Polypropylene-grafted multi-walled carbon nanotube reinforced polypropylene composite bipolar plates in polymer electrolyte membrane fuel cells

Abstract

Polypropylene-grafted multi-walled carbon nanotubes (MWCNTs/PP-g-MA) were prepared via a ring-opening reaction between polypropylene grafted maleic anhydride (PP-g-MA) and animated MWCNTs by a solution process. The prepared MWCNTs/PP-g-MA were introduced to the PP nanocomposite bipolar plates, to achieve a high compatibility and good adhesion between MWCNTs and the immiscible PP matrix through PP-g-MA chains. Replacement of amine-terminated groups by PP-g-MA on the MWCNTs leads to covalent grafting of longer copolymer chains to the MWCNTs, and to improve the dispersion of MWCNTs in the PP matrix. The resulting PP nanocomposite bipolar plates with 1, 2, and 4 wt% of MWCNTs/PP-g-MA demonstrates not only improved flexural strengths by 56.3, 68.5, and 70.9%, but also enhanced bulk electrical conductivities by 282, 425, and 473%, respectively, over those of the neat composite bipolar plates. The contact resistance of the MWCNTs/PP-g-MA/PP nanocomposite bipolar plate is 9.1 mOhm cm², which is lower than the D.O.E. target ∼10 mOhm cm² in the year 2010. The maximum current density and power density of the single cell test for the nanocomposite bipolar plate with 4 wt% MWCNTs/PP-g-MA are 1.41 A cm⁻² and 0.586 W cm⁻², respectively, which are 12.4 and 4.56% slightly lower than those of graphite plates. Comparing with pristine MWCNTs/PP nanocomposite bipolar plates, MWCNTs/PP-g-MA/PP nanocomposite bipolar plates are suitable for bipolar plates of polymer electrolyte membrane fuel cells.