Cation Insertion in Polymer Electrodes

Semiconducting pi-conjugated redox polymers have been intensively studied in the field of soft photoelectrochemistry for their ability to enhance polymer conductivity through ion insertion. This study focuses on electrochemical cation doping in n-type polymers P90 and N2200, each comprising alternating naphthalene dicarboximide (NDI) acceptor and bithiophene (T2) donor units. The NDI units in P90 alternately feature heptaethylene glycol (HEG, 90%) and 2-octyl dodecyl (OD, 10%) side chains, while N2200 contains 100% alkyl OD side chains. Considering the Gutmann donor number (DN) of the side chains and the polymer durability in different solvents, we investigated P90 in aqueous and N2200 in non-aqueous systems using spectroelectrochemical techniques and structural characterization to access how varying cation identify affect polymer electronic behavior. Specifically, we explored chloride salts (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) in aqueous electrolytes and PF₆ salts (Li⁺, K⁺, NH₄⁺, and tetrabutylammonium (TBA⁺)) in non-aqueous electrolytes. We analyzed trends in cation size and valence on the redox properties of the polymers using in-situ UV-Vis spectroelectrochemistry; kinetic Raman spectra showed a significant change to the C=O bond as it generally disappears with C-O<b> </b>vibration rising when potential goes more negative<b>. </b>grazing incidence wide angle X ray scattering (GIWAXS) confirmed that electrochemical doping drives ions into the crystallites, decreases the crystallinity, and increased the degree of the disorder. This study sheds light on cation insertion effects and their influence on polymer electronic behaviors, crucial for advancing energy conversion and storage applications.