Zeolitic imidazolate framework-67 derived Al-Co-S hierarchical sheets bridged by nitrogen-doped graphene: Incorporation of PANI derived carbon nanorods for solid-state asymmetric supercapacitors

Abstract

Metal sulfides have been widely enticed as battery-type electrodes in supercapacitor devices because of their maximal theoretical capacitance. Nevertheless, their lower conductivity and ion transport kinetics can largely restrict their rate performance, hence the practical usage in fields of demanding high power devices. Therefore, the design of new electrodes with higher energy and power densities remains a highly challenging task. To the best of our knowledge, a novel hierarchical composite of Al-CoS2 on nitrogen-doped graphene (NG) is prepared based on a zeolite imidazole framework using a simple and scalable hydrothermal process. In this hybrid, ultrathin Al-CoS2 nanosheet arrays are vertically orientated on the NG framework to limit self-aggregation, hence increasing the electrical property and cycle stability of composite. It is investigated that the Al/Co feeding ratio plays a crucial role in controlling the obtained hierarchical structure of Al-Co-S sheets and their electrode performance. Also, Al3+ can influence remarkably the morphology and electrochemical property of the resultant graphene composite. An effective synergism is noticed between the redox Al-CoS2 and NG resulting in fast electron transfer and charging-discharging processes. Surprisingly, when the as-developed composite is utilized as a positive electrode at an applied current density of 1 A/g, a specific capacitance of 1915.8 F/g is attained with ultra-long cycle stability (96%, 10,000 cycles) and an excellent retention rate (∼89%). As a consequence, when a solid-state asymmetric supercapacitor (ASC) device is made by combining an Al-CoS2@NG hybrid with a negative electrode made of polyaniline (PANI) derived carbon nanorods (PCNRs), it demonstrates remarkable specific capacitance (188 F/g), energy density (66.9 Wh/kg), and cyclic stability of 92% after 10,000 cycles. This may open the pathway for the application of the next-generation supercapacitors in the future.