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

Abstract Iron‐nitrogen‐carbon (Fe−N−C) single‐atom 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 operation. The construction of a new Fe coordination environment that is completely different from the square‐planar Fe−N 4 configuration in classic Fe−N−C catalyst is expected to break the current stability limits of Pt‐free catalysts, which however remains unexplored. Here, we report, for the first time, the conversion of Fe−N−C catalyst to a new FeN x Se y cluster catalyst, where the active Fe sites are three‐dimensionally (3D) co‐coordinated by N and Se atoms. Due to this unique Fe coordination configuration, the FeN x Se y catalyst exhibits much better 4e − ORR activity and selectivity than the state‐of‐the‐art Fe−N−C catalyst. Specifically, the yields of hydrogen peroxide (H 2 O 2 ) and ⋅OH radicals on the FeN x Se y catalyst are only one‐quarter and one‐third of that on the Fe−N−C counterpart, respectively. Therefore, the FeN x Se y catalyst exhibits outstanding cyclic stability, losing only 10 mV in half‐wave potential E 1/2 after 10,000 potential cycles, much smaller than that of the Fe−N−C catalyst (56 mV), representing the most stable Pt‐free catalysts ever reported for PEMFCs. More significantly, the 3D co‐coordination structure effectively inhibits the Fe demetallization of the FeN x Se y catalyst in the presence of H 2 O 2 . As a result, the FeN x Se y 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. Our work provides guidance for the development of next‐generation Pt‐free catalysts for PEMFCs.