Fe-N-C氧还原电催化剂中FeN4位点微观环境的调节 | Science Bulletin

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Tailoring the microenvironment in Fe–N–C electrocatalysts for optimal oxygen reduction reaction performance

Qing Wang, Ruihu Lu, Yuqi Yang, Xuanze Li, Guangbo Chen, Lu Shang, Lishan Peng, Dongxiao Sun-Waterhouse, Bruce C.C. Cowie, Xiangmin Meng, Yan Zhao, Tierui Zhang, Geoffrey I. N. Waterhouse

Science Bulletin, 2022, 67(12): 1264–1273

doi: 10.1016/j.scib.2022.04.022

简介

Fe-N-C电催化剂, 即FeN₄单原子位点负载于氮掺杂的碳载体上, 是一种优良的氧还原催化剂, 有望取代贵金属铂催化剂, 应用于金属空气电池和燃料电池. 目前, 提高Fe-N-C材料氧还原性能的策略包括: (1)提高铁单原子活性位点的数目; (2)调节铁单原子中心与含氧中间体的吸附能, 从而提高本征活性. 该工作报道了一种简单NaCl熔盐煅烧Fe掺杂金属有机配合物前驱体(Fe-ZIF)的方法, 可有效提高煅烧产物Fe-N-C催化剂中FeN₄单原子位点数量和本征活性. 原位透射电子显微镜(TEM)实验结果表明：在高温煅烧过程中, NaCl蒸发后沉积附着在Fe-ZIF颗粒表面, 加速Fe-ZIF中配体的分解和锌中心的挥发, 从而使煅烧产物中碳载体呈多孔结构, 并改变Fe单原子位点的配位环境. X射线吸收谱进一步表明, 该Fe-N-C催化剂中Fe单原子位点的Fe-N键变长, Fe的氧化态降低, 从而有利于氧还原反应中间体的脱附. 因此, 针对碱性氧还原反应过程, 该催化剂表现出比商业化铂碳催化剂更优异的性能, 并可作为锌空气电池阴极催化剂, 用于手机充电.

图文导读

Fig. 1.  (a) HAADF–STEM image, (b) TEM image and (c) HAADF–STEM image for r-Fe–NC. In-situ TEM results for a mixture of the Fe(acac)₃@ZIF-8 precursor and NaCl after heating at 600 ºC for (d) 0 s, (e) 1 min, and (f) 4 min. (g) EDX mapping images, (h) TEM image, (i) STEM image, (j) 3D reconstruction for the mixture of Fe(acac)₃@ZIF-8 precursor and NaCl after heating at 600 ºC for 10 min. 

Fig. 2.  (a) Fe K-edge XANES spectra for r-Fe–NC, Fe–NC and FePc. (b) Fe K-edge XANES spectra for r-Fe–NC, Fe–NC and reference materials. (c) Fe L-edge XANES spectra for r-Fe–NC and Fe–NC, (d) Fe K-edge XANES spectra for r-Fe–NC collected in air and in 0.1 mol L⁻¹ KOH solution. (e) Fourier-transformed Fe K-edge EXAFS spectra plotted in R space and (f) EXAFS fitting results and the FeN4O2 structure for r-Fe–NC, whereas the rose, blue and light yellow spheres represent Fe, N and O atoms, respectively.

Fig. 3. (a) ORR LSV curves. (b) J_k at 0.80 V and E_1/2. (c) Tafel slope. (d) Electron transfer number and H₂O₂ yield plots for r-Fe–NC, Fe–NC and Pt/C electrocatalysts.

Fig. 4. (a) Discharge polarization curves and corresponding power density versus current density curves. (b) Long-time galvanostatic discharge curves. (c) Discharge curves at the current densities of 10 mA cm⁻² for a zinc–air battery using r-Fe–NC as the air cathode electrocatalyst (changing the electrolyte every 24 h). (d) Open circuit voltages (OCV) for three zinc–air batteries in series, and a demonstration of smart phone (Huawei) charging by three zinc–air batteries linked in series.

Fig. 5. (a) Structural models for FeN₄C₈ and N-doped FeN₄C₈, where different atoms are represented by different colors, i.e., H (white), C (gray), N (blue), and Fe (gold). (b) Fe–N bond distance and Bader charge for model FeN₄C₈ and N-doped FeN₄C₈. (c) The free energy diagram for the ORR on FeN₄C₈ and N-doped FeN₄C₈.

通讯作者

Geoffrey I.N. Waterhouse 奥克兰大学教授. 主要研究方向: 太阳能捕获技术、光催化、光子带隙材料和生物传感器.    

张铁锐 中国科学院理化技术研究所研究员. 主要研究领域与兴趣: 能量转换纳米催化材料.

赵焱 武汉大学教授. 主要研究方向: 多尺度多场耦合仿真、计算材料模拟、纳米材料、新能源催化、3D打印.

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