Aikaterini K. Andreopoulou

Cross-linked high temperature polymer electrolytes through oxadiazole bond formation and their applications in HT PEM fuel cells

Chemical cross-linking of linear, high molecular weight polymer electrolytes has been performed herein, using thermally stable cross-linking bonds. Aromatic copolymeric or terpolymeric polyethers combining polar main chain pyridine units with side cross-linkable carboxylic acid groups were employed. The selected cross-linking chemistry was that of oxadiazole ring formation due to the synthetic versatility and the exceptional thermal and chemical stability of the formed linkages. Membranes of increased robustness and thermal stability were obtained after cross-linking that moreover presented higher doping levels than their linear analogues. Selected cross-linked membranes were formulated into membrane electrode assemblies (MEAs) that were tested in a single cell at temperatures up to 220 °C for 350 hours showing stable operation and high ionic conductivities close to 10−1 S cm−1. These facts point to the superiority of the cross-linked materials and their great potential as PEMs for fuel cells operating well above 180 °C.

An alternative methodology for anchoring organic sensitizers onto TiO2 semiconductors for photoelectrochemical applications

In the present work, we investigated alternative ways of connecting purely organic dyes onto the surface of TiO2 electrodes. For this purpose, perfluorophenyl ω-end rr-poly(3-alkyl thiophene)s were synthesized, which can react with the hydroxyl groups of TiO2 under mild alkaline conditions. Thus, stable non-hydrolysable Ti–O–C bonds are formed. Through this route, and after optimization of the reaction conditions, several poly(thiophene)-sensitized TiO2 photoanodes were prepared and tested in dye-sensitized solar cells. Moreover, a comparative study was performed for the dye/TiO2 stability after water and alkaline solution treatment revealing the particular methodologys efficiency. The above sensitizers have also proven to be functional in photoelectrochemical cells employed for water splitting applications in the presence of alkaline electrolytes.

A versatile approach for creating hybrid semiconducting polymer–fullerene architectures for organic electronics

A novel methodology, through which fullerenes are effectively introduced directly onto semiconducting species, is presented herein. Electron accepting perfluorophenyl-quinolines either as small molecules, as homopolymers, or as random copolymers with regioregular poly(3-alkyl thiophene), have been synthesized and further employed for the preparation of hybrid materials with C60 or PCBM. More specifically, via this route one of the fluorine atoms of the perfluorophenyl ring is transformed into an azide that undergoes [3+2]-cycloaddition onto the fullerenes surface, producing 1,6-azo bridged carbon nanostructure–organic semiconducting hybrids.

Copolymers of ionic liquids with polymeric or metallocomplex chromophores for quasi-solid-state DSSC applications

The development of copolymers based on ionic liquid vinyl monomers of the imidazole family combined with polymerizable chromophoric units is presented herein. For this end, ruthenium complexes bearing polymerizable vinyl groups or ω-end vinyl rr-poly(3-alkyl thiophene) were prepared and copolymerized with the ionic liquid monomers under free radical polymerization conditions, affording chromophore/polyelectrolyte combinations. Homopolymer ionic liquids were also synthesized to select the optimum conditions for the copolymers thereafter. All the monomers and polymers were characterized for their optical properties, and were also structurally characterized using various complementary techniques. Selected copolymers and homopolymers were tested in quasi-solid-state sensitized solar cells based on titania and regioregular poly(3-hexyl thiophene) acting as a hole-transporting semiconducting polymer. The ionic liquid, which is miscible with the hole-conductor and can be deposited with the latter, provides a functionality that, in some cases, supports an increase in open-circuit voltage, thus increasing cell efficiency.

Synthesis of Polythiophene–Fullerene Hybrid Additives as Potential Compatibilizers of BHJ Active Layers

Perfluorophenyl functionalities have been introduced as side chain substituents onto regioregular poly(3-hexyl thiophene) (rr-P3HT), under various percentages. These functional groups were then converted to azides which were used to create polymeric hybrid materials with fullerene species, either C60 or C70. The P3HT–fullerene hybrids thus formed were thereafter evaluated as potential compatibilizers of BHJ active layers comprising P3HT and fullerene based acceptors. Therefore, a systematic investigation of the optical and morphological properties of the purified polymer–fullerene hybrid materials was performed, via different complementary techniques. Additionally, P3HT:PC70BM blends containing various percentages of the herein synthesized hybrid material comprising rr-P3HT and C70 were investigated via Transmission Electron Microscopy (TEM) in an effort to understand the effect of the hybrids as additives on the morphology and nanophase separation of this typically used active layer blend for OPVs.

Semiconducting end-perfluorinated P3HT–fullerenic hybrids as potential additives for P3HT/IC70BA blends

An efficient route to synthesise hybrid polymers consisting of a semiconducting polymer and a fullerene unit, for BHJ OPV devices is presented herein. The synthetic procedure is based on the in situ functionalisation of regioregular polythiophenes of various molecular weights with perfluorophenyl moieties at the ω end position of the polymeric chains, after the GRIM polymerisation reaction. Each of the perfluorophenyl moieties is then decorated with an azide group, and employed in a [3 + 2] cycloaddition reaction with fullerene species, i.e. C70 or IC70MA, yielding P3HT–fullerene hybrids covalently linked via aziridine bridges. The effectiveness of the purification procedures of the above organic and hybrid materials were evaluated by extended spectroscopic and chromatographic methods. The optical and electrochemical characterisation of the resulting hybrid structures revealed that the unique optoelectronic properties of the P3HT polymers are retained in the hybrid materials. Whereas the morphological properties are largely affected by the introduction of the C70 and IC70MA fullerenes. The enhanced and tunable nanophase separation observed in the polymer–fullerene hybrid films coupled with their excellent optoelectronic properties makes them exciting potential polymeric additives for the P3HT:IC70BA active blends.

Pyridine Containing Aromatic Polyether Membranes

The chapter describes the development of aromatic poly(ether sulfone)s carrying main chain pyridine units as alternative to poly(benzimidazole) (PBI) polymer electrolytes for high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) applications operating at 180 °C. These polymeric materials present excellent thermal and oxidative stability both ex situ and in situ as well as high proton conductivities after doping with strong protic acids. The pathway from monomers’ design to polymerization conditions optimization and finally to membranes preparation and doping with phosphoric acid is analytically presented. Further structural and mechanical stabilization of such polyelectrolytes and their application in HT-PEMFCs operating above 180 °C even up to 220 °C has been achieved through cross-linking. The cross-linked materials’ superiority over linear analogues is depicted.

Influence of the Molecular Structure on the Properties and Fuel Cell Performance of High Temperature Polymer Electrolyte Membranes

High Temperature PEM Fuel Cells (130 C-200 C) offer the distinct advantages over traditional Low Temperature PEMs. Polymeric materials of specific properties should be used as electrolytes for high temperature MEAs in order to withstand the strong conditions during the fuel cell operation. Current research interest focuses on the development of new polymers with tailored basic sites that could improve the acid–base interactions of the membranes in order to acquire high proton conductivity (~10S/cm) at temperatures ranging between 150°C and 200°C Herein we present our approach to the synthesis of monomers and copolymers containing basic groups having high molecular weights, increased solubility and the ability to form complexes with strong acids. Different polymeric structures have been used in order to examine the influence of the detailed polymeric structure on the final membrane properties. It was found that the phosphoric acid doping ability is dramatically influenced by the presence of the polar groups, as well as the detailed copolymer structure. Even small differences on the pyridine content resulted in drastic difference on the phosphoric acid level in some cases as showed in Fig. 1.

Organic polymeric semiconductor materials for applications in photovoltaic cells

An overview of current trends in materials for polymer photovoltaics is given herein, with emphasis paid to the semiconductors composing the active photovoltaic layer. The different cases of polymeric electron donors that have appeared in recent literature holding the most promising results are categorized in respect to their monomeric counterparts (e.g., thiophene, carbazole, isoindigo, quinoxaline). On the other hand, electron acceptors are mostly based on fullerenes functionalized with different organic parts as solubilizing and miscibility enhancing groups. Organic small molecular and polymeric electron acceptors are also presented. Finally, hybrid systems containing both polymeric and fullerene parts are described.

Rigid–Flexible and Rod–Coil Copolymers

A large part of polymer material research has been devoted to block copolymers. One of the major focuses of research in this field has been on rod–coil block copolymers, which are produced by the skillful combination of rigid-rod and flexible-coil polymers. As a result, some of the most interesting self-assembling structures in nanometer length scales have been produced. Thus, the understanding of phase separation and self-organization concepts in polymers has been greatly expanded while applications in some of the most demanding and modern technological areas are nowadays considered. In this chapter, a summary of synthetic efforts devoted to the preparation of rod–coil block and rigid–flexible alternating copolymers is presented along with their self-assembly features and possible practical utilization areas.