Development of Sulfonated Poly(vinyl alcohol)/MoS2-Based Robust Composite Proton Exchange Membranes with Higher Selectivity

Selectivity is an essential property of proton exchange membranes. It is the ratio of proton conductivity to methanol permeability. In this study, we prepared mechanically robust composite proton exchange membranes (CPEMs) based on sulfonated poly(vinyl alcohol) (SPVA) and exfoliated molybdenum disulfide (MoS2) via solution casting. MoS2 nanoplatelets act as reinforcing fillers and enhance the barrier effect toward methanol permeation. The MoS2 loadings (wt %) were varied in the CPEMs to achieve higher selectivity by either enhancing the proton conductivity or reducing the methanol permeability of the membranes. To assess their physicochemical properties, the synthesized CPEMs were characterized for their water uptake, ion exchange capacity, proton conductivity, methanol permeability, and thermomechanical stabilities. The SPVA/MoS2-0.3% membranes with 0.3 wt % of MoS2 loading showed a proton conductivity of 48 +/- 7 mS/cm, which is the highest among all of the CPEMs and 1.8 times higher than that of SPVA tested at 25 degrees C and 98% RH. Due to the presence of MoS2 nanoplatelets, the CPEMs offered better resistance to methanol cross-over compared to pristine SPVA membranes. The SPVA/MoS2-0.3% membranes exhibit a methanol permeability of 1.72 x 10(-6) cm(2)/s at 25 degrees C, resulting in 5 and 37% reductions in methanol cross-over and 68 and 80% increase in selectivity than pristine SPVA and Nafion 117 membranes, respectively. Moreover, the SPVA/MoS2-0.3% membranes provided good mechanical stability with an enhanced proton conductivity of 54 +/- 5 mS/cm at 60 degrees C and 98% RH. Post-cross-linking of the SPVA/MoS2-0.3% membranes with glutaraldehyde was done to improve further their chemical, thermal, and mechanical stabilities for higher-temperature applications. The cross-linked CPEMs of 24X3.0SPVA/MoS2-0.3% exhibit considerably higher selectivity at elevated temperatures (ca. 80 degrees C) and 37 times higher selectivity than Nafion 117 at 60 degrees C. The above results indicate that the as-prepared SPVA/MoS2-0.3% and 24X3.0SPVA/MoS2-0.3% CPEMs have great potential for direct methanol fuel cell (DMFC) applications at moderately high temperatures.

Automated summary

This study focuses on the preparation of composite proton exchange membranes based on sulfonated poly(vinyl alcohol) and exfoliated molybdenum disulfide. The membranes exhibit excellent selectivity and proton conductivity, making them suitable for direct methanol fuel cell applications.