Grafting distance and molecular weight dependent proton conduction of polymer electrolyte brushes

Abstract

Proton conducting materials having reasonable proton conductivity over wide range of relative humidity are of great importance for their application in electrochemical or energy storage devices. Herein, we show that polymer electrolyte brushes on titanate nanotubes fabricated by surface-initiated free radical polymerization technique are effective proton conductors under both hydrated and anhydrous conditions. Both grafting distance and molecular weight of surface-attached polymer electrolyte chains exhibit significant influence on proton conductivity of the formed polymer brushes. With the decrease in average grafting distance of surface-attached polymer chains, the proton conductivity of the synthesized polymer brushes initially increases and then decreases after reaching a maximum value. Non-monotonic behavior of proton conductivity with the increase in molecular weight is also observed. Under optimized conditions, the proton conductivity values of the formed polymer electrolyte brush reach 0.095Scm−1 under 100% relative humidity and 0.01Scm−1 under anhydrous conditions at 140°C.