Structure-reactivity requirements with respect to nickel-salen based polymers for enhanced electrochemical stability

Abstract

We revealed a general guidance on preparation of electrochemically stable meso forms of nickel-salen based polymers suitable as new anode materials for electrochemical devices. Electrochemical performance of nickel-salen complexes, used as monomers of nickel-salen based polymers, was directly related to the salen ligand structure. We have considered it in specially designed and synthesized herein a new meso form of the nickel-salen polymer, vis., poly[meso-N,N′-bis-(3-methylosalicylidene)-2,3-butanediaminonickel(II)]. Then, electrochemical conditions for providing the environment appropriate for electropolymerization and charge transfer were optimized. In dependence upon the purpose of the use of the poly(meso-Ni-salen) films coated electrodes, it was possible to increase the amount of the charge stored in these conjugated polymer systems by proper tuning of both the chemical structure of the polymer and electrochemical conditions. Apparently, the charge transfer through nickel-salen polymers strongly depended upon steric hindrance between polymer layers, thus ensuring efficient counter ion doping. Therefore, this hindrance was carefully selected. We have defined steric requirements with respect to the type and position of moderately electrodonating substituents on imine bridges and phenolic rings of the nickel-salen polymers that must be met to achieve high conductivity and stability/durability during potential multi-cycling of the polymer films prepared.