Boosting Hybrid Supercapacitor Performance via Synergy between Ti-Doped Ni0.85Se Nanospheres and Ferrocyanide-Enhanced Electrolyte

The trade-off between energy and power density remains a major hurdle for supercapacitors (SCs). This work demonstrates a substantial performance enhancement in aqueous hybrid supercapacitors through synergistic electrode and electrolyte engineering. First, titanium-doped nickel selenide nanospheres (Ti-Ni 0.85 Se) are successfully synthesized via a hydrothermal method using trace Ti 3 C 2 T x MXene as a controllable titanium source. The incorporated Ti atoms induce a slight lattice expansion and optimize the electronic structure, significantly improving the intrinsic conductivity and charge-transfer kinetics of the material. In a 3 mol L -1 KOH electrolyte, the Ti-Ni 0.85 Se electrode delivers a high specific capacity of 586 C g -1 at 1 A g -1 . Furthermore, introducing K 4 [Fe(CN) 6 ] as a redox-active additive provides additional Faradaic capacity via the reversible [Fe(CN) 6 ] 3-/4- couple, boosting the specific capacity of Ti-Ni 0.85 Se to 861 C g -1 . The assembled Ti-Ni 0.85 Se//activated carbon hybrid supercapacitor achieves a high energy density of 35.7 Wh kg -1 at a power density of 1156 W kg -1 , with 71.6% capacitance retention after 3000 cycles. This study validates the synergistic strategy of electrode doping and electrolyte modulation as an effective pathway to break the performance bottlenecks of supercapacitors.