Electrochemical synthesis and characterization of poly [Ni(CH3Osalen)] with immobilized poly(styrenesulfonate) anion dopants

Highlights: • Ni salen-type polymers with polyanionic dopant show cationic transport. • Doping by PSS^– anion leads to higher average length of the formed polymer chain. • IDE/EIS combination allows to separate ionic and electronic transport components. • Ionic transport is a limiting factor of the charge transport. -- Abstract: Intrinsically conductive polymer poly(N,N′-bis(3-methoxysalicylidene)ethylenediamine nickel(II)) (poly[Ni(CH₃Osalen)]:PSS) has been synthesized by electrochemical polymerization from the [Ni(CH₃Osalen)] solution containing tetrabutylammonium poly(styrenesulfonate) (TBAPSS). Cyclic voltammetry and in situ EQCM data demonstrated that electrochemical properties of poly[Ni(CH₃Osalen)]:PSS are highly dependent on the nature of electrolyte solutions. A wider range of electrochemical activity, higher values of conductance and binary diffusion coefficient in TBAPSS solution are observed than in LiClO₄, but the capacity values of films are higher in LiClO₄ solution. The introduction of PSS⁻ polyanion during synthesis of polymer film induced cationic mode of charge transport for poly[Ni(CH₃Osalen)]. This type of PSS⁻ doped polymers can be used as ion-exchange membranes. The combined electrochemical impedance spectroscopy and in situ conductance measurements on interdigitated electrodes were analyzed using the model concepts of Matthias and Haas, and Einstein relation. This novel approach allowed separating the diffusion coefficient into its ionic and electronic constituents. The ionic diffusion was found to be the limiting factor. Strong association of lithium cation with both the PSS⁻ polyanion and methoxy-groups may be the cause of lower values of diffusion coefficients in LiClO₄ solutions. The proposed model is suitable for further studies of similar systems.