Geometrically intricate sheet-on-pillar/flake hierarchy embracing cobaltosic and manganese oxides over flexible carbon scaffold for binder-free high-energy-density supercapacitor

The proliferation of wearable electronics necessitates rational design and simple fabrication protocols of geometrically intricate multicomponent 3D hierarchical heterostructures over flexible scaffolds for high electrochemical performance and mechanically robust electrodes. In an attempt to meet the general design necessity for highly proficient supercapacitor electrodes by combining the strategies of conductivity modification, porous nanoform and lightweight substrate, we have realized a tailor-made hierarchical nanoform comprising 1D-2D and 2D-2D combination of cobaltosic and manganese oxides anchored on carbon cloth via simple hydrothermal techniques. Starting with bare carbon fiber, 1D nanopillar and 2D Co3O4 flake were developed on fabric initially, followed by which hierarchies were prepared via secondary growth of MnO2 sheet. Such typical arrangement makes full use of synergistic effects from both high specific capacitance of the morphology-tuned hybrid and high electrical conductivity of the underlying fiber, making them efficient electrodes for foldable supercapacitors. Carbon cloth-supported hybrid nanoforms deliver far superior performance compared to the individual structural units, where the optimized 2D-2D geometry shows maximum specific capacitance of 1396 F g(-1) at 0.3 A g(-1) and excellent rate capacity of 94% capacitance retention at 5 A g(-1). Discernable differences in the electrochemical behavior of different synthesized nanoforms were investigated in great detail on the basis of geometry-porosity-property correlation. Supercapacitors were assembled using the optimized Co3O4-MnO2 which exhibited an energy density of 91.9 Wh kg(-1) at a power density of 0.8 kW kg(-1) and delivered 90% of the initial specific capacitance after 5000 cycles at high current density. Such fascinating results of the as-fabricated supercapacitors highlight the combination of rational design and morphology tuning of nanoforms in maximizing the electrochemical performance and thereby providing a useful pathway to develop new electrode materials in the energy storage arena.