Cryogel Synthesis of Hierarchical Interconnected Macro-/Mesoporous Co₃O₄ with Superb Electrochemical Energy Storage

In this contribution, we report a facile synthesis of ultrafine Co 3 O 4 nanocrystals with an in situ construction of mesoporous and macroporous network for supercapacitor electrode material. The resultant ultrafine Co 3 O 4 nanocrystals form an interconnected macroporous network with mesoporous hierarchical structure. The unique architecture is realized through a modified sol–gel process to formulate highly porous cryogel using freeze-drying in the presence of a soft template. Small-angle X-ray scattering and transmission electron microscopy are used to investigate the organization of the Co 3 O 4 porous structure. The unique channels in this hierarchical pores network provide intimate electrolyte contact with cobalt oxide and facilitate electrolyte diffusion. This hierarchical structure presents superior electrochemical performance with a specific capacitance of 742.3 F g –1 measured at a potential window of 0.5 V, unveiling one of the highest performance for sol–gel synthesized oxides to date, to the best of our knowledge. The capacity retention was 86.2% after 2000 cycles. The synthesis strategy highlights a versatile and facile dual template approach to independently tailor the porosity and particle sizes using a spontaneous nucleation approach. This serves as a major milestone toward high-performance porous metal oxide material for supercapacitor electrodes.