Large-scale uniform α-Co(OH)₂ long nanowire arrays grown on graphite as pseudocapacitor electrodes.

Large-scale uniform α-Co(OH)₂ nanowire arrays (NWAs) with an average length of ∼20 μm grown on pyrolytic graphite (PG) were successfully synthesized by a hydrothermal method at 120 °C. Ultrasonication test was carried out toward the as-made nanoarray products and the result demonstrated their robust adhesion to graphitic substrate. After 300 s of sonication testing, α-Co(OH)₂ NWAs could still possess both integrated one-dimensional (1D) nanoarray architecture and good electronic connections with current collector. When investigated as electrochemical pseudocapacitor electrodes, α-Co(OH)₂ NWAs exhibited good energy-storage performance in terms of high specific capacitance of 642.5 F/g, good rate capability, and excellent capacity retention. Our work not only presents a cost-effective and scale-up synthetic method for α-Co(OH)₂ NWAs but also holds promise in general synthesis of long arrays of other metal hydroxides/oxide (TiO₂, Fe₂O₃, SnO₂, etc.) nanostructures on PG substrate by using α-Co(OH)₂ NWAs as sacrificial templates.