Mohammad Bagher Karimi

The aim of present study is to reduce the tortuosity of proton conductive pathways within the polymer electrolyte membranes (PEMs) for application in anhydrous PEM fuel cells. For this purpose, for the first time, microsize chopped fibers (modified glass wool fibers), modified nanosilica, and a deep eutectic solvent (DES) are incorporated into the Nafion matrix to extend proton conductive pathways. The long length of the fibers as new and cheap additives creates a continuous interface within the polymer matrix which significantly improves its proton conductivity, likely by reducing the tortuosity of proton conductive pathways. While nanosilica promotes the connectivity of the short fibers, EG/NaBr‐based DES is also used as a nonaqueous electrolyte to maintain proton conductivity at anhydrous conditions. The measurements show super proton conductivity beyond 1400 mS cm⁻¹ at 100 °C and anhydrous conditions for the Nafion/DES composite membrane containing 5 wt% short fibers and 2 wt% nanosilica. Furthermore, fuel cell performance of the prepared membranes shows a promising result by providing a maximum power density of 715 mW cm⁻² at 95 °C. This study clearly shows the important role of ionic paths within the PEMs to achieve desirable properties in the real condition of a fuel cell system.

In this research, deep eutectic solvents (DESs) were prepared and employed as the electrolyte in Nafion membranes. Different factors, such as the water content and Nafion counterions (H⁺, Li⁺, Na⁺ and K⁺), which could influence the PEM performance, were evaluated. The obtained results showed that the presence of water may have a constructive or destructive effect on the DES and Nafion/DES properties, which should be considered for their final applications. Also, the electronegativity of the counterion can significantly influence the Nafion/DES proton conductivity. The prepared Nafion/DES composite membranes showed superconducting properties as a result of a Grotthuss-like mechanism for proton conduction. The conductivities of the prepared membranes were compared to those of other membranes based on an upper bound concept, which showed the potential use of DESs as a promising alternative to conventional ionic liquids. Finally, the fuel cell performances of the prepared membranes at different temperatures were evaluated.