Selenene/WSe<sub>2</sub> Heterostructures for Efficient\nPhotoelectrocatalytic Hydrogen Evolution

The van der Waals (vdW) heterostructures, achieved by\nintegrating\natomically thin materials with distinct band structures and interfaces,\nexhibit diverse properties, enabling unprecedented opportunities for\nvarious device applications. Herein, we demonstrate controllable growth\nof vertically stacked heterobilayers (hBLs) of atomically thin selenene\nand WSe<sub>2</sub> through a single-step-confined space chemical\nvapor transport (CVT) strategy. With an aim to leverage the electrocatalytic\nactivity of the WSe<sub>2</sub> domain toward hydrogen generation,\nalong with the high photoresponsivity of CVT-grown selenene domains,\nwe fabricate a microreactor device assembly to study the photoenhanced\ncatalytic performance of the heterobilayer single domains toward hydrogen\nevolution. When exposed to light, the Se/WSe<sub>2</sub> hBL exhibits\na significant improvement in the hydrogen evolution reaction (HER)\nactivity with a much lower overpotential and a smaller Tafel slope\ncompared to their pristine counterparts. Control experiments carried\nout on mechanically stacked hBLs show poor HER activity, further confirming\nthe effect of the interface on the overall photoenhanced HER performance\nof the vertical bilayer structures. The mechanism of the enhanced\nHER activity of the hBL is explored through electrochemical impedance\nstudies and Ultraviolet photoelectron spectroscopy (UPS) measurements.\nThe enhanced catalytic efficiency is attributed to effective electrical\ncoupling and improved charge transfer in the Se/WSe<sub>2</sub> hBLs.