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An inexpensive and general-purpose carbon fiber was prepared using coal tar pitch. In contrast to the solvent extraction process employing expensive solvents, a low-cost centrifugal separation method facilitated the reduction of loss due to the pitch purification and an overall yield increase. The coal tar pitch purified by centrifugation and subsequently co-carbonized with pyrolysis fuel oil improved in spinnability. Moreover, the resulting spinnable pitch had a softening point of 250 °C. The obtained carbon fibers were heat-treated at 1000 °C for 5 min, resulting in a tensile strength of approximately 1000 MPa and an average diameter of 9 μm. In this study, we present an effective method for obtaining low-cost general-purpose isotropic carbon fibers.

High-density carbon blocks have excellent mechanical, thermal, and electrical properties. In particular, these blocks are applied in various fields while maintaining excellent physical properties even in harsh environments. In this study, binderless coke manufactured under certain conditions was used to form green bodies (GBs) under various pressure conditions of 50 to 250 MPa, and the bodies were carbonized to form a high-density carbon block (CB). Then, the effect of the β-resin and oxygen functional groups of binderless coke on the mechanical properties of the high-density carbon block according to molding pressure was considered. When molding at a pressure of under 200 MPa, the ratio of O and C (O/C) has a greater effect, and the larger the O/C, the higher the mechanical properties. On the other hand, when molding at a high pressure of 250 MPa, the β-resin content has a greater effect and steadily increases when the β-resin content is low and when the mechanical properties are sufficiently reduced. In particular, in the case of CB-N7A3–250, which has the highest β-resin content of 3.7 wt%, the density was 1.79 g/cm3, the flexural strength was 106 MPa, and the shore hardness was 99 HSD.

High-density carbon blocks have excellent mechanical, thermal, and electrical properties. In particular, these blocks are applied in various fields while maintaining excellent physical properties even in harsh environments. In this study, binderless coke manufactured under certain conditions was used to form green bodies (GBs) under various pressure conditions of 50 to 250 MPa, and the bodies were carbonized to form a high-density carbon block (CB). Then, the effect of the β-resin and oxygen functional groups of binderless coke on the mechanical properties of the high-density carbon block according to molding pressure was considered. When molding at a pressure of under 200 MPa, the ratio of O and C (O/C) has a greater effect, and the larger the O/C, the higher the mechanical properties. On the other hand, when molding at a high pressure of 250 MPa, the β-resin content has a greater effect and steadily increases when the β-resin content is low and when the mechanical properties are sufficiently reduced. In particular, in the case of CB-N7A3–250, which has the highest β-resin content of 3.7 wt%, the density was 1.79 g/cm3, the flexural strength was 106 MPa, and the shore hardness was 99 HSD.

Coal extract produced by solvent extraction of low-rank coal is not suitable for spinning due to its high oxygen content. In order to effectively overcome this limitation, soft pitch was produced by co-carbonization of coal extract and petroleum residues. The decrease in oxygen content was confirmed by physical property analyses of the soft pitches blended at different mixing ratios. A bridge/hydroaromatic structure of the soft pitch was observed during the co-carbonization. The produced spinnable pitch had a high spinnability and a softening point of 230 °C. This spinnable pitch, prepared by solvent extraction of low-rank coal, showed excellent spinnability and was heat-treated at 800 °C for 5 min to produce isotropic carbon fibers having diameters of 7 μm and a tensile strength of 1189 MPa. Thus, the co-carbonization of coal extract and petroleum residue is an effective method for the production of inexpensive spinnable pitch for isotropic carbon-fiber manufacture.

Mesoporous activated carbon was prepared from needle coke via two-stage steam activation process under high temperature. Two-stage steam activation method involves three main steps: 1st steam activation to generate mesopores and macropores above 2 nm; coating and impregnation of substances with a low molecular weight into the pores; 2nd steam activation to expand the pore size and micropore volume. The needle coke was characterized by elemental analysis, polarized light microscopy, and thermogravimetric analysis, and the porosity structure was analyzed by the Brunauer-Emmett-Teller (BET) method, the t-plot method, the Barrett-Joyner-Halenda (BJH) method, and the scanning electron microscopy (SEM). The maximum specific surface area and mesopore volume ratio of activated carbon manufactured by two-stage steam activation method was 1134 m2/g and 78%, respectively. The mesopore volume and average pore diameter increased as more coating and impregnation agents were added.

High-density carbon blocks are much lighter than metals and have excellent mechanical properties and are one of the materials garnering attention to replace existing metal parts. In this study, a binderless coke was produced by changing the flow rates of nitrogen and air as a carrier gas during heat treatment of coal tar pitch and using this, a green body was formed at 150 MPa and carbonized to produce a high-density carbon block. We express the binderless coke produced in this way by N10A0, N7A3, N5A5, N3A7, N0A10 according to the ratio of nitrogen and air, and in the case of carbon block, we have added CB in front of it. We then considered the effect of oxygen content in the binderless cokes on the optical, chemical, and mechanical properties. It was observed that the produced binderless cokes develop into a dense mosaic structure with a small particle size as the air flow rate increased. To survey the change in oxygen content of the produced binderless coke, O1s and C1s regions were measured using X-ray photoelectric spectroscopy (XPS), and O1s/C1s was calculated. The O1s/C1s ratio steadily increased as the air flow rate increased, and in the case of N0A10, it increased about twice as much as that of N10A0 to 11.20%. β-resin has a very large effect on the mechanical strength of the carbon block in addition to air in the pitch. And in the case of CB-N0A10, it shows the best mechanical strength with a density of 1.72 g/cm3, bending strength of 87 MPa, and shore hardness of 93 HSD.

In this study, surface oxidation of petroleum pitch was performed to enhance the thermal stability, specific surface area, and mesopore ratio of activated carbon. The oxygen uptake of the pitch by surface oxidation has a strong influence on the formation of the specific surface area and pore size of activated carbon. It was confirmed that the oxygen uptake from the surface to the inner side of the surface oxidized pitch was the highest at the temperature of 330 °C (IP330-AC), with a mesopore ratio of 63.35% and specific surface area of 1811 m2 g−1. The oxygen content of the surface oxidized pitch increased proportionately with the mesopore ratio in activated carbon. The specific surface area and mesopore ratio of IP330-AC were respectively 163% and 487% higher than those of petroleum-based commercial activated carbon (A-BAC), and 102% and 491% higher than those of coconut-based commercial activated carbon (P60).

We report on hierarchical porous carbons derived from rice husk (RH) through the combination of carbonization and two post-processing methods that were used as the electrode material for capacitive deionization (CDI). The carbonized RHs, consisting of carbon/inorganic composite materials, were used to control the hierarchical porous structures, depending on the existence of silicon domains. Hierarchical porous carbons, denoted as RHC-A and comprising dominant micropores and small fraction mesopores, were synthesized by steam activation to react with the carbon fraction in the presence of silicon components. On the other hand, mesopore-dominant porous carbons, denoted as RHC-H, were obtained selectively by removing silicon components acting as a natural template from carbonized RH by hydrofluoric acid treatment. In order to understand the effect of the pore structure on CDI performance, two RH-derived porous carbons were compared in terms of their performances in water purification. In the batch-mode experiment, the microporous activated carbon (AC) exhibited the highest maximum electrosorption capacity of 17.7 mg g−1, which was mainly determined by the specific surface area. Under the same conditions, however, the RHC-A was verified to have enhanced kinetic performance according to the Langmuir isotherm and the pseudo-second-order kinetic model. Here, the hierarchical porous structures with continuous mesopores interconnected by micropores contributed to the enhanced kinetic performance of the RHC-A, facilitating effective ion transport and adsorption. In a continuous mode similar to the practical CDI, the kinetically improved RHC-A achieved a higher salt-removal capacity of 8.09 mg g−1 than the 5.40 mg g−1 and 1.63 mg g−1 of the commercial activated carbon and RHC-H, respectively, at 1.5 V and with a feed rate of 20 mL min−1 in 100 ppm of NaCl solution.

This study examined the relationships among muscle mass and obesity, metabolic syndrome, and physical activity in elderly women. The 4th-5th (2008 to 2011) Korean national health and nutrition examination survey data were analyzed using the SPSS 23.0 package program. The results showed that sarcopenic obese group had significantly higher metabolic syndrome parameters, such as waist circumference, diastolic blood pressure, fasting blood glucose, and triacylglyceride, compared to non-sarcopenic non-obese group. The sarcopenic non-obese group showed a 2 times higher risk of metabolic syndrome, and the non-sarcopenic obese and sarcopenic obese groups showed a 6 times higher risk of metabolic syndrome than the non-sarcopenic non-obese group. The non-sarcopenic groups showed higher amounts of high intensity, moderate intensity, and total physical activities than the sarcopenic groups. In addition, non-sarcopenic groups participated more in high-intensity exercise but less in flexibility exercise than the sarcopenic groups. Furthermore, the participants had a carbohydrate dependent diet with a low intake of vitamins and mineral. These results suggest that the elderly women should consistently participate in physical activities and eat a balanced diet to decrease the risk of metabolic syndrome by maintaining their body weight and muscle mass to normal levels. Therefore, to reduce metabolic syndrome in elderly women, it is important develop and promote exercise and nutritional education programs to reduce metabolic syndrome in elderly women.

The impurities in methanol fuel, which is used for direct methanol fuel cells (DMFCs), greatly affect the performance of membrane electrode assemblies (MEAs). The effect of ethanol in methanol fuel on the MEA performance was evaluated using the five different kinds of methanol fuels for reagent grade and industrial use. The impurities in the different kinds of methanol fuels that affected the performance of the MEAs were mainly ethanol evident by the analysis of the methanol fuels. Thus, this study suggests that the ethanol concentration in methanol fuels should be limited to achieve a higher performance of the MEAs.

This study increased the surface area of a membrane by forming patterns on the Nafion resin membrane using a stainless steel mesh to enhance the performance of a direct methanol fuel cell (DMFC) because the triple-phase boundary is extended. Nafion resin (F-form ( SO3F)) was used which has melt-moldability to form a stable surface pattern and to directly coat the catalyst layer by the bar-coating method. The performance (polarization and power density curves) and the resistance of the membrane-electrode assembly (MEA) were analyzed with a single cell and an impedance analyzer. The surface area of the patterned membranes was increased 1.99, 2.10, and 2.12 times compared to the flat membrane, and the power density also increased 12.9, 18.6, and 24.2% at 0.4 V, respectively. The performance of the MEA with the patterned membrane had a lower concentration polarization than that of the MEA with the flat membrane. The performance of the MEAs with the patterned membranes had a greater impact on the cathode side of the membrane than on the anode side. The results of these experiments offer a solution to the problem of a low performance of MEA, which is one of the disadvantages of DMFCs.

Tubular type carbon nanofibers (TCNFs) are prepared and used as a catalyst support material for a cathode electrode of low temperature fuel cells through structural modification. The pristine TCNF is treated by graphitization and makes partially torn-tube shape through the surface expansion by rapid thermal treatment of the oxidized graphitized TCNF. Physical properties of the TCNF group are examined, and it is confirmed that the unique ripped texture along fiber axis with graphitic structure is obtained by the surface expansion. Platinum catalysts supported on these TCNF group are prepared and evaluated. Electrochemical properties are examined via cyclic voltammograms and polarization curves for oxygen reduction reaction activity. The platinum catalyst on the surface expanded TCNF has the enhanced activity at initial and the stable performance even after accelerated durability test due to their unique structure.

The carbonization and graphitization of carbon/carbon (C/C) composites prepared from mesocarbon microbeads (MCMB) and chopped carbon fiber (CCF) have been studied with a wide range of temperatures, CCF contents and MCMB sizes. Three different sizes of MCMB were prepared with coal tar pitch at three temperatures, 420, 430 and 440 °C, and identified as about 12.8, 16.0 and 20.1 µm, respectively. Each size of MCMB was mixed with CCFs at ratios of 2, 4, 6 and 8 wt. % and formed into block shape. After carbonization at 1200 °C, carbonized C/C blocks (CCBs) were graphitized at 2000, 2400 and 2800 °C. The CCB prepared with CCF content of 2 wt. % and an MCMB size of 16.0 µm exhibited the highest flexural strength of about 151 MPa. The graphitized C/C block (GCB) with CCF content of 2 wt. %, which was graphitized at 2000 °C showed the highest flexural strength of about 159 MPa.

High-strength and high-density carbonized carbon blocks from self-sintering coke were manufactured using coal tar and two-stage heat treatments (1st and 2nd stage treatments). First, the molecular weight distribution of the refined coal tar was controlled through a pressured heat treatment (1st stage treatment). Second, the 1st stage heat-treated coal tar (1S-CT) was treated using a delayed coking system (2nd stage treatment) to become the self-sintering coke. Finally, carbon blocks were molded from 2nd stage heat-treated coke (2S-C) and carbonized at 1200 °C for 1 h. Through rapid decomposition of the high molecular weight components in the coal tar at 360 °C in the 1st stage treatment, the molecular weight distribution of coal tar was confirmed to be controllable by the 1st stage treatment. Swelling during carbonization was observed in carbon blocks manufactured from 2S-C containing more than 15 wt% of volatile matter from 150–450 °C. The optimum conditions of the two-stage heat treatments were confirmed to be 300 °C for 3 h and 500 °C for 1 h. The highest density and flexural strength of the carbonized carbon blocks manufactured from 2S-C were 1.46 g/cm3 and 69.2 MPa, respectively.

Physical and electrochemical qualities were analyzed after KOH activation of a direct methanol fuel cell using needle coke as anode supporter. The results of research on support loaded with platinum-ruthenium suggest that an activated KOH needle coke container has the lowest onset potential and the highest degree of catalyst activity among all commercial catalysts. Through an analysis of the CO stripping voltammetry, we found that KOH activated catalysis showed a 21% higher electrochemical active surface area (ECSA), with a value of 31.37 m2/g, than the ECSA of deactivated catalyst (25.82 m2/g). The latter figure was 15% higher than the value of one specific commercial catalyst (TEC86E86).

In the present study, surface texture features and chemical properties of two types of cokes, made from coal tar by either 1-stage heat treatment or 2-stage heat treatment, were researched. The relationship between surface texture characteristics and the chemical properties was identified through molecular weight distribution, insolubility of coal tar, weight loss with temperature increase, coking yield, and polarized light microscope analysis. Rapidly cleared anisotropy texture in cokes was observed in accordance with the coking temperature rise. Quinoline insolubility and toluene insolubility of coal tar increased with a corresponding increases in coking temperature. In particular, the cokes produced by the 2-stage heat treatment (2S-C) showed surface structure of needle cokes at a temperature approximately 50°C lower than the 1-stage heat treatment (1S-C). Additionally, the coking yield of 2S-C increased by approximately 14% in comparison with 1S-C.

A membrane-assisted capacitive deionization (CDI) system was developed for the purification of water containing sodium chloride using activated carbon fibers (ACFs) as capacitor electrode materials. The ACFs have different degrees of activation with different surface areas and pore size distributions. Their desalination performance for sodium or chloride ions was investigated. Results indicate that the salt removal efficiency and surface area-normalized electrosorption capacity for each ion depend on the surface area, pore depth and the match between the pore sizes of the ACFs and the radius of each hydrated ion. A high surface area and shallow pores favor the salt removal efficiency and a high surface area-normalized electrosorption capacity. The ACF with a median pore size of 0.69 nm performs best for sodium ion removal and those with median pore sizes of 1.09 and 1.52 nm are best for chloride ion removal, which could be ascribed to the fact that the radius of a hydrated sodium ion (0.66 nm) is smaller than that of a hydrated chloride ion (0.72 nm). An asymmetric electrode material configuration is needed to optimize both the anion and cation adsorption in the membrane-assisted CDI system.

Spinnable pitches and carbon fibers were successfully prepared from petroleum or coal pyrolysis residues. After pyrolysis fuel oil (PFO), slurry oil, and coal tar were simply filtered to eliminate the solid impurities, the characteristics of the raw materials were evaluated by elemental analysis, 13C nuclear magnetic resonance spectrometer, matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOF-MS), and so on. Spinnable pitches were prepared for melt-spinning carbon fiber through a simple distillation under strong nitrogen flow, and further vacuum distillation to obtain a high softening point. Carbon fibers were produced from the above pitches by single-hole melt spinning and additional heat treatment, for oxidization and carbonization. Even though spinnable pitches and carbon fibers were processed under the same conditions, the melt-spinning and properties of the carbon fiber were different depending on the raw materials. A fine carbon fiber could not be prepared from slurry oil, and the different diameter carbon fibers were produced from the PFO and coal tar pitch. These results seem to be closely correlated with the initial characteristics of the raw materials, under this simple processing condition.

Nitrogen-doped carbon nanofibers (N-CNFs) with different nitrogen contents were synthesized from vaporized acetonitrile as a simultaneous carbon and nitrogen source via the chemical vapor deposition method. N-CNF synthesis was conducted at 640 °C for 2 h, and the ratio of nitrogen and hydrogen mixture as reactant gas was adjusted to control the nitrogen content in the N-CNFs. The amount of hydrogen in the reactant gas was varied in the range from 0 to 40 mL min − 1 . The physical and electrochemical properties of the N-CNFs were characterized. The content of introduced nitrogen decreased with the ratio of supplied hydrogen, as opposed to the growth yield of the N-CNFs. Additionally, the nitrogen content and chemical states of the N-CNFs were examined and compared to reveal their correlations with the electrochemical behavior. The N-CNFs were found to have a noticeable electrochemical behavior such as capacitance and oxygen reduction reaction activity that was determined by the total nitrogen contents, especially those of pyridinic-nitrogen.

Fuel cells have received worldwide attention as a next-generation renewable energy technology. However, catalyst cost and durability are the main issue hampering the commercialization of fuel cells. Many studies have focused on the physicochemical properties of the carbon support to improve the catalyst’s properties. Mesoporous carbons are suitable candidates because of their appropriate structural characteristics, including high surface area, large pore size, and regularly interconnected mesopores that permit efficient diffusion of the reactants and by-products. In this study, supports made from chestnut-like carbon consisting of platelet carbon nanofibers were fabricated by selective catalytic gasification of activated carbon. Pt/C catalysts were synthesized from these support structures using the impregnation method. Catalyst performance and characteristics were investigated by N2 adsorption/desorption isotherms, X-ray diffractions, and the rotating disk electrode technique for the oxygen reduction reaction.

A CMOS common-gate low noise amplifier (LNA) with dual cross coupled capacitive feedback is proposed. The first feedback loop is designed for transcoductance $({\rm g}_{\rm m})$ boosting which is widely known as the cross-coupled common gate (CCCG) topology. The other feedback loop is voltage-current feedback by cross-coupling between the drain node and the source node in the common gate topology. In particular, the first feedback loop is able to reduce the amplification of a second-order signal while it boosts the transconductance of a fundamental signal thus, it can reduce the second order harmonic feedback effect to the input-referred third-order intercept point (IIP3) which is one of the major bottlenecks of linearity enhancement using feedback. As the first feedback removes second-order harmonic distortion, the second feedback successfully enhances IIP3. The proposed LNA achieves excellent performance with low power consumption. The LNA is implemented with a 0.13 $\mu{\rm m}$ CMOS process and measured. The measurement results demonstrate a gain of 18 dB, a noise figure (NF) of 1.94 dB, an IIP3 of 9.06 dBm, an input matching (S11)/output matching (S22) of less than $-$ 10 dB at 900 MHz, and a power consumption of 2.4 mA with 1.2 V supply voltage.

The crystalline and microstructural transformations of two laboratory ashes and their quenched slags (from a gasifier) with similar chemical compositions [one with high silicon dioxide (SiO2) concentrations and the other with high aluminum oxide (Al2O3) concentrations] were systematically characterized using X-ray diffraction, multinuclear solid-state nuclear magnetic resonance, and a high-temperature viscometer. The results show that the content of SiO2 and Al2O3 in ash has significant influence on the crystal types and size of cristobalite clusters in the liquid slag during heat treatment. Consequently, the formed cristobalite clusters were crucial to the viscosities and rheological properties of liquid slags.

Chestnut-like structured carbon comprising platelet carbon nanofibers(PCNFs) grown on selective catalytic gasified activated carbon have shown promising results as application for electrodes. The Ni–Fe catalyst is generally prepared on the activated carbon by immersion process followed by a reduction of temperature at 350–450 °C. The growth of PCNFs then continue on for a predetermined time through the thermal decomposition of ethylene at 600 °C. The resulting structure, which comprises an intimately connected activated carbon and PCNFs, is shown to offer performance advantages with its specific surface properties and electrochemical characterizations. The mesoporous volume is 0.7564 cm 3 /g higher than that with purely activated carbon (0.1220 cm 3 /g). The specific surface area is 2401 m 2 /g higher than those with purely activated carbon (1800 m 2 /g). The specific capacitance is 136.86 F/cm 3 higher than those with P-60.

The effect of membrane thickness on the performance degradation of DMFCs was investigated during freeze-thaw cycling across temperatures ranging from −32 °C to 60 °C. Three cells with Nafion membranes of varying thickness were prepared: Nafion 112, Nafion 115 and Nafion 117. Performance degradation was evaluated by comparing the changes to electrode polarization, electrochemical impedance and cyclic voltammetry over a range of freeze-thaw cycles. It was determined that freeze-thaw cycling affected the performance of the three membrane electrode assemblies (MEA). A cell with a Nafion 112 membrane showed a more significant increase in cathode overpotential than cells with either a Nafion 115 or Nafion 117 membrane. The charge transfer resistance of the cell with a thin membrane was more affected by freeze-thaw cycles than the cells with thicker membranes. All three cells showed a significant decrease in ECSA after freeze-thaw cycles. Freeze-thaw cycles damaged the triple phase boundary region and decreased the ECSA of cells with thinner membranes, which cause rapid performance degradation. The use of thick membranes in MEAs was determined to be the effective method for reducing performance degradation during freeze-thaw cycling.

Tungsten carbides (WC) nanoparticles on platelet type-carbon nanofibers (p-CNFs) catalysts have been synthesized for alkaline direct ethanol fuel cells (ADEFC). Physical properties of WC/CNFs samples with various WC contents are analyzed by transmission electron microscope (TEM), thermal gravimetric analysis (TGA) and nitrogen isotherm (BET). The WC/CNFs catalysts showed an improved kinetics for the ethanol oxidation than p-CNFs did. It indicates that the significant increase in the catalytic activity for ethanol oxidation on WC/CNFs than p-CNFs did due to the synergistic structural effect between WC nanoparticles and the p-CNFs supports. WC/CNFs also showed good performances in ADEFC single cells. The maximum current density of P4W3 and P4W4 was 9.0 and 4.4 mA cm −2 , respectively. These catalysts can be used as the ethanol oxidation in direct ethanol fuel cells in alkaline media.

Proton exchange membranes were prepared by γ-ray radiation-induced grafting onto ETFE films, crosslinking with styrene/divinylbenzene (DVB) mixtures and a subsequent sulfonation. Effects of the DVB content on the membrane properties such as ion exchange capacity (IEC), proton conductivity, and methanol permeability were investigated. Membrane-electrode assemblies (MEA) containing the prepared membranes were fabricated for direct methanol fuel cells (DMFC), and the MEA performance was examined in operation with various concentrations of methanol. Durability of the MEAs was investigated using a 3 M methanol solution for 1000 h, and the polarization curves and impedance spectra were measured. Physicochemical properties of catalysts and membrane before and after the long-term operation were analyzed by TEM, XRD, IEC, and proton conductivity. Performance and durability of the selected membranes were also confirmed in the operation of a 6-cell stack with 3 M methanol solution.

This paper reports the effect of adding reduced graphene oxide (RGO) as a conductive material to the composition of an electrode for capacitive deionization (CDI), a process to remove salt from water using ionic adsorption and desorption driven by external applied voltage. RGO can be synthesized in an inexpensive way by the reduction and exfoliation of GO, and removing the oxygen-containing groups and recovering a conjugated structure. GO powder can be obtained from the modification of Hummers method and reduced into RGO using a thermal method. The physical and electrochemical characteristics of RGO material were evaluated and its desalination performance was tested with a CDI unit cell with a potentiostat and conductivity meter, by varying the applied voltage and feed rate of the salt solution. The performance of RGO was compared to graphite as a conductive material in a CDI electrode. The result showed RGO can increase the capacitance, reduce the equivalent series resistance, and improve the electrosorption capacity of CDI electrode.

The catalytic conversion of alkali metal carbonate (K2CO3) catalyst supported on perovskite oxide was carefully examined as an effective catalyst for low-temperature catalytic gasification of lignite. It showed much higher activity than K2CO3 alone as well as K2CO3 supported on γ-alumina under gasification conditions below 800 °C. Furthermore, catalyzed syngas had higher H2 and lower CO2 ratios than non-catalyzed syngas. Promisingly, there was also much less tar formation, less than 50 wt.% compared to non-catalyzed gasification. Also, less loss of K2CO3 and no coke formation on the catalyst surface were confirmed, comparing to the catalytic gasification with K2CO3 supported on γ-alumina.

Catalytic recovery after repeated uses of unsupported K2CO3 or K2CO3 supported on 3 kinds of perovskites (LaMn0.8Cu0.2O3, LaMn0.8Cu0.2O3/γ-alumina, and La0.9K0.1MnO3) was investigated during steam gasification of an Indonesian lignite (Adaro) at 700 °C. Perovskite supports effectively retained K2CO3 and maintained higher catalytic activity than K2CO3 alone. The supported catalysts were recovered from the ash after gasification based on their size and ferromagnetism. Quartz and alumina accumulation on the catalyst poisoned the ash due to reactivity with potassium. Catalytic activity as high as 90% carbon conversion was maintained up to seven cycles, and separation from the ash after gasification regenerated the activity.

Alumina-supported K2CO3–LaMn0.8Cu0.2O3 was investigated for the catalytic conversion of tar, produced from lignite, into syngas under inert and steam-reforming conditions. A double-bubble fluidized bed reactor system, equipped with a micro gas chromatograph and a collecting system to analyze permanent gases and condensable species, was developed to screen the catalytic conversion of tar components below 700 °C. The redox properties of catalysts, estimated by hydrogen temperature programmed reduction analyses, were correlated with their catalytic performance in tar conversion. The synthesized catalyst effectively converted tars into hydrogen-rich syngas and also improved tar reforming by inhibiting coke deposition.

In this study, we develop a one-dimensional (1-D), two-phase, transient-thermal DMFC model to investigate the effect of methanol concentration fluctuation that usually occurs in active-type direct methanol fuel cell (DMFC) systems. 1-D transient simulations are conducted and time-dependent behaviors of DMFCs are analyzed under various DMFC operating conditions such as anode/cathode stoichiometry, cell temperature, and cathode inlet humidification. The simulation results indicate that the effect of methanol concentration fluctuation on DMFC performance can be mitigated by proper control of anode/cathode stoichiometry, providing a guideline to optimize operating conditions of active DMFC systems.

Poly(tetrafluoroethylene- co -perfluoropropyl vinyl ether)-graft-poly(styrene sulfonic acid) (PFA- g -PSSA) membranes were prepared by γ -ray radiation-induced grafting of styrene onto 50 μm PFA films and a subsequent sulfonation. The properties of the PFA- g -PSSA membranes such as ion exchange capacity, water uptake, proton conductivity, and methanol permeability were evaluated and compared with commercial Nafion 115 membrane. The characteristic properties and direct methanol fuel cell (DMFC) performances with PFA- g -PSSA membrane were better than that with the Nafion 115 membrane. The power density of the single cell with PFA-PSSA30, PFA-PSSA50, PFA-PSSA80 membranes having different degree of grafting (DOG), and Nafion 115 membranes was 113, 123, 118, and 111 mW cm −2 at 0.4 V, respectively. To study the long-term durability of the prepared membrane electrode assembly (MEA) with a PFA-PSSA50 membrane, the single cell was tested for 2066 h in a galvanostatic mode under a constant load 150 mA cm −2 and at a temperature of 60 °C. The performance loss of the MEA after 2066 h operation was about 26.8%. Before and after the long-term performance test, the degradation of MEA with PFA- g -PSSA membrane was investigated by polarization curve technique, electrochemical impedance spectroscopy, TEM, X-ray diffraction, and ion exchange capacity.

Effects of a CrN/Cr coating layer on the durability of metal bipolar plates (stainless steel (STS) 430) are investigated in direct methanol fuel cells (DMFCs) with a fuel recirculation system, since under fuel recirculation the metal bipolar plates can be faced with a tougher corrosion environment. Before the fuel recirculation, the performance losses of the cells consisting of metal bipolar plates are ascribed to cathode degradation, due to a high corrosion level of the cathode side. However, after fuel recirculation, corrosion of the anode metal bipolar plate by pH decrease and overpotential increase brings about severe anode degradation. It is found that damage by corrosion of the cathode metal bipolar plate is limited to degradation of the cathode catalyst, whereas corrosion of the anode metal bipolar plate deteriorates not only the catalysts but also the electrolyte membrane. These durability tests show that the CrN/Cr coatings deposited on the STS 430 improve the corrosion resistance of the metal substrate and lead to low performance degradation.

To investigate the effects of the microstructure and powder compositions for the micro-porous layer (MPL) of an anode on the cell performance of a direct methanol fuel cell (DMFC) using a highly concentrated methanol solution up to 7 M, various powders and their compositions were applied as a filler of the MPL in the membrane electrode assembly (MEA). Several nano- and microstructured carbons such as commercial carbon black (CB), spherical activated carbon (AC), multi-walled carbon nanotube (MWCNT), and platelet carbon nanofiber (PCNF) were selected with different morphology and surface properties, and a meso-porous silica (one of SBA series) was also included for its porous and hydrophilic properties. The coating morphology and physical properties such as porosity and gas permeability were measured, and electrochemical properties of MEA with the MPL were examined by using current–voltage polarization, electrochemical impedance spectroscopy, and voltammetric analyses. A mixture of different carbons was found to be effective for lowering methanol crossover with sustaining electrical conductivity and gas permeability. A MEA with modified-anode MPLs made of CB (50 vol%) and PCNF (50 vol%) powders showed a maximum power density of 67.7 mW cm−2 under operation with a 7 M concentration of methanol.

Polymer electrolyte membranes have been widely investigated for high performance fuel cells. Here, we report the synthesis of ionic conductive Nafion/graphene oxide (GO) composite membranes for application in direct methanol fuel cells. GOs interact with both the non-polar backbone and the polar ionic clusters of Nafion because of their amphiphilic characteristics attributable to hydrophobic conjugation and hydrophilic functional groups. Accordingly, GO sheets serve to modify the microstructures of two domains of Nafion. In particular, the transport properties of Nafion are favorably manipulated by the incorporation of GO. This modulated the ionic channels of Nafion and decrease methanol crossover while preserving ionic conductivity. Furthermore, strong interfacial interactions due to the insertion of GO nanofillers into the Nafion matrix improve the thermal and mechanical properties of the material. In particular, we exploit Nafion/GO composite membrane as electrolyte material for direct methanol fuel cell (DMFC) in order to resolve current issue of methanol crossover. This composite membrane-based DMFC compared to the Nafion 112-based DMFC remarkably enhanced cell performance, especially in severe operating conditions.

Sulfonated polyethersulfones (sPES) with thermally crosslinkable allyl or propargyl endgroups were synthesized and evaluated as methanol-tolerant proton exchange membranes (PEMs) for use in a direct methanol fuel cell (DMFC). sPES with a controlled degree of sulfonation (DS) were generated by direct copolycondensation of sulfonated and nonsulfonated dichloro-monomers with bisphenol-A, and synthesis of crosslinkable sPES was completed by subsequent end group modification with allyl or propargyl halide. Dissolved polymers were simply cast to tough membranes that underwent thermal crosslinking at an elevated temperature. The final PEMs were obtained after further cation exchange of the membranes to generate the protonated form. The PEM films were rigorously characterized to elucidate their electrochemical and mechanical properties. It was found that the allyl-terminated sPES generally showed higher proton conductivity and methanol permeability than the propargyl-terminated counterparts with a similar DS, plausibly due to lower crosslinking reactivity of the allyl group relative to the propargyl groups. The allyl-terminated sPES was successfully fabricated into a membrane electrode assembly (MEA) by using sPES/Nafion mixed ionomers as the binder, and a power performance of 23.5 mW/cm2 was achieved in a DMFC single cell test in air-breathing semi-passive mode after activation for six days.

Freeze-thaw cycles were used to investigate performance degradation in direct methanol fuel cells (DMFC). The freeze-thaw cycles were carried out across the temperature range of −32 °C–60 °C. The details of the performance degradation were analyzed by comparing the change of polarization of each electrode and the electrochemical impedance spectrum according to the number of freeze-thaw cycles. It was found that freeze-thaw cycles caused the increase in the cathode overpotential to affect performance degradation and the increase in the charge transfer resistance which means distinct damages in the triple phase boundary of the catalyst layer. Different purging scenarios before freezing were adopted, namely the cathode purge and the anode–cathode purge, to reduce any performance degradation caused by the freeze-thaw cycles. The cells purged by nitrogen gas were found to have less performance loss than the cells that were not purged during the freeze-thaw cycles. The changes in the cell resistance and the cathode electrochemical surface areas were also smaller when the cells were purged compared with those cells that were not purged. The introduction of air purging had similar positive influences with nitrogen purging on the performance of the DMFCs and their impedance. It was also determined that air was better at purging only the cathode than purging both electrodes.

This study experimentally and numerically investigates the effects of the four different types of serpentine flow-field geometry on the performance of a direct methanol fuel cells (DMFCs). To elucidate the effect of different channel/rib aspect ratios, the through/in-plane transport of methanol and air, the current density distribution, the anode and cathode polarization, the impedance and the cathode pressure drop are numerically and/or experimentally observed. The sub-rib convection significantly affects the cell performance with the serpentine flow fields. Thus, a narrow rib width and a suitable channel/rib aspect ratio are needed to increase the cell performance of serpentine DMFCs. This flow channel, for example, an F2-type flow channel (channel width: 1.0 mm, rib width: 0.5 mm), leads to formation of a narrower rib chain as well as a higher current density distribution in the rib, and thereby it brings about improvement of the two-phase flow in DMFCs, which is supported through the high performance difference in the high current density regions and the long-term stability test of 700 h.

Strontium- and copper-doped lanthanum ferrite (LaSrCuFe) was used as new cathode material for solid oxide fuel cells (SOFCs) with scandia-stabilized zirconia electrolyte at intermediate temperatures. The performance of an anode-supported single cell prepared using a Ni/YSZ anode, ScMnSZ ((ZrO2)0.89(Sc2O3)0.1(MnO2)0.01) electrolyte, and a LaSrCuFe cathode was evaluated. The effects on the cell performance of the GDC (GD0.1Ce0.9O1.95) interlayer between the electrolyte and cathode were also investigated. The microstructure and chemical composition of the cell were analyzed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (EDS). AC impedance spectroscopy was used to measure the polarization resistance of a single cell. The results highlight the promising combination of ScMnSZ electrolyte and LaSrCuFe cathode material in terms of chemical compatibility and electrical performance.

Various silica particles were adopted as catalyst supports, and silica-supported PtRu catalysts were evaluated as catalysts for the anode of direct methanol fuel cells at methanol concentrations of 1–10 M through single cell tests. Compared to a carbon black supported Pt–Ru catalysts, the silica-supported Pt–Ru catalysts exhibited higher performance in MEA, especially with high concentration over 3 M, and the maximum power density reached to 90 mW cm−2 and 60 mW cm−2 with 5 M and 10 M, respectively, which were 1.5 and 3 times higher than the reference carbon black supported catalysts. It was found that the silica particles as a catalyst support have a significant effect on reduction of methanol crossover and control of fuel feeding. Such a high performance in the operation with high concentrations was confirmed in the long-term durability test.

The outer micro-porous layer (MPL) between the gas diffusion layer and channel of the bipolar plate was studied for both sides of the electrodes in DMFC, with particular attention to the effects of the hydrophobicity of the MPL on mass transport as well as cell performance. Water-transport behavior from the electrodes to the channel was observed through the transparent window of the single cell with membrane-electrode assemblies (MEAs) including three combinations of outer MPLs. The crossover amount of methanol as well as water through the membrane was measured, and the mass balance, based on the measured flux, was established to understand the mass transport in MEAs. The design of outer MPLs is discussed for the best cell performance.

According to the conventional MEA test, methanol and water crossover are the main factors to determine performance of a passive DMFC. Thus, to ensure the high cell performance of a passive DMFC using high concentration methanol of 50–95 vol%, the MEA in this study introduces the barrier layer to limit the crossover of high concentration methanol, a hydrophobic layer to reduce water crossover, and a hydrophilic layer to enhance the water recovery from the cathode to the anode. The functional layers of the MEA have the effect of improving the performance of the passive DMFC by decreasing the methanol and water crossover. In spite of the operation with 95 vol% methanol, the MEA with multi-layer electrodes for high concentration methanol DMFCs shows a maximum power density of 35.1 mW cm−2 and maintains a high power density of 30 mW cm−2 (0.405 V) under constant current operation.

The chemical stability and durability of PtRu catalysts supported on carbon nanofibers (CNFs) for the anode electrode of a direct methanol fuel cell (DMFC) are investigated by Pt and Ru dissolution tests in sulfuric acid and long-term performance tests of a single cell discharging at a constant current density of 150 mA cm−2 for approximately 2000 h. A CNF with a herringbone-type structure, which is characterized by the alignment of graphene symmetrically angled to the fiber axis, was selected as the catalyst support because it has an edge-rich surface and a high surface area. In the metal dissolution test, the PtRu/CNF catalysts showed 1.5–2 times lower Ru leaching than a tested commercial catalyst (supported on activated carbon). The results of long-term performance tests also prove the higher durability of the anode catalyst compared with the commercial catalyst, when the anode polarization is compared before and after operation for 2000 h. Some analytical measurements, including X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy were conducted to study the degradation of the catalyst activity.

Highly dispersed Pd nanoparticles were prepared by borohydride reduction of Pd(acac)(2) in 1,2-propanediol at an elevated temperature. They were uniformly dispersed on carbon black without significant aggregation. X-ray diffraction showed that carbons from the Pd precursor dissolved in Pd, increasing its lattice parameter. A modified reduction process was tested to remove the carbon impurities. Carbon removal greatly enhanced catalytic activity toward the oxygen reduction reaction. It also generated an inconsistency between the electronic modifications obtained from X-ray photoelectron spectroscopy and the electrochemical method. CO displacement measurements showed that the formation of Pd-C bonds decreased the work function of the surface Pd atoms.