Etching-induced electronic modulation in Prussian blue analogue-derived metal sulfides for advanced hybrid supercapacitors

Abstract

Designing electrode materials with optimized morphology and electronic structure is crucial for improving the performance of supercapacitors. Herein, a concave-structured Ni–Fe Prussian blue analogue (E9-Ni-FePBA) is fabricated via a controlled KOH etching process, followed by thermal sulfidation to obtain a multi-phase metal sulfide (E9-Ni-FePBA-S). The etching process effectively tunes the crystal orientation and exposes more active sites of E9-Ni-FePBA. The subsequent sulfidation further induces the formation of NiS₂, Ni₉S₈, and FeS₂, and therefore enhances its intrinsic conductivity and electrochemical activity. X-ray photoelectron spectroscopy analysis reveals strong Ni–S and Fe–S electronic coupling, resulting in optimized charge density distribution and improved redox kinetics. Benefiting from these structural and electronic synergies, E9-Ni-FePBA-S exhibits a high specific capacitance of 2509.6 F g⁻¹ at 2 A g⁻¹, along with a low charge-transfer resistance. The hybrid supercapacitor assembled by E9-Ni-FePBA-S and activated carbon (AC) (E9-Ni-FePBA-S//AC) achieves an extended voltage window of 1.6 V, a large maximum energy density of 31.4 W h kg⁻¹ at 1.6 kW kg⁻¹, and a remarkable cycling stability with a high capacitance retention of 88.68% after 10 000 cycles. This work provides a feasible strategy for engineering Prussian blue-derived metal sulfides with enhanced redox activity and long-term durability for next-generation energy storage applications.