Nafion-TiO2 composite DMFC membranes: physico-chemical properties of the filler versus electrochemical performance

TiO2 nanometric powders were prepared via a sol-gel procedure and calcined at various temperatures to obtain different surface and bulk properties. The calcined powders were used as fillers in composite Nafion membranes for application in high temperature direct methanol fuel cells (DMFCs). The powder physico-chemical properties were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and pH measurements. The observed characteristics were correlated to the DMFC electrochemical behaviour. Analysis of the high temperature conductivity and DMFC performance reveals a significant influence of the surface characteristics of the ceramic oxide, such as oxygen functional groups and surface area, on the membrane electrochemical behaviour. A maximum DMFC power density of 350 mW cm−2 was achieved under oxygen feed at 145 °C in a pressurized DMFC (2.5 bar, anode and cathode) equipped with TiO2 nano-particles based composite membranes.