Effect of Varying Oxidation Degrees and Sulfonation of Graphene Oxide on Proton Transport in Polyaniline Composite Membranes

ABSTRACT

This work reports the sequential optimization of the degree of oxidation of graphene oxide (GO), GO loading, the degree of GO sulfonation, and sulfonated graphene oxide (SGO) loading in GO/PANI and SGO/PANI proton exchange membranes to establish structure–property relationships governing proton transport. The effects of these modifications on membrane chemistry, hydration behavior, proton transport, and mechanical integrity were systematically investigated. The optimized GO/PANI membrane (GP‐0.45‐3), containing 3 wt% GO with an intermediate degree of oxidation, exhibited a proton conductivity of 10.12 mS cm ⁻¹ . Sulfonation further enhanced proton transport through the introduction of acidic –SO ₃ H groups, increasing the conductivity of the optimized SGO/PANI membrane (SGP‐1.5) to 17.98 mS cm ⁻¹ . Subsequent optimization of SGO loading produced the SGP‐1.5‐1 membrane with the highest proton conductivity of 31.84 mS cm ⁻¹ while maintaining excellent mechanical integrity. FTIR, Raman spectroscopy, x‐ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, ion‐exchange capacity, and water uptake analyses demonstrate that enhanced proton transport arises from the synergistic effects of controlled GO oxidation, sulfonation, optimized nanofiller loading, and effective utilization of absorbed water. These findings provide a practical strategy for designing GO/SGO–PANI proton exchange membranes for proton‐conducting electrochemical devices, including proton exchange membrane fuel cells.