• Bulletin of the Korean Chemical Society
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• v.21 no.6
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• pp.588-594
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• 2000

Structural changes of an iron phthalocyanine (FePC) monolayer induced by adsorption and externally applied potential on high area carbon surface have been investigated in situ by iron K-edge X-ray absorption fine structure (XAFS) in 0.5 M $H_2S0_4.$ Fine structures shown in the X-ray absorption near edge structure (XANES) for microcrystalline FePC decreased upon adsorption and further diminished under electrochemical conditions. Fe(II)PC(-2) showed a 1s ${\rightarrow}$ 4p transition as poorly resolved shoulder to the main absorption edge rather than a distinct peak and a weak 1s ${\rightarrow}$ 3d transition. The absorption edge position measured at half maximum was shifted from 7121.8 eV for Fe(lI)PC(-2) to 7124.8 eV for $[Fe(III)PC(-2)]^+$ as well as the 1s ${\rightarrow}$ 3d pre-edge peak being slightly enhanced. However, essentially no absorption edge shift was observed by the 1-electron reduction of Fe(Il)PC(-2), indicating that the species formed is $[Fe(II)PC(-3)]^-$. Structural parameters were obtained by analyzing extended X-ray absorption fine structure (EXAFS) oscillations with theoretical phases and amplitudes calculated from FEFF 6.01 using multiple-scattering theory. When applied to the powder FePC, the average iron-to-phthalocyanine nitrogen distance, d(Fe-$N_p$) and the coordination number were found to be 1.933 $\AA$ and 3.2, respectively, and these values are the same, within experimental error, as those reported ( $1.927\AA$ and 4). Virtually no structural changes were found upon adsorption except for the increased Debye-Wailer factor of $0.005\AA^2$ from $0.003\AA^2.$ Oxidation of Fe(II)PC(-2) to $[Fe(III)PC(-2)]^+$ yielded an increased d(Fe-Np) (1 $.98\AA)$ and Debye-Wailer factor $(0.005\AA^2).$ The formation of $[Fe(II)PC(-3)]^-$, however, produced a shorter d(Fe-$N_p$) of $1.91\AA$ the same as that of crystalline FePC within experimental error, and about the same DebyeWaller $factor(0.006\AA^2)$.

• Environmental Engineering Research
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• v.23 no.4
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• pp.383-389
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• 2018

Microbial fuel cell (MFC) is an innovative environmental and energy system that converts organic wastewater into electrical energy. For practical implementation of MFC as a wastewater treatment process, a number of limitations need to be overcome. Improving cathodic performance is one of major challenges, and introduction of a current collector can be an easy and practical solution. In this study, three types of current collectors made of stainless steel (SS) were tested in a single-chamber cubic MFC. The three current collectors had different contact areas to the cathode (P $1.0cm^2$; PC $4.3cm^2$; PM $6.5cm^2$) and increasing the contacting area enhanced the power and current generations and coulombic and energy recoveries by mainly decreasing cathodic charge transfer impedance. Application of the SS mesh to the cathode (PM) improved maximum power density, optimum current density and maximum current density by 8.8%, 3.6% and 6.7%, respectively, comparing with P of no SS mesh. The SS mesh decreased cathodic polarization resistance by up to 16%, and cathodic charge transfer impedance by up to 39%, possibly because the SS mesh enhanced electron transport and oxygen reduction reaction. However, application of the SS mesh had little effect on ohmic impedance.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.425-431
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• 2019

As rechargeable metal-air batteries will be ideal energy storage devices in the future, an active cathode electrocatalyst is required with bi-functionality on both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharge and charge, respectively. Here, a class of perovskite cathode catalyst with a micro-tubular structure has been developed by controlling bi-functionality from different Ru and Ni dopant ratios. A micro-tubular structure is achieved by the activated carbon fiber (ACF) templating method, which provides uniform size and shape. At the perovskite formula of $LaCrO_3$, the dual dopant system is successfully synthesized with a perfect incorporation into the single perovskite structure. The chemical oxidation states for each Ni and Ru also confirm the partial substitution to B-site of Cr without any changes in the major perovskite structure. From the electrochemical measurements, the micro-tubular feature reveals much more efficient catalytic activity on ORR and OER, comparing to the grain catalyst with same perovskite composition. By changing the Ru and Ni ratio, the $LaCr_{0.8}Ru_{0.1}Ni_{0.1}O_3$ micro-tubular catalyst exhibits great bi-functionality, especially on ORR, with low metal loading, which is comparable to the commercial catalyst of Pt and Ir. This advanced catalytic property on the micro-tubular structure and Ru/Ni synergy effect at the perovskite material may provide a new direction for the next-generation cathode catalyst in metal-air battery system.

• Korean Journal of Materials Research
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• v.32 no.1
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• pp.14-22
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• 2022

To improve light absorption ability in the visible light region and the efficiency of the charge transfer reaction, Pd nanoparticles decorated with reduced TiO₂ nanotube photocatalyst were synthesized. The reduced TiO₂ nanotube photocatalyst was fabricated by anodic oxidation of Ti plate, followed by an electrochemical reduction process using applied cathodic potential. For TiO₂ photocatalyst electrochemically reduced using an applied voltage of -1.3 V for 10 min, 38% of Ti⁴⁺ ions on TiO₂ surface were converted to Ti³⁺ ion. The formation of Ti³⁺ species leads to the decrease in the band gap energy, resulting in an increase in the light absorption ability in the visible range. To obtain better photocatalytic efficiency, Pd nanoparticles were decorated through photoreduction process on the surface of reduced TiO₂ nanotube photocatalyst (r10-TNT). The Pd nanoparticles decorated with reduced TiO₂ nanotube photocatalyst exhibited enhanced photocurrent response, and high efficiency and rate constant for aniline blue degradation; these were ascribed to the synergistic effect of the new electronic state of the TiO₂ band gap energy induced by formation of Ti³⁺ species on TiO₂, and by improvement of the charge transfer reaction.

• Korean Journal of Materials Research
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• v.32 no.11
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• pp.466-473
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• 2022

The effect of Cr and Mo contents on the hydrogen embrittlement of tempered martensitic steels was investigated in this study. After the steels with different Cr and Mo contents were austenitized at 820 ℃ for 90 min, they were tempered at 630 ℃ for 120 min. The steels were composed of fully tempered martensite with a lath-type microstructure, but the characteristics of the carbides were dependent on the Cr and Mo contents. As the Cr and Mo contents increased, the volume fraction of film-like cementite and prior austenite grain size decreased. After hydrogen was introduced into tensile specimens by electrochemical charging, a slow strain-rate test (SSRT) was conducted to investigate hydrogen embrittlement behavior. The SSRT results revealed that the steel with lower Cr or lower Mo content showed relatively poor hydrogen embrittlement resistance. The hydrogen embrittlement resistance of the tempered martensitic steels increased with increasing Mo content, because the reduction in the film-like cementite and prior austenite grain size plays an important role in improving hydrogen embrittlement resistance. The results indicate that controlling the Cr and Mo contents is essential to achieving a tempered martensitic steel with a combination of high strength and excellent hydrogen embrittlement resistance.

• Corrosion Science and Technology
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• v.22 no.3
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• pp.201-213
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• 2023

Corrosion management of an aircraft and its engine relies on rinsing and cleaning using tap water. Few studies have reported effects of tap water species on corrosion behaviors of structural materials. In this study, a series of experiments were conducted based on the design of experiment. Solutions with different levels of chloride and sulfate ions were prepared using a full factorial design. Two structural materials (aluminum alloy and steel) were used for an alternate immersion test. Weight loss was then measured. In addition, a silver specimen was utilized as a sensor for chloride deposition measurement. The silver specimen was examined using the electrochemical reduction method, XPS, and SEM-EDS. Surface analysis revealed that levels of chloride and sulfate ions were sufficient for the formation of silver chloride and silver surface. Statistical analysis of weight loss and chloride deposition rate showed significant differences in measured values. Concentration of chloride ions greatly affected corrosion behaviors of structural materials. Sulfate ion hindered the adsorption reaction. These results emphasize the importance of controlling ion concentration of tap water used for cleaning and rinsing an aircraft.

• Journal of the Korean Electrochemical Society
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• v.1 no.1
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• pp.1-7
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• 1998

For the purpose of finding new cathode materials for medium-temperature $(700\~800^{\circ}C)$ solid oxide fuel cells, $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$ are prepared, and their thermal stability and conductivity characteristics are investigated. Also, the cathodic activities are measured after the cathode layer being attached on CGO (cerium-gadolinium oxide) electrolyte disk. The X-ray analyses indicate that the materials prepared by calcining the citrate-gels at $800^{\circ}C$ have the orthorhombic perovskite structure without discernible impurities. The thermal stability of the undoped Co perovskite is so poor that it is decomposed to the individual binary oxide even at $1300^{\circ}C$. But the partially Fe-doped cobaltates exhibit a better thermal stability to retain their structural integrity up to $1400^{\circ}C$. The observation whereby both the undoped and Fe-doped cobaltates melt at ca. $1300^{\circ}C$ leads us to perform the electrode adhesion at <$1300^{\circ}C$. The cathodic activity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$, electrodes is superior to $La_{0.9}Sr_{0.1}MnO_3$, among the samples of $x=0.0\~0.5$, the x=0.2 cathode shows the best activity for the oxygen reduction reaction. It is likely that the Fe-doping provides a better thermal stability to the materials but in turn imparts an inferior cathodic activity, such that the optimum trade-off is made at x=0.2 between the two factors. The total electrical conductivity and ion conductivity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3$, are measured to be 51 S/cm and $6.0\times10^{-4}S/cm\;at\;800^{\circ}C$, respectively. The conductivity values illustrate that the materials are a mixed conductor and the reaction sites can be expanded to the overall electrode surface, thereby providing a better cathodic activity than $La_{0.9}Sr_{0.1}MnO_3$.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.157-162
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• 2014

In this research, we investigate electrical performance and electrochemical properties of carbon supported Pt (Pt/C) that is synthesized by polyol method. With the Polyol_Pt/C that is adopted for oxygen reduction reaction (ORR) as cathode of proton exchange membrane fuel cells (PEMFCs), their catalytic activity and ORR performance and electrical performance are estimated and compared with commercial Pt/C(Johnson Mattey) catalyst. Their electrochemically active surface (EAS) area are measured by cyclic voltammetry (CV), respectively. On the other hand, regarding ORR activity and electrical performance of the catalysts, (i) linear sweeping voltammetry by rotating disk electrode and (ii) PEMFC single cell tests are used. The CV measurement demonstrate EAS of Polyol_Pt/C is compared with commercial JM_Pt/C. In case of Polyol_Pt/C, its half-wave potential, kinetic current density are excellent. Based on data obtained by half-cell test, when PEMFC single cell tests are carried out, current density measured at 0.6V and maximum power density of the PEMFC single cell employing Polyol_Pt/C are better than those employing commercial Pt/C. Conclusively, Polyol_Pt/C synthesized by modified polyol process shows better ORR catalytic activity and PEMFC performance than other catalysts.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.250-254
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• 2002

Intergranular corrosion of austenitic stainless steels is a conventional and momentous problem during welding and high temperature use. One of the major reasons for such intergranular corrosion is so-called sensitization, i.e., chromium depletion due to chromium carbide precipitation at grain boundaries. Conventional methods for preventing sensitization of austenitic stainless steels include reduction of carbon content in the material, stabilization of carbon atoms as non-chromium carbides by the addition of titanium, niobium or zirconium, local solution-heat-treatment by laser beam, etc. These methods, however, are not without drawbacks. Recent grain boundary structure studies have demonstrated that grain boundary phenomena strongly depend on the crystallographic nature and atomic structure of the grain boundary, and that grain boundaries with coincidence site lattices are immune to intergranular corrosion. The concept of "grain boundary design and control", which involves a desirable grain boundary character distribution, has been developed as grain boundary engineering. The feasibility of grain boundary engineering has been demonstrated mainly by thermomechanical treatments. In the present study, a thermomechanical treatment was tried to improve the resistance to the sensitization by grain boundary engineering. A type 304 austenitic stainless steel was pre-strained and heat-treated, and then sensitized, varying the parameters (pre-strain, temperature, time, etc.) during the thermomechanical treatment. The grain boundary character distribution was examined by orientation imaging microscopy. The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of coincidence-site-lattice boundaries indicated a maximum at a small strain. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanically-treated specimen than in the base material. An excellent intergranular corrosion resistance was obtained by a small strain annealing at a relatively low temperature for long time. The optimum parameters created a uniform distribution of a high frequency of coincidence site lattice boundaries in the specimen where corrosive random boundaries were isolated. The results suggest that the thermomechanical treatment can introduce low energy segments in the grain boundary network by annealing twins and can arrest the percolation of intergranular corrosion from the surface.

• Journal of Environmental Science International
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• v.24 no.11
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• pp.1485-1491
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• 2015

There are two treatment processes that are currently applied to ships are the biological treatment process using the activated sludge and the electrochemical treatment. However, neither of them are able to remove both nitrogen and phosphorus due to their limited ability to remove organic matters, which are main causes of the red tide. This study was conducted to identify the characteristics of nitrogen removal factors from manure wastewater by replacing the final settling tank in SBR (Sequencing Batch Reactor) process and applying immersion type hollow fiber membrane. SBR process is known to have an advantage of the least land requirement in special environment such as in ship and the immersion type hollow fiber membrane is more stable in water quality change. As the result, the average in the cases of DO (Dissolved Oxygen) is 2.9(0. 6~3.9) mg/L which was determined to be the denitrifying microorganism activity in anaerobic conditions. The average in the cases of ORP (Oxidation Reduction Potential) is 98.4~237.3 mV which was determined to be the termination of nitrification since the inflection point was formed on the ORP curve due to decrease in the stirring treatment after the aeration, same as in the cases of DO. Little or no variation in the pH was determined to have positive effect on the nitrification. T-N (Total Nitrigen) removal efficiencies of the finally treated water were 71.4%, 72.3% and 66.5% in relatively average figures, thus was not a distinct prominence. In being applied in ships in the future, the operating conditions and structure improvements are deemed necessary since the MEPC (Marine Environment Protection Committee). 227(64) ship sewage nitrogen is less than the standard of 20 Qi/Qe mg/L or the removal rate of 70%.