Grafting design: a strategy to increase the performance of radiation-grafted membranes

Aryl ether-free polymer electrolytes for electrochemical and energy devices

Anion exchange polymers (AEPs) play a crucial role in green hydrogen production through anion exchange membrane water electrolysis. The chemical stability of AEPs is paramount for stable system operation in electrolysers and other electrochemical devices. Given the instability of aryl ether-containing AEPs under high pH conditions, recent research has focused on quaternized aryl ether-free variants. The primary goal of this review is to provide a greater depth of knowledge on the synthesis of aryl ether-free AEPs targeted for electrochemical devices. Synthetic pathways that yield polyaromatic AEPs include acid-catalysed polyhydroxyalkylation, metal-promoted coupling reactions, ionene synthesis via nucleophilic substitution, alkylation of polybenzimidazole, and Diels-Alder polymerization. Polyolefinic AEPs are prepared through addition polymerization, ring-opening metathesis, radiation grafting reactions, and anionic polymerization. Discussions cover structure-property-performance relationships of AEPs in fuel cells, redox flow batteries, and water and CO2 electrolysers, along with the current status of scale-up synthesis and commercialization.

Membranes Based on Polyvinylidene Fluoride and Radiation-Grafted Sulfonated Polystyrene and Their Performance in Proton-Exchange Membrane Fuel Cells

Proton-exchange membranes based on gamma-irradiated films of PVDF and radiation-grafted sulfonated polystyrene with an ion-exchange capacity of 1.8 meq/g and crosslinking degrees of 0 and 3% were synthesized. A solvent-free, environmentally friendly method of styrene grafting from its aqueous emulsion, with a styrene content of only 5 vol.% was used. Energy dispersive X-ray mapping analysis showed that the grafted sulfonated polystyrene is uniformly distributed throughout the membrane thickness. The obtained materials had a proton conductivity up to 132 mS/cm at 80 °C and a hydrogen permeability of up to 5.2 cm²/s at 30 °C, which significantly exceeded similar values for Nafion^®-212 membranes. The resulting membranes exhibited a H₂/O₂ fuel cell peak power density of up to 0.4 W/cm² at 65 °C. Accelerated stability tests showed that adding a crosslinking agent could significantly increase the stability of the membranes in the fuel cells. The thermal properties and crystallinity of the membranes were investigated through differential scanning calorimetry and X-ray powder diffraction methods. The conductivity, water uptake, and mechanical properties of the membranes (stress–strain curves) were also characterized.

Performance evaluation of microbial fuel cell using a radiation synthesized low density polyethylene-grafted-poly (glycidyl methacrylate-co-vinyl acetate) as a proton exchange membrane

ABSTRACTThe present work focuses on the synthesis of a proton exchange membrane to be assembled in a microbial fuel cell (MFC) for simultaneous bioelectricity production and domestic wastewater treatment. The indigenous membrane was prepared by ionizing irradiation-induced graft copolymerization of glycidyl methacrylate (GMA) and vinyl acetate (VAc) onto low-density polyethylene and subsequently, the prepared grafted sheets were sulfonated via epoxy ring-opening of PGMA moieties. Parameters affecting the grafting degree were investigated and the prepared membranes were characterized by investigating their structural, thermal, mechanical, and electrical properties. Some physicochemical characteristics including ion exchange capacity, sulfonation density, and proton conductivity were also evaluated. The data confirmed the success of the preparation protocol to obtain a suitable membrane for the proposed application. Moreover, the performance of the assembled MFC was thoroughly investigated through the evaluation of its electrochemical behaviour including cyclic voltammetry, electrochemical impedance spectroscopy, columbic efficiency, and wastewater treatment capability. The sulfonated LDPE-g-P(GMA-co-VAc) membrane of 80% grafting degree shows substantial removal of chemical oxygen demand up to about 90% with columbic efficiency of 10.1%, columbic recovery of 8.7%, rate of energy harvest of 2.1 C/h and power density of 2.72 W m^-2. However, the use of 10 mM of KMnO₄ as electron acceptor drastically increase the harvested power density to reach 356.4 W m^-2.

A Raman spectro-microscopic investigation of ETFE-based radiation-grafted anion-exchange membranes

Raman spectro-microscopy on a radiation-grafted anion-exchange membrane detected alkali degradation throughout its cross-section that quantitatively matched loss of ion-exchange capacity.