One-dimensional β-Ni(OH)2nanostructures: Ionic liquidetching synthesis, formation mechanism, and application for electrochemical capacitors

Abstract

A trifluoroacetate-functionalized task-specific ionic liquid has been introduced for the synthesis of β-Ni(OH)₂ microspheres composed of nanowires. The cation C₁₆mim⁺ and the anion CF₃COO⁻ played synergetic roles on the formation of β-Ni(OH)₂ microspheres composed of nanowires. The hydrolysis of anion CF₃COO⁻ provides controlled quantities of OH⁻ ions for the formation of β-Ni(OH)₂ microspheres composed of nanosheets. While the OH⁻ supplies the precipitation of β-Ni(OH)₂, the CF₃COOH of the system increases continually. CF₃COOH is responsible for the etching of β-Ni(OH)₂ nanosheets. The conjunction of microsheets and nanowires, which are the intermediates during the ionic liquid etching process, present the obvious detail for the etching process. Via the ionic liquid etching process, β-Ni(OH)₂ microspheres composed of nanosheets evolved into β-Ni(OH)₂ microspheres composed of nanowires. With the morphologies changed from nanosheets to nanowires, the BET surface areas of β-Ni(OH)₂ have been significantly increased from 53 m² g⁻¹ to 249 m² g⁻¹ and the specific capacitance of β-Ni(OH)₂ have also been increased from 412 F g⁻¹ to 1250 F g⁻¹.