Unveiling the capacitive energy storage of linear CTAB or tetrahedral TBAB organic-molecule intercalated MoS2

Abstract

Organic-molecule insertion into MoS₂ is becoming a research hotspot owing to the expanded interlayer spacing and improved electrochemical energy storage. Up to now, the effect of organic molecules with different configurations on capacitive energy storage has not been clarified. Herein, we have innovatively selected two types of organic molecules to insert into MoS₂, whose configurations are linear long-chain (cetyltrimethylammonium bromide, CTAB) and tetrahedral symmetrical branched-chain (tetrabutylammonium bromide, TBAB). The interlayer spacing extends from 6.3 Å to 9.8 Å and 10.3 Å after TBAB and CTAB intercalation, respectively. Additionally, the insertion of organic molecules not only increases the content of high-valent Mo (Mo⁵⁺, Mo⁶⁺), but also introduces pyrrolic N, pyridinic N and N⁺, which are beneficial for capacitive energy storage. Interestingly, the linear long-chain CTAB causes MoS₂ to present a broken shell hollow sphere, which can provide more channels and space for ion storage. More importantly, the migration barrier energy of Na ions between MoS₂ layers and CTAB molecules is 1.01 eV, which is significantly lower than that of Na ions between MoS₂ and TBAB (1.85 eV), indicating that linear organic molecules are more appropriate for ion-diffusion kinetics. This work provides a prototype for studying the effect of the organic molecular configuration on the capacitive energy storage of intercalated MoS₂.