Elucidating Mn<SUP>2+</SUP>/Mn<SUP>3+</SUP> and Ni<SUP>0</SUP>/Ni<SUP>2+</SUP> Redox Synergy in Hair-Derived Carbon-Supported Ag/Ni-MnO x Supercapacitor

Abstract

Despite their critical importance, developing sustainable high-performance supercapacitor (SC) electrodes with long-term stability poses significant challenges. Herein, we report a novel ternary composite electrode in which Ag/Ni-doped manganese oxide (Ag/NiO x @Mn y O z ) is supported on human hair-derived activated carbon (HHC). This composite is synthesized via a one-pot hydrothermal process followed by thermal annealing at 800 degrees C, a strategy that creates a conductive Ag/Ni bimetallic network and abundant oxygen vacancies in the NiO x and Mn y O z phases. During operation, operando X-ray absorption spectroscopy (XAS) confirms reversible dual-ion redox transitions (Mn2+/Mn3+ and Ni0/Ni2+) in the cathode, highlighting the material's enhanced redox activity. As a result, HHC-supported Ag/NiO x @Mn y O z exhibits an exceptional specific capacitance (Cs) of 1770 F g-1 at 5 mV s-1 in three-electrode tests. When assembled into an asymmetric hybrid supercapacitor (AHSC), the device delivers a high energy density of 37.53 Wh kg-1 and a power density of 2251.8 W kg-1 at 3 A g-1 while retaining similar to 82% of its initial capacitance after 5000 charge-discharge cycles. These results confirm the effectiveness of our sustainable HHC-supported Ag/NiO x @Mn y O z framework in addressing the enduring trade-off between energy density, power density, and cycling stability in next-generation SCs.