סמינר מיוחד בכימיה פיזיקלית: How does charge injection reorder the mesoscale microstructure of mixed ionic–electronic conducting polymers?

Abstract:

Polymeric organic mixed ionic–electronic conductors (OMIECs) are materials that integrate coupled ionic and electronic transport, enabling key device technologies including bioelectronics and energy storage [1]. One of OMIECs’ key advantages over inorganic conductors is their synthetic modularity, which enables precise tuning of polymer properties for specific applications. Accordingly, extensive efforts have focused on rational chemical structure design, resulting in promising new classes of OMIECs, outperforming previous candidates. While mesoscale microstructure represents another critical structural length scale governing these materials’ performance, a comprehensive understanding of OMIEC microstructure—particularly under electrochemical operating conditions—remains limited. Existing operando structural techniques primarily probe ensemble-averaged bulk responses, and do not resolve how structural transformations emerge and propagate locally [2].

Cryogenic four-dimensional scanning transmission electron microscopy (cryo-4D-STEM) has recently emerged as a complementary real-space method for probing polymer microstructure in electrochemically relevant environments [3,4]. 

Here, we extend cryo-4D-STEM to electrochemically doped OMIECs, prepared under operationally relevant conditions using an adapted electrified cryo-EM sample preparation strategy [5]. We apply this methodology to two model OMIECs from a recently developed class of glycolated polymers, p(g3T2) and PB2T-TEG, which exhibit distinct electrochemical responses and corresponding structural reorganization [4,6].

For p(g3T2), charge injection induces anisotropic and heterogeneous microstructural changes, with π–π stacking remaining largely robust to doping, while backbone registry shows pronounced sensitivity. Loss of registry concentrates in narrow defect lines between ordered domains. Upon excessive oxidation, the three-dimensional (registered) order collapses, yielding small registered domains embedded in a predominantly two-dimensional ordered matrix that lacks the backbone Bragg peak. 

For PB2T-TEG, we observe spatially confined structural motifs at the interface between the charged and discharged phases, including a border of expanded lamellar order, adjacent regions with little crystalline signal, and chain alignment along the phase interface.

This work elucidates the complex interplay between charge injection and microstructural evolution, providing new insights into the design of efficient OMIECs for next-generation soft electronic devices.

References:

1. Tropp, J., Meli, D. & Rivnay, J. Organic mixed conductors for electrochemical transistors. Matter 6, 3132–3164 (2023).  

2. Quill, T. J. et al. Charge Carrier Induced Structural Ordering And Disordering in Organic Mixed Ionic Electronic Conductors. Adv. Mater. 36, 2310157 (2024). 

3. Ophus, Colin. "Four-dimensional scanning transmission electron microscopy (4D-STEM): From scanning nanodiffraction to ptychography and beyond." Microscopy and Microanalysis. 25, 563-582 (2019).

4. Tsarfati, Y. et al. The hierarchical structure of organic mixed ionic–electronic conductors and its evolution in water. Nat. Mater. 24, 101–108 (2025).

5. Li, Y. et al. Electrified Operando-Freezing of Electrocatalytic CO2 Reduction Cells for Cryogenic Electron Microscopy. Nano Lett. 24, 10409–10417 (2024). 

6. Connor G. Bischak et al. A Reversible Structural Phase Transition by Electrochemically Driven Ion Injection into a Conjugated Polymer. Journal of the American Chemical Society, 142 (16), 7434-7442 (2020)  

7. Savitzky, B. H. et al. py4DSTEM: a software package for fourdimensional scanning transmission electron microscopy data analysis. Microscopy and Microanalysis. 27, 712–743 (2021).

8. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of  Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

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