Ta–TiO x nanoparticles as radical scavengers to improve the durability of Fe–N–C oxygen reduction catalysts

Highly active and durable platinum group metal-free catalysts for the oxygen reduction reaction, such as Fe–N–C materials, are needed to lower the cost of proton-exchange membrane fuel cells. However, their durability is impaired by the attack of oxidizing radicals such as ·OH and HO 2 · that form from incomplete reduction of O 2 via H 2 O 2 . Here we demonstrate that Ta–TiO x nanoparticle additives protect Fe–N–C catalysts from such degradation via radical scavenging. The 5 nm Ta–TiO x nanoparticles were uniformly synthesized on a Ketjenblack substrate using a high-temperature pulse technique, forming the rutile TaO 2 phase. We found that Ta–TiO x nanoparticles suppressed the H 2 O 2 yield by 51% at 0.7 V in an aqueous rotating ring disk electrode test. After an accelerated durability test, a fuel cell prepared with the scavengers showed a current density decay of 3% at 0.9 V iR-free (internal resistance-compensated voltage); a fuel cell without scavengers showed 33% decay. Thus, addition of Ta–TiO x provides an active defence strategy to improve the durability of oxygen reduction reaction catalysts.