Toward Understanding the Enhanced Pseudocapacitive Storage in 3D SnS/MXene Architectures Enabled by Engineered Surface Reactions.

The optimization of three-dimensional (3D) MXene-based electrodes with desired electrochemical performances is highly demanded. Here, a precursor-guided strategy is reported for fabricating the 3D SnS/MXene architecture with tiny SnS nanocrystals (≈5 nm in size) covalently decorated on the wrinkled Ti3 C2 Tx nanosheets through Ti-S bonds (denoted as SnS/Ti3 C2 Tx -O). The formation of Ti-S bonds between SnS and Ti3 C2 Tx was confirmed by extended X-ray absorption fine structure (EXAFS). Rather than bulky SnS plates decorated on Ti3 C2 Tx (SnS/Ti3 C2 Tx -H) by one-step hydrothermal sulfidation followed by post annealing, this SnS/Ti3 C2 Tx -O presents size-dependent structural and dynamic properties. The as-formed 3D hierarchical structure can provide short ion-diffusion pathways and electron transport distances because of the more accessible surface sites. In addition, benefiting from the tiny SnS nanocrystals that can effectively improve Na+ diffusion and suppress structural variation upon charge/discharge processes, the as-obtained SnS/Ti3 C2 Tx -O can generate pseudocapacitance-dominated storage behavior enabled by engineered surface reactions. As predicted, this electrode exhibits an enhanced Na storage capacity of 565 mAh g-1 at 0.1 A g-1 after 75 cycles, outperforming SnS/Ti3 C2 Tx -H (336 mAh g-1 ), SnS (212 mAh g-1 ), and Ti3 C2 Tx (104 mAh g-1 ) electrodes.