Engineering MXene/nickel‑silver sulfide composites for high-performance hybrid supercapacitors: Synthesis and electrochemical insights

Two-dimensional (2D) layered MXene (Ti₃C₂) has emerged as a promising electrode material for hybrid supercapacitors owing to its unique structure, high surface area, metallic conductivity, thermal and chemical stability, rapid surface redox kinetics, and excellent electrochemical properties. However, issues like spontaneous layer collapse and the limitations of single-component materials hinder its broader application in energy storage field. In this work, Ag₂S microcorals and NiAg₂S hexagonal microstructures are synthesized using one-step hydrothermal method and characterized using various techniques. The bimetallic NiAg₂S exhibited higher specific capacitance of 837 F·g⁻¹ compared to Ag₂S (383 F·g⁻¹) at 1 A·g⁻¹. Further, MXene is synthesized by selective etching Al-layer from Ti₃AlC₂ MAX phase using HF solution. To improve the performance of bimetallic sulfide (NiAg₂S) and mitigate the restacking tendency of MXene (Ti₃C₂) sheets, MXene/NiAg₂S hybrid composite is engineered by incorporating a small amount of MXene into NiAg₂S. The specific capacitance of 1255 F·g⁻¹ at 1 A·g⁻¹ is delivered by MXene/NiAg₂S hybrid electrode which is found to be higher than pristine MXene (245 F·g⁻¹) and NiAg₂S (837 F·g⁻¹). Furthermore, a hybrid supercapacitor (HSC) device is assembled using MXene/NiAg₂S as positive electrode and activated carbon (AC) as negative electrode, delivering high energy density of 50.38 Wh·kg⁻¹ with power density of 775 W·kg⁻¹ at 1 A·g⁻¹. Moreover, two series-connected MXene/NiAg₂S//AC HSCs are successfully employed to power the practical electronic components including LEDs, a toy motor fan, digital humidity meter and a kitchen timer, showcasing the real-world application potential. This work provides a promising strategy to overcome the MXene restacking and bimetallic sulfide limitations for next-generation energy storage devices.