Core–shell structured materials constructed by using Fe/Fe₃C cores and nitrogen doped carbon shells represent a type of promising non-precious oxygen reduction reaction (ORR) catalyst due to well-established active sites at the interface positions. However, the traditional liquid phase polymerization route for preparing such materials normally leads to a compact macropore-deficient structure with randomly dispersed metallic nanoparticles, which is not beneficial for mass transfer and the formation of a high-density dispersion of active sites. Herein, we report an “in situ solid phase polymerization strategy” in which a frozen block containing uniformly dispersed oligomers is firstly achieved by combining a well-controlled hydrothermal reaction and a subsequent liquid nitrogen-facilitated fast solidification. During the following freeze-dry process, the oligomers in situ polymerize into a 3D highly cross-linked network in the confined space of the ice block which not only effectively avoids the direct stacking of polymerized intermediates, but also prevents the agglomeration of metallic nanoparticles. The finally obtained monodisperse Fe/Fe₃C nanoparticles embedded in nitrogen-doped carbon aerogel catalyst, in the ORR, delivers an ultrahigh activity as the half-wave potential and the kinetic current density at 0.9 V reach 0.919 V and 7.83 mA cm⁻² respectively in an alkaline solution. Using this route, a range of aerogel materials with improved performances for various applications may be explored.

中文翻译：

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通过原位固相聚合制备用于电催化氧还原的嵌入碳气凝胶的单分散含铁纳米粒子。

通过使用Fe / Fe ₃ C核和掺杂氮的碳壳构造的核-壳结构材料由于其在界面位置的活性位点良好，因此是一种很有前途的非贵金属氧还原反应（ORR）催化剂。然而，用于制备此类材料的传统液相聚合路线通常导致具有随机分散的金属纳米颗粒的致密的大孔缺陷结构，这不利于传质和形成活性位点的高密度分散体。在此，我们报告“原位”固相聚合策略”，其中首先通过将良好控制的水热反应与随后的液氮促进的快速固化相结合来实现包含均匀分散的低聚物的冷冻嵌段。在随后的冷冻干燥过程中，低聚物在冰块的密闭空间中原位聚合成3D高度交联的网络，这不仅有效避免了聚合中间体的直接堆叠，而且还防止了金属纳米粒子的团聚。最终获得的单分散Fe / Fe ₃ C纳米颗粒嵌入ORR的氮掺杂碳气凝胶催化剂中，具有超高的活性，因为半波电势和0.9 V时的动电流密度分别达到0.919 V和7.83 mA cm^-2分别在碱性溶液中。使用这种方法，可以探索各种性能得到改善的气凝胶材料，以用于各种应用。