Direct Exfoliation of High‐Quality, Atomically Thin MoSe₂ Layers in Water

Abstract The discovery of 2D materials has brought us to a conceptually new, wonderful microscopic world. Large surface areas combined with extraordinary electronic, electrochemical, and thermal properties make these atomically thin, layered materials fascinating candidates for diverse applications, ranging from sensing to energy storage and electrocatalytic hydrogen evolution. However, it is essential to solve the problem of scalable and green production of 2D materials before being able to bring them from laboratory to industry. In this sense, the exfoliation of 2D materials in water, free from any stabilizer, is very important since it is a gateway technology toward their production as well as future applications. This Communication reports the direct exfoliation of atomically thin MoSe₂ layers in water, which bypasses the Hansen solubility parameters theory and suggests potential for liquid‐phase exfoliation of 2D materials. A combination of long‐time sonication and high‐speed centrifugation results in a substantial fraction of monolayers. When applied in the field of electrocatalytic hydrogen evolution, these atomically thin MoSe₂ layers can significantly outperform bulk MoSe₂. The finding may point towards industrial scale production of 2D materials by simultaneously ensuring high product quality, laudable monolayer yield, and good environmental compatibility.