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 °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 × 10−2 g cm−2 h−1) and permeability of ferric ions (3.5 × 10−5 cm2 min−1) were comparable to those of commercial Nafion 117 membrane. The dependence of the proton conductivity on the concentration of H2SO4 at 22 °C was studied that allowed us to predict the intrinsic proton conductivity of the p-PVA membrane (5.5 × 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+/H2 redox fuel cell showing power density of 71 mW cm−2 at 200 mA cm−2.

► A novel method for preparation of phosphorylated PVA membranes developed.
► A pathway of PVA phosphorylation with formation of P–C bonds suggested based on IR-spectra.
► A mechanism of proton transport within phosphorylated PVA membrane suggested.
► The membrane allowed to obtain power density of 71 mW cm−2 at 200 mA cm−2 in a Fe3+/H2 redox fuel cell.