云南大学郭洪教授团队Chem Cat. 调节电子自旋态增强氧还原- 大数跨境

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云南大学郭洪教授团队Chem Cat. 调节电子自旋态增强氧还原

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2023-09-29

导读：云南大学郭洪教授团队Chem Cat. 调节电子自旋态增强氧还原

文章信息

云南大学郭洪教授团队Chem Cat. 调节电子自旋态增强氧还原

第一作者：王利莲

通讯作者：郭洪*

单位：云南大学

研究背景

锌空气电池是一种有发展前景的可持续能源技术，其工作效率和使用寿命在本质上取决于氧还原反应(ORR)中使用的电催化剂。由于氧分子(O₂)的顺磁性，它们形成抗磁性的OH-/H₂O涉及自旋相关的轨道相互作用和电子转移，使得ORR反应的热力学和动力学对自旋态敏感。值得注意的是，原子分散的金属位点可以表现出类似自由的原子状地电子结构，允许其自旋态、电子态密度、带隙和表面氧化态可以被显著调节。此外，近年来的研究表明，由于活性中心的电子调制，双金属催化剂比单金属原子催化剂表现出更高的活性和稳定性。在这些开创性研究的启发下，我们发现，与单金属催化剂不同，引入另一种异质金属可以通过它们之间的耦合作用来调节电子自旋态，从而显著提高服从Sabatier原理的ORR催化活性。特别是具有成本效益的3d过渡金属基催化剂，其氧电催化性能与自旋有关，值得研究。遗憾的是，到目前为止，对自旋电子催化机理的研究还不是很清楚如何方便地调节电子自旋状态并对其进行深入的机制解释仍然是极具挑战性的。

文章简介

近日，云南大学郭洪教授团队在国际知名期刊Chem Catalysis上发表题为 “Modulating the electronic spin state of atomically dispersed iron sites by adjacent zinc atoms for enhanced spin dependent oxygen electrocatalysis” 的研究型论文。该论文提出了一种双金属铁锌原子催化剂，并用原位光谱电化学和分子轨道理论相结合的方法理解了其主要的自旋电子催化机理。双金属之间的电子/电荷相互作用会引起电子自旋态的转变和活性中心电荷密度的变化。机理研究表明，这些改变可以优化中间体与活性中心之间轨道相互作用的键序值。这使得其ORR活性和稳定性与全pH电解质中的基准Pt/C相当甚至超过。此外，Fe,Zn/N-C驱动的碱性和中性锌空气电池的峰值功率密度分别为211.7 mW cm^-2和95.0 mW cm^-2，表现出满意的性能。这项工作为设计更高效的电催化剂和进一步了解自旋电子氧电催化提供了途径。

本文要点

要点一：均匀分散的双金属原子位点催化剂的设计理论基础和表征

通过DFT计算来证实Fe,Zn/N-C设计的合理性，并揭示其在全pH范围内高ORR活性的起源。此外，通过HAADF-STEM、EDS、球差电镜、XRD、高分辨率XPS光谱和同步辐射等先进表征证实催化剂的成功合成以及双金属在碳基材上的的均匀原子分散。

Figure 1. Theoretical study of as-synthesized catalysts. (A) The free energy of two containing-Fe samples for 1*H and 2*H protonation process. (B) Density of states of all catalysts. (C) Overlap of Fe 3d-Zn 3d. (D-F) Charge density difference of all samples.

(G) The theoretical free energy difference between the rate-determining step for 4e and 2e ORR processes (ΔGH₂O - ΔGH₂O₂). (H and I) The free energy diagrams for Fe,Zn/N-C and Fe/N-C. (J) pH-corrected free energy diagram of Fe,Zn/N-C.

Figure 2. Structural characterizations of as-prepared catalysts. (A and B) AC-HAADF-STEM and enlarged image of Fe,Zn/N-C.(C) Raman of all samples. (D) High-resolution Fe 2p XPS spectra of Fe/N-C and Fe,Zn/N-C. (E) High-resolution XPS Zn 2p spectra of Zn/N-C and Fe,Zn/N-C. (F) Wavelet transform (WT) contour plots of Fe,Zn/N-C. (G) XANES of Fe K-edge for Fe,Zn/N-C and Fe foil. (H) FT EXAFS in R space for Fe,Zn/N-C and Fe foil. (I) Corresponding EXAFS fitting curves at the Fe K-edge of Fe,Zn/N-C.(J) XANES of Zn K-edge for Fe,Zn/N-C and Zn foil.(K) FT EXAFS in R space for Fe,Zn/N-C and Zn foil. (L) Corresponding EXAFS fitting curves at the Zn K-edge of Fe,Zn/N-C.

要点二：对双金属Fe-Zn催化剂电子构型调控的全面理解

双金属之间的电子/电荷相互作用会引起电子自旋态的转变和活性中心电荷密度的变化。机理研究表明，这些改变可以优化中间体与活性中心之间轨道相互作用的键序值。这使得其ORR活性和稳定性与全pH电解质中的基准Pt/C相当甚至超过。

Figure 3. Insight into 3d-orbital electronic configurations and in situ spectroelectrochemistry of as-synthesized samples. (A) M-T plots and the unpaired 3d-electron number of all containing-metal samples. (B) Schematic diagram of the 3d-orbital splitting manner for five-coordinated Fe atoms. (C) 3d-electron configurations of iron cations in different spin state on the surface of catalysts. (D) The transformation and orientation of the five d orbitals of Fe. (E) The orbital interactions between iron cations over Fe,Zn/N-C and oxygen-containing intermediates. (F and G) The Raman spectra and contour maps of Fe,Zn/N-C polarized at different potentials in O₂ saturated alkaline solutions.(H) Schematic of the in-situ Raman electrochemical device.

要点三：全pH范围内氧还原反应和碱性/中性锌空气电池的显著电化学性能

双金属Fe-Zn催化剂在全pH范围内具有良好的ORR活性，表现在0.90 V（0.1 M KOH）、0.79 V（0.5 M H₂SO₄）和0.65 V（0.1 M PBS）的满意半波电位(E_1/2)。Fe,Zn/N-C还表现出强大的甲醇耐受性，具有持久的电流稳定性。此外，Fe,Zn/N-C驱动的碱性和中性锌空气电池的峰值功率密度分别为211.7 mW cm^-2和95.0 mW cm^-2，表现出满意的性能。

Figure 4. Oxygen electrocatalytic performance of Fe,Zn/N-C and other comparison samples. (A) LSV polarization curves of Fe,Zn/N-C and other comparison samples in 0.1 M KOH. (B) Bar graphs comparing half-wave potentials and kinetic current densities of all samples in 0.1 M KOH (the colors of parameters for the samples correspond to those of LSV curves).(C) Tafel plots of all catalysts in alkaline solution. (D) LSV polarization curves of Fe,Zn/N-C and other comparison samples in 0.5 M H₂SO₄ (HClO₄ solution for Pt/C).

(E) Bar graphs comparing half-wave potentials and kinetic current densities of all samples in 0.5 M H₂SO₄ (HClO₄ solution for Pt/C) (the colors of parameters for the samples correspond to those of LSV curves). (F) The chronoamperometric stability tests of Fe,Zn/N-C and Pt/C under acidic condition.(G) LSV polarization curves of Fe,Zn/N-C and other comparison samples in 0.1 M PBS.(H) Bar graphs comparing half-wave potentials and kinetic current densities of all samples in 0.1 M PBS (the colors of parameters for the samples correspond to those of LSV curves). (I) CVs of all samples for ORR catalysis in 0.1 M PBS solution before (solid line) and after (dashed line) adding methanol.

Figure 5. The performance of alkaline, neutral, and flexible Zinc-air batteries driven by Fe,Zn/N-C and the commercial Pt/C. (A) Polarization and power density of alkaline and neutral ZABs driven by Fe,Zn/N-C and Pt/C catalysts. (B) Specific capacities of Fe,Zn/N-C, and Pt/C, normalized by the consumed Zn mass (inset).(C) Galvanostatic discharge of both alkaline and neutral ZABs with Fe,Zn/N-C and Pt/C as electrocatalysts at different current densities. (D) Galvanostatic discharge-charge cycling of two alkaline ZABs (top), and two neutral ZABs (bottom). (E) Comparison of peak power density and current density of Fe,Zn/N-C and other previous report as listed in Table S11. (F) Schematic illustration of a homemade flexible quasi-solid-state ZAB. (G) Cycling plots of flexible ZAB upon different deformations.

文章链接

Modulating the electronic spin state of atomically dispersed iron sites by adjacent zinc atoms for enhanced spin dependent oxygen electrocatalysis

https://doi.org/10.1016/j.checat.2023.100758

通讯作者简介

郭洪，云南大学教授，博士生导师，博士后合作导师，享受云南省政府津贴的专家学者，云南大学东陆学者，中国硅酸盐学会固态离子学分会理事（CSSI），国际能源与电化学科学研究院(IAOEES理事，国际电化学会（ISE）会员。主持973计划课题、国家自然科学基金、云南省重大科技专项等20余项省部级及以上课题。主要从事电化学储能及环境催化研究。以第一作者及通讯作者在Adv. Mater.，Angew Chem. Int. Edit.等学术期刊发表论文150余篇，引用超过7000次，申请及授权30余项中国发明专利。