Phosphorylated polyvinyl alcohol membranes for redox Fe3+/H2 flow cells

A novel method for preparation of phosphorylated polyvinyl alcohol (p-PVA) membranes was developed and used to synthesize a series of membranes with different degree of phosphorylation (4-9 wt % of phosphorus). The optimal mass ratio of PVA:H3PO2 was found to be 4.0:1.0, while the optimal curing time was 3 h at a temperature of 120 degrees C. The membranes possessed good mechanical robustness and chemical stability in acidic media. The possible pathway of PVA phosphorylation leading to formation of P-C bonds was suggested based on IR-spectra of the membranes. The water flux (6.08 x 10(-2) g cm(-2) h(-1)) and permeability of ferric ions (3.5 x 10(-5) cm(2) min(-1)) were comparable to those of commercial Nafion 117 membrane. The dependence of the proton conductivity on the concentration of H2SO4 at 22 degrees C was studied that allowed us to predict the intrinsic proton conductivity of the p-PVA membrane (5.5 x 10(-3) S cm(-1)). The partial charges on oxygen atoms in the proposed structural units were calculated and the results permitted to suggest a mechanism of proton transport. The performance of the p-PVA membrane was tested in a Fe3+/H-2 redox fuel cell showing power density of 71 mW cm(-2) at 200 mA cm(-2). (c) 2012 Elsevier B.V. All rights reserved.