A hollow nano-flower NiCo2O4@Nb2CTx MXene heterostructure via interfacial engineering for high-performance flexible supercapacitor electrodes

Abstract

Interfacial engineering has the potential to be a highly effective approach to overcome the key bottleneck for supercapacitor electrodes caused by sluggish reaction kinetics. Herein, hollow nano-flower NiCo₂O₄@Nb₂CTx MXene heterostructures are successfully prepared, where NiCo₂O₄ nanomaterials are grown on the surface of Nb₂CTx MXene as a carrier using a simple hydrothermal-calcination coupling method. A unique heterojunction can fundamentally tune the electronic structure of the composite interface to enhance electrical conductivity. Appropriate characterization analysis and reasonable DFT calculations reveal the enhanced OH– adsorption properties of composites with the adsorption energy from −2.2 eV of pure NiCo₂O₄ to −2.5 eV of NiCo₂O₄@Nb₂CTx-2 products, which makes it advantageous for fast redox kinetic processes and obtain high potential out of the electrode material. NiCo₂O₄@Nb₂CTx-2 electrode exhibits a large capacity of 1030 C g⁻¹ (1873 F g⁻¹) at 1 A g⁻¹ and 750 C g⁻¹ (1363 F g⁻¹) at 50 A g⁻¹, showing excellent rate performance. In addition, the NiCo₂O₄@Nb₂CTx-2 electrode exhibits desirable durability with 94.3% of initial capacity undergoing 5000 cycles and excellent flexibility. Furthermore, NiCo₂O₄@Nb₂CTx//AC asymmetric supercapacitors assembled with NiCo₂O₄@Nb₂CTx-2 (cathode) and commercial activated carbon (AC, anode) display a larger energy density of 45.4 W h kg⁻¹ at a power density of 163 W kg⁻¹ and tremendous long-cycle durability with 97.1% initial capacity after 5000 cycles. This study explores a feasible approach for developing superior anode materials for battery-type supercapacitors with enhanced electrochemical performance.