Nanocomposites of digestively ripened copper oxide quantum dots and graphene oxide as a binder free battery-like supercapacitor electrode material

Ultra-small (r < 2 nm), semiconductor quantum dots (QDs) based composites are underexplored in electrochemical energy-storage devices. This is due to practical challenges associated with synthesis of QDs such as (i) stabilization, (ii) scalability, and (iii) achieving monodispersed population. In this context, ultra-small, highly monodispersed copper oxide QDs (similar to 2.5 +/- 0.4 nm) have been synthesized by using soft-chemical and scalable approach based on digestive ripening. Composites of digestively ripened (DRd) copper oxide QDs deposited on graphene oxide are tested electrochemically for battery-like supercapacitor. The composites are grown in-situ on a Ni-foam to make binder-free battery-like supercapacitor electrode by hydrothermal process. Results indicates that battery-like behavior of the composites. Among the composites, 50%QDs-GO provides maximum specific capacity of 191 mA h g(-1) at 2 mV s(-1) which is maintained up to 63 mA h g(-1) even at a high scan rate of 200 mV s(-1). The specific capacity increases similar to 4 times for the 50%QDs-GO composite, compared to the graphene oxide. The maximum energy density provided by the system is 57.2 Wh kg(-1) at 2 mV s(-1). Specific capacity and charge-discharge stability of the composites are found to be improved with increasing concentration of QDs. This is the first report on deployment of DRd copper oxide QDs in battery-like supercapacitors and it opens up possibilities for further exploration of other DRd QDs. (C) 2019 Elsevier Ltd. All rights reserved.