Poly(phenylene sulfide benzimidazole) has been synthesized and tested as a potential material for high-temperature proton transport. A high content of sulfide bonds has been implemented in the polymer chains to endow a high antioxidant capacity and, in combination with bulky benzimidazole pendant units, to significantly suppress crystallinity and thereby improve the solubility in highly polar aprotic solvents. The amorphous polymer has high thermal stability and high glass transition temperature (Tg). Freestanding, insoluble, and robust membranes were obtained via thermal cross-linking of the benzimidazole moieties with octa-glycidyl polyhedral oligomeric silsesquioxane (g-POSS). The series of hybrid networks (cPPSBi_X, with X being the g-POSS content wt %) showed excellent oxidative stability, with cPPSBi_15 having weight loss lower than 5% after 264 h in Fenton's reagent at 80 °C. Elastic moduli as high as 868 MPa with reduced strain at break (1.8%) were obtained. After doping the membranes with phosphoric acid, proton conductivity in the range of 2.3 × 10–2 S cm–1 at 180 °C was obtained, and the membranes show a stress at break of 2.3 MPa. Dimensional and mechanical stability were maintained also at high doping levels thanks to the inclusion of g-POSS which provides the resulting hybrid networks with increased free volume and high cross-link density.
The synthesis and characterization of novel proton conducting ABA triblock copolymers are reported. Structure-properties relationship of the block copolymers has been investigated at both the microscopic and macroscopic levels.
The development of high-performance electrochemical energy devices (EEDs), is a critical aspect in the ongoing energy transition towards renewable sources and electrification of transports and facilities. The substantial change in energy production, storage and usage, requires the revamping of known technologies, the discovery of new ones and the enhancement of energy materials. Ion conducting polymers play a pivotal role in the new energetic scenario due to their main application as solid polymer electrolytes (SPEs) in EEDs such as batteries, fuel cells and supercapacitors. The use of SPEs drastically increases the performance, safety and sustainability of EEDs compared to liquid-based systems. Polymeric electrolyte materials must comply with different stringent pre-requisites depending on the final application. The presence and distribution of charges along the backbone, the chemical stability, chain stiffness and nanomorphology are only examples of critical variables to be taken into account in designing SPEs for EEDs.In this work, we focus on ion conducting polymers suitable for proton exchange membranes (PEMs) and lithium or magnesium SPEs. PEMs are materials with potential application in polymer electrolyte membrane fuel cells, whereas SPEs are a promising alternative to liquid electrolytes for metal-ion batteries. We investigate the synthesis and properties of different types of polymers and block-copolymers. The interplay between chemistry, nanostructure and ion conductivity in solid ion conducting polymers has proven to be a critical factor in the optimization of polymer electrolyte performances, and it represents the main topic of this PhD thesis.
A new simple and cost-effective method for the synthesis of sulfonated aromatic monomers is presented, offering a drastic reduction in the number of purification procedures and waste production.
Renewable energy and water electrolysis (WE) are deemed to be the pillars over which the incoming green hydrogen era and energy transition will stand. Water electrolysis can undergo in both acidic and alkaline conditions. In modern times, solid polymer electrolyte WE has attracted particular interest, due to the advantage of a compact design combined with the possibility to operate at higher pressure and temperatures even using pure water. Still to date, the most used membranes in PEMWE are poly(perfluorosulfonic) acids (PFSAs) (e.g., Nafion™) due to their mechanical strength, strong chemical resistance, and high proton conductivity. However, recent concerns regarding their cost, environmental impact due to fluorine chemistry, mechanical instability above 80 °C, and low gas barrier (especially H 2 ) require urgent development of suitable hydrocarbon alternatives. Sulfonated poly(phenylene sulfones) (sPPS) represent a valuable hydrocarbon alternative to PFSAs as they exhibit lower gas crossover, higher conductivity, better thermal stability and low production cost. [1] [2] This class of polymer is able to outperform Nafion™ in PEMWE thanks to their higher proton conductivity (Fig. 1 b)). [1] To improve long term-stability of these polymers in operative PEMWE conditions (T = 80°C, > 1 Acm -2 ), fluorine-free reinforcement and Ce-based “damage-reparation” [3] strategies have been successfully implemented extending their stability in the range of thousands of hours. A major drawback of PEMWE technology is the reliance on platinum group metals (PGMs) (i.e. Pt and Ir). This stimulated the research of alternative strategies to respond to the demand of green H 2 necessary to mitigate global warming reduction. AEMWE is the ideal alternative to PEMWE since it can be performed efficiently with non-PGMs, i.e., iron and nickel. The main shortcoming in AEMWE comes from the need of an alkaline electrolyte, which drastically limited the development of AEM technology in past decades. The harsh alkaline and electrochemical stress present in AEMWE have only recently been overcome by a new class of polyphenylene piperidinium and polynorbornene-based polymers which are also commercially available as Piperion™ and Pention™ respectively. The first are obtained by super-acidic Friedel-Craft addition [4] while the polynorbornene chemistry requires special catalysts. [5] Inspired by these results, in our lab, we have dedicated particular efforts to develop hydrocarbon AEM materials implementing phosphorous superbases as anion conducting functionalities to eliminate the presence of constant charges close to the polymer chain. AEMs based on polynorbornenes are proposed, including stable amino-linkage inspired by previous work. [6] Additionally, anion exchange ionomers (AEI) for catalyst layers with enhanced gas permeability were synthesized based on “canal” polynorbornene and novel crosslinked polyarylpiperidinium. The main synthetic strategies and properties (e.g., IEC, WU, alkaline resistance) of the resulting polymers are presented.
Abstract Knowledge of the transitions occurring during the formation of ion‐conducting polymer films and membranes is crucial to optimize material performances. The use of non‐destructive scattering techniques that offer high spatio‐temporal resolution is essential to investigating such structural transitions, especially when combined with complementary techniques probing at different time and spatial scales. Here, a simultaneous multi‐technique study is performed on the membrane formation mechanism and the subsequent hydration of two ion‐conducting polymers, the well‐known commercial Nafion and a synthesized sulfonated poly(phenylene sulfide sulfone) (sPSS). The X‐ray data distinguish the multi‐stage processes occurring during drying. A sol‐gel‐membrane transition sequence is observed for both polymers. However, while Nafion membrane evolves from a micellar solution through the formation of a phase‐separated gel, forming an oriented supported membrane, sPSS membrane evolves from a solution of dispersed polyelectrolyte chains via formation of an inhomogeneous gel, showing assembly and ionic phase separation only at the end of the drying process. Impedance spectroscopy data confirm the occurrence of the sol‐gel transitions, while gel‐membrane transitions are detected by optical reflectance data. The simultaneous multi‐technique approach presented here can connect the nanoscale to the macroscopic behavior, unraveling information essential to optimize membrane formation of different ion‐conducting polymers.
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