Organic Solution Synthesis of Ultrathin Molybdenum Disulfide Nanosheets and Their Size- and Stacking-Dependent Electrocatalysis

A novel organic solvothermal approach is developed for the synthesis of ultrathin molybdenum disulfide (MoS₂) nanosheets. By coupling the thermal decomposition of molybdenum carbonyl and sulfurization with element sulfur, MoS₂ nanosheets of a few (<3) layers thick were obtained via preferential in-plane growth.  The in-plane size of the nanosheets is tunable in the range of <5 to 20 nm by controlling the growth time. Thermal treatments were applied to remove the organic surfactant and manipulate the stacking along c axis from <3 to ~10 molecular layers without causing significant agglomeration in-plane. The treated nanosheets possess enhanced electrocatalytic activity for the hydrogen evolution reaction (HER), with an improvement factor of ~3 compared to commercial MoS₂. The electrochemical studies further show size- and stacking-dependent catalytic activities, which can be ascribed to the edge sites being as active sites and likely also a molecular hindrance mechanism.