Bio-inspired Mn3O4@N, P-doped carbon cathode for 2.6 V flexible aqueous asymmetric supercapacitors

Abstract

Optimizing the performance of electrode materials is crucial for improving the energy density of aqueous supercapacitors. Herein, a novel strategy inspired by biomimetic mineralization is developed to acquire a hierarchical flower-like Mn3O4@N, P-doped carbon (NPC) composite, which consists of multi-intercalated Mn3O4 nanosheets and NPC cores. The Mn3O4 nanosheets offer abundant active regions, and their C-O-Mn bonds with NPC ensure the fast electron transfer kinetics. It is noteworthy that the intercalation pseudocapacitance mechanism of Mn3+/Mn4+ transformation in Mn3O4@NPC not only extends the potential window to 0–1.3 V (vs Ag/AgCl) but also significantly increased pseudocapacitance. Benefits from the advantages of structure and energy storage mechanism, the Mn3O4@NPC electrode delivers a high specific capacitance of 370.8 F g−1 and superior rate performance. A 2.6 V flexible aqueous asymmetric supercapacitor (FAAS) is fabricated by integrating Mn3O4@NPC cathode with an electrochemically reduced porouscarbon anode and a PVA-Na2SO4 hydrogel electrolyte. Notably, the FAAS delivers a high energy density of 76.96 Wh kg−1 as well as excellent rate capability. The device exhibited an excellent stability during 10,000 cycles and additional 240 h floating test. The strategy will pave the way for the development of electrode materials for FAASs.