Summary

氧化还原-活性金属-有机骨架固态电化学中中间体的磁力表征

Published: June 09, 2023
doi:

Summary

非原位 磁力调查可以直接提供磁电极上的体量和局部信息,逐步揭示其电荷存储机理。本文证明了电子自旋共振(ESR)和磁化率,以监测顺磁性物质及其在氧化还原活性金属有机框架(MOF)中的浓度的评估。

Abstract

电化学储能是近5年来被广泛讨论的氧化还原活性金属有机骨架(MOFs)应用。尽管MOF在重量或面电容和循环稳定性方面表现出出色的性能,但不幸的是,在大多数情况下,它们的电化学机制尚未得到很好的理解。传统的光谱技术,如X射线光电子能谱(XPS)和X射线吸收精细结构(XAFS),只提供了关于某些元素价变化的模糊和定性信息,基于这些信息提出的机制往往存在很大争议。在本文中,我们报告了一系列标准化方法,包括固态电化学电池的制造,电化学测量,电池的拆卸,MOF电化学中间体的收集以及惰性气体保护下中间体的物理测量。通过使用这些方法定量阐明氧化还原活性MOFs的单个电化学步骤中的电子和自旋态演变,人们不仅可以清楚地了解MOFs的电化学储能机制的性质,还可以为具有强相关电子结构的所有其他材料提供清晰的见解。

Introduction

自 1990 年代后期引入金属有机框架 (MOF) 一词以来,尤其是在 2010 年代,关于 MOF 的最具代表性的科学概念源于其结构孔隙率,包括客体封装、分离、催化特性和分子传感 1,2,3,4 .与此同时,科学家们很快意识到,MOF必须具有刺激响应的电子特性,以便将它们集成到现代智能设备中。这一想法引发了过去10年导电二维(2D)MOF家族的产生和繁荣,从而为MOF在电子5中发挥关键作用打开了大门,更具吸引力的是,在电化学储能器件6中发挥关键作用。这些二维MOFs已作为活性材料掺入碱金属电池,水电池,赝电容器和超级电容器7,8,9并表现出巨大的容量和出色的稳定性。然而,为了设计性能更好的2D MOF,详细了解其电荷存储机制至关重要。因此,本文旨在全面了解MOFs的电化学机理,有助于合理设计性能较好的储能MOFs。

2014年,我们首次报道了金属阳离子和配体10,11上具有氧化还原活性位点的MOF的固态电化学机制。这些机制在各种原和非原位光谱技术的帮助下进行了解释,例如X射线光电子能谱(XPS),X射线吸收精细结构(XAFS),X射线衍射(XRD)和固态核磁共振(NMR)。从那时起,这种研究范式已成为分子基材料固态电化学研究的趋势12。这些方法适用于鉴定具有羧酸桥接配体的常规MOF的氧化还原事件,因为金属簇构建块和有机配体的分子轨道和能级在此类MOF中几乎彼此独立12,13

然而,当遇到具有显着π-d偶联的强相关2D MOF时,暴露了这些光谱方法的局限性。其中一个限制是,大多数上述2D MOF的能带水平不能被视为金属簇和配体的简单组合,而是它们的杂交,而大多数光谱方法仅提供有关氧化态的平均定性信息14。另一个限制是,这些数据的解释总是基于局部原子轨道的假设。因此,具有金属-配体杂化和离域电子态的中间态通常被忽略,并且仅用这些光谱方法描述不正确15。有必要为这些电化学中间体的电子状态开发新的探针,不仅包括二维MOF,还包括具有相似共轭或强相关电子结构的其他材料,例如共价有机框架16,分子导体和共轭聚合物17

评估材料电子结构的最常见和最强大的工具是电子自旋共振(ESR)和超导量子干涉器件(SQUID)磁化率测量18,19。由于两者都依赖于系统中的不成对电子,这些工具可以提供有关自旋密度、自旋分布和自旋-自旋相互作用的暂定信息。ESR提供对未成对电子的灵敏检测,而磁化率测量为上层属性提供更多定量信号20。不幸的是,这两种技术在用于分析电化学中间体时都不可避免地面临巨大挑战。这是因为目标样品不是纯净的,而是目标材料、导电添加剂、粘合剂和电解质副产物的混合物,因此获得的数据21,22 是材料和杂质的贡献之和。同时,大多数中间体对环境敏感,包括空气、水、某些电解质或任何其他不可预测的扰动;在处理和测量中间体时必须格外小心。在处理电极材料和电解质的新组合时,通常需要反复试验。

在这里,我们提出了一种新的范式,称为电化学磁力测量法,用于使用一系列技术分析2D MOF和类似材料的电子状态或自旋态,利用电化学和温度可变的位ESR光谱以及非原位磁化率测量20。为了证明这种方法的有效性,我们使用具有代表性的2D MOF的Cu3THQ 2(THQ = 1,2,4,5-四羟基苯醌;称为Cu-THQ)为例。我们解释了导电添加剂和电解质的选择,电极和电化学电池的制造,以及样品处理和测量的详细信息,包括测量过程中可能出现的问题。通过与XRD和XAFS等经典表征进行比较,电化学磁力计可以全面了解大多数MOF的电化学机理。这种方法能够捕获独特的中间状态并避免氧化还原事件的错误分配。使用电化学磁力计阐明储能机制也有助于更好地理解MOF中的结构 – 功能关系,从而为MOF和其他共轭材料提供更智能的合成策略。

Protocol

1. 电极制造 合成铜-THQ MOF注意:Cu-THQ MOF多晶粉末是按照先前发布的程序14,20,23通过水热法合成的。将 60 mg 四羟基醌放入 20 mL 安瓿中,然后加入 10 mL 脱气水。在单独的玻璃小瓶中,将 110 mg 硝酸铜 (II) 三水合物溶解在另外 10 mL 脱气水中。使用移液管加入 46 μL 竞争配体乙二胺。注意:?…

Representative Results

我们之前的工作包括详细讨论电化学循环CuTHQ20的异位ESR波谱和离位磁化率测量。在这里,我们提出了根据本文描述的协议可以获得的最有代表性和最详细的结果。 图 2:锂/铜 / CuTHQ电池的电化学性能 。 (A</…

Discussion

为了生产阴极,有必要将活性材料与导电碳混合,以在电化学过程中实现低极化。碳添加剂是 非原位 磁力测量的第一个临界点;如果碳有自由基缺陷,则在ESR光谱中无法观察到电化学诱导有机自由基的出现。这使得难以精确确定自旋浓度或有机自由基浓度,因为这两种类型的自由基具有相似的g值,并且它们的ESR线可能重叠。此外,如果碳含有少量的铁磁杂质,其磁化率在高温区域占主导地…

Divulgations

The authors have nothing to disclose.

Acknowledgements

这项研究得到了日本科学促进会(JSPS)KAKENHI资助(JP20H05621)的支持。Z. Zhang还感谢立松基金会和丰田理研奖学金的资金支持。

Materials

1-Methyl-2-pyrrolidone FUJIFILM Wako Chemicals 139-17611 Super Dehydrated
1mol/L LiBF4 EC:DEC (1:1 v/v%) Kishida LBG-96533 electrolyte
4-Hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl FUJIFILM Wako Chemicals 089-04191 TEMPOL, for Spin Labeling 
Ampule tube Maruemu Corporation 5-124-05 20mL
Carbon black, Super P Conductive Alfa Aesar H30253
Conductive Carbon Black Mitsubishi Chemical
Copper (II) Nitrate Trihydrate FUJIFILM Wako Chemicals 033-12502 deleterious substances
Dimethyl Carbonate FUJIFILM Wako Chemicals 046-31935 battery grade
Ethylenediamine FUJIFILM Wako Chemicals 053-00936 deleterious substances
Graphene Nanoplatelets Tokyo Chemical Industry G0442 6-8nm(thick), 15µm(wide)
Poly(vinylidene fluoride) Sigma Aldrich 182702
Potassium Bromide FUJIFILM Wako Chemicals 165-17111 for Infrared Spectrophotometry
Sodium Alginate  FUJIFILM Wako Chemicals 199-09961 500-600 cP
SQUID Magnetometer Quantum Design MPMS-XL 5
Tetrahydroxy-1,4-benzoquinone Hydrate Tokyo Chemical Industry T1090
X-Band ESR JEOL JES-F A200

References

  1. Lee, J., et al. Metal-organic framework materials as catalysts. Chemical Society Reviews. 38 (5), 1450-1459 (2009).
  2. Dolgopolova, E. A., Rice, A. M., Martin, C. R., Shustova, N. B. Photochemistry and photophysics of MOFs: steps towards MOF-based sensing enhancements. Chemical Society Reviews. 47 (13), 4710-4728 (2018).
  3. Qian, Q., et al. MOF-based membranes for gas separations. Chemical Reviews. 120 (16), 8161-8266 (2020).
  4. Wang, Q., Astruc, D. State of the art and prospects in metal-organic framework (MOF)-based and MOF-derived nanocatalysis. Chemical Reviews. 120 (2), 1438-1511 (2020).
  5. Wang, M., Dong, R., Feng, X. Two-dimensional conjugated metal-organic frameworks (2D c-MOFs): chemistry and function for MOFtronics. Chemical Society Reviews. 50 (4), 2764-2793 (2021).
  6. Baumann, A. E., Burns, D. A., Liu, B., Thoi, V. S. Metal-organic framework functionalization and design strategies for advanced electrochemical energy storage devices. Communications Chemistry. 2 (1), 86 (2019).
  7. Nam, K. W., et al. Conductive 2D metal-organic framework for high-performance cathodes in aqueous rechargeable zinc batteries. Nature Communications. 10 (1), 4948 (2019).
  8. Sheberla, D., et al. Conductive MOF electrodes for stable supercapacitors with high areal capacitance. Nature Materials. 16 (2), 220-224 (2017).
  9. Wang, Z., et al. Ultrathin two-dimensional conjugated metal-organic framework single-crystalline nanosheets enabled by surfactant-assisted synthesis. Chemical Science. 11 (29), 7665-7671 (2020).
  10. Zhang, Z., Yoshikawa, H., Awaga, K. Monitoring the solid-state electrochemistry of Cu(2,7-AQDC) (AQDC = anthraquinone dicarboxylate) in a lithium battery: Coexistence of metal and ligand redox activities in a metal-organic framework. Journal of the American Chemical Society. 136 (46), 16112-16115 (2014).
  11. Zhang, Z., Yoshikawa, H., Awaga, K. Discovery of a "bipolar charging" mechanism in the solid-state electrochemical process of a flexible metal-organic framework. Chemistry of Materials. 28 (5), 1298-1303 (2016).
  12. Li, C., Hu, X., Hu, B. Cobalt(II) dicarboxylate-based metal-organic framework for long-cycling and high-rate potassium-ion battery anode. Electrochimica Acta. 253, 439-444 (2017).
  13. Liu, J., et al. Reversible formation of coordination bonds in Sn-based metal-organic frameworks for high-performance lithium storage. Nature Communications. 12 (1), 3131 (2021).
  14. Jiang, Q., et al. A redox-active 2D metal-organic framework for efficient lithium storage with extraordinary high capacity. Angewandte Chemie. 59 (13), 5273-5277 (2020).
  15. Sakaushi, K., Nishihara, H. Two-dimensional π-conjugated frameworks as a model system to unveil a multielectron-transfer-based energy storage mechanism. Accounts of Chemical Research. 54 (15), 3003-3015 (2021).
  16. Li, H., et al. 2D organic radical conjugated skeletons with paramagnetic behaviors. Advanced Materials Interfaces. 8 (18), 2100943 (2021).
  17. Peeks, M. D., et al. Electronic delocalization in the radical cations of porphyrin oligomer molecular wires. Journal of the American Chemical Society. 139 (30), 10461-10471 (2017).
  18. Krug von Nidda, H. A., et al. Anisotropic exchange in LiCuVO4 probed by ESR. Physical Review B. 65 (13), 134445 (2002).
  19. Zeng, Z., et al. Pro-aromatic and anti-aromatic π-conjugated molecules: An irresistible wish to be diradicals. Chemical Society Reviews. 44 (18), 6578-6596 (2015).
  20. Chen, Q., Adeniran, O., Liu, Z. F., Zhang, Z., Awaga, K. Graphite-like charge storage mechanism in a 2D π-d conjugated metal-organic framework revealed by stepwise magnetic monitoring. Journal of the American Chemical Society. 145 (2), 1062-1071 (2023).
  21. Julien, C. M., Mauger, A., Groult, H., Zhang, X., Gendron, F. LiCo1-yByO2 as cathode materials for rechargeable lithium batteries. Chemistry of Materials. 23 (2), 208-218 (2011).
  22. Niemöller, A., Jakes, P., Eichel, R. A., Granwehr, J. In operando EPR investigation of redox mechanisms in LiCoO2. Chemical Physics Letters. 716, 231-236 (2019).
  23. Park, J., et al. Synthetic routes for a 2D semiconductive copper hexahydroxybenzene metal-organic framework. Journal of the American Chemical Society. 140 (44), 14533-14537 (2018).
  24. Rondeau, R. E. A technique for degassing liquid samples. Journal of Chemical Education. 44 (9), 530 (1967).
  25. Flores-Llamas, H. Inhomogeneously broadened EPR lineshape of axial powder. Applied Magnetic Resonance. 9 (2), 289-298 (1995).
  26. Sun, L., et al. Room-temperature quantitative quantum sensing of lithium ions with a radical-embedded metal-organic framework. Journal of the American Chemical Society. 144 (41), 19008-19016 (2022).
  27. Chen, Y., et al. Successive storage of cations and anions by ligands of π-d-conjugated coordination polymers enabling robust sodium-ion batteries. Angewandte Chemie. 60 (34), 18769-18776 (2021).
  28. Roessler, M. M., Salvadori, E. Principles and applications of EPR spectroscopy in the chemical sciences. Chemical Society Reviews. 47 (8), 2534-2553 (2018).
  29. Ji, X., et al. Pauli paramagnetism of stable analogues of pernigraniline salt featuring ladder-type constitution. Journal of the American Chemical Society. 142 (1), 641-648 (2020).
  30. Noel, M., Santhanam, R. Electrochemistry of graphite intercalation compounds. Journal of Power Sources. 72 (1), 53-65 (1998).
  31. Wu, K. H., Ting, T. H., Wang, G. P., Ho, W. D., Shih, C. C. Effect of carbon black content on electrical and microwave absorbing properties of polyaniline/carbon black nanocomposites. Polymer Degradation and Stability. 93 (2), 483-488 (2008).
  32. Yao, M., Taguchi, N., Ando, H., Takeichi, N., Kiyobayashi, T. Improved gravimetric energy density and cycle life in organic lithium-ion batteries with naphthazarin-based electrode materials. Communications Materials. 1 (1), 70 (2020).
  33. Krzystek, J., et al. EPR spectra from "EPR-silent" species: High-frequency and high-field EPR spectroscopy of pseudotetrahedral complexes of nickel(II). Inorganic Chemistry. 41 (17), 4478-4487 (2002).

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Chen, Q., Zhang, Z., Awaga, K. Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks. J. Vis. Exp. (196), e65335, doi:10.3791/65335 (2023).

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