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 H-2 production, where quick evolution of H-2 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.