فهرست مطالب

  • Volume:6 Issue: 2, 2019
  • تاریخ انتشار: 1398/06/10
  • تعداد عناوین: 5
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  • M Khorshidian *, Majid Sedighi Pages 91-115

    This paper reviewed over 100 articles on the subject of the mechanism of catalyst layer (CL) degradation and the effect of various contaminations in the polymer electrolyte membrane fuel cell (PEMFC). Also the recovery of PEMFC via different types of methods, the causes and fundamental mechanisms of cell degradation and their influence on long- term performance of PEM fuel cell were discussed in this review paper. The most important mechanism of CL degradation in PEMFC includes the effect of different contaminations  such as carbon monoxide, carbon dioxide, hydrogen sulphide, sulfur dioxide, , (NO, ), (SO, ), and ammonia, agglomeration of catalyst, reactant gas starvation, and oxide and hydroxide formation are investigated. Afterward, as some of these CL degradations procedures are reversible, different recovery methods for retrieving the catalyst electrochemical active surface area (ECSA) are presented. Some recovery methods including recovery by H2 purge, direct and indirect zone, short circuit method, water steam, and the reduction method are presented in this review article. The review results show that the high and effective performance of the PEMFC was achieved by applying ozone method, water steam, and reduction method. However, only H2 purge and reduction methods are applicable to the stack of fuel cells. Therefore, in light of the facts outlined above, it is safe to illustrate that the reduction method is one of the most effective methods for the recovery of reversible CL degradations. Finally, the flowchart of studying cell degradation and its recovery is also presented at the end of the paper. This review was focused on the degradation mechanism of catalyst layer in different research aspects such as contamination impacts on the performance of fuel cell, various mechanism approaches and mitigation development. As the result, we hope that this brief overview provides good perspective of the important issues that should be addressed to extend the lifetime and durability of next-generation of fuel cells for the engineers and researchers in this field.

    Keywords: PEMFC, Catalyst Layer (CL), Degradation, recovery, performance loss
  • Rahbar Rahimi *, Farshid Mahmoodi Pages 117-132
    The PEMFC heat generation was utilized to desorb hydrogen from a LaNi5 filled MH–Hydrogen Storage tank. Heat pipes were used to transfer of heat from the FC to the MH- tank. The study was conducted using CFD simulation. Results showed that the increase of initial pressure of the MH tank and the cooling temperature of 303 K led to a rise in the hydrogen adsorption performance. In the desorption stage, after passing 4000 s, the amount of 5.39 g of hydrogen is purged from the hydride tank. Additionally, results demonstrated that the total hydrogen discharge rate of 0.304 slpm was achieved only to the expense of 7.36 W of a total of 23.43 W generated heats in the fuel cell. Furthermore, the hydrogen desorption flow rate has gained 45 % for the presented geometry compared to a similar system. Moreover, a very good agreement was found between the present work simulation results and the literature data
    Keywords: PEM fuel cell, Metal hydride hydrogen storage, Heat pipes, Thermal coupling, CFD simulation
  • Soolmaz Jamali, Ahmad Moshaii *, Kyana Mohammadi Pages 133-140
    In this paper we report on a notable improvement of the photoelectrochemical (PEC) properties of highly ordered Ag loaded TiO2 nanotube arrays (Ag/TNT). Electrochemical anodization and sequential chemical bath deposition with an optimum ratio of precursors were employed for the production of an Ag/TNT nanocomposite. X-ray diffraction analysis (XRD) and scanning electron microscopy SEM images indicate that the Ag nanoparticles were deposited completely on the surface of the pore wall of TiO2 nanotube arrays. The photoelectrochemical measurements, including LSV, chronoamperometry and EIS, indicate that the Ag/TNT sample with a ratio of 1 precursors exhibited the maximum photoelectrochemical efficiency with a photocurrent density of about 300 µA, which is at least 3 times greater than a pure TNT sample. PEC and EIS measurements show that because of the localized surface plasmon resonance (LSPR) effects of Ag nanoparticles, an effective separation of photogenerated electron-hole pairs occurs that led to a reduction of charge transfer resistance at the interface and enhanced the PEC properties of the Ag/TNT sample.
    Keywords: Ag, TNT nanocomposite, semiconductor, photoelectrochemical water splitting, surface plasmon resonance
  • Maryam Yaldagard * Pages 141-161
    In this research, nanocomposites of Platinum Graphene-Polyallylamine (Pt/PAA/GNP) were developed to increase the methanol electro-oxidation activity and stability of commercial Pt/C electrocatalyst. After the synthesis process, graphene oxide was functionalized with Polyallylamine via the cross linking approach, then Pt as a catalyst was dispersed on the as prepared support by a novel process, which is a polyol synthesis method assisted by microwaves. X-ray diffraction (XRD) results showed that Pt particles, with a mean particle size of about 6.17 , were dispersed on the support. FESEM images showed that the Pt nanoparticles were successfully dispersed on the functionalized graphene nanoplates. Based on the electrochemical properties characterized by cyclic voltammetry (CV), including CO stripping measurements, it was found that the prepared Pt/PAA/GNP electrocatalyst exhibited a comparable activity for methanol oxidation reaction with respect to the commercial one. A significant reduction in the potential of the CO electro-oxidation peak from 0.93V for the Pt/C to 0.89 V for the Pt/PAA/GNP electrocatalyst indicates that there was a significant increase in the CO electro-oxidation activity, which is achieved by replacing the voulcan. Also, the as prepared Pt/PAA/GNP electrocatalyst exhibits high catalytic activity for the MOR in terms of electrochemical surface with respect to Pt/C (40.53 vs 17.61 m2/mgPt ), which may be attributed to structural changes caused by the high specific surface area of the PAA modified graphene nanoplates catalyst support. Moreover, chronoamerometry results showed that in the presence of methanol, the Pt/PAA/GNP electrocatalyst still maintains a higher current density than Pt/C.
    Keywords: Graphene, polyallylamine, Nanocomposite, microwave assisted polyol process, methanol, fuel cell
  • Rabia KIRKGEÇİT, Handan ÖZLÜ TORUN* Pages 163-170

    Solid oxide fuel cells are electrochemical systems. One of the most important compounds in their structure is the ceramic electrolyte. The ceramic electrolyte property of the CeO2 compound is currently being investigated in many studies. In this study, we tried to synthesize different CeO2 compounds. Ce0.85-x-yLaxGdyO2 nanocrystalline powders were prepared via the hydrothermal method. Phases identification was completed through X-ray diffraction, SEM-EDS, thermal and impedance analysis. XRD data showed that all the obtained powders had a cubic fluorite structure. After examining the surface images, it was seen that the particle sizes were on the micron scale. Impedance measurements of the pelletized sample were also made. The Ce0.85-x-yLaxGdyO2 powder was sintered at 1250 °C. Increased conductivity value was calculated with increasing temperature. The best conductivity was observed at 750 oC and the conductivity value was 0.0022 S.cm-1. The results indicated that the degree of electrical conductivity was found to be low regarding the applications in intermediate temperature solid oxide fuel cells.

    Keywords: CeO2, intermediate temperature solid oxide fuel cell, solid electrolyte