Lentini, Domenico (2025) SYNTHESIS AND CHARACTERIZATION OF POLYMERIC MEMBRANES FOR ALKALINE WATER ELECTROLYSIS. [Tesi di dottorato]

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Abstract

Hydrogen plays a crucial role in various industrial sectors such as ammonia synthesis, petroleum refining, and metallurgical applications, while its potential as a clean energy carrier and fuel is gaining increasing interest. At present, its production relies mainly on methane steam reforming, a process with a considerable environmental impact. Water electrolysis represents a sustainable alternative, particularly when integrated with electricity generated from renewable sources, enabling low-carbon hydrogen production. When performed in alkaline media, it does not require noble-metal-based electrocatalysts or expensive corrosion-resistant materials for cell construction, thereby offering the potential to reduce overall costs. Devices capable of performing this type of electrolysis rely on polymer membranes that can conduct hydroxide ions and effectively separate the generated gases, enabling efficient coupling with renewable energy sources. Unfortunately, the polymer membranes currently available exhibit limited durability, which hinders the practical deployment of these systems. This PhD research project addresses this technological gap, an area that has been the focus of extensive academic and industrial research in recent years. Two types of membranes for alkaline electrolysis have been investigated in this work: Anion Exchange Membranes (AEMs) and Ion-Solvating Membranes (ISMs), with one membrane of each type developed, characterized, and tested. Although designed for the same purpose, these two classes differ in the nature of the polymers used, a factor that resizes the operational strategies of the devices in which they are integrated. For the AEM, a copolymer based on diallyldimethylammonium chloride and vinyl acetate was synthesized, hydrolyzed, and incorporated into a polypropylene composite, with the aim of expanding the family of polydiallylazacycloalkanes, which have already shown promising results for AEM development. The ISM involved the design of a styrene–acrylic acid copolymer, also processed into a polypropylene-based composite membrane, with the objective of diversifying and reducing the cost of polymer structures employed in the emerging ISM concept, which are predominantly based on polybenzimidazoles. Alongside the development of these membranes, noble-metal-free electrocatalysts suitable for integration into alkaline electrolyzer cells were also investigated through the synthesis and characterization of FeNi3/FeNiOx, FeCo3/FeCoOx, and Ni1-xCox/NiCoOx nanoparticles, which were developed concurrently within a doctoral project at the University of Milano-Bicocca.

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