Proton Transport within Acid Aggregates in a Hydrated Precise Sulfophenylated Polyethylene

Abstract

Hydrated acid aggregates in a precise sulfophenylated polyethylene exhibit high proton conductivity. This study focuses on a new precise polymer synthesized by ring-opening polymerization, p5PhSA, that has a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon. The structure of p5PhSA is characterized with X-ray scattering and the proton conductivity is measured by electrical impedance spectroscopy. Experiments are performed as a function of relative humidity and temperature. Water uptake in p5PhSA is determined by sorption measurements as a function of humidity. Atomistic molecular dynamics simulations are used to elucidate the structure of the acid aggregates in the amorphous polymer matrix and are directly compared to absolute X-ray scattering data. At 40°C and 90% relative humidity, the proton conductivity of p5PhSA is 0.23 S/cm, exceeding that of Nafion at the same conditions. At room temperature, the interaggregate distance nearly doubles from 1.8 nm at 0% relative humidity to 3.4 nm at 100% relative humidity. The swelling of these acid aggregates with water is reversible and facilitates the proton transport through p5PhSA. Figure 1