Hierarchical Microspheres Based on α-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 α-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 microsphere 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.