Cryogel synthesis of hierarchical interconnected macro-/mesoporous Co ₃O ₄ with superb electrochemical energy storage

In this contribution, we report a facile synthesis of ultrafine Co ₃O ₄ nanocrystals with an in situ construction of mesoporous and macroporous network for supercapacitor electrode material. The resultant ultrafine Co ₃O 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 ₃O 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.