Two-Dimensional Cobalt Coordination Polymers Based on Anionic Modulation and Application in Supercapacitors

Abstract

Supercapacitors are promising energy storage device due to their rapid charge/discharge, high power density and long cycle life. Two-dimensional (2D) Coordination Polymers (CPs) exhibit significant potential for electrochemical energy storage. However, controlling the morphology of 2D CPs remains challenging. Controlling the morphology of 2D CPs remains challenging. In this study, pseudohalide anions (SeCN^–, SCN^–) were employed as crystal growth modifiers to achieve precise morphological control, leveraging their distinct coordination capacities and steric hindrance effects. Specifically, the large atomic radius and high polarizability of Se in SeCN^– facilitate the lateral growth of CPs, leading to the formation of uniform lamellar structures. Co-CP-Se delivered a specific capacitance of 1483 F g^–1 at 1 A g^–1 and maintained 93.23% of its initial capacitance after 5000 cycles at 10 A g^–1. A hybrid supercapacitor (Co-CP-Se//AC) demonstrated a power density of 750 W kg^–1 at an energy density of 42.14 Wh kg^–1 while maintaining 90.12% capacitance retention after 5000 cycles (10 A g^–1). Mechanistic investigations revealed that partial substitution of −SeCN by OH^– during cycling generated Co(OH)₂, which synergistically contributed to the capacitance together with Co-CP-Se. The uniform lamellar architecture optimized the electrolyte-electrode interface contact and offered critical insights for the structural design of 2D CPs toward high-performance energy storage applications.