Addressing the detrimental effect of CeO2 radical scavenger on the durability of polymer electrolyte membrane fuel cells

A radical scavenger, CeO2, effectively improves the chemical durability of fuel cell membranes, however, Ce4+ ions eluted from the CeO2 lead to Pt/C degradation and diminished power performance. To address the detrimental effect, we prepared a carbon nitride (C2N) coating on CeO2 nanoparticles. The C2N protective layer reduced the Ce4+ dissolution rate 11-fold compared with pristine CeO2. Density functional theory calculations suggest that the C2N structure suppresses Ce4+ dissolution by strongly binding the Ce4+. Furthermore, it has a profoundly lowered band gap in contact with CeO2, enabling C2N-mediated electron transfer for efficient radical scavenging reaction. A membrane electrode assembly fabricated using the C2N-coated CeO2 exhibited excellent open circuit voltage durability for more than 600 h, without any loss in power performance. The judicious surface engineering of CeO2 avoids the deep-rooted trade-off between membrane and catalyst layer durability.