Hierarchical Microspheres Based on alpha-Ni(OH)2 Nanosheets Intercalated with Different Anions: Synthesis, Anion Exchange, and Effect of Intercalated Anions on Electrochemical Capacitance

Abstract

Hierarchical microspheres composed of wrinkled alpha-Ni(OH)(2) nanosheets were synthesized from an aqueous solution containing nickel salts, hexamethylenetetramine, 1-butanol, and dodecyl sulfate. The exchange of intercalated dodecyl sulfate anions within the microspheres by smaller anions (Cl-, NO3-, OAc-, and SO42-) resulted in retention of morphology. A possible growth mechanism is proposed based on the observation of the effects the parameter variation (different nickel and hydroxide sources, several alcohols, with and without dodecyl sulfate as well as 1-butanol) had on rnicrosphere formation. Electrochemical and capacitive properties of the anion-exchanged microspheres were studied by cyclic voltammetry and galvanostatic charging-discharging. Interestingly, the specific capacitance was determined by size of the intercalated anions and not by the basal spacing; for example, the largest anion, SO42-, gave the lowest specific capacitance, whereas the smallest anion, Cl-, gave the highest specific capacitance. Our data support the notion that larger anions impede the mobility of OH- ions toward the surface of Ni(OH)(2) sheets to a greater extent than smaller ions.