Electrospinning-Enabled Structural Control of Proton-Conducting Composite Membranes

Abstract

Proton exchange membrane fuel cells (PEMFCs) have garnered increasing attention as a promising power source for use in portable electronic devices, electric vehicles, and residential energy supplies, owing to their eco-friendly attributes and high energy efficiency. One of the key components that significantly affect the performance of the PEMFCs is the proton exchange membrane (PEM), as its primary roles are to allow proton conduction from the anode to cathode and also to maintain electrical isolation between the electrodes. Currently, most widely used PEM are based on water-swollen polymer electrolyte membranes containing sulfonic acid groups (e.g., Nafion and sulfonated hydrocarbon copolymers). Considering practical application to PEMFCs, these hydrated polymer electrolyte membranes have many advantageous features, including excellent proton conductivity, mechanical strength, and electrochemical resistance to membrane decomposition. However, serious issues (specifically, high cost, limited ion conductivity, humidity-dependent mass transport/dimensional change and loss of electrochemical activities at dehydrated conditions) still lie ahead in widening its application fields. Therefore, development of advanced PEM to outperform the currently available materials is strongly required. Among various approaches to achieve this challenging goal, in addition to continuous pursuit of synthesizing PEM with new chemical structures or combination of different material mixtures can be suggested as a simple and efficient way. Recently, the design of nano-composite PEMs combined organic/inorganic materials with electrospun materials have generated great interests in the fields of PEMFCs due to their improved and enhanced properties and applicability. This electrospinning technique, i.e., physical mixing of two or more individual material components, is a well-known technique for making a nano-composite materials. In this study, we demonstrate the new nano-composite PEMs take advantage of the electrospun nonwovens reinforced, flexible proton-conductive phosphosilicate glass composite membranes and dual electrospray (DES)-assisted forced polyelectrolyte blending membranes for use in PEMFCs. The new reinforced composite membrane is fabricated via the impregnation of a 3-glycidyloxypropyl trimethoxysilane (GPTMS)/orthophosphoric acid (H3PO4) mixture into a PI nonwoven substrate followed by in-situ sol-gel synthesis and hydrothermal treatment. This unique structural integrity enables the reinforced composite membrane to provide unprecedented improvement in the mechanical properties (notably flexibility and thickness) over typical bulk phosphosilicate glasses that are highly fragile and thick. At the same time, the reinforced composite membrane is higher proton conductivity at dehumidified conditions, as compared to a hydration-dependent polymer electrolyte membrane such as sulfonated poly(arylene ether sulfone) (SPAES). Also, we demonstrate a new class of dual electrospray (DES)-assisted forced polymer blending membrans. As a model system to explore the feasibility of this blending approach, Nafion and multiblock sulfonated hydrocarbon copolymer (denoted as sBlock) are chosen. The processing uniqueness and simplicity of the DES blending technique enable the successful fabrication of Nafion/sBlock blends (referred to as N/B blends) that are difficult to achieve with conventional blending methods due to their large miscibility difference. More notably, during the DES blending, nonsolvent-induced nanophase morphology reconstruction occurs in the N/B Blend, eventually giving rise to some difference in proton conductivity between experimental values and theoretically predicted ones.