Synergistic Integration of Ni–Fe Sulfide and Single-Layered Ti ₃ C ₂ T <i> _x </i> Mxene for Ultra-Stable and High-Capacity Asymmetric Hybrid Supercapacitors

Exploring new and efficient electrode materials based on metal sulfides has taken significant attention for developing high-performance energy storage devices. However, sluggish ion transfer kinetics has restricted its applications. To overcome this problem, ethyl xanthate was first employed in this study as a source of sulfide ions in synthesizing nickel iron sulfide (NFS) via in situ one-step solvothermal reaction over a single-layered (SL)-Ti 3 C 2 T x MXene on Ni foam (NF). The resulting NFS@SL-Ti 3 C 2 T x /NF supercapacitor electrode exhibited a strong synergistic effect of SL-Ti 3 C 2 T x MXene, significantly enhancing its electrochemical performance. Dunn’s method and ex situ XPS analysis confirmed the promotion of K + ion diffusion and the charge storage mechanism. The NFS@SL-Ti 3 C 2 T x /NF electrode demonstrated an impressive specific capacity of 1690 C g −1 (4230 F g −1 ) at 1 A g −1 , with a high-rate capability of 80.2% at 15 A g −1 and outstanding cycling stability, retaining 98.5% of its capacity over 15,000 cycles. In addition, an asymmetric hybrid supercapacitor device was assembled by coupling NFS@SL-Ti 3 C 2 T x MXene/NF as a positive electrode and activated carbon (AC)/NF as a negative electrode (NFS@SL-Ti 3 C 2 T x MXene/NF//AC/NF). This device delivered a high capacity of 369 C g −1 at 1 A g −1 and maintained 98.8% cycling stability over 15,000 cycles. Moreover, it exhibited an ultra-high energy density of 82 Wh kg −1 with a high power density of 8.0 kW kg −1 . This study provides valuable insight into the role of SL-Ti 3 C 2 T x MXene in enhancing the electrochemical performance of metal sulfides and offers a theoretical understanding of the charge storage mechanism. The remarkable electrochemical performance obtained can pave the way for developing efficient electrode materials for various energy storage devices in the coming decades. Figure 1