Engineering grain boundaries at the 2D limit for the hydrogen evolution reaction

Abstract

Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~10¹² cm⁻². We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec⁻¹), thus indicating an intrinsically high activation of the TMD GBs.

Transition metal dichalcogenides demonstrate fascinating capabilities for electrocatalytic H₂ evolution, although the activities vary widely depending on nanomaterial sites available. Here, authors show the grain boundaries of atomically thin MoS₂ to be especially active sites for H₂ evolution.