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 –, NO 3 –, OAc –, and SO 4 2– ) 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, SO 4 2–, 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.