• Applied Chemistry for Engineering
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• v.23 no.5
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• pp.445-449
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• 2012

The activation process of the membrane-electrode assembly (MEA) is important for the mass production of the polymer electrolyte membrane fuel cell. The conventional activation process for the MEA requires excessive time and hydrogen gas and it might become the barrier for the commercialization of the fuel cell. The conventional activation process is based on hydrolysis of ion conducting membrane. In the study, we suggest the cyclic voltammetry (CV) technique as an on-line activation process and the CV activation process consists of two steps : 1) the humidification of the polymer electrolyte membrane and the electrode with 100% RH humidified nitrogen ($N_{2}$) gas, and 2) the removal step of the oxide layer on the surface of the Pt catalyst with CV cycling. The cycling reduces the activation time of the MEA by 2.5 h and use of hydrogen gas by 1/4.

• Korean Journal of Materials Research
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• v.31 no.9
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• pp.502-510
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• 2021

Hierarchically porous carbon materials with high nitrogen functionalities are extensively studied as high-performance supercapacitor electrode materials. In this study, nitrogen-doped porous carbon textile (N-PCT) with hierarchical pore structures is prepared as an electrode material for supercapacitors from a waste cotton T-shirt (WCT). Porous carbon textile (PCT) is first prepared from WCT by two-step heat treatment of stabilization and carbonization. The PCT is then nitrogen-doped with urea at various concentrations. The obtained N-PCT is found to have multi-modal pore structures with a high specific surface area of 1,299 m² g^-1 and large total pore volume of 1.01 cm³ g^-1. The N-PCT-based electrode shows excellent electrochemical performance in a 3-electrode system, such as a specific capacitance of 235 F g^-1 at 1 A g^-1, excellent cycling stability of 100 % at 5 A g^-1 after 1,000 cycles, and a power density of 2,500 W kg^-1 at an energy density of 3.593 Wh kg^-1. Thus, the prepared N-PCT can be used as an electrode material for supercapacitors.

• Korean Journal of Agricultural Science
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• v.42 no.4
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• pp.431-437
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• 2015

Recently, assessment of nitrogen balance has been required for environmental agriculture. Nutrient management using organic matters in farmlands has been strongly required as a means of extending resource-cycling agriculture and reduction of nitrogen balance. Organic matters-derived nutrients and soil-available nitrogen should be necessarily considered to manage nutrient balance in soil-plant system. In this study, we reviewed the amount of N supply according to types of organic matter such as livestock compost and green manure in arable land. In case of applied livestock compost in soil, nitrogen mineralization was influenced by nitrogen amount of livestock manure and mixed materials. And nitrogen mineralization of green manure in arable land was influenced by types of crop and return period of green manure because of change of C/N ratio. Also, nitrogen supply by organic matter in arable land can be changed by environmental factors such as temperature, moisture in soil. Therefore, nitrogen supply according to C/N ratio of organic matter and analysis method for estimation of soil nitrogen supply availability should be evaluated to set up the nutrient management model.

• The Korean Journal of Ecology
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• v.27 no.3
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• pp.155-159
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• 2004

In order to gain a better understanding of how forests participate in the cycling of carbon, effects of nitrogen addition on soil respiration were investigated on the oak forest in Kongju, Korea. Study site was divided into control, treatment f and treatment 2 plots, with 5 replication in each plot. In each replicate of treatment 1 and treatment 2 were fertilized with ammonium nitrate (NH$_4$NO$_3$), 30 g/$m^2$ and 60 g/$m^2$, respectively. Soil respiration, soil temperature, ammonium-N and nitrate-N were measured during the experimental period. Ammonium-N and nitrate-N in Ta were higher than those in control and T$_1$. Ammonium-N and nitrate-N in top-soil and sub-soil decreased sharply in August after bi9 rainfall in July in T$_1$ and T$_2$, however, those in control plot increased. Soil respiration in T$_2$ Plot showed consistently higher than those in control and T$_1$ until the end of July. However, soil respiration was similar among the control, T$_1$ and T$_2$ in mid-August and September The amount of Co$_2$ released from soil respiration in control, T$_1$ and T$_2$ in mid-August was 8.0$\pm$0.4, 9.3$\pm$0.6 and 10.2$\pm$0.5 $\mu$mol$^{-1}$ ㆍm$^{-2}$ ㆍs$^{-1}$ , respectively. However, those in control, T$_1$ and T$_2$in mid-August was 13.0$\pm$0.4, 13.5$\pm$0.5, 13.3$\pm$0.6 $\mu$mol$^{-1}$ ㆍm$^{-2}$ ㆍ$^{-1}$ , respectively. The results suggest that nitrogen addition in this oak forest has a positive effect on soil respiration.

• Electronic Materials Letters
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• v.14 no.6
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• pp.755-765
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• 2018

In situ nitrogen doped hard carbon nanotubes (NHCNT) were fabricated by pyrolyzing tubular nitrogen doped conjugated microporous polymer. KOH activated NHCNT (K-NHCNT) were also prepared to improve their porous structure. XRD, SEM, TEM, EDS, XPS, Raman spectra, $N_2$ adsorption-desorption, galvanostatic charging-discharge, cyclic voltammetry and EIS were used to characterize the structure and performance of NHCNT and K-NHCNT. XRD and Raman spectra reveal K-NHCNT own a more disorder carbon. SEM indicate that the diameters of K-NHCNT are smaller than that of NHCNT. TEM and EDS further indicate that K-NHCNT are hollow carbon nanotubes with nitrogen uniformly distributed. $N_2$ adsorption-desorption analysis reveals that K-NHCNT have an ultra high specific surface area of $1787.37m^2g^{-1}$, which is much larger than that of NHCNT ($531.98m^2g^{-1}$). K-NHCNT delivers a high reversible capacity of $918mAh\;g^{-1}$ at $0.6A\;g^{-1}$. Even after 350 times cycling, the capacity of K-NHCNT cycled after 350 cycles at $0.6A\;g^{-1}$ is still as high as $591.6mAh\;g^{-1}$. Such outstanding electrochemical performance of the K-NHCNT are clearly attributed by its superior characters, which have great advantages over those commercial available carbon nanotubes ($200-450mAh\;g^{-1}$) not only for its desired electrochemical performance but also for its easily and scaling-up preparation.

• Journal of Environmental Science International
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• v.30 no.3
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• pp.195-206
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• 2021

Contaminated marine sediment is a secondary pollution source in the coastal areas, which can result in increased nutrients concentrations in the overlying water. We analyzed the nutrients release characteristics into overlying water from sediments and the interaction among benthic circulation of nitrogen, phosphorus, iron, and sulfur were investigated in a preset sediment/water column. Profiles of pH, ORP, sulfur, iron, nitrogen, phosphorus pools were determined in the sediment and three different layers of overlying water. Variety types of sulfur in the sediments plays a significant role on nutrients transfer into overlying water. Dissimilatory nitrate reduction and various sulfur species interaction are predominantly embodied by the enhancing effects of sulfide on nitrogen reduction. Contaminant sediment take on high organic matter, which is decomposed by bacteria, as a result promote bacterial sulfate reduction and generate sulfide in the sediment. The sulfur and iron interactions had also influence on phosphorus cycling and released from sediment into overlying water may ensue over the dissolution of ferric iron intercede by iron-reducing bacteria. The nutrients release rate was calculated followed by release rate equation. The results showed that the sediments released large-scale quantity of ammonium nitrogen and phosphate, which are main inner source of overlying water pollution. A mechanical migration of key nutrients such as ammonia and inorganic phosphate was depicted numerically with Fick's diffusion law, which showed a fair agreement to most of the experimental data.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.1
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• pp.47-52
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• 2013

Despite the usefulness of nitrogen isotope tracer experiments in nitrogen cycling studies, there are not such many measurement data mainly due to the difficulties in analytical methods. Although Gardner et al. (1996) developed a relatively simple and accurate method that can measure ammonium isotope using HPLC and used it widely in various N dynamics studies, the technique was not adopted to other laboratories. An HPLC-RTS system using updated HPLC pumps that can perform the same measurements as that of Gardner et al. (1996) was built. The result of standard sample showed linear increase of RTS with the $^{15}N$ proportions. Centroid retention times calculated with Matlab$^{(R)}$ program enhanced the linearity of the response. In a sea water incubation experiment spiked with $^{15}NH_4{^+}$, the uptake and regeneration of ammonium could be separately estimated using the temporal change of $^{15}N/^{14}N$.

• Journal of Ecology and Environment
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• v.34 no.4
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• pp.333-345
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• 2011

Aquatic macrophytes, often also called hydrophytes, are key components of aquatic and wetland ecosystems. This review is to briefly summarizes various macrophyte classifications, and covers numerous aspects of macrophytes' role in wetland ecosystems, namely in nutrient cycling. The most widely accepted macrophyte classification differentiates between freely floating macrophytes and those attached to the substrate, with the attached, or rooted macrophytes further divided into three categories: floating-leaved, submerged and emergent. Biogeochemical processes in the water column and sediments are to a large extent influenced by the type of macrophytes. Macrophytes vary in their biomass production, capability to recycle nutrients, and impacts on the rhizosphere by release of oxygen and organic carbon, as well as their capability to serve as a conduit for methane. With increasing eutrophication, the species diversity of wetland macrophytes generally declines, and the speciose communities are being replaced by monoculture-forming strong competitors. A similar situation often happens with invasive species. The roles of macrophytes and sediment microorganisms in wetland ecosystems are closely connected and should be studied simultaneously rather than in isolation.

• Journal of Environmental Science International
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• v.29 no.3
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• pp.299-306
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• 2020

This study analyzed the changes in the concentrations of the pollutants of constructed treatment wetlands which come from the discharge water of a sewage treatment plant. According to the results of budgets in constructed wetlands, the net production of the organic carbon, nitrogen and phosphorus were 368 kgC/month, 306 kgN/month and -49 kgP/month, respectively. The high particle form of pollutants are mostly removed due to settlement and absorption when passing through wetlands, but because a low processing efficiency for pollutants was shown when sewage treatment plant wastewater flows in, there is a need for a water management system that can reduce the organic matter load through monitoring. The low removal efficiency of constructed wetlands were caused by both structural and operational problems. Therefore, to enable to play a role as a reduction facility of pollutants, an appropriate design and operation manuals for constructed wetlands is urgently needed.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.9 no.4
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• pp.179-195
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• 2004

The trophic state of the coastal waters of the southern part of Korea was assessed using biogeochemical data obtained from the National Marine Environmental Monitoring Program conducted by the National Fisheries Research and Development Institute for six years. The trophic state of different areas, analyzed by non-metric multi-dimensional scaling (MDS) analysis, could divide the areas into three groups. Masan Bay, with suboxic water masses and/or the highest concentrations of dissolved inorganic nitrogen and phosphorus occurred, was assessed as being in a hypertrophic state. Ulsan Bay, Onsan Bay, Busan and Jinhae Bay, located near strong point sources, were in a eutrophic state. Other areas, including Tongyong, Yosu, Mokpo and Jeju island, were evaluated as being in a mesotrophic state. During 1997 to 2002, the average values of excess nitrogen, which is the difference between the measured dissolved inorganic nitrogen (DIN) and the corrected DIN using the Redfield ratio, were positive at Ulsan, Onsan, and Busan, where there were inflows from polluted rivers. In contrast, those were negative values in Haengam Bay, Gwangyang Bay and nearby Yosu. This suggests that the limiting element for phytoplankton growth differed among sites. The time series data of excess nitrogen showed gradual decrease over time in the hypertrophic waters, but the opposite trend in the mesotrophic waters. This indicated that the ratio of nitrogen to phosphate varied according to the trophic state of the coastal waters. The enrichment of organic matter in sediment in eutrophic waters would disturb the normal pattern of biogeochemical cycling of nitrogen and phosphate. In order to assess the condition of the coastal environment, the benthic boundary layer should be considered.