Dual-function highly oxidative potassium salts empowering high-performance transition metal oxide/activated carbon for hybrid aqueous supercapacitors

In this work, a novel strategy of high-temperature oxidation-activation followed by rapid low-temperature aqueous-reflux treatment is developed to prepare transition metal oxide-activated carbon (TMO-AC) composites for supercapacitor applications. The super-absorbent polymer is selected as the carbon source, and the highly oxidative potassium salts K2FeO4/KMnO4 serve as both precursors for TMO and activators for AC. AC possesses a well-developed porous structure. Moreover, TMO grows uniformly in-situ on AC surface and displays a small size below 10 nm. The prepared Fe2O3-ACFe and MnO2-ACMn composites exhibit remarkable specific capacitance of 645.0 and 548.0 F g−1, respectively. Hybrid aqueous supercapacitors are assembled with Fe2O3-ACFe and MnO2-ACMn as negative and positive electrodes, respectively. A stable operating voltage of 1.2 V is achieved in the KOH electrolyte, resulting in a remarkable 90.2% capacitance retention over 10,000 cycles. Furthermore, in the Na2SO4 electrolyte, a wide 1.6 V voltage window is obtained, contributing to a substantial energy density of 49.35 Wh kg−1. This work provides an interesting approach for the fabrication of high-performance TMO-carbon composite electrodes.