(Ni,Co)Se₂ nanoparticles on vertical graphene nanosheets@carbon microtubes for high-performance solid-state asymmetric supercapacitors

Much attention has been draw to transitional metal selenides (TMSe) for energy storage, especially the high-performance supercapacitor devices, so it is research hotspots to construct free-standing electrode with TMSe loading. In this work, 3D carbon microtubes (CMTs) wrapped by vertical graphene nanosheets (VGNs), were fabricated by plasma-enhanced chemical vapor deposition (PECVD) method using SiO₂ nanowires as templates, which were served as free-standing, conductive and flexible substrates for supporting (Ni,Co)Se₂ nanoparticles. Benefiting from the structural merits, such as the interwoven CMTs network, high conductive VGNs substrate, and the synergistical effect of nanostructured (Ni,Co)Se₂, the fabricated CMTs@VGNs@(Ni,Co)Se₂ membrane electrode exhibits excellent electrochemical performance in terms of high specific capacitance (1740 F g⁻¹ at 1 A g⁻¹), good rate capability (71.8 % capacitance retention at 20 A g⁻¹), and superior cycling stability (89.6 % capacitance retention after 10,000 cycles). Notably, the solid-state asymmetric supercapacitor (ASC) assembled with CMTs@VGNs@(Ni,Co)Se₂ membrane and activated carbon (AC), not only delivers a high energy density of 41.6 Wh kg⁻¹ at a power density of 0.75 kW kg⁻¹, but also shows long cycle life with excellent performance stability. More impressively, our work provides a new idea for structural construction of 3D carbon-based nano-substrates and self-supporting electrodes for supercapacitors.