Porous gC₃N₄-Gd₂Zr₂O₇ enables the high-temperature operation of Nafion membranes in polymer electrolyte fuel cells over 500 hours

Nafion, a perfluorosulfonic acid (PFSA) polymer, is a vital electrolyte that extensively contributes to the commercialization of polymer electrolyte fuel cells (PEFCs). However, adopting Nafion in high-temperature (HT) PEFCs (HT-PEFCs) is still a great challenge. Herein, we present a potential additive (carbon nitride-gadolinium zirconium oxide (gC₃N₄-Gd₂Zr₂O₇)) to simultaneously extend the power density and lifetime of Nafion in HT-PEFCs. Owing to the porous nature, radical-scavenging ability, and thermal stability of gC₃N₄-Gd₂Zr₂O₇, the Nafion/gC₃N₄-Gd₂Zr₂O₇ membrane exhibited high water uptake, oxidative stability, and thermomechanical stability compared to the unmodified Nafion membrane. At 100 °C under 30% RH, the maximum power density of Nafion/gC₃N₄-Gd₂Zr₂O₇ was 504 mW cm⁻² at a load current density of 804 mA cm⁻², which is 1.9 and 2.3 fold higher than that of commercial Nafion-212 and pristine Nafion membranes. Moreover, Nafion/gC₃N₄-Gd₂Zr₂O₇ displays an open-circuit voltage (OCV) decay of 0.1 mV h⁻¹ during 515 h of continuous operation, which is significantly lower than that of the Nafion membrane during the 300 h durability operation (2.8 mV h⁻¹). When increasing the operating temperature to 125 °C under 15% RH, the Nafion/gC₃N₄-Gd₂Zr₂O₇ based PEFC largely outperforms the Nafion-212 and pristine Nafion-based PEFCs, achieving an output of 380 mW cm⁻², one of the most competitive HT-PEFC power densities reported for Nafion-based membranes. Post durability tests further ensure the superior stability of Nafion/gC₃N₄-Gd₂Zr₂O₇ during HT-PEFC operation. The present study provides deep insight into developing and understanding of advanced Nafion composite membranes applicable for HT-PEFCs.