Toward extended durability and power output of high temperature proton exchange membrane fuel cells with Gd2Zr2O7-C3N4 composite membrane

State-of-the-art proton exchange membrane fuel cell (PEMFC) that operate at 80 degrees C and 100% relative humidity (RH) requires an external humidifier, noble electrocatalyst, and expensive Nafion membrane to obtain appreciable power output and durability. High temperature (HT) operation over 100 degrees C provides an ideal solution to avoid costly components in PEMFC application. However, HT-PEMFC frequently loses its performance excessively because of phosphoric acid leaching from the conventional polybenzimidazole-based membranes. Herein, we present a gadolinium zirconium oxide (Gd2Zr2O7)-carbon nitride (C3N4) (GdZr-CN) additive that reasonably improves the power output, chemical durability, and operational stability of sulfonated poly(ether ether ketone) (SPEEK) membrane in HT-PEMFC. When use SPEEK/GdZr-CN composite membrane in HT-PEMFC, the metal cations (Zr4+ and Gd3+) decompose the free radicals, while the acid-base interactions between functional groups (-SO3H, -NH, -NH2, and -OH) involve the anhydrous proton conduction. Using SPEEK/GdZr-CN composite membrane, we obtain a HT-PEMFC exhibiting a maximal power output of 315 mW cm-2 at 110 degrees C under 15% RH, with minimal chemical degradation after 300 h of operation. Although the incorporation of GdZr-CN significantly enhances the durability of the composite membrane by scavenging free radicals and increasing glass transition temperature, the minimal degradation observed is primarily attributed to the inherent vulnerability of ether linkages in SPEEK backbones to free radical attacks and hygrothermal stress during prolonged operation. This study unveils that SPEEK/GdZr-CN composite membrane is a cost-competitive, energy-efficient, and durable PEM from the perspective of HT-PEMFC.