Air Stable Photo-Redox Active Elusive Cr(III)-Tri-dithiolene-radical Complexes as a New Class of Pseudo-Supercapacitor with High Capacitance: Enhancement of Energy Storage with Heavier Chalcogenide

Chromium, an earth-abundant metal with exceptionally high theoretical specific capacity (1546 mAh g⁻¹) at an accessible redox potential -0.74 V vs. RHE, emerges as a promising element for designing high energy density supercapacitors. Besides their exciting chemistry, energy storage devices employing stable redox-active radicals of main-group elements gain increasing attention for sustainable applications. Herein, we present the pseudosupercapacitor properties of two unprecedented, photo-redox active, air-stable Cr(III)-triradical complexes with the general formula [Cr(III)(SS-NHC=EElectrochemical anodes fabricated by coating these complexes onto stainless-steel substrates demonstrate excellent supercapacitance performance. Complex 1 delivers a specific capacitance of 145.2 F g⁻¹, while complex 2 achieves a markedly higher 340.9 F g⁻¹ at 5 mV s⁻¹, centered at E₁/₂ = -0.72 V. Cycling stability is found to reach 81.2% for 1 and 87.3% for 2 after 3000 cycles. The superior activity of 2 arises from substituting sulfur with selenium in the SS-NHC=E •‾ ligand, enhancing redox activity, conductivity, and ion transport. Ragone plot analysis confirms higher energy density (14.63 Wh kg⁻¹ at 252 W kg⁻¹) for 2 compared to 1 (8.76 Wh kg⁻¹ at 211 W kg⁻¹). ... mehrMechanistic studies reveal that 1 operates via mixed surfaceand diffusion-controlled processes, while 2 predominantly follows diffusion control, enabling efficient charge transport and improved pseudocapacitive behavior.