Mg-Doped GaN Nanosheets with Extended Charge Carrier Lifetime for Solar-Driven Hydrogen Production from Methanol

Tuning the bulk and surface structures of semiconductors provides one of the most effective ways to improve the efficiency of solar energy conversion. In this work, Mg-doped GaN nanosheets with a unique hierarchical morphology, suppressed defect states, and long-lived charge carriers were successfully prepared via a facile flux-assisted method, which possess a regular wurtzite structure with exposed nonpolar (100) and (110) planes. Mechanistic studies reveal that the incorporation of Mg not only plays a crucial role in regulating the crystal morphology but, more importantly, suppresses the defects within the crystal, thereby reducing charge carrier recombination. Especially, the charge carrier dynamics are elucidated for an individual Mg-doped GaN nanosheet by single-particle photoluminescence (PL) spectroscopy measurements. Compared with undoped GaN, Mg-doped GaN nanosheets exhibit a longer PL lifetime (over 30 ns, more than five times longer), indicating the reduced number of recombination centers after Mg incorporation, thus enhancing the retention of electrons and holes. Following the loading of the Rh2-yCryO3 cocatalyst, Mg-doped GaN nanosheets exhibited significantly enhanced H2 production, which was about 300 times higher than that of undoped GaN/Rh2-yCryO3 bulks. This study provides a guideline for the preparation of facet-controlled nitride or oxynitride semiconductors for an efficient photochemical conversion.