蜂窝状碳负载铁基单原子催化剂的制备及ORR催化性能研究

doi:10.15541/jim20200624

摘要/Abstract

摘要：

单原子催化剂(SACs)以近100%的原子利用率以及优秀的催化活性等, 在促进多相催化方面受到了广泛关注。然而, 由于金属原子在高温下易烧结, SACs的合成仍然具有挑战性。本研究利用熔融盐(MS)提供的强极性环境, 制备了以氮掺杂碳为载体的铁基单原子催化剂(Fe SA-NC)。结果表明, Fe SA-NC显示出蜂窝状的多孔形貌, 比表面积高达2072 m²·g^-1, 其中Fe元素的重量百分比含量为0.57%。通过球差电镜直接观察到了孤立存在的Fe单原子, 并通过X射线吸收精细结构(XAFS)分析确定Fe单原子以Fe-N₄配位体形式分散在碳基材料上。Fe SA-NC催化剂在0.1 mol/L KOH 溶液中半波电位为0.85 V, 极限电流密度为5.79 mA·cm^-2, 优于商业Pt/C催化剂。Fe SA-NC催化剂不仅对ORR四电子途径显示出高选择性(H₂O₂产率<2%, 转移电子数为3.9), 同时表现出优秀的抗甲醇性能。

关键词: 单原子催化剂, 多孔, 氮掺杂碳, 氧还原反应

Abstract:

Single atom catalysts (SACs) have emerged as an attractive concept for promoting heterogeneous reactions due to the unique properties, such as high activity and nearly 100% atom utilization. However, the synthesis of SACs remains a challenge due to the sintering of metal atoms at high temperature. In this study, Fe single atom on N doped porous carbon (Fe SA-NC) catalyst was obtained by ultrastrong polarity of molten salt (MS). Fe SA-NC shows honeycomb-like porous morphology and possesses a high specific surface area of 2072 m²·g^-1. The content of Fe element in Fe SA-NC is 0.57wt%. The isolated Fe atoms are observed by AC HAADF-STEM, and the X-ray absorption fine structure (XAFS) analysis confirms that Fe atoms disperse in the form of Fe-N₄ on the carbon substrate. Fe SA-NC shows 0.85 V half-wave potential and 5.79 mA·cm^-2maximum current density for ORR in 0.1 mol/L KOH solution. Fe SA-NC displays high selectivity for ORR four electron pathway (H₂O₂ yield<2%, electron transfer number is 3.9), outstanding stability, and good methanol tolerance.

Key words: single atom catalyst, porous, nitrogen-doped carbons, oxygen reduction reaction

中图分类号:

O646

刘自若, 刘炜, 郝策, 胡金文, 史彦涛. 蜂窝状碳负载铁基单原子催化剂的制备及ORR催化性能研究[J]. 无机材料学报, 2021, 36(9): 943-949.

LIU Ziruo, LIU Wei, HAO Ce, HU Jinwen, SHI Yantao. Honeycomb-like Carbon-supported Fe Single Atom Catalyst: Preparation and Electrocatalytic Performance in Oxygen Reduction Reaction[J]. Journal of Inorganic Materials, 2021, 36(9): 943-949.

图/表 8

图1 (a)Fe-NC和(b)Fe SA-NC的扫描电镜照片; (c)Fe SA-NC在77 K下的N2吸脱附曲线; (d) Fe SA-NC的孔径分布图

Fig. 1 SEM images of (a) Fe-NC and (b)Fe SA-NC, (c)nitrogen adsorption/desorption plots of Fe SA-NC at 77 K, and (d) pore size distribution of Fe SA-NC

图2 (a)次黄嘌呤以及次黄嘌呤和熔融盐共存时的TGA曲线; Fe SA-NC和Fe-NC的催化剂的(b)拉曼光谱以及(c)XRD图谱

Fig. 2 (a) TGA curves of hypoxanthine and hypoxanthine with molten salt; (b) Raman spectra and (c) XRD patterns of Fe SA-NC and Fe-NC

图3 Fe SA-NC的(a, b)球差矫正高角环形暗场扫描透射电镜照片, (c)N1s和(d)Fe2p的高分辨XPS图谱

Fig. 3 (a, b) AC HAADF-STEM images, high-resolution X-ray photoelectron spectra (XPS) of (c) N1s and (c) Fe2p of the Fe SA-NC catalyst

表1 Fe SA-NC催化剂中各元素含量的XPS测试结果

Table 1 XPS results of element composition in Fe SA-NC catalyst

Element	C	N	O	Fe
Atomatic percent/%	74.54	14.18	10.15	0.60

图4 Fe SA-NC、FePc、FeO和Fe2O3的Fe K边(a)X射线吸收近边结构(XANES)光谱和(b)径向结构函数; (c)Fe SA-NC的R空间EXAFS拟合曲线

Fig. 4 Fe K-edge (a) XANES spectra (b) k2-weighted FT spectra for the Fe SA-NC, FePc, FeO and Fe2O3 and (c) EXAFS fitting curves in R space for Fe SA-NC Insets in (c): EXAFS fitting curves in k space (up) and schematic models of Fe SA-NC (down); C (gray), N (blue), Fe (orange), O (red)

表2 Fe SA-NC样品的EXAFS拟合参数

Table 2 EXAFS fitting parameters of Fe SA-NC sample

Sample	Path	N	R/nm	σ²/(×10^-5, nm²)	ΔE₀/eV	R factor
Fe SA-NC	Fe-N	3.9	0.209	5.7	4.7	0.093
Fe SA-NC	Fe-O	1.0	0.190	5.7	4.7	0.093

图5 (a)Fe SA-NC在氮气和氧气饱和的0.1 mol/L KOH电解质溶液中的 CV 曲线; (b)氧饱和的0.1 mol/L KOH电解质溶液(1600 r/min, 10 mV s-1)中不同催化剂的LSV曲线; (c)Fe SA-NC在氧气饱和0.1 mol/L KOH 溶液条件中, 不同转速条件的LSV曲线; (d)图(c)对应的K-L方程图; (e)Fe SA-NC的ORR转移电子数和H2O2产率; (f)氧气饱和溶液中不同催化剂材料的塔菲尔斜率

Fig. 5 (a) CV curves of the Fe SA-NC in a N2-saturated and O2-saturated 0.1 mol/L KOH solution, respectively; (b) LSV curves of Fe SA-NC, NC and Pt/C in O2-saturated 0.1 mol/L KOH solution (1600 r/min, 10 mV·s-1); (c) ORR polarization curves of Fe SA-NC recorded at different rotating speeds; (d) K-L plots derived from Fig. (c); (e) ORR electron transfer number and H2O2 yield of Fe SA-NC; (f) Tafel slopes of Fe SA-NC, NC and Pt/C in O2-saturated 0.1 mol/L KOH solution

图6 Fe SA-NC在1600 r/min转速下氧气饱和0.1 mol/L KOH溶液中的(a)耐久性试验和(b)抗甲醇能力测试

Fig. 6 (a) Durability test and (b) methanol resistance test for Fe SA-NC in O2-saturated 0.1 mol/L KOH solution (1600 r/min)

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