Electrochemical intercalation of sodium in vertically aligned molybdenum disulfide for hydrogen evolution reaction

The intercalation of alkaline cations such as lithium and sodium into two-dimensional (2D) van der Waals materials effectively modifies their electronic structure. Here, we show an electrochemical intercalation process of an alkaline ion (Li+ or Na+), into vertically aligned molybdenum disulfide (MoS2) thin films by using a three-electrode flooded vessel cell, and its application as electrocatalyst for hydrogen evolution reaction. The electrochemical intercalation method is controlled by the applied current density. After electrochemical insertion, the vertically alligned MoS2 layers display an extended Wan der Waals gap. The Li and Na intercalated vertically alligned MoS2 layers demonstrate an overpotential of 0.29 V at 10 mA cm(-2) towards hydrogen evolution reaction (HER) in 0.5 M H2SO4. The intercalation of Li+ or Na+ leads to the partial exfoliation of the 2D layered material. Nevertheless, the Na intercalated catalyst can sustain the HER for 1000 cycles while Li intercalated catalyst show an activity fading, possibly due to restacking of the MoS2 layers.