A High-Energy Ni ²⁺ /Bi ³⁺ Layered Double Hydroxide/MXene Heterostructure Electrode Using a Supercritical Fluid Approach

Herein, we introduce an ultra-fast supercritical fluid (SCF) approach to engineer high-performance NiBi layered double hydroxide (LDH)/MXene 2D/2D heterostructure. By leveraging the unique properties of supercritical water, we have achieved an unprecedented LDH interlayer expansion of 8.6 Å through Bi3+ cation insertion and chaotropic NO3– intercalation. The SCF-synthesized materials are then analysed by different structural, morphological and compositional characterizations. This structural modulation, combined with the MXene scaffold, facilitates rapid ion transport and synergistic charge storage. The optimized NBTC 5 nanoarchitecture (LDH and MXene 5%) electrode delivers a specific capacitance of 1603 F.g–1, while the asymmetric supercapacitor reaches an energy density of as high as 109.14 Wh.kg–1 in aqueous electrolyte and 215 Wh.kg–1 in EMIM-TFSI ionic liquid system. Furthermore, the device exhibits a stable electrochemical performance up to 73% capacitance retention over 5000 cycles, supported by a pseudocapacitive contribution exceeding 80%. These findings demonstrate that SCF-assisted interlayer engineering and 2D/2D heterostructure offer a standalone approach towards high-energy electrode materials for advanced supercapacitors.