Converting Fe–N–C single-atom catalyst to a new FeNxSey cluster catalyst for proton-exchange membrane fuel cells

Abstract

Fe–N–C catalyst is the most promising alternative to platinum catalyst for proton-exchange membrane fuel cells (PEMFCs), however its high performance cannot be maintained for a long enough time in device. The construction of a new Fe coordination environment that is different from the square-planar Fe–N 4 configuration in Fe–N–C catalyst is expected to break current stability limits, which however remains unexplored. Here, we report the conversion of Fe–N–C to a new FeNxSey catalyst, where the Fe sites are three-dimensionally (3D) co-coordinated by N and Se atoms. The FeNxSey catalyst exhibits much better 4e– ORR activity and selectivity than the Fe–N–C catalyst. Specifically, the yields of H2O2 and ·OH radicals on FeNxSey are only one-quarter and one-third of that on Fe–N–C, respectively. Therefore, the FeNxSey catalyst exhibits outstanding stability, losing only 10 mV in E1/2 after 10,000 cycles, much smaller than that of the Fe–N–C catalyst (56 mV), representing the most stable Pt-free catalysts ever reported. Moreover, the 3D co-coordination structure inhibits the Fe demetallization in the presence of H2O2. As a result, the FeNxSey based PEMFC shows excellent durability, with the current density attenuation significantly lower than that of the Fe–N–C based device after accelerated durability testing.