3D Hierarchical Ti 3 C 2 T X @PANI-Reduced Graphene Oxide Heterostructure Hydrogel Anode and Defective Reduced Graphene Oxide Hydrogel Cathode for High-Performance Zinc Ion Capacitors.

The practical application of supercapacitors (SCs) has been known to be restricted by low energy density, and zinc ion capacitors (ZICs) with a capacitive cathode and a battery-type anode have emerged as a unique technology that can effectively mitigate the issue. To this end, the design of electrodes with low electrochemical impedance, high specific capacitance, and outstanding reaction stability represents a critical first step. Herein, we report the synthesis of hierarchical Ti 3 C 2 T X @PANI heterostructures by uniform deposition of conductive polyaniline (PANI) polymer nanofibers on the exposed surface of the Ti 3 C 2 T X nanosheets, which are then assembled into a three-dimensional (3D) cross-linking framework by a graphene oxide (GO)-assisted self-convergence hydrothermal strategy. This resulting 3D Ti 3 C 2 T X @PANI-reduced graphene oxide (Ti 3 C 2 T X @PANI-RGO) heterostructure hydrogel shows a large surface area (488.75 F g -1 at 0.5 A g -1 ), outstanding electrical conductivity, and fast reaction kinetics, making it a promising electrode material. Separately, defective RGO (DRGO) hydrogels are prepared by a patterning process, and they exhibit a broad and uniform distribution of mesopores, which is conducive to ion transport with an excellent specific capacitance (223.52 F g -1 at 0.5 A g -1 ). A ZIC is subsequently constructed by utilizing Ti 3 C 2 T X @PANI-RGO as the anode and DRGO as the cathode, which displays an extensive operating voltage (0-3.0 V), prominent energy density (1060.96 Wh kg -1 at 761.32 W kg -1 , 439.87 Wh kg -1 at 9786.86 W kg -1 ), and durable cycle stability (retaining 67.9% of the original capacitance after 4000 cycles at 6 A g -1 ). This study underscores the immense prospect of the Ti 3 C 2 T X -based heterostructure hydrogel and DRGO as a feasible anode and cathode for ZICs, respectively.