Effect of a Proton Conducting Filler on the Physico‐Chemical Properties of SPEEK‐Based Membranes

Abstract

Composite membranes based on sulphonated polyetherether ketone (SPEEK) having a 60% degree of sulphonation (DS = 0.6) and containing 23 and 50 wt.‐% hydrated tin oxide (SnO2·nH2O) were prepared and characterised. The lower water uptake (WU) and the higher conductivity values recorded for the composite membranes with respect to pure SPEEK reference suggested the involvement of SnO2·nH2O in the proton conduction mechanism. Pulsed‐field‐gradient spin‐echo (PFGSE) NMR was employed to obtain a direct measurement of water self‐diffusion coefficient in the membranes. Differences were observed between the unfilled SPEEK and the composites, including departures from the normal correlation between water diffusivity and proton conductivity in the case of composites. To better understand the SnO2·nH2O effect on the proton transport properties of the SPEEK‐based membrane, we employed an analytical model that predicts the membrane conductivity as a function of its hydration level and porous structure. The comparison of the model results with the experimental proton conductivity values demonstrated that the tin oxide phase provides additional paths between the water clusters for proton transport, resulting in reduced tortuosity and enhanced proton conductivity. Moreover, the composite showed reduced methanol crossover with respect to the unfilled membrane.

Development of Nafion/Tin Oxide Composite MEA for DMFC Applications

“…Hydrated tin oxide (SnO 2 ·nH 2 O) was prepared according to the procedure previously reported [27,28]. Sulfated tin oxide (S-SnO 2 ) was obtained as follows [29]: SnO 2 ·nH 2 O was suspended in 3 M sulfuric acid and stirred for 1 h at room temperature, then filtered and dried at room temperature for 1 h. Finally, the powder was calcined at 500 °C in air for 3 h and then milled in an agate mortar.…”

“…SnO 2 nH 2 O is an inorganic proton conductor; when used as filler in a sulfonated polyether ether ketone (SPEEK) matrix gives rise to composites characterized by higher proton conductivity and lower methanol crossover than those of an unfilled SPEEK due to its capability to selectively reduce the tortuosity of the SPEEK membrane for proton transport and to avoid methanol permeation through the membrane [27,28]. Among all known solids, sulfated tin oxide (S-SnO 2 ) is currently recognized as one of the strongest superacids [29,30].While largely used as catalyst [31,32], to our knowledge S-SnO 2 has never been explored as filler in composite polymer electrolyte membranes.…”

Development of glucose oxidase-based bioanodes for enzyme fuel cell applications

“…SPEEK offers versatile properties such as chemical inertness, thermal stability, and proton conductivity dependent on sulfonation degree, i.e., number of protogenic carriers per monomer unit, and therefore tunable via control of synthetic conditions [27,28]. The use of SPEEK in EFC systems has not been reported so far in the literature and represents a viable economic alternative to commercial Nafion membranes.…”

Composite Polymer Electrolytes for Fuel Cell Applications: Filler‐Induced Effect on Water Sorption and Transport Properties

“…[6] When exposed to water, both Nafion and SAPs undergo phase separation in hydrophilic and hydrophobic domains: the hydrophobic domains consist of the perfluorinated or polyaromatic backbone for Nafion and SAPs, respectively, and the hydrophilic domains are formed by the SO 3 H groups bound to water molecules. [10,11] Coupled with the decrease in methanol permeability, however, a decrease of proton conductivity with respect to unmodified ionomers is often observed upon filler addition, [12][13][14] even though results obtained by different researchers on these composites are somehow contradictory. As a result of the lower hydrophobicity of the backbone and the lower acidity and polarity of the sulfonic acid functional groups, the hydrophobic/hydrophilic separation of SAPs is less pronounced than Nafion.…”

“…Ion exchange capacity (IEC) values of the filler and membrane samples were determined by acid-base titrations following a previously published procedure [11] and the hydration grade of the membranes, that is, the number of water molecules per acid group (l), was calculated by using Equation (5):…”