Fig. 1: InSe/Gr anode for PEC measurements.

a Schematic of our experiment setup. The illumination used in this report is simulated sunlight: AM 1.5 G one-sun (100 mW cm⁻²). b Band structure of InSe/Gr heterostructure. c DFT simulation of hydroxide species adsorption on InSe/Gr heterostructure surface. Left is the top view. Right is the side view. Red, white, gray, purple, and green balls represent oxygen, hydrogen, carbon, indium and selenium atoms, respectively. The hydroxide species adsorbs on top of the graphene carbon atom. d Linear sweep voltammetry of a representative monolayer InSe/Gr device measured at different illumination times. The original linear-scale curves are shown in Supplementary Fig. 5. The Ti electrodes and graphene top layer have little (<1%) contribution to the measured total photocurrent (Supplementary Fig. 6). e Photocurrent density of the PEC cell as a function of the time when light was on or off. In this report, all the J–t curves are measured at a potential of 1.23 V vs. RHE. The blank dot is the saturated maximum current density averaged from 4 samples. The error bar represents the standard deviation error.