Tuning cationic transport in Nisalen polymers via pseudo-crown functionality

Abstract

Polymeric films based on nickel complexes with salen-type ligands have received considerable attention recently owing to electrocatalytic, electrochromic, and charge storing properties. The latter makes them suitable metal-organic materials for electrochemical power sources, i.e., batteries and supercapacitors. Optimization of the properties of electrode materials is closely linked to the understanding of charge storage mechanisms. The introduction of CH3O substituent into the molecule results in peculiar ionic transport mechanism, owing to the possibility of alkaline ions coordination. Here we study the recharging mechanism of poly[Ni(CH3Osalen)] films in various electrolyte solutions. In presence of alkali ions, the electronic effects of methoxy substituent provide mixed anionic and cationic charge compensation mechanism, as cations reversibly coordinate to the present pseudo-crown functionality. By applying the combination of XRD, CV/EQCM and EIS methods to the film in electrolytes containing Li+, Na+, K+, and Et4N+ cations, and BF4−, ClO4− and bistrifluoromethanesulfonimidate (TFSI−) anions, we propose a model that describes the ionic transport in such polymeric films and allows to estimate the anionic and cationic contribution to the total amount of transferred species during charging and discharging.