Study of the Catalytic Layer in Polybenzimidazole-based High Temperature PEMFC: Effect of Platinum Content on the Carbon Support

International audienceIn this work, the effect of platinum content on the carbon support in commercial catalyst for electrodes to be used in a Polybenzimidazole (PBI)-based PEMFC has been studied. Three contents of platinum on a carbon support were studied (20 %, 40 % and 60 %). In all cases, the same quantity of PBI in the catalyst layer, which is required as a “binder” was used. From Hg porosimetry analyses, pore size distribution, porosity, mean pore size, and tortuosity of all electrodes were obtained. In all cases, a similar electrode mesostructure was observed. The electrochemical characterization was performed by voltamperometric studies, assessing the electrochemical surface area (ESA) of the electrodes, and by impedance spectroscopy (IS), determining the polarization resistance, and by the corresponding fuel cell measurements. The best results were obtained for the electrodes with a content of 40 % of platinum that led to power densities of 0.55 W/cm2 and 0.3 W/cm2 using O2 and air respectively, at 125 ºC. It has been demonstrated that the temperature has a favouring effect on fuel cell performance and flow humidification did not have remarkable effects as it was expected

Development of new polymeric electrolytes and study of the proton conduction mechanism in high temperature fuels cells

Polymer electrolyte fuel cells are an efficient and environmentally friendly technology of power generation, while they are considered the most promising candidate for vehicular transportation. Operation at elevated temperatures (above 100°C) has many advantages. Research is underway to find the appropriate polymeric electrolyte, which combines certain prerequisites. Our approach is based on the synthesis of copolymers with aromatic polyether structure, which bear polar units (pyridines or imidazo-pyridines) on the main chain. The materials were characterized with conventional methods. The majority of the studied materials showed excellent mechanical properties, thermal and oxidative stability and high ionic conductivities. In other words, from this work, polymers that fulfil all the prerequisites for high temperature operation were obtained. After optimization, some materials were chosen and were applied in single fuel cells. The fuel cell performance was therefore studied. Also, the effect of different parameters such as temperature and water steam, on cell performance was investigated. Last, conclusions were extracted concerning the proton conduction mechanism.Τα κελιά καυσίμου είναι μια τεχνολογία παραγωγής ενέργειας, πιο αποδοτική και φιλική προς το περιβάλλον, ενώ αποτελούν τον βασικό υποψήφιο για χρήση σε μέσα μεταφοράς. Λειτουργία σε θερμοκρασίες πάνω από 100°C έχει διάφορα πλεονεκτήματα. Η έρευνα βρίσκεται σε εξέλιξη για την εύρεση του κατάλληλου πολυμερικού υλικού για ηλεκτρολύτη, το οποίο να συνδυάζει διάφορες ιδιότητες. Η δική μας προσέγγιση βασίζεται στη σύνθεση συμπολυμερών με δομή αρωματικών πολυαιθέρων τα οποία φέρουν πολικές ομάδες (πυριδίνες ή ημιδαζο-πυριδίνες) στην κύρια αλυσίδα. Τα υλικά χαρακτηρίστηκαν με συμβατές τεχνικές. Προέκυψαν πολυμερή με εξαιρετικές μηχανικές ιδιότητες, θερμική και οξειδωτική σταθερότητα, και υψηλή ιοντικής αγωγιμότητα. Με άλλα λόγια προέκυψαν υλικά που πληρούν όλες τις προϋποθέσεις για λειτουργία ως ηλεκτρολύτες υψηλών θερμοκρασιών. Στην συνέχεια έγινε επιλογή ορισμένων ηλεκτρολυτών και εφαρμογή τους σε μοναδιαίο κελί καυσίμου. Μελετήθηκε η απόδοση του κελιού αλλά και η επίδραση παραγόντων όπως η θερμοκρασία και οι υδρατμοί σε αυτή. Τέλος, έγινε εξαγωγή συμπερασμάτων για το μηχανισμό αγωγής πρωτονίων

The influence of methanol on the chemical state of PtRu anodes in a high temperature direct methanol fuel cell studied in situ by synchrotron based near ambient pressure x ray photoelectron spectroscopy

Synchrotron radiation based near ambient pressure x ray photoelectron spectroscopy NAP XPS has recently become a powerful tool for the investigation of interfacial phenomena in electrochemical power sources such as batteries and fuel cells. Here we present an in situ NAP XPS study of the anode of a high temperature direct methanol fuel cell with a phosphoric acid doped hydrocarbon membrane, which reveals an enhanced flooding of the Pt3Ru anode with phosphoric acid in the presence of methanol. An analysis of the electrode surface composition depending on the cell voltage and on the presence of methanol reveals the strong influence of the latter on the extent of Pt oxidation and on the transformation of Ru into Ru IV hydroxid

Study of the Role of Void and Residual Silicon Dioxide on the Electrochemical Performance of Silicon Nanoparticles Encapsulated by Graphene

Silicon nanoparticles are used to enhance the anode specific capacity for the lithium-ion cell technology. Due to the mechanical deficiencies of silicon during lithiation and delithiation, one of the many strategies that have been proposed consists of enwrapping the silicon nanoparticles with graphene and creating a void area between them so as to accommodate the large volume changes that occur in the silicon nanoparticle. This work aims to investigate the electrochemical performance and the associated kinetics of the hollow outer shell nanoparticles. To this end, we prepared hollow outer shell silicon nanoparticles (nps) enwrapped with graphene by using thermally grown silicon dioxide as a sacrificial layer, ball milling to enwrap silicon particles with graphene and hydro fluorine (HF) to etch the sacrificial SiO2 layer. In addition, in order to offer a wider vision on the electrochemical behavior of the hollow outer shell Si nps, we also prepared all the possible in-between process stages of nps and corresponding electrodes (i.e., bare Si nps, bare Si nps enwrapped with graphene, Si/SiO2 nps and Si/SiO2 nps enwrapped with graphene). The morphology of all particles revealed the existence of graphene encapsulation, void, and a residual layer of silicon dioxide depending on the process of each nanoparticle. Corresponding electrodes were prepared and studied in half cell configurations by means of galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy. It was observed that nanoparticles encapsulated with graphene demonstrated high specific capacity but limited cycle life. In contrast, nanoparticles with void and/or SiO2 were able to deliver improved cycle life. It is suggested that the existence of the void and/or residual SiO2 layer limits the formation of rich LiXSi alloys in the core silicon nanoparticle, providing higher mechanical stability during the lithiation and delithiation processes

High Temperature PEM Fuel Cell Stacks with Advent TPS Meas

High power/high energy applications are expected to greatly benefit from high temperature Polymer Electrolyte Membrane Fuel Cells (PEMFCs). In this work, a combinatorial approach is presented, in which separately developed and evaluated MEAs, design and engineering are employed to result in reliable and effective stacks operating above 180°C and having the characteristics well matched to applications including auxiliary power, micro combined heat and power, and telecommunication satellites

Synergistic effect of Yttrium and pyridine-functionalized carbon nanotube on platinum nanoparticles toward the oxygen reduction reaction in acid medium

International audienc

A Highly Efficient and Stable Oxygen Reduction Reaction on Pt/CeOx/C Electrocatalyst Obtained via a Sacrificial Precursor Based on a Metal-Organic Framework

International audienceAdvanced Pt/CeOx/C nanocomposite, where C = porous carbon and multi-walled carbon nanotube (MWCNT), was synthesized using a precursor based on Ce-containing metal organic framework (MOF), via carbonyl chemical route, followed by heat-treatment at 900 °C under argon atmosphere. Based on the analyses of powder X-ray diffraction (pXRD) data, and via the Williamson-Hall method, the lattice parameter, stacking fault and micro-strain values on Pt/CeOx/C was found to decrease, whereas the crystallite size increased with respect to the as-prepared sample. Combined with the results of transmission electron microscopy (TEM), these changes were related to the in-situ formation of intimately contacted Pt/CeOx nanoparticles (NPs), well-dispersed onto MWCNT support. However, both the pXRD and TEM results showed that the Pt NPs were agglomerated upon heating and finally detached from the support in the MOF-free samples. Thus, MOF could protect Pt nanoparticles (NPs) from agglomeration at high temperature. The X-ray photoelectron spectroscopy (XPS) showed that the Pt surface was less oxidized in Pt/CeOx/C nanocomposite in comparison to as-prepared and MOF-free samples. Moreover, only the Ce3+ was detected in the nanocomposite. These facts together with Raman spectroscopy and surface electrochemistry experiments assessed the stabilization of the electronic state of Pt° and Ce3+ via the interaction between Pt and CeOx. In addition, enhanced catalytic activity towards the oxygen reduction reaction (ORR) was observed in acid medium. The specific and mass activity at 0.9 V/RHE on Pt/CeOx/C were ca. 1279 μA cm−2Pt and 870 mA mg−1Pt, respectively, ca. 10–11 fold higher than commercial Pt/C (Johnson Matthey, JM) in half-cell. Accelerating durability tests (ADT), after 16,000 potential cycles, demonstrated higher stability of Pt/CeOx/C in contrast to oxide-free and Pt/C (JM) catalyst. Compared with other homemade or commercial Pt/C (JM) cathodes, the innovative cathode catalyst showed enhanced cell performance in a H2/O2 micro-laminar flow fuel cell syste

High Temperature PEM Fuel Cell Stacks with Advent TPS Meas

High power/high energy applications are expected to greatly benefit from high temperature Polymer Electrolyte Membrane Fuel Cells (PEMFCs). In this work, a combinatorial approach is presented, in which separately developed and evaluated MEAs, design and engineering are employed to result in reliable and effective stacks operating above 180°C and having the characteristics well matched to applications including auxiliary power, micro combined heat and power, and telecommunication satellites