Organic mixed ionic-electronic conductors (OMIECs) are conjugated materials that transport electronic charges, and readily uptake and transport ionic charges. The unique properties of OMIECs make them highly attractive in biomedical and energy applications. In situ/operando characterization plays an important role in revealing mass/charge transfer kinetics and the structure-property relationships in OMIEC operation. Compared to ex situ studies, in situ/operando characterization avoids the mismatch between ex situ requirements and the operating environment, including the reversible changes of the structure, chemical composition, and mechanical properties. Here, we will present our progresses in exploring the OMIEC-electrode interface changes under different voltage using operando techniques. Operando grazing incident wide-angle X-ray scattering (GIWAXS) of PEDOT:PSS revealed the degree of polymer-electrolyte interaction, resulting moderate lamellar expansions with electrolyte exposure, following a lamellar spacing relaxation upon electrochemical doping. Combining the operando GIWAXS results with time resolved electrochemical quartz crystal microbalance (EQCM), electro spectrochemistry, and device measurements, we subdivide the OMIEC response under electrochemical cycling into three steps, namely the fast polarization of electrode and the polymer, charge carrier population kinetics and macroscale transport, and the slow relaxation. The ionic charge transport and the ionic composition inside the material was also revealed by in situ moving front X-ray fluorescence spectroscopy (XRF). In situ XRF is also combined with operando GIWAXS to explore the structure-composition coupling under electrochemical doping state, and simultaneously reveals the ionic distribution in the crystalline phase of OMIECs. Based on these, we performed in situ grazing X-ray photon correlation spectroscopy (XPCS) to further investigate the response of the OMIEC-electrode interface in mesoscale under electrochemical cycling. By analyzing the scattered speckle, we deconvoluted the strain, phase contrast and aggregate dynamics of PEDOT:PSS under different voltage profiles.

<i>Operando</i> characterization of charge transport kinetics in organic mixed ionic-electronic conductors (OMIECs)

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Operando characterization of charge transport kinetics in organic mixed ionic-electronic conductors (OMIECs)