Integration of Polymorphic Co _x Se _y on MXene-Incorporated Self-Templated Three-Dimensional Graphene Foam to Augment Supercapacitor Performance through Componential and Structural Modifications

Transition metal selenides (TMSes) possess rich redox chemistry and, consequently, are potential candidates for supercapacitor applications. Unfortunately, the actual capacitance behavior of TMSes is generally lower than the theoretical value due to a small number of exposed active sites, sluggish charge transfer, and inferior ion diffusivity. Moreover, the dramatic volume changes during the charge/discharge process adversely affects the stability of active materials. Herein, polymorphic CoxSey (Co0.85Se and CoSe2) have been synthesized and integrated into Ti3C2Tx MXene flake reinforced three-dimensional (3D) rGO foam (denoted as CoxSey@TC/rGOF) through a self-templating hydrothermal method. The well-constructed foam-like architecture with 3D buildup of Ti3C2Tx MXene and rGO sheets provides fast ion/mass transport to a large number of accessible active sites of spatially arranged CoxSey in three dimensions, decreases ion diffusion distance, and provides an additional carbon content that enables capacitive characteristics. The structural advantages and intercomponent synergy lead to a superior charge storage performance for CoxSey@TC/rGOF. Accordingly, CoxSey@TC/rGOF delivers high specific capacities of 243.1 mAh g(-1) at 1 A g(-1) and 178 mAh g(-1) at 12 A g(,)(-1) greater than its counterparts, i.e., CoxSey@rGOF (147.2 mAh g(-1) at 1 A g(-1)) and CoxSey (79.4 mAh g(-1) at 1 A g(-1)). The specific capacity and Coulombic efficiency for CoxSey@TC/rGOF retain 91.3 and 93.8% of their initial value after 5000 charge/discharge cycles, respectively. Impedance measurement shows small values of R-s (1.04 Omega) and R-CT (3.92 Omega) for CoxSey@TC/rGOF. In addition, this work presents a feasible scheme to provide a basic understanding of enhanced charge storage and structural stability.