Water-Dispersible, Sulfonated Hyperbranched Poly(ether-ketone) Grafted Multiwalled Carbon Nanotubes as Oxygen Reduction Catalysts

To endorse sufficient water affinity to multiwalled carbon nanotubes (MWCNTs), dendritic hyperbranched poly(ether-ketone) (HPEK) was first covalently grafted to the surface of a MWCNT via a Friedel–Crafts acylation reaction. The resultant HPEK-grafted MWCNT (HPEK-g-MWCNT) was subsequently sulfonated in chlorosulfonic acid to produce sulfonated HPEK-g-MWCNT (SHPEK-g-MWCNT), which is dispersible well in water showing a zeta potential value of −57.8 mV. The SHPEK-g-MWCNT paper simply formed by filtration of aqueous dispersion has a sheet resistance as low as 63 Ω/sq. Its thin film shows a high electrocatalytic activity for oxygen reduction reaction (ORR). Thus, the newly produced water-dispersible MWCNT is a new class of high performance cathode material for ORR.