Here we report new H3PO4-doped cross-linked benzoxazine–benzimidazole copolymer membranes showing high proton conductivity and long-term durability for use in proton-exchange membrane fuel cells at ...elevated temperatures (>100 °C). The cross-linked copolymer membranes were prepared by mixing of poly2,2′-(m-phenylene)-5,5′-bibenzimidazole (PBI) with 3-phenyl-3,4-dihydro-6-tert-butyl-2H-1,3-benzoxazine (pBUa) in N,N -dimethylacetamide, with subsequent stepwise heating to 220 °C, and even large-sized films (30 cm × 140 m) could be easily prepared. The membranes showed high proton conductivities of up to 0.12 S cm–1 at 150 °C under anhydrous conditions. Membrane–electrode assemblies (MEAs) employing the membranes showed operating voltages of 0.71 V at 0.2 A cm–2. Furthermore, the MEAs displayed long-term durability up to 1999 cycles, with much slower performance decay, −0.03 mV h–1, than those prepared using the PBI membrane in in situ accelerated lifetime mode (load cycling testing).
For polymer electrolyte membrane fuel cell (PEMFC) applications at elevated temperature (>100 °C), a series of cross-linked benzoxazine–benzimidazole copolymer, P(HFa-co-BI), membranes are prepared ...by casting a solution of poly2,2′-(m-phenylene)-5,5′-bibenzimidazole (PBI) and di-functional benzoxazine monomer, 6,6′-(hexafluoroisopropylidene)bis(3-phenyl-3,4-dihydro-2H-benzoxazine) (HFa), in N,N-dimethylacetamide prior to stepwise heating to 250 °C. The films are also viable to manufacture to large quantities and area by roll-to-roll coating. The resulting cross-linked copolymer, P(HFa-co-BI), membranes are found to be thermally and mechanically stable. Although the proton conductivity values of P(HFa-co-BI) membranes are smaller than that of the PBI membrane, their cell performance (0.68 V at 0.2 A cm−2 at 150 °C) is close to that of PBI membrane and their long-term durability (ca. 3116 cycles on in situ accelerated lifetime mode of load cycling testing) is found to be far superior to the PBI membrane.
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► Cross-linked copolymers were prepared by PBI and difunctional benzoxazine. ► Excellent thermal and mechanical stabilities of cross-linked copolymer membranes. ► Performance and durability of cross-linked copolymer membranes was highly enhanced.
The pore structure and pore volume of catalyst layer (CL) were controlled by utilizing multi-walled carbon nanotube (MWCNT). According to the increase in MWCNT ratio in CL, the primary pore (below ...100 nm) volume concerning with the phosphoric acid penetration to the reaction site was decreased and the secondary pore (approximately 1 μm) volume relating with oxygen gas transportation was increased, respectively. However, the excessive addition of MWCNT was detrimental to electrochemical properties due to the difficulty of phosphoric acid penetration to the reaction site and the opposite influx of phosphoric acid to the secondary pore. Furthermore, the adhesion strength between CL and gas diffusion layer (GDL) was improved by only 10% addition of MWCNT. Therefore, it is suggested that the ratio of MWCNT in CL can be key role for obtaining the optimized pore volume, enhanced adhesion strength, and good performance of polymer electrolyte membrane fuel cell (PEMFC).
•Pore volume and pore structure were controlled by utilizing MWCNT.•Adhesion strength of catalyst layer on gas diffusion layer was improved by MWCNT.•The single cell prepared with MWCNT shows better performance than without MWCNT.
The ionomer content in electrode is one of the most important parameters for the high performance of fuel cells. The high temperature PEMFC based on phosphoric acid (PA)-doped polymer membrane with ...unhumidified reactant gases has a difficulty in controlling the liquid state PA ionomer content in electrode. To evaluate the PA content in electrode, the three techniques of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and acid–base titration (ABT) are carried out in situ or ex situ. The properties of membrane electrode assembly (MEA) such as electrochemical surface area (ESA), ohmic resistance, charge transfer resistance, double layer capacitance and the amount of PA in MEA components (anode, cathode and membrane) are extracted by each technique. Ex situ CV with the usage of dry gases has a limitation in assessing the reliable ESA of unhumidified PEMFC. While in situ EIS presents some informative values of resistance and capacitance for understanding the PA distribution in MEA, its sensitivity to the PA content in MEA components needs to be higher for detecting a subtle change in PA distribution. Ex situ ABT supplies a clear PA distribution in MEA at room temperature but does not seem to reflect the operating state well at high temperatures. However, it can be used as a detection tool for the loss of the initial acid content in membrane during a long-term MEA durability study.
Lithium-metal-based batteries, owing to the extremely high specific energy, have been attracting intense interests as post-Li-ion batteries. However, their main drawback is that ...consumption/de-activation of lithium metal can be accelerated when O
or S used in the cathode crosses over to the metal, reducing the lifetime of the batteries. In use of ceramic solid state electrolyte (SSE) separator, despite the capability of gas blocking, thick and heavy plates (~0.3 mm) are necessitated to compensate its mechanical fragility, which ruin the high specific energy of the batteries. Here, we demonstrate fabrication of a new membrane made of micron-sized SSE particles as Li-ion channels embedded in polymer matrix, which enable both high Li-ion conduction and gas-impermeability. Bimodal surface-modification was used to control the energy of the particle/polymer interface, which consequently allowed channel formation via a simple one-step solution process. The practical cell with the new membrane provides a cell-specific energy of over 500 Wh kg
, which is the highest values ever reported.
The poisoning effect of carbon monoxide (CO) on high-temperature proton-exchange membrane fuel cells (PEMFCs) is investigated with respect to CO concentration, operating temperature, fuel feed mode, ...and anode Pt loading. The loss in cell voltage when CO is added to pure hydrogen anode gas is a function of fuel utilization and anode Pt loading as well as obvious factors such as CO concentration, temperature and current density. The tolerance to CO can be varied significantly using a different experimental design of fuel utilization and anode Pt loading. A difference in cell performance with CO-containing hydrogen is observed when two cells with different flow channel geometries are used, although the two cells show similar cell performance with pure hydrogen. A different combination of fuel utilization, anode Pt loading and flow channel design can cause an order of magnitude difference in CO tolerance under identical experimental conditions of temperature and current density.
Elevated-temperature (100~200 °C) polymer electrolyte membrane (PEM) fuel cells have many features, such as their high efficiency and simple system design, that make them ideal for residential ...micro-combined heat and power systems and as a power source for fuel cell electric vehicles. A proton-conducting solid-electrolyte membrane having high conductivity and durability at elevated temperatures is essential, and phosphoric-acid-containing polymeric material synthesized from cross-linked polybenzoxazine has demonstrated feasible characteristics. This paper reviews the design rules, synthesis schemes, and characteristics of this unique polymeric material. Additionally, a membrane electrode assembly (MEA) utilizing this polymer membrane is evaluated in terms of its power density and lifecycle by an in situ accelerated lifetime test. This paper also covers an in-depth discussion ranging from the polymer material design to the cell performance in consideration of commercialization requirements.
일부지역 노인들의 주관적인 구취에 대한 인식 및 실태에 관한 연구 이영수; Young Soo Lee; 박화순 ...
Han'guk Ch'iwisaeng Hakhoe chi,
10/2014, Letnik:
14, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Objectives : The purpose of the study is to investigate the appropriate prevention and management of halitosis and management for the elderly. Methods : A self-reported questionnaire was filled out ...by 320 elderly over 65 years old in Seoul and Gyeonggi from June to October, 2013. Except 28 incomplete answers, 292 copies were used for the analysis. Results : The correlation coefficient was 0.702 which was the degree of present halitosis and everyday halitosis. Elderly within 65-69 years old felt the halitosis very seriously. the level of halitosis felt everyday was also highest in those within 65-69 years old with mean 2.00±0.862 points. Conclusions : The dissemination of correct knowledge of halitosis management can improve the subjective perception of the elderly oral health care.
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