Reversible and selective ion intercalation through the top surface of few-layer MoS2

Abstract

Electrochemical intercalation of ions into the van der Waals gap of two-dimensional (2D) layered materials is a promising low-temperature synthesis strategy to tune their physical and chemical properties. It is widely believed that ions prefer intercalation into the van der Waals gap through the edges of the 2D flake, which generally causes wrinkling and distortion. Here we demonstrate that the ions can also intercalate through the top surface of few-layer MoS2 and this type of intercalation is more reversible and stable compared to the intercalation through the edges. Density functional theory calculations show that this intercalation is enabled by the existence of natural defects in exfoliated MoS2 flakes. Furthermore, we reveal that sealed-edge MoS2 allows intercalation of small alkali metal ions (e.g., Li+ and Na+) and rejects large ions (e.g., K+). These findings imply potential applications in developing functional 2D-material-based devices with high tunability and ion selectivity.

Faradaic Electrodes Open a New Era for Capacitive Deionization

“…[296,311] It is noteworthy that, material modification can generate electrodes with ion selectivity. For example, as reported by Zhang et al, [299] by sealing the edges of MoS 2 flakes with natural defects, the MoS 2 shows insertion preference for alkali metal ions with small ionic radius (e.g., Li + and Na + ) through the top surface, and rejects the ions with a large ionic radius (e.g., K + ) (Figure 28e). DFT calculations (Figure 28f) indicate that the insertion is enabled by the existence of intrinsic defects in exfoliated MoS 2 flakes, and the energy barrier for the insertion of K + through these intrinsic defects is much higher than for Li + or Na + , resulting in the ion selectivity of sealed-edge MoS 2 material.…”

“…The selective insertion through the top surface was also applied to other similar 2D layered material such as MoSe 2 . [299] In addition to the ionic size, charge number, and hydration free energy, the shape of cations also affects the selective insertion processes for different topotactic insertion chemistries. [300] Recently, Dong et al [300] investigated the topotactic insertion of NH 4…”

Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation

“…The plasmonic resonance 34 , newly observed ferromagnetic properties 35 , and high conductivity of hydrogen-doped MoO 3 enable analysis of the interaction of PhPs with plasmon and magnetic fields. Furthermore, using other intercalators, such as ions (Li + , Na + ) 36,37 , metal atoms (Co, Fe) 38,39 , and polymers 40 , programmable in-plane heterostructures and flat metasurfaces could be constructed, and applications combining scalable planar optics with photomagnetics, photoelectronics and topological photonics could be realized.…”

A generic method to control hysteresis and memory effect in Van der Waals hybrids

“…This severely limits the T range for practical applications of TIs since the surface transport regime remains inaccessible. This problem can be circumnavigated either by going to very low temperatures, where the bulk doping is suppressed, which is not a feasible solution for several practical applications, or by using an ionic liquid top gate, can degrade the device characteristics due to intercalation of ions [60][61][62][63][64][65]. To address this, we have utilized capacitance amplification to access the Dirac Fermion dominated transport regime, even at high T. To fabricate the devices, the TI Bi 1.6 Sb 0.4 Te 2 Se was used, which offers reduced bulk number density due to compensation doping, and the transport below T<50 K for samples with thickness d<100 nm is primarily through the surface [66][67][68].…”