Functionalized Al2O3 particles as additives in proton-conducting polymer electrolyte membranes for fuel cell applications

This study reports on the synthesis and characterization of sulfated Al2O3 and of composite membranes, prepared by dispersing the functionalized oxide in Nafion, acting as electrolytes in proton-exchange membrane fuel cells. Different synthetic routes were explored to obtain nanometric alumina particles with sulfate groups. Structural and morphological characteristics of the inorganic compounds and the nature of the bond of the sulfates with the oxide were investigated by x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption and thermal gravimetric analysis. Key properties of the hybrid membranes were elucidated in terms of thermal characteristics, water uptake and ionic exchange capacity. Functionality of the nanocomposite membranes, compared with plain Nafion, was tested in hydrogen-fed fuel cells. Polarization and power density curves and in-situ electrochemical impedance spectroscopy were accomplished to evaluate the effect of temperature on the cell performance. It is shown that well-addressed variations in the synthetic routes are able to determine different morphologies and dimensions of the particles and different degrees of functionalization. The incorporation of alumina in Nafion changes the characteristics of the membrane, with special regard towards hydration. In-situ fuel cell electrochemical tests reveal improved electrode-composite membrane interface properties as the working temperature of the cell increases.