Reusing of Alkaline Red Mud as Self-supplied Electrolyte and Positive Active Material for Aqueous Supercapacitors

ABSTRACT Red mud (RM), as an industrial waste, has long been threatening environmental resources due to its high alkalinity and corrosiveness. In this study, we report reusing of alkaline RM as self‐supplied electrolytes (aRMS‐electrolyte) and positive active material for aqueous supercapacitors. We designed three different structures of supercapacitors RM(+)/aRMS‐electrolyte/AC(‐), AC(+)/aRMS‐electrolyte/RM(‐), and RM(+)/aRMS‐electrolyte/RM(‐). The electrochemical results show that RM(+)/aRMS‐electrolyte/AC(‐) has a larger specific capacity (13.8 mF/g for RM(+)/aRMS‐electrolyte/AC(‐), 9.0 mF/g for AC(+)/aRMS‐electrolyte/RM(‐) and 9.8 mF/g for RM(+)/aRMS‐electrolyte/RM(‐) at 0.2 mA/g). The unique feature of this work lies in: (1) The electrolyte is entirely derived from the dissolution of the base in the RM. (2) Raw RM is directly applied to supercapacitors without any pretreatment, which is a very simple and straightforward solution. (3) The transformation from industrial waste to electrode materials has achieved high value of RM. (4) Using the alkaline sodium hydroxide naturally provided by red mud as an electrolyte in electrochemical devices may provide inspiration for electrochemical detection or electrochemical purification and refinement. In conclusion, this work has explored a possible path for the high value utilization of RM and the construction of new type electrochemical devices.