Shen Di, Sun Fanfei, Liang Zhijian, Fu Honggang, Wang Lei
Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of the People's Republic of China, Heilongjiang University, Harbin, 150080, China.
Shanghai Institute of Applied Physics, Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201204, China.
Angew Chem Int Ed Engl. 2025 Aug 11;64(33):e202505937. doi: 10.1002/anie.202505937. Epub 2025 Jun 23.
Atomically dispersed Fe-based catalyst represents a promising alternative to platinum for the oxygen reduction reaction (ORR). However, the prevalent FeN configuration exhibits limited intrinsic activity in acidic media owing to its inherent instability, thereby restricting its application in proton exchange membrane fuel cell (PEMFC). Herein, we introduce axial-N coordination to enhance the activity and stability of atomically dispersed Fe sites for acidic ORR by establishing a barrier to prevent Fe dissolution. Compared to the FeN configuration, the axial-N ligand in the FeN, FeN-Fe and FeNC configurations induces a square-pyramidal crystal field, which diminishes the spin polarization in the d , d, and d orbitals, and alters the electronic delocalization of Fe atom. In a 0.10 M HClO electrolyte, the ORR activity increases with enhanced electronic delocalization, following the trend: FeN>FeN+Fe>FeNC>FeN. Operando technique further reveals that the dissociation of Fe─N bond in the FeN configuration occurs alongside the insertion of oxygen, leading to the formation of FeNO and FeNO structures that could accelerate the ORR kinetics. Consequently, the FeN configuration shows a positive shift of 30 mV in half-wave potential compared to Pt/C and achieves a peak power of 1.2 W cm at 3.2 A cm in PEMFC.
原子分散的铁基催化剂是氧还原反应（ORR）中铂的一种有前途的替代物。然而，普遍存在的FeN构型由于其固有的不稳定性，在酸性介质中表现出有限的本征活性，从而限制了其在质子交换膜燃料电池（PEMFC）中的应用。在此，我们引入轴向氮配位，通过建立一个防止铁溶解的屏障，来提高原子分散的铁位点对酸性ORR的活性和稳定性。与FeN构型相比，FeN、FeN-Fe和FeNC构型中的轴向氮配体诱导出一个四方锥晶体场，这减少了d、d和d轨道中的自旋极化，并改变了铁原子的电子离域。在0.10 M HClO电解质中，ORR活性随着电子离域的增强而增加，顺序为：FeN>FeN+Fe>FeNC>FeN。原位技术进一步揭示，FeN构型中Fe─N键的解离与氧的插入同时发生，导致形成可加速ORR动力学的FeNO和FeNO结构。因此，与Pt/C相比，FeN构型在半波电位上正移30 mV，并在PEMFC中于3.2 A cm时实现了1.2 W cm的峰值功率。
