【Small】衢州大学沈行加|1.8 s⁻¹与0.92 V的跨越！超小Fe/Fe₂O₃纳米颗粒远距离调控单原子Fe─N─C实现高效氧还原
文章标题：Boosting Oxygen Reduction Catalysis on Fe─N─C via Long‐Range Electronic Metal–Support Interaction from Ultrasmall Fe/Fe2O3
通讯作者：Hangjia Shen
Synthesis and texture property of FF/Fe-NC. (a) Schematic illustration of FF/Fe-NC synthesized via chemical vapor deposition. (b) SEM image. (c) TEM image. (d) and (e) HAADF-STEM images; in the enlarged view of region 2, single Fe atoms at different distances from the cluster are marked by green, blue and yellow circles, respectively. (f–i) Elemental mapping distributions of C, N, Fe, and O.
文章概要
引言
金属-氮-碳单原子催化剂由于具有极高的原子利用率和可调控的活性中心，被视为极具潜力的低成本燃料电池氧还原催化剂。然而，传统的孤立单原子位点往往面临电子结构难以进一步优化、对反应中间体吸附过强的瓶颈。近年来，科学家发现催化剂制备过程中残留的金属纳米颗粒并非完全无用，而是可以通过长远距离的电子相互作用来调节周围单原子位点的状态。如何精准设计并阐明这些纳米颗粒与单原子之间的距离效应及作用机制，是当前低成本高效催化剂开发的核心挑战之一。
(a) High-resolution N 1s XPS spectra. (b) Fe K-edge XANES spectra of FF/Fe-NC and Fe-NC in comparison with the reference Fe foil, Fe2O3 and FePc. (c) Valence state of central Fe atoms. (d) Fourier transform k2-weighted Fe K-edge EXAFS spectra. (e) Corresponding wavelet transform (WT) EXAFS spectra. (f) N2-sorption isotherm curves, inset is the pore size distribution. (g) Electrochemical double layer capacitance. (h) Active site quantification via nitrite stripping in acetate buffer (0.5 m, pH = 5.2).
主要实验及结论
研究团队通过一种简便的化学气相沉积方法，以ZIF-8衍生的氮掺杂碳为载体，成功构筑了一种同时含有表层可接近的超小Fe/Fe₂O₃纳米颗粒和原子级分散Fe─N₄位点的复合催化剂。高角环形暗场扫描透射电子显微镜和同步辐射X射线吸收谱测试表明，这些纳米颗粒的平均尺寸仅为1纳米左右，且周围紧密环绕着单原子铁位点。电化学测试结果表明，在碱性介质中，该催化剂展现出优异的四电子氧还原活性，其半波电位高达0.92 V，在0.9 V电压下的周转频率达到1.8 s⁻¹，不仅远超不含纳米颗粒的对照样品，也显著优于商业铂碳催化剂。将其作为阴极组装成锌空电池时，更实现了218 mW cm⁻²的峰值功率密度以及超过160小时的杰出循环稳定性。
Electrocatalytic ORR performance 0.1 m KOH. (a) LSV curves of the catalyst (electrode rotating speed is 1600 rpm; scan rate is10 mV s−1). (b) Tafel plots. (c) Comparison of JK at various potentials. (d) Comparison of the TOFs at 0.85 and 0.9 V. (e) Polarization curves of FF/Fe-NC catalyst at different rotating speeds from 400 to 1600 rpm and (f) K-L plots at different potentials. (g) H2O2 yield plots determined from the RRDE measurements. LSV curves of FF/Fe-NC (h) and (i) Pt/C before and after ADT test (10 000 cycles).
Zinc–air battery performance using FF/Fe-NC or Pt/C cathodes. (a) Schematic illustration of the tri-electrode system of rechargeable ZAB. (b) Open-circuit voltage curves. (c) Specific discharge capacity at 10 mA cm−2. (d) Discharge polarization curves and the corresponding power densities. (e) Rate performances at different current densities (5, 10, 20, 50 and 100 mA cm−2). (f) Long-term stability test of rechargeable ZAB at 10 mA cm−2. The voltage drop of (g) FF/Fe-NC and (h) Pt/C cathode after 800 charge-discharge cycles.
理论计算与原位拉曼光谱进一步揭示了其性能跃升的微观机制。研究表明，超小纳米颗粒与邻近单原子位点之间存在独特的长程电子金属-载体相互作用，这种作用成功降低了中心铁原子的电荷态。随着两者之间距离的缩短，氧还原反应的限速步骤发生动态转移，从而有效减弱了单原子位点上原本过强的氧源中间体吸附，加速了整体反应动力学。原位拉曼实验中观察到的羟基中间体稳定吸附信号，强有力地证实了由距离调控的协同催化路径对四电子反应的高效促进作用。
(a) Bader charge analysis of the optimized structure with different distances between Fe/Fe2O3 cluster and Fe─N4. Blue and yellow regions represent electron depletion and accumulation, respectively. (b) Scaling relationship between the charge state and distances. (c) Free energy barrier of rate determining step for ORR. (d,e) Schematic illustration of ORR mechanism on (d) M0 and (e) M4. (f,g) In situ Raman spectra of (f) FF/Fe-NC and (g) Fe-NC.
总结及展望
该工作成功为金属和氮共掺杂碳催化剂的理性设计提供了一条高效策略。通过构筑超小金属/金属氧化物纳米颗粒与单原子位点的共存体系，不仅打破了传统单原子催化剂固有电子结构的限制，更实现了远距离电子调控在实际电池器件中的稳定应用。这种对纳米颗粒与活性中心距离效应的深刻理解，将为未来开发高性能、长寿命的高能绿色转换技术和先进材料奠定坚实的科学理论基础。