Fe@C2N: A highly-efficient indirect-contact oxygen reduction catalyst

Abstract

Converting unstable earth-abundant group VIIIB transition metals into stable catalysts with high oxygen reduction reaction (ORR) performances remains a critical challenge for electrochemical technologies. Iron (Fe)-nitrogen (N)-carbon (C)-based electrocatalysts have recently demonstrated ORR performances comparable to platinum (Pt)-based catalysts. However, as their poor stability remains a critical issue, which needs to be resolved to satisfy commercial requirements. Here, we describe a methodology for preparing a high-performance and stable Fe-based ORR catalyst. The catalyst was obtained by the in-situ sandwiching of a Fe3+ precursor in a nitrogenated holey two-dimensional network (denoted as C2N). Reduction of the sandwiched Fe3+ results in the formation of Fe oxide (FexOy) nanoparticles, which are simultaneously transformed into highly crystalline Fe0 nanoparticle cores, while the C2N is catalysed into well-defined, encapsulating, nitrogenated graphitic shells (Fe@C2N nanoparticles) during heat-treatment. The resultant Fe0@C2N nanoparticles are uniformly distributed on the C2N substrate, becoming the Fe@C2N catalyst, which displayed ORR activities superior to commercial Pt/C in both acidic and alkaline media. Furthermore, the Fe@C2N catalyst remained rust-free during harsh electrochemical testing even after 650 h, suggesting that its unusual durability originates from indirect-contact electrocatalysis.