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

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.