Unleashing and harnessing capacity performance by a diffusion dominant process of CoNi-ZIF for high energy density asymmetric supercapacitors

Abstract

We report here the synergy of tailored cobalt nickel-based zeolitic imidazole frameworks as cathode and activated carbon (AC) as anode materials, which tends to bridge the void between energy density and power density of asymmetric supercapacitors (ASCs). CoNi-ZIF exhibits a mesoporous structure along with a specific surface area of 1126 m² g⁻¹ and a pore size of 3.128 nm. The specific capacity and capacitance of CoNi-ZIF and AC electrodes are found to be 49.06 mAh g⁻¹ and 333 F g⁻¹, respectively. The CoNi-ZIF structure exhibits a mesoporous structure, which helps explore the underlying capacitance due to the presence of bulk and surface chemical states of the ZIF structure. XPS analysis reveals that the deconvoluted peaks of nitrogen and its associated organic moieties contribute to the capacitance by increasing the hydrophilicity of the framework, which causes rapid ion diffusion. A systematic electrochemical study has been performed using cyclic voltammetry (CV) to analyze electrode kinetics during the charge storage-discharge process, and Dunn's model was employed, which validates the diffusion dominance of CoNi-ZIF. This systematic approach unveils framework kinetics and diffusion dynamics of ZIF-based electrodes, which enhances the ASC device performance. The diffusion-dominant mechanism of CoNi-ZIF electrodes at low scan rates is about 85% through a pseudocapacitive process, and a double-layer capacitive percentage of about 15% presents a device capacitance of 54.9 mAh g⁻¹ and yields an energy density of 17.04 Wh kg⁻¹ at a power density of 1241.53 W kg⁻¹. The ASC device showcases a good capacity retention of about 95.2% after prolonged 10 000 cycles.