was well stabilized within HPU membrane and exhibited good reversibility and stability. The sensitivity was 0.2 $nA{\cdot}{\mu}M^{-1}$ and the detection limit was 28 ${\mu}M$ with a response time of 50 s ($t_{90%}$). The capability for NADH sensor was also observed on the PSV/DI/HPU electrode.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.93-94
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• 2006

In this research, the enhancement of electron-transfer activity of hemoglobin (Hb) in dodecanoic acid film was investigated for the first time. This type of composite film was made on glassy carbon electrode by casting method. Cyclic voltammetric result of the modified electrode displays a well defined redox peaks which was attributed to the direct electrochemical response of Rb. Our results illustrate that Rb exchange electrons directly with electrode and exhibits the characteristics of peroxidase. When we apply this modified electrode as a biosensor, it gives excellent performances in the electrocatalytic reduction of hydrogen peroxide ($H_{2}O_{2}$). Through the optimal conditions, the proposed biosensor shows the linear range for H2O2 determination was from $1{\times}10^{-5}$ to $1.25{\times}10^{-4}mol/L$ with a detection limit of $1{\times}10^{-7}mol/L$. The biosensor retained more than 90% of the initial response after 14 days.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.1013-1016
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• 2008

Nitrogen in the form of nitrate was electrochemically reduced with different cathode materials including Fe, Ni, Cu, and Zn. Zn cathode shows the greatest electrocatalytic activity on the transformation of nitrate ions into ammonia and the $NO_3^-$ removal efficiency has highest value at pH 8.5. Nitrogen in the form of nitrate was initially reduced into nitrite and sequentially, converted into nitrogen inside $NH_3$. Nitrogen in the form of ammonia was completely removed by the reaction with HOCl.