Ultra-high specific capacitance of β-Ni(OH)2 monolayer nanosheets synthesized by an exfoliation-free sol–gel route

In this work, β-Ni(OH)2 monolayer nanosheets were prepared in benzyl alcohol by a facile exfoliation-free sol–gel route. The hydrolysis reaction of metal ions was started with the ring-opening reaction of epoxide. The in situ modification of benzyl alcohol molecules on the surface of secondary growth unit of hydroxide allowed the formation of β-Ni(OH)2 monolayer nanosheets and 100 % monolayer state of β-Ni(OH)2 in the resultant suspension. As proven in the electrochemical measurement, the maximum specific capacitance of 1735 F g−1 was obtained at scan rate of 5 mV s−1 within potential window of 0.6 V in 6 mol l−1 KOH aqueous solution, which is equal to the theoretical value of β-Ni(OH)2. This high electrochemical performance is attributed to the complete exposure of every structure unit of β-Ni(OH)2 to electrolyte. This work demonstrates that monolayer nanosheets can generate from the brucite-type nickel hydroxide through this bottom-up strategy although it had been theoretically considered to be impossible.