Constructing highly utilizable Fe-N4 single-atom sites by one-step gradient pyrolysis for electroreduction of O2 and CO2

Abstract

Fe-N4 single-atom catalysts (SACs) have been investigated extensively in various energy conversion reaction. However, large amount of untouchable Fe-N4 sites buried in the dense carbon skeletons greatly restrict the maximization of catalytic performance. Therefore, rational construction of catalyst nanostructure to effectively expose Fe-N4 single atom sites is eagerly desired. Here, we report a one-step gradient pyrolysis method by using quaternary ammonia polysulfone (QAPS) polymer with a lower carbonization temperature to segregate precursor particles (ZIF-8 and polyaniline) to construct mesopores at 4–9 nm, thereby tellingly increasing the accessibility of Fe-N4 single atom sites. Nitrite reduction method revealed that the prepared catalyst had a three-fold increase in active sites density compared to catalyst without QAPS. Thus, it exhibits a terrific peak power density (1.15 W cm−2) in proton exchange membrane fuel cells and a superior CO partial current density (121 mA cm−2) with 99 % Faradaic efficiency for CO at 0.5 V in flow cells.