Enhanced proton conductivity of proton exchange membranes by incorporating phosphorylated hollow titania spheres

Phosphorylated hollow titania spheres (PHTS) with a superior water retention property are synthesized via a soft-template method and introduced into a sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate SPEEK/PHTS hybrid membranes. The incorporation of PHTS renders hybrid membranes with higher water uptake but lower swelling degree. The increased water retention capacity and additional proton transfer sites in the organic-inorganic interfacial zones lead to an enhancement in membrane proton conductivity. The highest proton conductivity (σ) of 0.228 S cm-1 at 70 °C under 100% RH for the hybrid membrane with 20 wt% of PHTS is achieved, which is two orders of magnitude higher than the pristine SPEEK membrane. Moreover, the PHTS fillers also prolong the tortuous pathways for methanol transport, conferring the hybrid membranes lower methanol permeability (P) in the range of 3.8-4.4 × 10-7 cm2 s-1. The maximum selectivity (σ/P) of as-prepared hybrid membranes is 2.09 × 105 S s cm-3, twice higher than a pristine SPEEK membrane.