A facile solvent regulated method for phase control of two-dimensional nickel-cobalt hydroxide nanosheets: Towards improved performance hybrid supercapacitors

Manipulating the crystal phase has been proved to be a crucial strategy to access metastable structures with desirable properties. For nickel and cobalt hydroxides, the α-phase with enhanced electrochemical performance is more unstable than the β-phase, which limits its technological applications in hybrid supercapacitors. Here, a facile solvent regulated method for phase control of two-dimensional nickel and cobalt hydroxide is firstly developed, and the α-phase nickel and cobalt hydroxides can be stably obtained. Significantly, the phase control process can be simply achieved by varying the solvents between ethylene glycol (Eg) and ethanol (Et). Notably, the obtained α-phase nickel-cobalt hydroxide can deliver an impressive specific capacitance of 2366.6 F g⁻¹ (1 A g⁻¹), which is almost 13.4 times higher than β-Co(OH)₂. Moreover, α-phase nickel-cobalt hydroxide||activated carbon hybrid supercapacitor exhibits a maximum energy density of 38.5 Wh kg⁻¹ at the power density of 800 W kg⁻¹. This work provide an important strategy for phase control of nickel and cobalt hydroxides, and the excellent electrochemical performance presented by α-phase nickel-cobalt hydroxide demonstrates its promising application for high performance hybrid supercapacitors.