Novel Redox Active Vanadium(V)-Dithiolene Complexes for Efficient Supercapacitive Energy Storage: Role of Selenium Functionalization on Pseudo-capacitive Properties

Abstract

Supercapacitors have been established as efficient storage devices for intermittent renewable energy, bridging the gap between batteries and conventional capacitors by offering high power density, rapid charge-discharge rates, and long cycle life; however, superior electrochemical performance remains a key challenge. In this regard, present work emphasizes on the synthesis and characterization of two photo-redox active anionic V(V)-dithiolene complexes [(THF)4Li][V(V)(SSNHC=E)3] (E = S (1), Se (2)), reacting the dithiolene radical anions [(THF)2Li(SS–NHC=S)] and [(THF)2Li(SS–NHC=Se)] with V(III)Cl3 in THF, respectively. These complexes were thoroughly characterized using UV-vis-NIR, IR, Raman and EPR spectroscopy techniques, confirming their structural and electronic properties, which are well correlated for their electrochemical energy storage capabilities using cyclic voltammetry, galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and stability tests. Electrochemical studies reveal that both complexes can exhibit remarkable pseudocapacitive behavior in transition metal-dithiolene-based materials with excellent charge storage capacity and cycling stability. The unique electronic structures of these vanadium dithiolene complexes contribute to their efficient redox activity, making them a promising class of supercapacitor materials. Moreover, variations in electrolyte composition significantly influenced the performance, underscoring the crucial role of ion–electrode interactions. Impedance analysis further confirmed low charge transfer resistance, suggesting efficient ion diffusion and active redox processes. The materials exhibited good cycling stability, highlighting the robust redox active sites and their suitability for long-term energy storage applications. Complex 1 exhibited slightly better specific capacitance of 82.82 F/g (areal 82.82 mF/cm2) than complex 2 (76.56 F/g, areal 76.56 mF/cm2) at 5 mV/s while complex 2 exhibited excellent capacitive retention of 104.39% after 2000 cycles. Complex 1 showed some degradation over prolonged cycling. This study also highlights the potential of redox-non-innocent dithiolene ligands in designing advanced and next-generation energy storage materials for the first time.