Polyketone-Based Anion-Exchange Membranes for Alkaline Water Electrolysis

Abstract

Anion-exchange membranes (AEMs) are involved in a wide range of applications, including fuel cells and water electrolysis. A straightforward method for the preparation of efficient AEMs consists of polymer functionalization with robust anion-exchange sites. In this work, an aliphatic polyketone was functionalized with 1-(3-aminopropyl)imidazole through the Paal–Knorr reaction, with a carbonyl (CCO %) conversion of 33%. The anion-exchange groups were generated by the imidazole quaternization by using two different types of alkyl halides, i.e., 1,4-iodobutane and 1-iodobutane, with the aim of modulating the degree of crosslinking of the derived membrane. All of the membranes were amorphous (Tg ∼ 30 °C), thermally resistant up to 130 °C, and had a minimum Young’s modulus of 372 ± 30 MPa and a maximum of 86 ± 5 % for the elongation at break for the least-crosslinked system. The ionic conductivity of the AEMs was determined at 25 °C by electrochemical impedance spectroscopy (EIS), with a maximum of 9.69 mS/cm, i.e., comparable with that of 9.66 mS/cm measured using a commercially available AEM (Fumasep-PK-130). Future efforts will be directed toward increasing the robustness of these PK-based AEMs to meet all the requirements needed for their application in electrolytic cells.

Functionalization of polyketone (PK) with 1‐(3‐aminopropyl)piperidine for the preparation of anion exchange membranes

“…The polyketone PK-30 has been functionalized using an adaptation of the procedure reported by Racchi et al 9 A schematic representation of the reaction is reported in Figure 1. No solvent is needed since the amine is liquid and the polyketone acts as a viscous liquid at 110 C.…”

“…This shift can be related to the presence of sidechains that hinder the backbone mobility as reported in previous investigations. 9 However, the glass transition remains below room temperature. This behavior could result in membranes characterized by good flexibility, which is beneficial for the final application as AEMs.…”

“…The functionalized polyketone PK-30_Pip-36 was used to produce AEMs by using a procedure similar to that previously investigated by Racchi et al 9 Notably, during solution-casting and membrane formation by solvent evaporation, the quaternization of the piperidine moieties occurs. A diiodide, specifically diiodobutane (DIB) was used in this process in order to promote membrane crosslinking and to provide the required mechanical stability.…”

“…Among aliphatic PKs, those containing 1,4-diketones (1,4-PKs) are among the most studied for a wide range of applications. [9][10][11][12][13][14] The main advantage of this class of polymers lies in the ease of functionalization because 1,4-diketones can be involved in a Paal-Knorr reaction with a primary amine to form an N-substituted pyrrolic ring on the backbone. This reaction allows for the insertion of a sidechain that can contain different kinds of functional groups.…”

“…We used the Paal-Knorr reaction starting from the 1-(3-aminopropyl)piperidine as diamine for the first time, thus leading to propyl-piperidine sidechains. This approach has been previously reported with different diamines, [9][10][11]15,16 but it appears worthwhile since the amine is commercially available, liquid and thus used as solvent. Notably, the primary amine is involved in the Paal-Knorr reaction for the formation of the pyrrole units on the macromolecular PK-30 backbone, whereas the piperidine pendant groups experiences quaternization by means of alkyl iodides.…”