Novel Nafion nanocomposite membranes embedded with TiO2-decorated MWCNTs for high-temperature/low relative humidity fuel cell systems

Abstract

AbstractExtending the operation of proton exchange membrane fuel cells (PEMFCs) at high temperature (i.e., 120 °C) and/or low relative humidity (< 50% RH) remains a significant challenge due to dehydration and subsequent performance failure of the Nafion electrolyte. We approached this problem by integrating the Nafion matrix with a novel hybrid nanofiller, created through direct growth of TiO2 nanoparticles on the surface of carbon nanotubes. This synthetic approach allowed to preserve an effective nanodispersion of Titania particles in the hosting matrix, thereby boosting dimensional stability, hydrophilicity, and physiochemical properties of the Nafion/MWCNTs-TiO2 (NMT-x) nanocomposites compared to parental Nafion. At optimal concentration (i.e., 3 wt% with respect to the polymer), the nanocomposite membrane exhibited high transport characteristics with impressive water retention capabilities, resulting in a proton conductivity of 8.3 mS cm− 1 at 80 °C and 20% RH. The Titania nanoparticles plays a key role in retaining water molecules even under dehydrating conditions, while also directly contributing to proton transport. Additionally, the long carbon nanotubes promote the formation of additional paths for proton conductivity. These combined features enabled the NMT-3 membrane to achieve a maximum power output of 307.7 mW/cm2 in a single H2/air fuel cell (5 cm2 active electrode area and 0.5 mg Pt/cm2 at both electrodes) under very challenging conditions, specifically at 120 °C and 30% RH. This represents a significant advancement towards overcoming the limitations of traditional Nafion membranes and opens up new possibilities for high-temperature, low-humidity H2/air fuel cell applications.