Facile one-pot synthesis of NiCo₂O₄ hollow spheres with controllable number of shells for high-performance supercapacitors

In this work, single- and double-shelled NiCo₂O₄ hollow spheres have been synthesized in situ by a one-pot solvothermal method assisted by xylose, followed by heat treatment. Employed as supercapacitor electrode materials, the double-shelled NiCo₂O₄ hollow spheres exhibit a remarkable specific capacitance (1, 204.4 F·g^-1 at a current density of 2.0 A·g^-1) and excellent cycling stability (103.6% retention after 10, 000 cycles at a current density of 10 A·g^-1). Such outstanding electrochemical performance can be attributed to their unique internal morphology, which provides a higher surface area with a larger number of active sites available to interact with the electrolyte. The versatility of this method was demonstrated by applying it to other binary metal oxide materials, such as ZnCo₂O₄, ZnMn₂O₄, and CoMn₂O₄. The present study thus illustrates a simple and general strategy for the preparation of binary transition metal oxide hollow spheres with a controllable number of shells. This approach shows great promise for the development of next-generation high-performance electrochemical materials.