The rational design of electrode materials is pivotal for optimizing the performance of energy storage and conversion systems such as supercapattery and electrocatalysis. In this study, a one-step supercritical fluid synthesis is presented to craft a unique heteroepitaxial composite, incorporating nickel di-selenide nanoparticles on niobium carbide MXene nanosheets in various ratios. The integration of 2D nanosheets enhances the kinetics of the electrode reaction process, while NiSe2 facilitates efficient charge transport in MXene. The composite demonstrated superior performance with the 1:2 ratio of NiSe2/Nb(2)CTx demonstrates an impressive specific capacitance of 1309 C g(-1) at 2 A g(-1) current density in a three-electrode system. Furthermore, the asymmetric supercapattery, featuring NiSe2/Nb(2)CTx 1:2 (positive electrode) and bio-derived activated carbon (AC) (negative electrode) achieves a gravimetric capacitance of 205 C/g at 0.5 A g(-1) current density, a power density of 10,800 W kg(-1) at the energy density of 64 Wh kg(-1), with 90% retention after 12 000 cycles. As a catalyst for water oxidation, the NiSe2/Nb(2)CTx 1:2 exhibits the lowest over potential of 359 mV at the current density 10 mA cm(-2) and Tafel slope of 105 mV dec(-1). This investigation introduces an innovative approach for developing high-performance supercapattery electrode materials and electrocatalysts using MXene.

Supercapacitor devices are increasingly significant in energy storage applications due to their excellent power density, quick charging/discharging capabilities, and long cycle ability. Due to their unique features, polymeric electrode materials have recently attracted attention. Here, we report the synthesis of two different viologen-based covalent organic polymers (COPs), COP-1 with a hollow sphere and COP-2 with hollow tube morphology, which were synthesized via the Zincke reaction by altering the polarity of the solvent. Their ultimate stability and p-extended conjugation rectify major bottlenecks of inhomogeneous aggregation brought on by structural deficiencies, restacking after repeated cycles, and inadequate connections during assembly observed on usual polymer electrodes. When employed as the dynamic electrode material in a three-electrode supercapacitor with 1 M H2SO4 as the aqueous electrolyte, COP-2 displayed remarkable electrochemical performance. Additionally, it showed astounding stability with 100 % capacitance retention after 50,000 cycles. In three electrode investigations, it also showed a specific capacitance of 604 F g(-1) at a current density of 2 A g(-1), and 404 F g(-1) at 0.5 A g(-1) for full cell studies. This research also offers a method for creating different morphology-driven COPs in high-performance supercapacitors.

Layered 2D/2D heterointerface composites experience interesting properties that greatly stimulate the recent surge in the attention as robust supercapacitor electrode materials, especially the MXene-based 2D/2D heterointerface for its robust energy storage compatibility. This report unveils a synergistically in situ prepared 2D/2D Nb2C/Ti3C2 MXene (NCTC) heterointerface nanoarchitecture by facile one-pot chemical etching. The methodology adopted enables the interconnected and simultaneous growth of MXenes exposing and retaining their active surfaces for enhanced ion diffusion pathways, charge storage dynamics, microstructural stability, and a noticeable potential window. Henceforth, the in situ developed NCTC heterointerface electrode delivered an excellent specific capacitance of 584 F/g at 2 A/g with a commendable energy density of 38.5 W h/kg in MXene supercapacitors owing to the augmented surface- and redox-based charge storage at the interface. Finally, the developed all-solid-state system demonstrated a superior cycling retention of 98% capacitance after 50,000 cycles. These superlative results encourage the exploration of such prospective 2D/2D heterointerfaces with intriguing charge storage and microstructural attributes for designing next-generation energy storage systems.