Enhanced electrochemical storage capability of NiCo2O4 nanosheet/nanowires hybrid arrays via synergistic collaborative MXene/Graphene

Abstract

Transition metal oxides (TMOs) are potential high-performance electrode materials for supercapacitors, but their application is hindered by poor electrical conductivity and slow reaction kinetics. To overcome these challenges, self-supporting NiCo₂O₄ (NCO) nanosheet-nanowire hybrid arrays were synthesized through a two-step hydrothermal process. The hierarchical architecture is constructed by successively growing NCO on reduced graphene oxide (rGO)-coated Ni foam and subsequently wrapping with 2D Ti₃C₂T_x MXene layers. NCO serves as the energy storage material, while rGO and MXene collaboratively establish a three-dimensional conductive network, enhancing both electron transport and structural robustness. In the nanoarray, the composite denoted as MXene/NCO@rGO-NF exhibits strengthened interface effects (charge redistribution and lowered energy barriers at heterogeneous interfaces) and rapid electron transfer (uninterrupted electron pathways via MXene-rGO bridging). This design further promotes hydroxide ions (OH⁻) adsorption on NCO, accelerating redox reaction kinetics. As expected, the MXene/NCO@rGO-NF electrode delivers an outstanding specific capacity of 1236.5 C g⁻¹ at 1 A g⁻¹. When assembled into a hybrid supercapacitor, it achieves a maximum energy density of 34.6 Wh kg⁻¹ at 375 W kg⁻¹, with 82.5 % capacitance retention after 8000 cycles. This work demonstrates a stepwise assembly strategy to boost the electrochemical performance of TMOs with high-capacity electrodes with enhanced cycling stability.