Micron/nanoporous architecture sculptured on Ni wire via direct-flame treatment with tunable porosity for fiber-shaped supercapacitors

It is important to design and fabricate porous metal wire with optimized microstructures for miniature devices. However, this is still a challenge to uniformly construct porous structures on a small area and high hardness metal wire, more so far for the sophisticated micron/nanoporous structures. The micron/nanoporous architecture could be in-suit sculptured on commercial Ni wire (300 μm in diameter) by the direct-flame approach which is simple and economical. In this study, the influence of the treatment time of flame on the formation of porosity of Ni wire is investigated. It is found that porous Ni wire with a tunable porosity can be fabricated by controlling the flame treatment time and the optimized treatment time is 5 min in terms of the pore size and porosity. The micron/nanoporous Ni wires could be used as an effective substrate to construct fiber-shaped supercapacitors electrodes by coating MnO₂ on their surfaces. The optimized energy wire exhibits a high specific capacitance of 264.8 F g⁻¹ and 25.1 mF cm^–2 with a higher rate capability, and excellent cycling stability in a neutral solution of Na₂SO₄. This study reveals the evolution process of the porous structure on NW under the direct-flame process and guides the development of efficient micron/nanoporous NW substrates for various miniature devices through a reasonable selection of processing conditions.