Highly Stable Solid Alkaline Electrolyte Membranes from Poly(vinyl alcohol)/Poly(vinyl pyrrolidone) Based on Chemical Cross-Linking

The stability of alkaline electrolyte membranes is recognized as a key factor that affects their electrochemical applications, especially, in alkaline medium at temperatures above 60 ℃ and high KOH concentration. In this article, poly(vinyl alcohol)/poly(vinyl pyrrolidone)/KOH (PVA/PVP/KOH) alkaline membranes were succesfully prepared by direct blending and chemical cross-linking modifications. In particular, the molecular structure, thermal stability, chemical stability, oxidative stability, and mechanical strength stability of the composite membranes were studied in detail using fourier transform infrared spectra (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and alternating current impedance technique. FTIR results indicated that PVP was successfully incorporated into the PVA matrix due to the strong PVP C=O I peak centered at 1672 cm-1. From the TGA, the increasing concentration of the doped KOH into membranes has little effect on the thermal stability. The homogeneous and compact morphology of the cross-section of the membranes were observed by SEM after conditioned at elevatedtemperatures and high concentration of KOH (80 ℃, 10 mol·L-1). The conductivity of the membrans (1.58×10-3 S·cm-1) in 10 mol·L-1 KOH at 80 ℃ was 91.5% higher than that in 10 mol·L-1 KOH at room temperature, which demonstrated the perfect chemical stability of the PVA/PVP alkaline membranes. In addition, the membranes displayed very high oxidative durability. Still 89% and 85% mass of the membrane were retained after 150 h treatment in 3% and 10% H2O2 solution at 60 ℃ , respectively. Due to the high dense cross-linkages in polymer matrics, the PVA/PVP/KOH membranes showed good isotropy and conductivity stability in pure water during the measuring time lasted for more than 800 h.