Mixed Membrane Matrices Based on Nafion/UiO-66/SO₃H-UiO-66 Nano-MOFs: Revealing the Effect of Crystal Size, Sulfonation, and Filler Loading on the Mechanical and Conductivity Properties

Abstract

Mixed membrane matrices (MMMs) made up with Nafion and nanocrystals of zirconium metal-organic framework (MOF) UiO-66 or the analogous sulfonated SOH-UiO-66 were prepared by varying the filler loading and the size of the crystals. The combined effects of size and loading, together with the presence of sulfonic groups covalently linked to the MOFs, were studied with regard to the conductivity and mechanical properties of the obtained composite matrices. A large screening of membranes was preliminarily made and, on the most promising samples, an accurate conductivity study at different relative humidities and temperatures was also carried out. The results showed that membranes containing large crystals (200 nm average size) in low amounts (around 2%) displayed the best results in terms of proton conductivity values, reaching values by 30% higher than those of pure Nafion, while leaving the mechanical properties substantially unchanged. On the contrary, MMMs containing MOFs of small size (20 nm average size) did not show any conductivity improvements if compared to pure Nafion membranes. The effect of MOF sulfonation was negligible at low filler loading whereas it became important at loading values around 10%. Finally, membranes with a high filler loading (up to 60 wt %) of sulfonated UiO-66 showed a slight reduction of conductivity in comparison with membranes loaded at 20% of nonsulfonated ones.

Ultra‐High Ion Selectivity of a Modified Nafion Composite Membrane for Vanadium Redox Flow Battery by Incorporation of Phosphotungstic Acid Coupled UiO‐66‐NH2

“…The SEM image in Figure a and TEM image in Figure d reveal that the morphology of the synthesized UiO‐66‐NH 2 particles present the typical octahedral morphology that is in favorable consistency with the theoretical structure . Moreover, the XRD pattern of the synthesized sample presents a high degree of agreement with the simulated UiO‐66‐NH 2 pattern (Figure c), which indicates the MOFs synthesized by us possess a good crystalline structure –,. According to Figure b and 2e, the particles morphology reflects a certain irregularity and is no longer a regular octahedral structure, meaning that the surface of UiO‐66‐NH 2 has been successfully modified by other substances.…”

Recent Progress in the Development of Composite Membranes Based on Polybenzimidazole for High Temperature Proton Exchange Membrane (PEM) Fuel Cell Applications

“…The introduction of MOFs into organic polymer results in the enhanced thermal chemical stability of the formed composites under harsh conditions, making them suitable for industrial application [ 193 ]. For elaboration of these membranes, polymers such as perfulorosulfonic acid [ 194 ], sulfonated poly (ether ether ketone) [ 195 ], and poly(vinyl alcohol) [ 196 ] have been used.…”

Proton Conductivity of Composite Polyelectrolyte Membranes with Metal‐Organic Frameworks for Fuel Cell Applications

“…In a similar study, Costantino and co‐workers synthesized Zr‐based UiO‐66 with two different average crystal sizes (20 and 200 nm) and its sulfonated derivative (UiO‐66‐SO 3 H) with an average crystal size in the range 100−200 nm . These fillers incorporated into Nafion membranes and a systematic study of the influence of the MOF size, filler loading, and sulfonation on proton conductivity was conducted.…”

“…Plot of proton conductivity (at 95% RH and 80 °C) of Nafion composite membranes with different loadings of UiO‐66 and UiO‐66‐SO 3 H …”