  Aqueous supercapacitors (SCs) encounter limitations in operational voltage
and energy density due to the low decomposition voltage of water. Here, we
fabricate aqueous symmetric supercapacitors (ASSCs) employing DyFeO3 as an
electrode material. This hybrid SC in a 0.5 M Na2SO4 aqueous electrolyte
exhibits a significantly high working voltage of 2.5 V, with an energy density
of 41.81 Wh/kg at a power density of 1250 W/kg, maintaining 94% capacitance
retention after 5000 cycles. By incorporating 20% volume of acetonitrile with
water in the electrolyte, we extend the potential window to 3.1 V, with an
energy density of 84.43 Wh/kg at a power density of 1550 W/kg. The
as-fabricated ASSC shows promising stability during a 300-hour float voltage
test with almost intact capacitance retention and Coulombic efficiency. For the
first time, our study unveils the potential of porous DyFeO3 as an electrode
material for advancing ASSCs, featuring an unprecedented ultra-wide voltage
window, along with significantly large energy and power densities.
