Potential bifunctional filler (CeO₂-ACNTs) for nafion matrix toward extended electrochemical power density and durability in proton-exchange membrane fuel cells operating at reduced relative humidity

Cerium oxide-anchored amine-functionalized carbon nanotubes (CeO₂-ACNTs) are applied as radical scavengers as well as solid proton conductors to realize hybrids with Nafion (Nafion/CeO₂-ACNTs) for a proton-exchange membrane fuel cell (PEMFC) operating at low relative humidity (RH). Reinforcement due to the existence of ACNTs offers good mechanical strength and proton conductivity to hybrid, and addition of CeO₂ mitigates the chemical degradation of hybrid. The proton conductivity of Nafion/CeO₂-ACNTs at 20% RH is 12.2 mS cm^-1, which is 4 and 5 times better than that of recast Nafion and Nafion-212, respectively. PEMFC integrated with Nafion/CeO₂-ACNTs delivers a maximum power density of 174.25 mW cm^-2 at a load current density of 334.66 mA cm^-2 while operating at 60 °C under 20% RH. In contrast, under identical condition, the maximum power densities of 83.14 and 72.55 mW cm^-2 are achieved by recast Nafion and Nafion-212, respectively. Additionally, PEMFC integrated with Nafion/CeO₂-ACNTs exhibits a decay of only 0.21 mV h^-1 over 200 h while keeping at 60 °C under 20% RH. Compared to Nafion/CeO₂-ACNTs, the recast Nafion and Nafion-212 are experienced the accelerated decay (recast Nafion, 0.65 mV h^-1 Nafion-212, 0.59 mV h^-1). PEMFC performance, hydrogen crossover as well as morphology of specimens are probed before and after durability test; the Nafion/CeO₂-ACNTs exhibits high stability than other specimens. Thus, Nafion/CeO₂-ACNTs can be exploited to address various critical issues associated with commercial Nafion in PEMFC applications.