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.

Fe-N ₄单原子催化剂（SACs）已在各种能量转换反应中得到广泛研究。然而，埋藏在致密碳骨架中的大量不可接触的Fe-N _{4位点极大地限制了催化性能的最大化。}因此，迫切需要合理构建催化剂纳米结构以有效暴露Fe-N ₄单原子位点。在这里，我们报告了一种一步梯度热解方法，该方法使用具有较低碳化温度的季铵聚砜 (QAPS) 聚合物分离前体颗粒（ZIF-8 和聚苯胺）以构建 4-9 nm 的中孔，从而显着提高可及性Fe-N _4的单原子位点。亚硝酸盐还原方法表明，与没有 QAPS 的催化剂相比，制备的催化剂的活性位点密度增加了三倍。因此，它在质子交换膜燃料电池中表现出极好的峰值功率密度 (1.15 W cm ^-2 )，在流动电池中对 0.5 V 的 CO 具有 99% 的法拉第效率，具有出色的 CO 分电流密度 (121 mA cm ^{-2 )。}