Synthesis of nickel carbonate hydroxide@zeolitic imidazolate framework-67 (Ni2CO3(OH)2@ZIF-67) for pseudocapacitor applications

Zeolitic imidazolate framework-67 (ZIF-67), nickel carbonate hydroxide (Ni2CO3(OH)(2)), and Ni2CO3(OH)(2)@ZIF-67 composite were synthesized by a typical hydrothermal method. During the synthesis of Ni2CO3(OH)(2)@ZIF-67, ZIF-67 acts as a host for the growth of Ni2CO3(OH)(2). The structure and morphology were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results confirmed that the porous morphology of Ni2CO3(OH)(2)@ZIF-67 was an urchin-like structure with fibers as basic structures. The porous structure combined with Ni2CO3(OH)(2) maximized the utilization of active material, resulting in a high specific capacitance. The electrochemical performance of the sample was evaluated using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy. The electrochemical measurements showed that ZIF-67, Ni2CO3(OH)(2) and Ni2CO3(OH)(2)@ZIF-67 electrodes delivered maximum capacitances of 65, 712 and 1,037 F g(-1), respectively, at a scan rate of 5 mV s(-1). About 80 % of the specific capacitance of Ni2CO3(OH)(2)@ZIF-67 was retained after 1,600 cycles at a scan rate of 10 mV s(-1) in 6 M KOH electrolyte solutions. All the results indicated that the Ni2CO3(OH)(2)@ZIF-67 composite was a promising material for supercapacitors.