Effect of different substrates, inks composition and rheology on coating deposition of microporous layer (MPL) for PEM-FCs

The rheology of microporous layer (MPL) inks for polymer electrolyte membrane fuel cell (PEM-FC) applications was investigated, and its effect on thickness and morphology of final layer, prepared via doctor-blade technique, was examined. The effect of the carbon black (CB) on slurry viscosity was studied in the range CB/water = 0.11/0.17 (g/g) as well as the effect of surfactant and PTFE (Teflon®) addition. Slurry viscosity is mainly determined by the CB/water and CB/surfactant ratios, while PTFE addition has minor influence. Viscosities in the range 0.05–0.06 Pa s (at shear rate 100 s−1) were found to be appropriate for coating deposition. Two substrates of different morphology, a carbon cloth (CC) and a woven non-woven (WNW), were coated with slurries of different composition but showing the same rheology. Notwithstanding the use of slurries with the same rheological behavior, different MPL coating thicknesses were obtained. This suggested that the substrate morphology has a non-negligible influence on the final MPL thickness. The MPL layer definitely increased the hydrophobicity, and in some samples the region of superhydrophobicity (contact angle >150°) was reached. In-plane electrical resistance of gas diffusion layers (GDLs), i.e. substrate coated with MPL, was measured and it was found that the two different substrates have no influence on it (about 0.8 Ω). FCs assembling different GDLs showed different electrochemical performances in terms of I–V curves: MPLs coated onto WNW gave somewhat higher power densities (0.40 W/cm2 at 0.5 V).