A three dimensional numerical analysis was performed to study the PEMFC performance characteristics. Operating pressure and operating temperature were selected as simulation parameters. Operating pressure was varied as 1, 2, 3, 4, and 5 atm. Operating temperature was varied as 323, 333, 343, 353, and 363 K. For a constant cell voltage condition, the maximum current density was obtained at operating pressure of 5 atm and operating temperature of 323 K. As operating pressure increases, current density increases because concentration of reactant gases increases. As operating temperature increases, current density decreases because concentration of reactant gases decreases due to high overpotential condition for the considered PEMFC.

In the segmented-in-series solid-oxide fuel cells (SIS-SOFCs), fabrication techniques which use decalcomania paper have many advantages, i.e., an increased active area of the electrode; better interfacial adhesion property between the anode, electrolyte and cathode; and improved layer thickness uniformity. In this work, a cell-stack was fabricated on porous ceramic flattened tube supports using decalcomania paper, which consists of an anode, electrolyte, and a cathode. The anode layer was 40μm thick, and was porous. The electrolyte layers exhibited a uniform thickness of about 20μm with a dense structure. Interfacial adhesion was improved due to the dense structure. The cathode layers was 30μm thick with porous structure, good adhesion to the electrolyte. The ohmic resistance levels at 800, 750 and 700˚C were measured, showing values of 1.49, 1.58 and 1.65Ω·cm2, respectively. The polarization resistances at 800, 750 and 700˚C were measured to be 1.63, 2.61 and 4.17cm2, respectively. These lower resistance values originated from the excellent interfacial adhesion between the anode, electrolyte and cathode. In a two-cell-stack SOFC, open-circuit voltages(OCVs) of 1.915, 1.942 and 1.957 V and maximum power densities(MPD) of 289.9, 276.1 and 220.4mW/cm2 were measured at 800, 750 and 700˚C, respectively. The proposed fabrication technique using decalcomania paper was shown to be feasible for the easy fabrication of segmented-in-series flattened tube SOFCs.

본 연구에서는 연료극 또는 공기극에 함유된 불순물인 황화합물의 도입을 차단할 수 있는 GDL을 제조하여, 이를 평가용 단위전지에 체결하여 H2S와 SO2를 연료극과 공기극에 각각 동시에 공급하여 PEMFC의 성능 저하 및 회복에 관한 연구를 수행하였다. 그 결과 H2S와 SO2의 농도가 증가함에 따라 전지의 성능이 감소하며 특히 10 ppm 이상의 농도에서는 10분 이내에 약 10-15% 정도 성능이 감소하였다. 특히 GDL 표면의 기공이 없는 CN-2 GDL을 체결한 단위전지의 경우 피독에 의한 성능 감소 속도가 더 빠른 것을 확인하였다. 그리고 단위전지 피독 후 황화합물이 혼합되지 않은 순수 가스를 1시간 이상 공급하였을 때 전지의 성능이 GDL의 종류에 따라 90%에서 95% 이상 회복되며 CN-1 GDL의 경우가 가장 회복이 우수하였다.

In this paper, a three dimensional numerical analysis tool was applied to study the PEMFC performance characteristics. The porosity and electrical conductivity of GDL and CL as well as the relative humidity of anode and cathode channel gas were selected as simulation parameters. The porosity of GDL and CL was varied as 0.3, 0.5, and 0.7. The relative humidity of anode and cathode was varied as 0, 20, 40, 60, 80, and 100 percent. The electrical conductivity of GDL and CL was varied as 1, 5, 10, 50, 102, and 104 1/Ω·m. For a constant cell voltage condition, the maximum current density was obtained at GDL porosity of 0.7, anode relative humidity of 100 percent, cathode relative humidity of 60 percent, and electrical conductivity of 104 1/Ω·m for GDL and CL. As the porosity of GDL and CL increases, current density increases because reactant gases diffuse well. As the electrical conductivity of GDL and CL increases, current density increases due to increased electron transfer rate. As anode relative humidity increases, current density increases. Unlike anode, current density increases when cathode relative humidity increases from 0 percent to 60 percent. Then current density decreases when cathode relative humidity increases from 60 percent to 100 percent.

A numerical analysis was performed to study PEMFC characteristics depending on the flow direction of reactant gas in cathode gas channel using the Fluent. As cathode relative humidity increases, water mass fraction increases due to back diffusion from cathode. For the both of co-flow and counter-flow cases, water mass fraction is higher near the hydrogen inlet region where the chemical reaction rate is high. In overall, counter-flow case gives higher current density compared to co-flow case for the same operating conditions. However, the difference in the current density is not high. The temperature is also higher near the hydrogen inlet region due to the chemical reaction rate for the both of co-flow and counter-flow cases.

In this paper, a three dimensional numerical analysis tool was applied to study the PEMFC performance characteristics. The porosity and electrical conductivity of GDL and CL as well as the relative humidity of anode and cathode channel gas were selected as simulation parameters. As the porosity of GDL and CL increases, current density and temperature increase because reactant gases diffuse well. As the electrical conductivity of GDL and CL increases, current density and temperature increase due to increased electron transfer rate. As anode relative humidity increases, current density and temperature increase. Unlike anode, current density and temperature increase when cathode relative humidity increases from 0 percent to 60 percent. Then current density and temperature decrease when cathode relative humidity increases from 60 percent to 100 percent.

고분자 전해질막 연료전지는 연료극의 연료와 공기극의 공기에 각각 H2S와 SO2이 포함되어 있을 때 그 성능이 심각하게 감소한다. 본 연구는 고분자전해질막 연료전지의 공기극과 연료극에 1 ppm에서 10 ppm의 불순물 가스를 공급하여 전기적 성능측정을 통해 복합적인 황불순물이 단위전지에 미치는 영향을 확인하였다. 최적의 운전조건에서 불순물가스를 피독하였을 때 SO2와 H2S의 농도가 증가할수록 성능이 급격히 감소하였다(단위전지 온도 65℃, 상대습도 100%). 그리고 황의 흡착은 MEA의 백금 촉매층 표면서 일어나며, 불순물 가스가 MEA에 누적되는 것을 확인하였다. 1, 3, 5, 및 10 ppm 4회의 연속적인 피독 후 연료전지의 성능이 0.71 V에서 0.54 V(76 %)로 감소하였다.

In this paper, the PEMFC performance was studied using three dimensional numerical analysis. The effect of GDL porosity and cathode inlet humidity on the cell polarization curve was analyzed. The GDL porosity of 0.3, 0.5, 0.7 and cathode inlet humidity of 20, 40, 60, 80, 100 percent were selected as simulation cases while the anode inlet humidity was maintained as 100 percent. For a constant cell voltage condition, the highest current density was obtained at GDL porosity of 0.7 and cathode inlet humidity of 20 percent. As GDL porosity increases, the amount of hydrogen diffusion to membrane from the anode increases and chemical reaction also increases. As cathode inlet humidity decreases, oxygen mass fraction of cathode gas channel increases and chemical reaction also increases.

La1-xSrxMnO3(LSM,0≤x≤0.5) powders as the air electrode for solid oxide fuel cell were synthesized by a glycine-nitrate combustion process. The powders were then examined by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The as-formed powders were composed of very fine ash particles linked together in chains. X-ray maps of the LSM powders milled for 1.5 h showed that the metallic elements are homogeneously distributed inside each grain and in the different grains. The powder XRD patterns of the LSM with x< 0.3 showed a rhombohedral phase; the phase changes to the cubic phase at higher compositions(x≥0.3) calcined in air at 1200˚C for 4 h. Also, the SEM micrographs showed that the average grain size decreases as Sr content increases. Composite air electrodes made of 50/50 vol% of the resulting LSM powders and yttria stabilized zirconia(YSZ) powders were prepared by colloidal deposition technique. The electrodes were studied by ac impedance spectroscopy in order to improve the performance of a solid oxide fuel cell(SOFC). Reproducible impedance spectra were confirmed using the improved cell, which consisted of LSM-YSZ/YSZ. The composite electrode of LSM and YSZ was found to yield a lower cathodic resistivity than that of the non-composite one. Also, the addition of YSZ to the La1-xSrxMnO3 (0.1≤x≤0.2) electrode led to a pronounced, large decrease in the cathodic resistivity of the LSM-YSZ composite electrodes.

불소관능기인 perfluorocyclobutane (PFCB)기를 포함하는 후술폰화 poly (arylene ether sulfone) 랜덤 공중합체를 다공성 Polytetrafluoroethylene (PTFE) 막에 함침시켜 새로운 복합막을 제조하였다. 후술폰화 랜덤 공중합체는 trifluorovinyloxy 그룹을 양말단에 포함하는 biphenyl계와 sulfonyl계 단량체로부터 제조되었는데, biphenyl계와 sulfonyl계의 비율을 6 : 4와 4 : 6으로 조절 후 중부가반응 형태의 열중합과 chlorosulfonic acid (CSA)를 이용한 후술폰화 반응을 통하여 얻어졌다. 이렇게 제조된 랜덤 공중합체의 농도를 달리하면서(5~20 wt%) 다공성 PTFE 막에 함침시켜 복합막을 제조하였고, 이온 교환 능력(IEC), 함수율, 이온전도도를 측정하여 강화되지 않은 랜덤공중합체 및 Nafion과 비교하였다. 제조된 단량체 및 고분자의 구조와 순도는 각각 1H-NMR, 19F-NMR와 FT-IR를 통하여 확인하였으며, 제조된 복합막의 형태는 SEM으로 관찰하였다.

연료전지는 석유엔진과 비교하여 높은 전류밀도와 효율성, 그리고 친환경적이기 때문에 21세기 들어 대체 발전시스템으로서 각광받아왔다. 연료전지 시스템에서 고분자 전해질 막은 핵심부품으로써 현재 Nafion막이 연료전지시스템에서 사용 중이지만 높은 제조단가와 고온에서 낮은 전도도를 가지는 단점을 가지고 있다. 그러므로 많은 학자들이 낮은 제조단가, 높은 물리적 특성들을 달성하기 위한 연구를 진행하여 왔으며 연료전지의 상용화와 동시에 고성능의 연료전지의 개발을 위하여 많은 방법들이 개발되어 왔다. 그중, 유무기 복합막은 유기물과 무기물의 물성을 균일하게 조합할 수 있으므로 잠재성을 가지고 있는 제조방법이다. 본고에서는 다양한 무기물이 사용되어 제조된 유무기 복합막의 연구동향에 대하여 조사하였다.

황화수소가 고분자 전해질막 연료전지의 연료극에 공급되었을 때 전지 성능의 저하와 황화수소 피독 후 순환전류 전압법(CV) 스캔을 통해 전지의 성능 회복에 관한 연구를 수행하였다. 수소에 30 ppm의 황화수소를 희석하여 연료극에 공급하고 전류밀도를 0.5A/cm2로 고정하여 1시간 동안 3차례 피독한 후 CV를 5회 스캔하여 단위전지의 성능회복을 확인한 결과 피독 전 단위전지의 초기 성능은 0.60 V에서 1.16A/cm2이였으며, 30 ppm의 황화수소를 한 시간 동안 피독한 결과 0.77A/cm2로 그 성능이 감소하였고, 피독 횟수가 증가함에 따라 성능이 0.57 V까지 감소하였다. 그리고 황화수소 피독 후 각 스텝에서 CV 스캔을 5회 실시하였을 때 단위전지의 성능이 90.3%까지 회복하는 것을 알 수 있었다. 또한, 황화수소 피독 후 단순히 고순도의 수소 가스만 연료극에 주입하여도 약 80% 정도의 성능회복이 가능하였다. 이러한 현상으로 판단할 때 황화수소 가스의 백금 촉매층에의 흡착은 그리 강하지 않음을 알 수 있었다.

본 연구에서는 용액 캐스팅법을 이용하여 각기 다른 함량의 VMT가 첨가된 SPAES/VMT 복합막이 제조되었다. SPAES 매트릭스 내의 VMT입자 분산은 전자주사현미경으로 관찰된 평균분포에 의해 확인되었다. 1 wt%보다 적은 함량을 포함한 복합막은 고분자 매트릭스 내에 좋은 분산성을 나타내어 막의 상부층과 하부층에 매끈한 표면을 가졌다. 복합막의 함수율은 온도가 증가함에 따라 급격하게 증가되었으며 VMT는 높은 이온교환능력으로 인하여 강한 수분친화도를 가짐으로 인해 높은 모든 흡착된 수분은 bound water인 것으로 확인하였다. VMT의 함량이 1 wt%보다 적게 첨가된 복합막에서 증가된 이온전도도와 낮아진 메탄올 투과도를 확인할 수 있었다. 모든 복합막 중에서 SPAES/VMT 1.0 wt% 복합막은 선택도 측면에서 가장 뛰어난 연료전지 성능을 가졌으며 Nafion 112과 비교하여 두배 이상 우수한 값을 나타내었다. 이것은 SPAES/VMT 1.0 wt% 복합막이 직접메탄올 연료전지의 구동을 위한 가장 우수한 조건이 될것이라 사료된다.

The air blowers for fuel cell electric vehicle usually have big difference between inlet and outlet pressure. When the casing of the air blowers is designed, the stress analysis is required. (Approximately Inlet pressure is 0.5bar and outlet pressure is 2bar.) Gap distance between the casing and the impeller is 0.3mm. Therefore, if the amount of maximum deformation of casing is larger than 0.3mm, impeller crashed the casing. In order to avoid crashing, both the thickness and number of rims are changed and carried out simulations on each cases.

본 연구는 고내구성을 가진 고분자 전해질 막을 제조하는 것으로 연료전지에 적용하기 위하여 poly(vinyl alcohol)를 주쇄부로 하여 poly(styrene sulfonic acid-co-maleic acid) (PSSA-MA)와 3-(trihydroxysilyl)-1-propanesulfonic acid (THS-PSA)를 polyethylene막에 함침시켜 막을 제조하였다. 제조된 막을 함수율, 접촉각, FT-IR, 수소이온전도도, 탄성계수 등의 측정을 통해 친수성 고분자가 함침된 막의 특성평가를 실시하였다. FT-IR 분석과 접촉각 측정을 통해 PE막에 함친된 막에서 친수성기의 유무를 확인하였다. 수소이온전도도를 측정한 결과 30% THS-PSA의 막이 55℃에서 1.27×10 ­1S/㎝의 값을 나타내어 우수한 수소이온전도도를 나타내었으며, 탄성계수의 측정을 통해 polyethylene막에 비하여 THS-PSA가 함침된 막의 기계적 강도가 15%까지는 최대 7배까지 향상되어 막의 내구성이 향상되었음을 확인하였다.

기질 고분자인 sulfonated PEEK (sPEEK)와 가교제(cross-linking reagent) 4,4'-ethyldianiline (EdAn), 그래프트제(grafting reagent) 2-phenylethylamine (PEA)을 용매 dimethylacetamide (DMAc)에 녹여 용매증발법을 이용하여 제막하였다. 이민화 반응(imination)과 술폰화(sulfonation) 과정을 거쳐 최종 이온교환막인 cross-linked and grafted sPEEK (CG-sPEEK)막을 제조하였다. FT-IR 분석을 통해 술폰화 및 이민화 반응여부를 확인할 수 있었다. Proton conductivity와 water uptake, volume change를 측정하여 상용화된 Nafion115와 비교함으로써 이온교환막으로서의 활용가능성을 평가하였다. 제조된 CG-sPEEK막의 proton conductivity (0.17 S/cm) 값이 Nafion115 (0.10 S/cm) 보다 우수하게 나타나 이온교환막으로서의 적용가능성을 보여주었다. 다만 높은 water uptake (130%)는 CG-sPEEK의 치수안정성을 위해서 저감시킬 필요가 있다.

Nanosized Pt, Pt-Ru and Pt-CeO2 electrocatalysts supported on acid-treated carbon nanotube (CNT) were synthesized by microwave-assisted heating of polyol process using H2Cl6Pt·6H2O, RuCl3, CeCl3 precursors, respectively, and were characterized by XRD and TEM. And then the electrochemical activity of methanol oxidation for catalyst/CNT nanocomposite electrodes was investigated. The microwave assisted polyol process produced the nano-sized crystalline catalysts particles on CNT. The size of Pt supported on CNT was 7~12 nm but it decreased to 3~5 nm in which 10wt% sodium acetate was added as a stabilizer during the polyol process. This fine Pt catalyst particles resulted in a higher current density for Pt/CNT electrode. It was also found that 10 nm size of PtRu alloys were formed by polyol process and the onset potential decreased with Ru addition. Cyclic voltammetry analysis revealed that the Pt75Ru25/CNT electrode had the highest electrochemical activity owing to a higher ratio of the forward to reverse anodic peak current. And the chronoamperemetry test showed that Pt75Ru25 catalyst had a good catalyst stability. The activity of Pt was also found to be improved with the addition of CeO2.

Polymer electrolyte membrane fuel cell (PEMFC) performance degrades when hydrogen sulfide (H2S) is present in the fuel hydrogen gas; this is referred to as H2S poisoning. This paper reveals H2S poisoning on PEMFC by measuring electrical performance of single cell FC under various operating conditions. The severity of H2S poisoning depended on H2S concentration under best operating conditions(65℃ of cell temperature and 100% of anode humidification). H2S adsorption occured on the surface of catalyst layer on MEA, but not on the gas diffusion layer(GDL) by analyzing SEM/EDX data. In addition, MEA poisoning by H2S was cumulative but reversible. After poisoning for less than 150 min, performance of PEMFC was recovered up to 80% by just inert nitrogen gas purging.