High Efficiency n-Type Electrochemical Doping of Homogeneous Polymeric Mixed Conductors by Aromatic Cation Insertion in Aqueous Electrolyte.

Electrochemical doping is central to energy storage, neuromorphic computing, and biosensing, yet the mechanisms governing efficient n-type doping and ion-structure correlations remain poorly understood. Here, efficient n-type electrochemical doping is reported in the polymeric mixed conductor gDPP-tB₀ through tailored organic cation interactions, investigated via cyclic voltammetry, in situ spectroelectrochemistry, grazing-incidence wide-angle X-ray scattering, and molecular dynamics simulations. Compared to the choline cation (Ch⁺) system, the 1-ethylpyridinium cation (EPy⁺) system exhibited superior doping kinetics, achieving a higher reduction current density (0.47 mA cm^-2), faster ion diffusion coefficient (6.77 × 10^-9 cm² s^-1), more pronounced polaron generation, and improved OECT performance (µC* up to 18.7 F cm^-1 V^-1 s^-1). These improvements stem from EPy⁺'s preferential backbone localization, which minimizes polymer distortion, maintains high crystallinity, and optimizes ion-electron coupling, thus resulting in more efficient n-type electrochemical doping. Moreover, further gains in doping efficiency are realized by tuning the pyridyl cation concentration and alkyl chain length. The work reveals a new paradigm for efficient n-type electrochemical doping in polymeric mixed conductors via organic cation engineering, offering new insights into the rational design of ionic liquids for enhancing n-type electrochemical doping and accelerating the development of wearable bioelectronics.