Engineering a Carbon-Iodine covalent bond charge transport channel in γ-CuI/Polymeric carbon nitride for solar Light-Driven hydrogen production

Abstract

The π-conjugated polymeric carbon nitride (PCN) is a potential low-cost material for solar energy conversion applications. However, it suffers from poor charge transport and low surface area, which hinders its solar energy conversion efficiency. Herein, we report for the first time the synthesis of a covalently bonded γ-CuI/PCN hybrid photocatalyst via a facile wet-impregnation route. The PCN sheets were exfoliated via the dynamic gas template method and a specific surface area of 214 m2/g was obtained. Even though such a high specific surface area was achieved, the hydrogen production rate of the exfoliated PCN sheets remained negligible. However, the introduction of γ-CuI into PCN sheets resulted in a 35 (methanol) and 43 (TEOA) times enhancement in hydrogen production rate, despite the reduction of the specific surface area to 183 m2/g and no significant changes in the visible light absorption. Furthermore, time-resolved photoluminescence spectra have revealed a ∼ 93 % increase in the lifetime of electrons in the shallow trap states at 540 nm. A C-I covalent bond formation is proposed between the γ-CuI and PCN sheets and corroborated by XPS and ESR measurements. The C-I covalent bond formation in γ-CuI/PCN resulted in a greatly enhanced charge separation efficiency, as evident from the electrochemical impedance spectroscopy, photocurrent, and photoluminescence measurements. The high hydrogen production activity and stability are mainly attributed to the formation of C-I covalent bond and p-n heterojunction at the interface of γ-CuI/PCN. The design of such unique and stable PCN nanostructures with covalent attachment, instead of a physical blending is expected to be a potential candidate for solar energy conversion applications.