Optimal loading of quaternized chitosan nanofillers in functionalized polyvinyl alcohol polymer membrane for effective hydroxide ion conduction and suppressed alcohol transport

Abstract

A polymer composite was prepared by incorporating 5-20 wt% quaternized chitosan (Q-chitosan) nanoparticles into quaternized polyvinyl alcohol (Q-PVA) to enhance the dimensional stability and conductive properties. Compared with the pristine Q-PVA membrane, the ionic conductivity of the Q-PVA composites with 5–10 wt% Q-chitosan was improved due to increased polymeric free volume hole density. The methanol permeability is suppressed in these Q-PVA/Q-chitosan composites because of the confined swelling in the presence of the fillers, shrinking the free volume size. The Q-PVA/5%Q-chitosan composite exhibits higher peak power density (Pmax) than other Q-PVA membranes in direct methanol fuel cells. A Pmax of 92 mW cm−2 is attained using the Q-PVA/5%Q-chitosan composite at 90 °C with 5–6 mg cm−2 catalyst loads on micro-porous layer-containing carbon cloth. The high load of 20 wt% Q-chitosan does not benefit ionic conduction and power generation, probably due to interfacial resistance at rough surfaces. Using the Q-PVA/5%Q-chitosan composite and reduced catalyst loads of 1–2 mg cm−2 on pristine carbon cloth, Pmax of 90 mW cm−2 can be achieved at 60 °C for both methanol and ethanol fuel cells, but declined at 90 °C due to insufficient catalysts. Overall the Q-PVA/Q-chitosan composite offers a potential electrolyte for energy devices operating in an alkaline environment.