Effects of relative humidity on performance of Pt/zeolite-chitosan membrane in PEM fuel cell

Abstract

To study the effects of relative humidity on performance of Pt/zeolite-chitosan membrane in PEM fuel cell. The studied membranes were uncrosslinked chitosan, crosslinked chitosan and doped crosslinked chitosan membranes. The doping solution was 2% by weight of sulfuric acid. Zeolite A was incorporated in the range of 0-30% by weight of chitosan. It was found that the ion exchange capacity and proton conductivity was increased with zeolite content however the tensile strength and gas permeability was decreased. The proton conductivity in planar view at 60oC of 30% crosslinked chitosan-zeolite membranes was 0.043±0.006 S/cm and increased to 0.123 ± 0.024 S/cm in doped membranes. After Pt plating by electroless technique at 60℃ for 90 min, the proton conductivity of 30% doped crosslinked chitosan-zeolite membrane was increased to 0.312±0.008 S/cm. In single cell testing at 30oC, the current density at 0.5 V of 30% crosslinked chitosan-zeolite membrane was increased from 2.9 ± 0.1 mA/cm2 at fully hydration (RH at anode-cathode sides are 100%-100%) to 5.1 ± 0.1 mA/sq.cm for zero hydration (RH at anode-cathode sides are 0%-0%) at both sides. Amongst the studied chitosan based membranes, it was found that the 30% doped crosslinked chitosan-zeolite membrane provided the best performance. The current densities at 0.5 V without external humidifier at 30, 60 and 90℃ were 9.5 ± 0.01, 9.8 ± 0.01, and 10.1 ± 0.01 mA/sq.cm, respectively.