Unveiling the bifunctional roles of Cetyltrimethylammonium bromide in construction of Nb2CTx@MoSe2 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 Nb 2 CT x @MoSe 2 heterostructure. Firstly, functionalization of CTAB on the surface of Nb 2 CT x could influence the subsequent growth of MoSe 2 by electrostatic effect, stereochemical effect and the synergetic Lewis acid-base interaction, leading to the formation of Nb 2 CT x @MoSe 2 with tiled heterostructure. Secondly, the interlayer spacing of Nb 2 CT x 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 −1 (406 mA h g −1 ) to 1000 mA g −1 concerning rate capability and the specific capacity maintained at 240 mA h g −1 (at 2000 mA g −1 ) over 300 cycles. The calculated D K values from Galvanostatic intermittent titration technique (GITT) measurement of the titled C-T-Nb 2 CT x @MoSe 2 @C electrode is two orders of magnitude larger than the traditional T-Nb 2 CT x @MoSe 2 @C electrode, further confirming intimate interface between MoSe 2 and Nb 2 CT x 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.