Spontaneous doping of the basal plane of MoS2 single-layers through oxygen substitution under ambient conditions

TL;DR

This study reveals that oxygen spontaneously substitutes sulfur atoms in MoS2 single-layers under ambient conditions, creating active sites that significantly enhance catalytic activity for hydrogen evolution.

Contribution

It uncovers the spontaneous oxygen doping process in MoS2 basal planes and links it to increased catalytic performance, a novel insight into MoS2 chemistry.

Findings

Oxygen atoms incorporate into MoS2 basal plane during ambient exposure.

Oxygen substitution creates active sites for catalysis.

Enhanced electrochemical H2 evolution activity observed.

Abstract

The chemical inertness of the defect-free basal plane confers environmental stability to MoS2 single-layers, but it also limits their chemical versatility and catalytic activity. The stability of the pristine MoS2 basal plane against oxidation under ambient conditions is a widely accepted assumption in the interpretation of various studies and applications. However, single-atom level structural investigations reported here reveal that oxygen atoms spontaneously incorporate into the basal plane of MoS2 single layers during ambient exposure. Our scanning tunneling microscopy investigations reveal a slow oxygen substitution reaction, upon which individual sulfur atoms are one by one replaced by oxygen, giving rise to solid solution type 2D MoS2-xOx crystals. O substitution sites present all over the basal plane act as single-atomic active reaction centers, substantially increasing the catalytic activity of the entire MoS2 basal plane for the electrochemical H2 evolution reaction.