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. [ABSTRACT FROM AUTHOR]