In Situ Monitoring of Redox Electrochemistry of Perylene Diimide Electrodes by UV–Vis–NIR Spectroscopy

By virtue of sustainability and redox functionality, organic materials are an emerging class of electrodes for multivalent metal-ion batteries. However, the inevitable dissolution of radical anions in electrolyte media during electrochemical reduction poses a challenge to electrochemical reversibility and stability. The stable and electrochemical reversible formation of dianions of cationic perylene diimide (cPDI) in aqueous calcium-ion electrolyte is reported. Electrostatically assembled cPDI onto functional titanium carbide Ti₃C₂T_x MXene is processed in the form of semi-transparent thin films to probe characteristic spectral changes during reduction-oxidation cycles. In situ UV-Vis-NIR spectroscopy studies confirm the potential dependent reversible formation of radical anions and dianions of cPDI at -0.3 and -0.6 V versus Ag wire, respectively. Moreover, the bridging of Ca²⁺ ions between two molecules of perylene diimide also causes the change of electron density at the titanium atoms, as observed from the shift in the transverse surface plasmonic peak of MXene. This clearly signifies the role of non-covalent interactions between Ti₃C₂T_x and perylene diimide in stabilizing dianions in aqueous media, thus suppressing the dissolution effects. This study opens avenues for the exploitation of non-covalent interactions in the design of stable functional organic charge storage hosts for multivalent metal-ions.