Hierarchically Hybrid Porous Co₃O₄@NiMoO₄/CoMoO₄ Heterostructures for High-Performance Electrochemical Energy Storage

Hierarchical, ultrathin, and porous NiMoO₄@CoMoO₄ on Co₃O₄ hollow bones were successfully designed and synthesized by a hydrothermal route from the Co-precursor, followed by a KOH (potassium hydroxide) activation process. The hydrothermally synthesized Co₃O₄ nanowires act as the scaffold for anchoring the NiMoO₄@CoMoO₄ units but also show more compatibility with NiMoO₄, leading to high conductivity in the heterojunction. The intriguing morphological features endow the hierarchical Co₃O₄@NiMoO₄@CoMoO₄ better electrochemical performance where the capacity of the Co₃O₄@NiMoO₄@CoMoO₄ heterojunction being 272 mA·h·g^-1 at 1 A·g^-1 can be achieved with a superior retention of 84.5% over 1000 cycles. The enhanced utilization of single/few NiMoO₄@CoMoO₄ shell layers on the Co₃O₄ core make it easy to accept extra electrons, enhancing the adsorption of OH^- at the shell surface, which contribute to the high capacity. In our work, an asymmetric supercapacitor utilizing the optimized Co₃O₄@NiMoO₄@CoMoO₄ activated carbon (AC) as electrode materials was assembled, namely, Co₃O₄@NiMoO₄@CoMoO₄//AC device, yielding a maximum high energy density of 53.9 W·h·kg^-1 at 1000 W·kg^-1. It can retain 25.92 W·h·kg^-1 even at 8100 W·kg^-1, revealing its potential and viability for applications. The good power densities are ascribed to the porous feature from the robust architecture with recreated abundant mesopores on the composite, which assure improved conductivity and enhanced diffusion of OH^- and also the electron transport. The work demonstrated here holds great promise for synthesizing other heterojunction materials M₃O₄@MMoO₄@MMoO₄ (M = Fe, Ni, Sn, etc).