Intrinsic Electrocatalytic Activity of Single MoS2 Quantum Dot Collision on Ag Ultramicroelectrodes

It is still a challenge to identify the intrinsic electrocatalytic activity of single MoS2 quantum dots (QDs) because their characterization usually dissects contributions from a large amount of particles. Herein, we demonstrate a single-entity electrochemical method to help us investigate the enhancing hydrogen evolution reaction (HER) activity at the single MoS2 QD level by using silver ultramicroelectrodes (UMEs). At Ag UMEs, the i–t response for MoS2 QD collision consists of repeated current “spikes” that return to the background level as hydrogen formation and covering the QD surface. In contrast, a stepwise “staircase” i–t response is observed for MoS2 QDs colliding on carbon UMEs (C UMEs). The results also show that the current density of single MoS2 QD collision on Ag UMEs is much higher than on C UMEs, revealing the impact of the unique property of the metal–MoS2 interface on HER performance, which has been demonstrated by thermodynamic analysis and density functional theory (DFT) calculations. It has been found that the interactions between MoS2 QDs and substrate UMEs lead to significant changes in the hydrogen adsorption energies (ΔEads) and Gibbs free energy (ΔGH), resulting in the difference in HER activity.