Tailoring uniform γ-MnO₂ nanosheets on highly conductive three-dimensional current collectors for high-performance supercapacitor electrodes

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Recent efforts have focused on the fabrication and application of three-dimensional (3-D) nanoarchitecture electrodes, which can exhibit excellent electrochemical performance. Herein, a novel strategy towards the design and synthesis of size- and thickness-tunable two-dimensional (2-D) MnO₂ nanosheets on highly conductive one-dimensional (1-D) backbone arrays has been developed via a facile, one-step enhanced chemical bath deposition (ECBD) method at a low temperature (∼50 °C). Inclusion of an oxidizing agent, BrO₃ ⁻, in the solution was crucial in controlling the heterogeneous nucleation and growth of the nanosheets, and in inducing the formation of the tailored and uniformly arranged nanosheet arrays. We fabricated supercapacitor devices based on 3-D MnO₂ nanosheets with conductive Sb-doped SnO₂ nanobelts as the backbone. They achieved a specific capacitance of 162 F·g⁻¹ at an extremely high current density of 20 A·g⁻¹, and good cycling stability that shows a capacitance retention of ≈92% of its initial value, along with a coulombic efficiency of almost 100% after 5,000 cycles in an aqueous solution of 1 M Na₂SO₄. The results were attributed to the unique hierarchical structures, which provided a short diffusion path of electrolyte ions by means of the 2-D sheets and direct electrical connections to the current collector by 1-D arrays as well as the prevention of aggregation by virtue of the well-aligned 3-D structure.