Two Birds with One Stone: Self-Supporting Anodes and Cathodes for Quasi-Solid-State Asymmetric Supercapacitors via Reactions of 2-Thiobarbituric Acid with Fe and Co Foams

Advanced electrode materials with simple manufacturing processes and wide voltage windows are needed for the commercialization of high energy density supercapacitors. Herein, a facile method is presented for fabricating self-supporting anodes and cathodes for quasi-solid-state asymmetric supercapacitors (QASCs) by hydrothermally reacting 2-thiobarbituric acid (TBA) with Fe foam (IF) and Co foam (CF), yielding FeTBA₄/FeOOH/IF and Co₉S₈/CF electrodes, respectively. Due to the perfect match between the two electrodes, the redox-active TBA ligands in FeTBA₄, the 2D ultrathin nanosheet structure of FeTBA₄/FeOOH/IF, and multiple pairs of reversible redox reactions for suppressing water splitting, the configured Co₉S₈/CF//FeTBA₄/FeOOH/IF QASC device delivers outstanding performance. The device possesses a wide operating voltage window of 1.6 V, leading to a high energy density of 82.64 Wh kg⁻¹ at 486.38 W kg⁻¹ and an equally impressive 35.36 Wh kg⁻¹ at 4595.92 W kg⁻¹. Furthermore, a 98.5% capacitance retention is realized after 10000 charging–discharging cycles. Impressively, density functional theory (DFT) calculations reveal the unique pseudocapacitive reactions on the surface of Co₉S₈/CF and FeTBA₄/FeOOH/IF electrodes. Importantly, this work guides the development of high-energy-density supercapacitors via the matching of electrodes and the use of redox-active complex electrodes.