Rational Design of Metal-Organic Framework Derived Hollow NiCo₂O₄ Arrays for Flexible Supercapacitor and Electrocatalysis

Metal-organic frameworks (MOFs) are promising porous precursors for the construction of various functional materials for high-performance electrochemical energy storage and conversion. Herein, a facile two-step solution method to rational design of a novel electrode of hollow NiCo₂O₄ nanowall arrays on flexible carbon cloth substrate is reported. Uniform 2D cobalt-based wall-like MOFs are first synthesized via a solution reaction, and then the 2D solid nanowall arrays are converted into hollow and porous NiCo₂O₄ nanostructures through an ion-exchange and etching process with an additional annealing treatment. The as-obtained NiCo₂O₄ nanostructure arrays can provide rich reaction sites and short ion diffusion path. When evaluated as a flexible electrode material for supercapacitor, the as-fabricated NiCo₂O₄ nanowall electrode shows remarkable electrochemical performance with excellent rate capability and long cycle life. In addition, the hollow NiCo₂O₄ nanowall electrode exhibits promising electrocatalytic activity for oxygen evolution reaction. This work provides an example of rational design of hollow nanostructured metal oxide arrays with high electrochemical performance and mechanical flexibility, holding great potential for future flexible multifunctional electronic devices.