Proton exchange membrane fuel cells (PEMFCs) are promising power sources emerging among alternative energy conversion systems, because they can operate at relatively low temperature and offer numerous benefits, such as high efficiency, high power density and low polluting emissions. The present dissertation deals with the development of new proton conducting membranes having good conductivity, chemical and thermal stability, low methanol permeability and low cost. The main strategy used in this work was the preparation of sulfonated and silylated polyetheretherketone (PEEK) and polyphenylsulfone (PPSU) as membrane materials, because this synthetic approach represents a powerful tool to modulate the proton conductivity and hydrolytic stability of the electrolyte by the dosage of sulfonic acid groups and inorganic moieties covalently bound to the aromatic chains. Several types of proton exchange membranes were studied. Sulfonated and silylated PEEK and/or PPSU were used to prepare systems where two components resulted crosslinked by physical interactions or covalent bonds, obtaining the synergic effect of polymers having different conductivity and mechanical properties. • Sulfonated and silylated polyetheretherketone PhSi0.1S0.9PEEK (degree of sulfonation DS=0.9, and degree of silylation DSi=0.1) was synthesized via (i) sulfonation of PEEK, (ii) conversion of sulfonated polyetheretherketone (S0.9PEEK) into sulfonyl chlorinated derivative (PEEKSO2Cl), (iii) lithiation of PEEKSO2Cl and subsequent addition of PhSiCl3, followed by hydrolysis. The solubility of PEEKSO2Cl in organic solvent allows the silylation reaction to be carried out in homogeneous conditions. The structural characterization of the products by 1H and 13C NMR and ATR/FTIR spectroscopies highlighted the success of the synthetic pathway. The thermogravimetric analysis of PEEK derivatives indicated that the presence of the inorganic moieties stabilizes the aromatic matrix of the sulfonated polyetheretherketone. Blends of PhSi0.1S0.9PEEK and S0.5PEEK (DS=0.5) were prepared using different weight ratios of the two polymers. The membranes were characterized by water uptake measurements and electrochemical impedance spectroscopy (EIS). The results converge to indicate that the developed materials are promising electrolytes for PEMFC application. • Silylated and sulfonated polyphenylsulfone PhSi0.2S2PPSU (DS=2.0 and DSi=0.2) was synthesized via (i) lithiation of PPSU and subsequent addition of PhSiCl3, followed by hydrolysis, (ii) sulfonation by reaction with concentrated sulphuric acid. The chemical structure of polymers was investigated by 1H and 13C NMR, and ATR/FTIR, verifying the success of the developed synthetic route. Blends of PhSi0.2S2PPSU and S0.5PEEK were prepared, obtaining electrolytes with higher hydrolytic stability and increased proton conductivity with respect to those of pure S0.5PEEK membrane. Blend membranes showed also better performance in DMFC, where a reduced methanol permeability and adequately high power density values were observed, at temperature values as high as 100°C. All these features identify the prepared blend membranes as promising electrolytes for DMFC operating at intermediate temperatures. • Two silylated and sulfonated PPSU derivatives: Si0.2S2PPSU (DS=2.0 and DSi=0.2) and Si0.03S0.05PPSU (DS=0.05 and DSi=0.03) were synthesized following two different routes. In the first one, PPSU was silylated by reaction with SiCl4, then sulfonated by reaction with concentrated sulphuric acid, and Si0.2S2PPSU was obtained. In the second route, the use of the mild sulfonating agent ClSO3Si(CH3)3 allowed a careful control of the degree of sulfonation, and PPSU with a lower DS was obtained. Subsequent silylation by reaction with SiCl4 led to the final product Si0.03S0.05PPSU. An organic-inorganic hybrid polymer HSiSPPSU was synthesized by non-hydrolytic sol–gel reaction of Si0.2S2PPSU and Si0.03S0.05PPSU. The condensation between the silanol groups of the two polymers led to the formation of Si-O-Si bonds, as highlighted by analysis of ATR/FTIR spectra. The electrochemical characterization of HSiSPPSU membranes by EIS showed adequately high conductivity values to make the hybrid polymer a suitable candidate for application in PEMFCs operating at T > 100°C. The strategies followed in this work seems to be an effective way to overcome some drawbacks related to conventional polymer membranes currently used, demonstrating the relevant role played by synthesis in the preparation of electrolytes for PEMFCs.

Le celle a combustibile con membrane a scambio protonico (PEMFCs) sono alternative sorgenti di energia che offrono numerosi vantaggi come l’alta efficienza, l’alta densità di potenza e la bassa emissione d’inquinanti. Esse sono impiegate nelle macchine ad idrogeno e nei dispositivi elettronici quali computer e cellulari alimentati con metanolo. La diffusione su larga scala di queste tecnologie punta sullo sviluppo di membrane a scambio protonico di nuova generazione, il cui costo di produzione sia compatibile con un mercato di massa. Tali conduttori protonici devono esibire una buona conducibilità, stabilità chimica e termica. Nel presente lavoro, diverse strategie sono state impiegate per la preparazione di materiali a conduzione protonica a partire dai polimeri termoplastici aromatici: polietereterchetone (PEEK) e polifenilsolfone (PPSU). Di particolare rilevanza è la funzionalizzazione di tali polimeri mediante l’introduzione sulla catena aromatica di gruppi solfonici e gruppi contenenti silicio. Infatti, questo approccio sintetico permette di controllare la microstruttura del polimero, modulando il rapporto tra la fase idrofila e quella idrofoba, da cui dipendono fortemente le prestazioni dell’elettrolita. Diversi tipi di membrane sono state preparate impiegando: PEEK solfonato (SPEEK) e/o PPSU solfonato, variamente funzionalizzati con gruppi contenenti silicio, al fine di ottenere l’effetto sinergico derivante dalla combinazione di polimeri aventi diverse conducibilità protonica e caratteristiche meccaniche. I sistemi ibridi sono stati preparati mediante la reazione sol-gel che ha portato alla formazione dei legami covalenti Si-O-Si tra due derivati del PPSU diversamente funzionalizzati. Le membrane blend sono state invece preparate mescolando, durante il processo di casting, derivati del PEEK e/o PPSU. La caratterizzazione dei materiali ha riguardato l’analisi della struttura dei polimeri sintetizzati e delle proprietà chimico-fisiche ed elettrochimiche delle membrane. Risultati molto positivi sono stati ottenuti dai test eseguiti sulle membrane in un prototipo di cella a combustibile operante a metanolo diretto.

De Bonis, C. (2009). Hybrid polymer electrolytes for proton exchange membrane fuel cells: synthesis and applications.

Hybrid polymer electrolytes for proton exchange membrane fuel cells: synthesis and applications

DE BONIS, CATIA
2009-09-21

Abstract

Le celle a combustibile con membrane a scambio protonico (PEMFCs) sono alternative sorgenti di energia che offrono numerosi vantaggi come l’alta efficienza, l’alta densità di potenza e la bassa emissione d’inquinanti. Esse sono impiegate nelle macchine ad idrogeno e nei dispositivi elettronici quali computer e cellulari alimentati con metanolo. La diffusione su larga scala di queste tecnologie punta sullo sviluppo di membrane a scambio protonico di nuova generazione, il cui costo di produzione sia compatibile con un mercato di massa. Tali conduttori protonici devono esibire una buona conducibilità, stabilità chimica e termica. Nel presente lavoro, diverse strategie sono state impiegate per la preparazione di materiali a conduzione protonica a partire dai polimeri termoplastici aromatici: polietereterchetone (PEEK) e polifenilsolfone (PPSU). Di particolare rilevanza è la funzionalizzazione di tali polimeri mediante l’introduzione sulla catena aromatica di gruppi solfonici e gruppi contenenti silicio. Infatti, questo approccio sintetico permette di controllare la microstruttura del polimero, modulando il rapporto tra la fase idrofila e quella idrofoba, da cui dipendono fortemente le prestazioni dell’elettrolita. Diversi tipi di membrane sono state preparate impiegando: PEEK solfonato (SPEEK) e/o PPSU solfonato, variamente funzionalizzati con gruppi contenenti silicio, al fine di ottenere l’effetto sinergico derivante dalla combinazione di polimeri aventi diverse conducibilità protonica e caratteristiche meccaniche. I sistemi ibridi sono stati preparati mediante la reazione sol-gel che ha portato alla formazione dei legami covalenti Si-O-Si tra due derivati del PPSU diversamente funzionalizzati. Le membrane blend sono state invece preparate mescolando, durante il processo di casting, derivati del PEEK e/o PPSU. La caratterizzazione dei materiali ha riguardato l’analisi della struttura dei polimeri sintetizzati e delle proprietà chimico-fisiche ed elettrochimiche delle membrane. Risultati molto positivi sono stati ottenuti dai test eseguiti sulle membrane in un prototipo di cella a combustibile operante a metanolo diretto.
A.A. 2008/2009
MATERIALS FOR ENVIRONMENT AND ENERGY
21.
Proton exchange membrane fuel cells (PEMFCs) are promising power sources emerging among alternative energy conversion systems, because they can operate at relatively low temperature and offer numerous benefits, such as high efficiency, high power density and low polluting emissions. The present dissertation deals with the development of new proton conducting membranes having good conductivity, chemical and thermal stability, low methanol permeability and low cost. The main strategy used in this work was the preparation of sulfonated and silylated polyetheretherketone (PEEK) and polyphenylsulfone (PPSU) as membrane materials, because this synthetic approach represents a powerful tool to modulate the proton conductivity and hydrolytic stability of the electrolyte by the dosage of sulfonic acid groups and inorganic moieties covalently bound to the aromatic chains. Several types of proton exchange membranes were studied. Sulfonated and silylated PEEK and/or PPSU were used to prepare systems where two components resulted crosslinked by physical interactions or covalent bonds, obtaining the synergic effect of polymers having different conductivity and mechanical properties. • Sulfonated and silylated polyetheretherketone PhSi0.1S0.9PEEK (degree of sulfonation DS=0.9, and degree of silylation DSi=0.1) was synthesized via (i) sulfonation of PEEK, (ii) conversion of sulfonated polyetheretherketone (S0.9PEEK) into sulfonyl chlorinated derivative (PEEKSO2Cl), (iii) lithiation of PEEKSO2Cl and subsequent addition of PhSiCl3, followed by hydrolysis. The solubility of PEEKSO2Cl in organic solvent allows the silylation reaction to be carried out in homogeneous conditions. The structural characterization of the products by 1H and 13C NMR and ATR/FTIR spectroscopies highlighted the success of the synthetic pathway. The thermogravimetric analysis of PEEK derivatives indicated that the presence of the inorganic moieties stabilizes the aromatic matrix of the sulfonated polyetheretherketone. Blends of PhSi0.1S0.9PEEK and S0.5PEEK (DS=0.5) were prepared using different weight ratios of the two polymers. The membranes were characterized by water uptake measurements and electrochemical impedance spectroscopy (EIS). The results converge to indicate that the developed materials are promising electrolytes for PEMFC application. • Silylated and sulfonated polyphenylsulfone PhSi0.2S2PPSU (DS=2.0 and DSi=0.2) was synthesized via (i) lithiation of PPSU and subsequent addition of PhSiCl3, followed by hydrolysis, (ii) sulfonation by reaction with concentrated sulphuric acid. The chemical structure of polymers was investigated by 1H and 13C NMR, and ATR/FTIR, verifying the success of the developed synthetic route. Blends of PhSi0.2S2PPSU and S0.5PEEK were prepared, obtaining electrolytes with higher hydrolytic stability and increased proton conductivity with respect to those of pure S0.5PEEK membrane. Blend membranes showed also better performance in DMFC, where a reduced methanol permeability and adequately high power density values were observed, at temperature values as high as 100°C. All these features identify the prepared blend membranes as promising electrolytes for DMFC operating at intermediate temperatures. • Two silylated and sulfonated PPSU derivatives: Si0.2S2PPSU (DS=2.0 and DSi=0.2) and Si0.03S0.05PPSU (DS=0.05 and DSi=0.03) were synthesized following two different routes. In the first one, PPSU was silylated by reaction with SiCl4, then sulfonated by reaction with concentrated sulphuric acid, and Si0.2S2PPSU was obtained. In the second route, the use of the mild sulfonating agent ClSO3Si(CH3)3 allowed a careful control of the degree of sulfonation, and PPSU with a lower DS was obtained. Subsequent silylation by reaction with SiCl4 led to the final product Si0.03S0.05PPSU. An organic-inorganic hybrid polymer HSiSPPSU was synthesized by non-hydrolytic sol–gel reaction of Si0.2S2PPSU and Si0.03S0.05PPSU. The condensation between the silanol groups of the two polymers led to the formation of Si-O-Si bonds, as highlighted by analysis of ATR/FTIR spectra. The electrochemical characterization of HSiSPPSU membranes by EIS showed adequately high conductivity values to make the hybrid polymer a suitable candidate for application in PEMFCs operating at T > 100°C. The strategies followed in this work seems to be an effective way to overcome some drawbacks related to conventional polymer membranes currently used, demonstrating the relevant role played by synthesis in the preparation of electrolytes for PEMFCs.
celle a combustibile; membrane a scambio protonico; polimeri termoplastici aromatici; sintesi; risonanza magnetica nucleare; spettroscopia infrarossa; spettroscopia d’impedenza elettrochimica
Settore CHIM/03 - Chimica Generale e Inorganica
Settore ING-IND/22 - Scienza e Tecnologia dei Materiali
English
Tesi di dottorato
De Bonis, C. (2009). Hybrid polymer electrolytes for proton exchange membrane fuel cells: synthesis and applications.
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