Electric-field oriented self-assembly of Mn₃O₄ nanostructures driven by liquid plasma discharge for super capacitor

Fabrication of low-cost, uniform size, and binder-free nanomaterials via contact glow discharge electrolysis (CGDE) for high performance supercapacitors is still a great challenge. In this work, by utilizing the CGDE method as a template, the rapid synthesis of two different morphologies of Mn₃O₄ nanostructures through a one-step liquid plasma discharge deposition (LPDD) method is proposed and demonstrated. The two uniform nano-octahedron and nano-sheet Mn₃O₄ structures are grown upon the different electric field orientations under a low DC voltage. The transportation of ions is dependent on the electrical field direction leading to the formation of different nanostructures. Upon the horizontal electric field to the grown substrate, the Ostwald ripening effect is dominant in the growth process of single-crystalline Mn₃O₄ nano-octahedra, which exhibits high crystallinity and geometric symmetry with a side length of 40 nm. In contrast, the hydrothermal effect assists in the formation of Mn₃O₄ nano-sheet when the electrical field is perpendicular to the substrate. The continuous transportation of ions promotes the fast growth of ultra-thin and porous Mn₃O₄ polycrystalline nano-sheets. The binder-free nano-sheet Mn₃O₄/carbon composite electrode delivers a higher specific capacitive (488 F g⁻¹) and remarkable cycle life (10,000 cycles; 99.1% capacity retention). This work addresses a facial, cost-effective, and scalable path of the production of nanostructures with different morphologies simply by the operation of an electric field.