Methanol and proton transport in layered double hydroxide and smectite clay-based composites: influence on the electrochemical behavior of direct methanol fuel cells at intermediate temperatures

Composite membranes based on Nafion with the inclusion of cationic and anionic nanoclays, Laponite, and layered double hydroxide (LDH), respectively, were used to increase the operating temperature of a direct methanol fuel cell (DMFC). The electrochemical behavior of the hybrid nanocomposites was investigated in a single cell at different temperatures (from 90 to 110 °C), and the results were compared with those obtained on the filler-free Nafion membrane. Cell resistance measurements showed a significant improvement of the water retention capability at intermediate temperature for the composite membranes, in particular the LDH-based one. This feature was investigated and explained by a thorough NMR study (diffusometry, relaxometry, and 1H spectral analysis) on the different membranes. Furthermore, the dispersion of 2D plate-like nanolayers in the polymeric matrix demonstrates to be a physical barrier, considerably reducing the methanol mobility through an increase of the tortuosity of the diffusional paths of methanol molecules.