Structure–property correlation of semifluorinated 6-membered co-SPIs for proton exchange membrane

Sulfonated co‐poly(ether imide)s with alkyne groups: Fabrication of crosslinked membranes and studies on PEM properties including MFC performance

A new diamine monomer having alkyne side‐groups (DADAF) has been successfully synthesized, and it was used to prepare a series of sulfonated co‐polyimides (DFN‐XX) when reacted with 1,4,5,8‐naphthalenetetracarboxylic dianhydride along with different mole% of 4,4′‐diaminostilbene‐2,2′‐disulfonic acid. The membrane was made from the copolymers by solution casting route, and one of the copolymers DFN‐70 was used to prepare crosslinked membranes by adding a different amount of 1,6‐hexanediazide during solution casting step. The morphological transformation from non‐crosslinked S‐coPI to crosslinked S‐coPI was observed by employing transmission electron microscopy, atomic force microscopy, and small‐angle X‐ray scattering analyses. Compared to the non‐crosslinked DFN‐XX membranes, crosslinked DFN‐70 copolymer membranes showed low water uptake and improved mechanical and peroxide radical stability. Also, crosslinked DFN‐70 copolymer membranes showed significantly higher proton conductivities (0.004‐0.06 S cm−1) compared to those of DFN‐70 (0.003‐0.05 S cm−1) particularly, at 80°C when the relative humidity increased from 40% to 98%. Furthermore, crosslinked DFN‐70 copolymer membranes exhibited significantly enhanced performance in a microbial fuel cell (MFC) as compared to those of non‐crosslinked DFN‐70 membrane.

Effect of Chemical Structure and Degree of Branching on the Stability of Proton Exchange Membranes Based on Sulfonated Polynaphthylimides

Hydrolytic stability and oxidative stability are the core properties of sulfonated polynaphthylimides (SPIs) as proton exchange membranes. The chemical structure of SPIs directly influences the performance. Herein, three different series of branched SPIs were designed and prepared using 1,3,5-tris (2-trifluoromethyl-4-aminophenoxy) benzene as a trifunctional monomer and three non-sulfonated diamine monomers, such as 4,4'-oxydianiline (ODA), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (6FODA), and 4,4'-(9-fluorenylidene)dianiline (BFDA). The effect of the chemical structure and degree of branching on SPIs properties is discussed. The results showed that by controlling the chemical structure and degree of branching, the chemical stability of SPIs changed significantly. SPI-6FODA with two ether linkages and a hydrophobic CF₃ group has higher hydrolytic stability than SPI-ODA with only one ether linkage. In addition, with the increase of the introduced B₃ monomer, the oxidation stability of SPI-6FODA has been greatly improved. We successfully synthesized SPIs with a high hydrolytic stability and oxidative stability.

Biofouling effects on the performance of microbial fuel cells and recent advances in biotechnological and chemical strategies for mitigation

The occurrence of biofouling in MFC can cause severe problems such as hindering proton transfer and increasing the ohmic and charge transfer resistance of cathodes, which results in a rapid decline in performance of MFC. This is one of the main reasons why scaling-up of MFCs has not yet been successfully accomplished. The present review article is a wide-ranging attempt to provide insights to the biofouling mechanisms on surfaces of MFC, mainly on proton exchange membranes and cathodes, and their effects on performance of MFC based on theoretical and practical evidence. Various biofouling mitigation techniques for membranes are discussed, including preparation of antifouling composite membranes, modification of the physical and chemical properties of existing membranes, and coating with antifouling agents. For cathodes of MFC, use of Ag nanoparticles, Ag-based composite nanoparticles, and antifouling chemicals is outlined in considerable detail. Finally, prospective techniques for mitigation of biofouling are discussed, which have not been given much previous attention in the field of MFC research. This article will help to enhance understanding of the severity of biofouling issues in MFCs and provides up-to-date solutions. It will be beneficial for scientific communities for further strengthening MFC research and will also help in progressing this cutting-edge technology to scale-up, using the most efficient methods as described here.