Proton conductivity and methanol rejection by ceramic membranes derived from ferroxane and alumoxane precursors

An iron-based ceramic material is shown to have favorable properties as an electrolyte material for proton exchange membranes in fuel cells. Iron (ferroxane) and aluminum (alumoxane) metal-oxane nanoparticles were prepared as precursor materials for membrane fabrication. The structure of ferroxane-derived ceramics was characterized with FTIR, TEM, and nitrogen adsorption–desorption. The protonic conductivity of the membranes was studied by electrochemical impedance spectroscopy (EIS) to determine their feasibility in fuel cell applications. Conductivities of sintered ferroxane samples were significantly higher than those of green bodies. Moreover, sintered samples displayed a relatively flat dependence of conductivity on relative humidity. The protonic conductivity of ferroxane derived ceramics fired at 300 °C ranged from 1.29 to 2.65 × 10−2 S cm−1 at relative humidities of 33–100% and room temperature. The permeabilities of ferroxane and alumoxane derived ceramics were 1.23 × 10−7 and 1.65 × 10−7 cm2 s−1, respectively. The conductivity of ferroxane was comparable to those of the Nafion® membrane with the advantages of lower methanol permeability, lower material costs, and less sensitivity to humidity.