Unveiling the bifunctional roles of Cetyltrimethylammonium bromide in construction of NbCT@MoSe heterojunction for fast potassium storage.

Exploring robust electrode materials which could permit fast and reversible insertion/extraction of large K is a crucial challenge for potassium-ion batteries (PIBs). Smart interfacial design could facilitate electron/ion transport as well as assure the integrity of electrode. Herein, Cetyltrimethylammonium bromide (CTAB) was found to play bifunctional roles in construction of NbCT@MoSe heterostructure. Firstly, functionalization of CTAB on the surface of NbCT could influence the subsequent growth of MoSe by electrostatic effect, stereochemical effect and the synergetic Lewis acid-base interaction, leading to the formation of NbCT@MoSe with tiled heterostructure. Secondly, the interlayer spacing of NbCT was expanded from 0.77 to 1.21 nm owing to the pillar effect of CTAB. As excepted, the capacity retention was 80 % from 100 mA g (406 mA h g) to 1000 mA g concerning rate capability and the specific capacity maintained at 240 mA h g (at 2000 mA g) over 300 cycles. The calculated D values from Galvanostatic intermittent titration technique (GITT) measurement of the titled C-T-NbCT@MoSe@C electrode is two orders of magnitude larger than the traditional T-NbCT@MoSe@C electrode, further confirming intimate interface between MoSe and NbCT could provide convenient potassium-ion transport channels and fast diffusion kinetics. Finally, ex-situ characterizations at different charging and discharging voltage stages, including ex-situ XRD/Raman/HRTEM/XPS have been carried out to reveal the potassium storage mechanism. This work provides a facile strategy for the regulation of interface engineering by the assist of CTAB which could extend to other MXenes-TMDs (Transition metal dichalcogenides) hybrid electrodes.