Highly Selective and Methanol Resistant Hybrid Proton Exchange Membranes From the Blends of Sulfonated Poly (ether ether ketone) and <scp>UiO</scp> ‐66‐ <scp> NH ₂ </scp> Metal–Organic Frameworks for Direct Methanol Fuel Cells

ABSTRACT Commonly used commercial Nafion membrane in fuel cells is costly and thermally less stable. Sulfonated aromatic hydrocarbon membranes are found to be a better substitute for Nafion since they possess long‐term stability and low cost. However, it needs to be modified to overcome the trade‐off between proton conductivity and fuel permeability to achieve high performance. In this study, UiO‐66‐NH 2 metal–organic frameworks (MOFs) were synthesized solvothermally from zirconyl chloride octahydrate and 2‐aminoterephthalic acid and incorporated with sulfonated poly (ether ether ketone) (SPEEK). The SPEEK/UiO‐66‐NH 2 hybrid proton exchange membranes (PEMs) were fabricated by solution casting method and tested for its applicability in direct methanol fuel cells (DMFCs). FTIR studies revealed that the successful incorporation of UiO‐66‐NH 2 into the SPEEK matrix was due to the interaction between the amino groups of MOF and the sulfonic acid groups of SPEEK. The SPEEK/UiO‐66‐NH 2 membranes exposed the block‐shaped particles with a uniform distribution and rough surfaces as shown in SEM and AFM images respectively. Further, these membranes exhibited superior water uptake, swelling ratio, hydrophilicity as well as higher thermal, mechanical and oxidative stability due to the synergistic effect of SPEEK and UiO‐66‐NH 2 . AC impedance spectroscopy and cyclic voltammetry were used to evaluate the membrane's proton conductivity and methanol permeability respectively. Among all, the SPEEK/UiO‐66‐NH 2 (1 wt%) membrane demonstrated reduced methanol permeability of 1.46 × 10 −8 cm 2 s −1 as well as higher proton conductivity of 6.74 × 10 −3 S cm −1 at 25°C and membrane selectivity of 4.61 × 10 5 S cm −3 s. Overall, due to their superior ex situ properties, SPEEK/UiO‐66‐NH 2 hybrid PEMs may be utilized in DMFCs; however, this is contingent upon their compatibility in the real fuel cell environment.