• Journal of Electrochemical Science and Technology
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• v.14 no.3
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• pp.243-251
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• 2023

Developing oxygen evolution reaction (OER) electrocatalysts is essential to accomplish viable CO₂ and water electrolysis. Herein, we report the fabrication and OER performance of Ni-foam (NF)-immobilized Ni₆ nanoclusters (NCs) (Ni₆/NF) prepared by a dip-coating process. The Ni₆/NF electrode exhibited a high current density of 500 mA/cm² for the OER at an overpotential as low as 0.39 V. Ni₆/NF exhibited high durability in an alkaline solution without corrosion. Electrokinetic studies revealed that OER can be easily initiated on Ni6 NC with fast electron-transfer rates. Finally, we demonstrated stable CO₂-to-CO electroreduction using an NC-based zero-gap CO₂ electrolyzer operated at a current density of 100 mA/cm² and a full-cell potential of 2.0 V for 12 h.

• Journal of Electrochemical Science and Technology
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• v.10 no.4
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• pp.416-423
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• 2019

A novel non-enzymatic oxalic acid (OA) sensor based on the platinum/carbon black-nickel-reduced graphene oxide (Pt/CBNi-rGO) nanocomposite is reported. The nanocomposites were prepared by the ethylene glycol reduction method. Their morphology and chemical composition were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The results clearly demonstrated the formation of the Pt/CB-Ni-rGO nanocomposite. The electrocatalytic activity of the Pt/CB-Ni-rGO electrode was investigated by cyclic voltammetry. It was determined that the appropriate amount of Pt enhanced the catalytic activity of Pt for oxalic acid electro-oxidation. Moreover, the modified electrode was determined to be highly selective for oxalic acid without interference from compounds commonly found in urine including uric acid and ascorbic acid. The chronoamperometric signal gave a wide linearity range of 20 μM-60 mM and the detection limit (3σ) was found to be 2.35 μM. The proposed method showed high selectivity, stability, and good reproducibility and could be used with micro-volumes of sample for the detection of oxalic acid. Finally, the oxalic acid content in artificial and control urine samples were successfully determined by our proposed electrode.

• Journal of the Korean Ceramic Society
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• v.47 no.1
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• pp.26-38
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• 2010

Degradation in Solid Oxide Fuel Cell performance can be ascribed to the following fundamental processes from the materials chemical point of view; that is, diffusion in solids and reaction with gaseous impurities. For SOFC materials, diffusion in solids is usually slow in operation temperatures $800\sim1000^{\circ}C$. Even at $800^{\circ}C$, however, a few processes are rapid enough to lead to some degradations; namely, Sr diffusion in doped ceria, cation diffusion in cathode materials, diffusion related with metal corrosion, and sintering of nickel anodes. For gaseous impurities, chromium containing vapors are important to know how the chemical stability of cathode materials is related with degradation of performance. For LSM as the most stable cathode among the perovskite-type cathodes, electrochemical reduction reaction of $CrO_3$(g) at the electrochemically active sites is crucial, whereas the rest of the cathodes have the $SrCrO_4$ formation at the point where cathodes meet with the gases, leading to rather complicated processes to the degradations, depending on the amount and distribution of reacted Cr component. These features can be easily generalized to other impurities in air or to the reaction of nickel anodes with gaseous impurities in anode atmosphere.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.89-92
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• 2007

Partail oxidation(POX) of n-butane was investigated in this research by employing ceria-promoted Ni/calcium hydroxyapatite catalysts ($Ce_xNi_{2.5}Ca_{10}(OH)_2(PO_4)_6$ ; x = $0.1{\sim}0.3$) which had recently been reported to exhibit good catalytic performance in POX of methane and propane. The experiments were carried out with changing ceria content, $O_2/n-C_4H_{10}$ ratio and temperature. As the $O_2/n-C_4H_{10}$ feed ratio increased up to 2.75, n-$C_4H_{10}$ conversion and $H_2$ yield increased and the selectivity of methane and other hydrocarbons decreased. But with $O_2/n-C_4H_{10}$ = 3.0, $n-C_4H_{10}$ conversion and $H_2$ yield decreased. This is considered due to that too much oxygen may inhibit the reduction of Ni or induce the oxidation of Ni, which results in poor catalytic activity. The optimum $O_2/n-C_4H_{10}$ ratio lay between 2.50 and 2.75. $Ce_{0.1}Ni_{2.5}Ca_{10}(OH)_2(PO_4)_6$ showed the highest $n-C_4H_{10}$ conversion and $H-2$ yield on the whole. In durability tests, higher hydrogen yield and better catalyst stability were obtained with the $O_2/n-C_4H_{10}$ ratio of 2.75 than with the ratio of 2.5.

• Journal of the Korean Chemical Society
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• v.36 no.1
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• pp.44-50
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• 1992

The ability to account for magnetic and spectra properties of complexes was investigated for the splitting of the degenerate d-orbitals and with nonaqueous solution by UV/vis-spectrophotometric method. The correlation of the magnetitude of 10Dq obtained from the spectra, the pairing energy, and the spin state of the complexes. The electrochemical behavior of complexes were investigated by the use of cyclic voltammetry in aprotic media. These reduction peak of $[(C_6H_5)3_P]_2Pd(II)(CH_3COO)_2$ and $[(C_6H_5)_3Pd]_2Pd(II)Cl_2$ were irreversible one-electron processes at peak $E_{pc1} = -1.32 V,\;E_{pc2} = -1.56 V$ and $E_{pc1} = -1.74 V,\;E_{pc2} = -1.88 V$ of these complexes vs. Ag/AgCl, but nickel complexes were not to be reducible.

• Journal of the Korea Institute of Building Construction
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• v.19 no.2
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• pp.105-112
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• 2019

Fine aggregate made of ferronickel slag(FNS) is similar to natural fine aggregates and is used in concrete structures both domestically and abroad, but its applications and research areas are limited. In this research, in order to expand the availability of FNS and improve the performance of cement mortar products, the applicability of FNS on dry mortar for floor was examined. Experimental results show that FNS improves flow of cement mortar because it has low absorption rate, spherical shape, and glassy surface. Also, the high stiffness of the FNS aggregate itself is considered to contribute to the improvement of cement mortar quality such as crack reduction by improving the compressive strength and shrinkage reducing. In addition, when FNS fine aggregate is applied, it was possible to secure the impact sound insulation performance equal to or higher than that of mortar using natural fine aggregate.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.28 no.4
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• pp.393-405
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• 2018

Objective: This study examines the types of hazardous factors in the working environment and the time-trend for their exposure levels over 10 years (2007 to 2016). Study Design and Method: The types of hazardous factors and exposure levels were drawn from the 19 measurement reports on the working environment over 10 years at a shock absorber manufacturing facility. Risk assessment of the types of factors and time-trend of exposure levels were evaluated using the factors and exposure levels. Results: A total of 34 hazardous factors were evaluated. The types were noise, 15 organic compounds, seven kinds of acid sand alkalis, eight kinds of heavy metals, and three other compounds. Special management materials used were nickel, hexavalent chrome, and sulfuric acid. Human carcinogens (1A) used were trichloroethylene, nickel, and sulfuric acid. There were six types of substances belonging to the IARC's 2B (body carcinogens) classification or higher, including, methyl isobutyl ketone, ethyl benzene, and trichloroethylene. No detection was found for 627 out of the 2065 total measurements in 19 exposure survey reports, representing 30.4%. Organic solvents, acid and alkali products, and heavy metals showed continuous low exposure concentrations. Noise, welding fumes, and the evaluation of mixed solvents show a gradual decrease in geometric mean and maximum over the time-trend of 10 years. Conclusions: In the case of a shock absorber manufacturing facility, the hazardous factors of noise and the evaluation of mixed solvents still indicate high concentrations exceeding the exposure limits and necessitate reduction studies. These two factors and welding fumes showed a continuous decrease in their ten-year tendency. Organic compounds, acids/alkalis, and heavy metals were managed smoothly in a work environment of continuous low concentrations.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.134-134
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• 2010

Fuel cell is a device that directly converts chemical energy in the form of a fuel into electrical energy by way of an electrochemical reaction. In the anode for a high temperature fuel cell, nickel or nickel alloy has been used in consideration of the cost, oxidation catalystic ability of hydrogen which is used as fuel, electron conductivity, and high temperature stability in reducing atmosphere. Most MCFC stacks currently operate at an average temperature of $650^{\circ}C$. There is some gains with decreased temperature in MCFC to diminish the electrolyte loss from evaporation and the material corrosion, which could improve the MCFC life. However, operating temperature has a strong related on a number of electrode reaction rates and ohmic losses. Baker et al. reported the effect of temperature (575 to $650^{\circ}C$). The rates of cell voltage loss were 1.4mV/$^{\circ}C$ for a reduction in temperature from 650 to $600^{\circ}C$, and 2.16mV/$^{\circ}C$ for a decrease from 600 to $575^{\circ}C$. The two major contributors responsible for the change in cell voltage with reducing operation temperature are the ohmic polarization and electrode polarization. It appears that in the temperature range of 550 to $650^{\circ}C$, about 1/3 of the total change in cell voltage with decreasing temperature is due to an increase in ohmic polarization, and the electrode polarization at the anode and cathode. In addition, the oxidation reaction of hydrogen on an ordinary nickel alloy anode in MCFC is generally considered to take place in the three phase zone, but anyway the area contributing to this reaction is limited. Therefore, in order to maintain a high performance of the fuel cell, it is necessary to keep this reaction responsible area as wide as possible, that is, it is needed to keep the porosity and specific surface area of the anode at a high level. In this study effective anodes are prepared for low temperature MCFC capable of enhancing the cell performance by using zirconium hydride at least in part of anode material.

• Journal of Powder Materials
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• v.13 no.5 s.58
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• pp.327-335
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• 2006

In the development of new hydrogen absorbing materials for a next generation of metal hydride electrodes for rechargeable batteries, metastable Mg-Ni-based compounds find currently special attention. Amor phous-nanocrystalline $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ alloys were produced by mechanical alloying and melt-spinning and characterized by means of XRD, TEM and DSC. On basis of mechanically alloyed Mg-Ni-Y powders, complex hydride electrodes were fabricated and their electrochemical behaviour in 6M KOH (pH=14,8) was investigated. The electrodes made from $Mg_{63}Ni_{30}Y_7$ powders, which were prepared under use of a SPEX shaker mill, with a major fraction of nanocrystalline phase reveal a higher electrochemical activity far hydrogen reduction and a higher maximum discharge capacity (247 mAh/g) than the electrodes from alloy powder with predominantly amorphous microstructure (216 mAh/g) obtained when using a Retsch planetary ball mill at low temperatures. Those discharge capacities are higher that those fur nanocrystalline $Mg_2Ni$ electrodes. However, the cyclic stability of those alloy powder electrodes was low. Therefore, fundamental stability studies were performed on $Mg_{63}Ni_{30}Y_7$ and $Mg_{50}Ni_{30}Y_{20}$ ribbon samples in the as-quenched state and after cathodic hydrogen charging by means of anodic and cathodic polarisation measurements. Gradual oxidation and dissolution of nickel governs the anodic behaviour before a passive state is attained. A stabilizing effect of higher fractions of yttrium in the alloy on the passivation was detected. During the cathodic hydrogen charging process the alloys exhibit a change in the surface state chemistry, i.e. an enrichment of nickel-species, causing preferential oxidation and dissolution during subsequent anodization. The effect of chemical pre-treatments in 1% HF and in $10\;mg/l\;YCl_3/1%\;H_2O_2$ solution on the surface degradation processes was investigated. A HF treatment can improve their anodic passivation behavior by inhibiting a preferential nickel oxidation-dissolution at low polarisation, whereas a $YCl_3/H_2O_2$ treatment has the opposite effect. Both pre-treatment methods lead to an enhancement of cathodically induced surface degradation processes.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.25 no.2
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• pp.134-145
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• 2015

Objectives: An objective of this study was to perform a risk assessment and social cost-benefit analysis for revising permissible exposure limits for seven substances: Nickel(Insoluble inorganic compounds), benzene, carbon disulfide, formaldehyde, cadmium(as compounds), trichloroethylene, touluene-2,4-diisocyanate. Materials and Methods: The research methods were divided into risk and hazard assessment and cost-benefit analysis. The risk and hazard assessment for the seven substances consists of four steps: An overview of GHS MSDS(1st), review of document of ACGIH's TLVs (2nd), comparison between international occupational exposure limits and domestic permissible exposure limits(3rd), and analysis of excess workplace and excess rate for occupational exposure limits based on previous work environment measurement data(4th). Total cost was estimated using cost of local exhaust ventilation, number of excess workplace and penalties for exceeding a permissible exposure limit. On the other hand, total benefit was calculated using the reduction rate of occupational disease, number of workplaces treating each substance and industrial accident compensation. Finally, the net benefit was calculated by subtracting total cost from total benefit. Results: All the substances investigated in this study were classified by CMR(Carcinogens, Mutagens or Reproductive toxicants) and their international occupational exposure limits were stricter than the domestic permissible exposure limits. As a result of excess rate analysis, trichloroethylene was the highest at 11%, whereas nickel was the lowest at 0.5%. The excess rates of all substances except for trichloroethylene were observed at less than 10%. Among the seven substances, the total cost was highest for trichloroethylene and lowest for carbon disulfide. The benefits for the seven substances were higher than costs estimated based on strengthening current permissible exposure limits. Thus, revising the permissible exposure limits of the seven substances was determined to be acceptable from a social perspective. Conclusions: The final revised permissible exposure limits suggested for the seven substances are as follows: $0.2mg/m^3$ for nickel, 0.5 ppm(TWA) and 2.5 ppm(STEL) for benzene, 1 ppm(TWA) for carbon disulfide, $0.01mg/m^3$(TWA) for cadmium, 10 ppm(TWA) and 25 ppm(STEL) for trichloroethylene, 0.3 ppm(TWA) for formaldehyde, and 0.005 ppm(TWA) and 0.02 ppm(STEL) for toluene diisocynate(isomers).