A comprehensive study of MIL-88a as a key component of hybrid polymer electrolytes for H2 fuel cells

In this work, an electrochemical study of the iron fumarate metal-organic framework structure MIL-88a was carried out. This MOF exhibits an exceptional characteristic: it alters the parameters of its crystal lattice in response to temperature variations and the specific guest molecules present. Through impedance spectroscopy, we investigated how guest molecules within the pores of MIL-88a influence the material's ionic conductivity and its responsiveness to changing environmental conditions. Based on the data obtained, hybrid membranes based on sulfonated multiblock copolymers of polysulfone and polyphenylsulfone (SPES) doped with MIL-88a were prepared. The distribution of crystallites in the membrane was assessed by using scanning electron microscopy. It was found that crystallites agglomerates reduce the tensile strength of the membrane from 87 to 69 MPa, and from 56 to 42 MPa in the dry and wet forms, respectively. The presence of this MOF doubles the water absorption of the hybrid membranes compared to the pure one, resulting in an improvement of their ionic conductivity from 15.8 to 26.5 mS/cm at 80 °C. Hybrid membranes show a high maximum power density (1040 mWcm −2 ) in the fuel single cell test that is comparable to that obtained for commercial perfluoro-sulfonic acid PEMs such as Nafion®. • Hybrid composite membranes based on MOF MIL-88a and polyethersulfone multiblock copolymers. • Electrochemical behavior of MIL-88a under different temperature and humidity cycles. • Hydrophilic hybrid membranes with high thermomechanical stability. • Proton-conducting hybrid membranes at the temperature range fuel cell operation. • Improved performances in the single fuel cell test.