Exploration of Charge Storage in an Anion-Exchanged Synthesized Sn–Co–Se Nanorod-Based Flexible Symmetric Supercapacitor

Flexible supercapacitors (SCs) have been considered next-generation promising high-energy storage systems due to their promising pertinency and feasibility, along with extreme bending and foldable features. In this work, we report the fabrication of a flexible symmetric supercapacitor device by combining redox and electrostatic effects on the same material electrodes. Newly developed material SnxCo1–xSe2 nanorods (NRs) are prepared via an anion exchange reaction of a metal organic framework with selenium and trapping of Sn2+. Optimized Sn0.17Co0.83Se2 NRs have a larger surface area and pore size and optimized ratio of Sn and Co for best synergistic interactions for electrochemical energy storage. The as-synthesized Sn0.17Co0.83Se2 NRs exhibit a high areal capacitance of 706 mF cm–2 at a current density of 1.3 mA cm–2 and a high rate capability of 68% at a high current density of 11.7 mA cm–2 in 2.0 M KOH electrolyte. A flexible symmetric supercapacitor device was assembled using Sn0.17Co0.83Se2||[EMIM][BF4]||Sn0.17Co0.83Se2 combination, and the device overcomes the low energy density limitation of normal supercapacitors by delivering high energy and power densities of 0.053 mWh cm–2 and 5.53 mW cm–2, respectively, long cycling stability, and high Coulombic efficiency over 10,000 charge–discharge cycles in a voltage window of 0–2.5 V. The device also can be used as a prompt energy source in a water splitting reaction for H2 production, where quick evolution of H2 is required. A detailed mechanistic study suggested the origin of charge transfer from a faster ion switching, surface-controlled redox process, and fast electrosorption sequence process, where the potential-induced adsorption of electrolyte ions onto the surface of charged electrodes takes place efficiently.