Efficiency of Neat and Quaternized-Cellulose Nanofibril Fillers in Chitosan Membranes for Direct Ethanol Fuel Cells

In this work, fully polysaccharide based membranes were presented as self-standing, solid polyelectrolytes for application in anion exchange membrane fuel cells (AEMFCs). For this purpose, cellulose nanofibrils (CNFs) were modified successfully with an organosilane reagent, resulting in quaternized CNFs (CNF (D)), as shown by Fourier Transform Infrared Spectroscopy (FTIR), Carbon-13 (C13) nuclear magnetic resonance (¹³C NMR), Thermogravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC), and ζ-potential measurements. Both the neat (CNF) and CNF(D) particles were incorporated in situ into the chitosan (CS) membrane during the solvent casting process, resulting in composite membranes that were studied extensively for morphology, potassium hydroxide (KOH) uptake and swelling ratio, ethanol (EtOH) permeability, mechanical properties, ionic conductivity, and cell performance. The results showed higher Young's modulus (119%), tensile strength (91%), ion exchange capacity (177%), and ionic conductivity (33%) of the CS-based membranes compared to the commercial Fumatech membrane. The addition of CNF filler improved the thermal stability of the CS membranes and reduced the overall mass loss. The CNF (D) filler provided the lowest (4.23 × 10^-5 cm² s^-1) EtOH permeability of the respective membrane, which is in the same range as that of the commercial membrane (3.47 × 10^-5 cm²s^-1). The most significant improvement (~78%) in power density at 80 °C was observed for the CS membrane with neat CNF compared to the commercial Fumatech membrane (62.4 mW cm^-2 vs. 35.1 mW cm^-2). Fuel cell tests showed that all CS-based anion exchange membranes (AEMs) exhibited higher maximum power densities than the commercial AEMs at 25 °C and 60 °C with humidified or non-humidified oxygen, demonstrating their potential for low-temperature direct ethanol fuel cell (DEFC) applications.