Synergistic Surface Modifications Enable Direct Photocatalytic Overall Water Splitting over a MgTa ₂ O _{6– <i>x</i>} N _<i>y</i> /TaON Heterostructure

Metal (oxy)nitride-based type II heterostructures with significantly promoted bulk charge separation are highly promising candidates for direct photocatalytic overall water splitting (OWS) to produce hydrogen compared to its counterparts. To date, however, no such particulate heterostructured photocatalyst can drive the direct OWS process under visible light, probably due to the challenge of poor surface charge carrier utilization encompassing severe surface charge recombination, sluggish water splitting reaction kinetics, and competitive reverse/side reactions. Herein, we employed the MgTa2O6–xNy/TaON heterostructure as a prototype, toward which a series of tailored surface modifications were systematically implemented and analyzed to address those challenges. The results reveal that ZrO2 modification inhibits surface charge recombination by suppressing the formation of reduced tantalum defect species. The deposition of dual cocatalysts (i.e., Cr2O3/Ru and CoOx) not only promotes charge carrier extraction but also facilitates the water splitting reaction and inhibits the reverse water formation reaction. Additionally, coating with a TiO2 thin layer effectively suppresses the side reaction of photocorrosion. Based on these integrated surface modifications, the metal (oxy)nitride-based type II heterostructure photocatalyst (i.e., MgTa2O6–xNy/TaON) for direct OWS into stoichiometric H2 and O2 can be achieved under visible light irradiation. This work demonstrates the importance and feasibility of multiple surface modifications in synergistically addressing the issue of surface charge utilization for the MgTa2O6–xNy/TaON heterostructure photocatalyst to enable its direct OWS under visible light, as it may become a blueprint of fabricating other metal (oxy)nitride-based photocatalysts for direct OWS.