Composite of CH 3 NH 3 PbI 3 with Reduced Graphene Oxide as a Highly Efficient and Stable Visible‐Light Photocatalyst for Hydrogen Evolution in Aqueous HI Solution

A facile and efficient photoreduction method is employed to synthesize the composite of methylammonium lead iodide perovskite (MAPbI 3 ) with reduced graphene oxide (rGO). This MAPbI 3 /rGO composite is shown to be an outstanding visible‐light photocatalyst for H 2 evolution in aqueous HI solution saturated with MAPbI 3 . Powder samples of MAPbI 3 /rGO (100 mg) show a H 2 evolution rate of 93.9 µmol h −1 , which is 67 times faster than that of pristine MAPbI 3 , under 120 mW cm −2 visible‐light (λ ≥ 420 nm) illumination, and the composite is highly stable showing no significant decrease in the catalytic activity after 200 h (i.e., 20 cycles) of repeated H 2 evolution experiments. The electrochemiluminescence performance of MAPbI 3 is investigated to explore the charge transfer process, to find that the photogenerated electrons in MAPbI 3 are transferred to the rGO sites, where protons are reduced to H 2 .