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Papadimitriou K.D.,University of Patras | Paloukis F.,Advent Technologies SA | Neophytides S.G.,Foundation for Research and Technology Hellas | Kallitsis J.K.,University of Patras | Kallitsis J.K.,Foundation for Research and Technology Hellas
Macromolecules | Year: 2011

Novel aromatic polyethers bearing polar pyridine units along the main chain and side cross-linkable propenyl groups have been successfully synthesized. Their properties relating to their ability to be used as polymer electrolyte membranes for high temperature fuel cell applications, were thoroughly investigated. Cross-linked membranes were obtained by thermal curing of the cross-linkable polymers with the use of a bisazide as the cross-linking agent. The glass transition temperatures of the cross-linked membranes were determined by dynamic mechanical analysis and found to be higher compared to the neat polymers proving the successful cross-linked network. The doping ability in phosphoric acid and the proton conductivity of the cross-linked membranes were higher compared to the noncross-linked analogues. Finally, membrane electrode assemblies (MEAs) were constructed and tested in a single cell at temperatures between 180 and 220 °C. The superior performance of the cross-linked membranes in combination with the operating stability at 200 °C for 48 h demonstrate the potential use of these materials as electrolytes for high temperature PEM fuel cells. © 2011 American Chemical Society. Source


Papadimitriou K.D.,University of Patras | Papadimitriou K.D.,Institute of Chemical Engineering science FORTH ICE HT | Geormezi M.,Advent Technologies SA | Neophytides S.G.,Institute of Chemical Engineering science FORTH ICE HT | And 2 more authors.
Journal of Membrane Science | Year: 2013

Cross-linkable aromatic polyethers combining main and side chain pyridine units as well as side double bonds were successfully synthesized and characterized. Aiming at the use of these materials as electrolytes at high temperature fuel cells, these polymers were subjected to covalent cross-linking in order to improve their mechanical properties and their stability in the doped state. The cross-linking was obtained via cationic polymerization of the double bonds, during the impregnation of the produced membranes in phosphoric acid. The cross-linking was confirmed by the increased glass transition temperatures, the improved thermal stability and the insolubility of the cross-linked membranes compared to their undoped non cross-linked counterparts. Selected cross-linked membranes were used for membrane electrode assembly (MEA) preparation and tested in a single cell at temperatures between 180 and 220°C. Long-term durability tests were also performed at 180°C and at a current density of 0.2A/cm2. The experiment showed a stable operation without degradation for 1000h. The promising performance and the durability of the tested materials in combination with the simple and convenient technique which used to produce cross-linked membranes, demonstrates the feasibility of this type of electrolytes to be used in high temperature PEM fuel cell applications. © 2013 Elsevier B.V. Source


Yau C.P.,Imperial College London | Fei Z.,Imperial College London | Ashraf R.S.,Imperial College London | Shahid M.,Imperial College London | And 6 more authors.
Advanced Functional Materials | Year: 2014

A series of donor-acceptor (D-A) conjugated polymers utilizing 4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophene (DTG) as the electron rich unit and three electron withdrawing units of varying strength, namely 2-octyl-2H-benzo[d][1,2,3]triazole (BTz), 5,6-difluorobenzo[c][1,2,5] thiadiazole (DFBT) and [1,2,5]thiadiazolo[3,4-c]pyridine (PT) are reported. It is demonstrated how the choice of the acceptor unit (BTz, DFBT, PT) influences the relative positions of the energy levels, the intramolecular transition energy (ICT), the optical band gap (Egopt), and the structural conformation of the DTG-based co-polymers. Moreover, the photovoltaic performance of poly[(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′] dithiophen-2-yl)-([1,2,5]thiadiazolo[3,4-c]pyridine)] (PDTG-PT), poly[(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophen-2-yl) -(2-octyl-2H-benzo[d][1,2,3]triazole)] (PDTG-BTz), and poly[(4,4-bis(2- ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophen-2-yl)-(5,6-difluorobenzo[c] [1,2,5]thiadiazole)] (PDTG-DFBT) is studied in blends with [6,6]-phenyl-C 70-butyric acid methyl ester (PC70BM). The highest power conversion efficiency (PCE) is obtained by PDTG-PT (5.2%) in normal architecture. The PCE of PDTG-PT is further improved to 6.6% when the device architecture is modified from normal to inverted. Therefore, PDTG-PT is an ideal candidate for application in tandem solar cells configuration due to its high efficiency at very low band gaps (Egopt = 1.32 eV). Finally, the 6.6% PCE is the highest reported for all the co-polymers containing bridged bithiophenes with 5-member fused rings in the central core and possessing an Egopt below 1.4 eV. The optoelectronic properties and photovoltaic device performance for a series of low band gap donor-acceptor polymers based upon dithienogermole are reported. One very low band gap polymer, PDTG-PT, (Egopt = 1.32 eV) is shown to exhibit a promising device efficiency of 6.6% when utilized in inverted photovoltaic devices, making it a promising candidate for incorporation in tandem solar cell devices. © 2013 The Authors. Advanced Functional Materials published by Wiley-VCH Verlag GmbH 8 Co. KGaA Weinheim. Source


Chochos C.L.,Advent Technologies SA | Chochos C.L.,Foundation for Research and Technology Hellas | Tagmatarchis N.,National Hellenic Research Foundation | Gregoriou V.G.,Advent Technologies SA | Gregoriou V.G.,Foundation for Research and Technology Hellas
RSC Advances | Year: 2013

The demand for further optimization of the photovoltaic efficiency has stimulated an intensive research effort both for new low-band-gap polymeric materials as electron donors and for new efficient electron-accepting materials. As regards the latter, less attention has been observed on the optimization of the electron acceptor material compared to the extensive studies on the electron donor polymer in organic photovoltaic (OPV) cells. The majority of the acceptor materials used so far in solar cells are organic (carbon based) materials, however other traditional acceptor materials include inorganic semiconductors, such as cadmium selenide (CdSe) nanocrystals, titanium oxide (TiO2) and zinc oxide (ZnO) nanoparticles. From the implemented organic materials high power conversion efficiencies PCEs (>9.0%) are observed in OPVs utilizing fullerene derivatives and especially [6,6]-phenyl-C61 butyric acid methyl ester (PC60BM) as the acceptor. Recently, very promising efficiencies of ∼5.0% have been also obtained by Polyera corporation utilizing soluble conjugated polymers as both the donor and the acceptor components. It is therefore expected that through improved materials design for enhancing the electron mobility, better tuning of the energy levels and absorption profile of organic materials, significant improvements in the device performance can still be expected. In this work, the current trends on the most promising solution processable n-type organic materials (fullerene derivatives, small molecules and conjugated polymers) will be presented in detail, emphasizing on the correlation between structure/optoelectronic properties/morphology characterization and device performances. © The Royal Society of Chemistry 2013. Source


Geormezi M.,Advent Technologies SA | Paloukis F.,Advent Technologies SA | Orfanidi A.,Foundation for Research and Technology Hellas | Shroti N.,Foundation for Research and Technology Hellas | And 2 more authors.
Journal of Power Sources | Year: 2015

Abstract The effect of reformate H2 mixture composition on Pt/C based high temperature PEMFC anode was thoroughly studied, in order to understand the anode's tolerance under varying CO and steam partial pressures. It is shown that under steam partial pressure over 12 kPa a high overpotential region appears at current densities over 0.3 A/cm2. This negative effect appears in relation to the structure of the electrochemical interface (EI), as this is specified by the amount of H3PO4 (PA) within the anode catalytic layer. As also shown, the sustainable operation of the anode under reformate containing steam and CO as high as 30 kPa and 2 kPa respectively requires significantly lower loadings of PA. This malfunctioning is attributed to the hydrophobic/hydrophilic properties of the Pt/C-PA EI and its modification when water from the gas phase is dissolved in the PA, in combination with the polarization and the adsorption of CO and H2 on Pt surface. These phenomena and the capillary forces within the catalytic layer are responsible for the alternating contraction (ganglia formation and loss of ionic link within the EI) and spreading (thin film formation and well developed EI) of PA, thus giving rise to oscillatory behavior and unstable performance of the anode. © 2015 Elsevier B.V. All rights reserved. Source

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